Technical Factors or Prime Factors

Bushong Ch 15

1

PRIME FACTORS

What is ldquotechniquerdquo

How does it affect the ldquoimagerdquo

2

Exposure Factors ndash 3 or 4

The four prime exposure factors are Voltage = kVp Current = mA Exposure time = seconds or fractions of a sec Source-to-image distance = SID

3

PRIME FACTORS

bull KVP

bull MAS

bull DISTANCE

4

kVp

Kilovolts controls how fast the electrons are sent across the tube

Controls quality penetrability amp contrast

Increasing kVp also increases scattered photons reducing image quality

Does kVp influence OD

5

kVp

bull Low kVp (50 ndash 60)

bull Short scale

bull High contrast

bull ldquoBone workrdquo

6

kVp

bull High kVp (90 ndash 120)

bull Long scale

bull Low contrast

bull ldquoChest imagesrdquo

7

mA

Determines the number of photons radiation quantity OD amp patient dose

Changing mA does not change the kinetic energy of e-

Available mA stations are usually 50 100 200 300 400 amp 600

8

Exposure Time

Should be kept as short as possible for most examinations To minimize the risk of patient motion

mA X s = mAs mAs controls OD

mAs determines the number of photons in the primary beam

9

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

PRIME FACTORS

What is ldquotechniquerdquo

How does it affect the ldquoimagerdquo

2

Exposure Factors ndash 3 or 4

The four prime exposure factors are Voltage = kVp Current = mA Exposure time = seconds or fractions of a sec Source-to-image distance = SID

3

PRIME FACTORS

bull KVP

bull MAS

bull DISTANCE

4

kVp

Kilovolts controls how fast the electrons are sent across the tube

Controls quality penetrability amp contrast

Increasing kVp also increases scattered photons reducing image quality

Does kVp influence OD

5

kVp

bull Low kVp (50 ndash 60)

bull Short scale

bull High contrast

bull ldquoBone workrdquo

6

kVp

bull High kVp (90 ndash 120)

bull Long scale

bull Low contrast

bull ldquoChest imagesrdquo

7

mA

Determines the number of photons radiation quantity OD amp patient dose

Changing mA does not change the kinetic energy of e-

Available mA stations are usually 50 100 200 300 400 amp 600

8

Exposure Time

Should be kept as short as possible for most examinations To minimize the risk of patient motion

mA X s = mAs mAs controls OD

mAs determines the number of photons in the primary beam

9

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Exposure Factors ndash 3 or 4

The four prime exposure factors are Voltage = kVp Current = mA Exposure time = seconds or fractions of a sec Source-to-image distance = SID

3

PRIME FACTORS

bull KVP

bull MAS

bull DISTANCE

4

kVp

Kilovolts controls how fast the electrons are sent across the tube

Controls quality penetrability amp contrast

Increasing kVp also increases scattered photons reducing image quality

Does kVp influence OD

5

kVp

bull Low kVp (50 ndash 60)

bull Short scale

bull High contrast

bull ldquoBone workrdquo

6

kVp

bull High kVp (90 ndash 120)

bull Long scale

bull Low contrast

bull ldquoChest imagesrdquo

7

mA

Determines the number of photons radiation quantity OD amp patient dose

Changing mA does not change the kinetic energy of e-

Available mA stations are usually 50 100 200 300 400 amp 600

8

Exposure Time

Should be kept as short as possible for most examinations To minimize the risk of patient motion

mA X s = mAs mAs controls OD

mAs determines the number of photons in the primary beam

9

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

PRIME FACTORS

bull KVP

bull MAS

bull DISTANCE

4

kVp

Kilovolts controls how fast the electrons are sent across the tube

Controls quality penetrability amp contrast

Increasing kVp also increases scattered photons reducing image quality

Does kVp influence OD

5

kVp

bull Low kVp (50 ndash 60)

bull Short scale

bull High contrast

bull ldquoBone workrdquo

6

kVp

bull High kVp (90 ndash 120)

bull Long scale

bull Low contrast

bull ldquoChest imagesrdquo

7

mA

Determines the number of photons radiation quantity OD amp patient dose

Changing mA does not change the kinetic energy of e-

Available mA stations are usually 50 100 200 300 400 amp 600

8

Exposure Time

Should be kept as short as possible for most examinations To minimize the risk of patient motion

mA X s = mAs mAs controls OD

mAs determines the number of photons in the primary beam

9

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

kVp

Kilovolts controls how fast the electrons are sent across the tube

Controls quality penetrability amp contrast

Increasing kVp also increases scattered photons reducing image quality

Does kVp influence OD

5

kVp

bull Low kVp (50 ndash 60)

bull Short scale

bull High contrast

bull ldquoBone workrdquo

6

kVp

bull High kVp (90 ndash 120)

bull Long scale

bull Low contrast

bull ldquoChest imagesrdquo

7

mA

Determines the number of photons radiation quantity OD amp patient dose

Changing mA does not change the kinetic energy of e-

Available mA stations are usually 50 100 200 300 400 amp 600

8

Exposure Time

Should be kept as short as possible for most examinations To minimize the risk of patient motion

mA X s = mAs mAs controls OD

mAs determines the number of photons in the primary beam

9

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

kVp

bull Low kVp (50 ndash 60)

bull Short scale

bull High contrast

bull ldquoBone workrdquo

6

kVp

bull High kVp (90 ndash 120)

bull Long scale

bull Low contrast

bull ldquoChest imagesrdquo

7

mA

Determines the number of photons radiation quantity OD amp patient dose

Changing mA does not change the kinetic energy of e-

Available mA stations are usually 50 100 200 300 400 amp 600

8

Exposure Time

Should be kept as short as possible for most examinations To minimize the risk of patient motion

mA X s = mAs mAs controls OD

mAs determines the number of photons in the primary beam

9

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

kVp

bull High kVp (90 ndash 120)

bull Long scale

bull Low contrast

bull ldquoChest imagesrdquo

7

mA

Determines the number of photons radiation quantity OD amp patient dose

Changing mA does not change the kinetic energy of e-

Available mA stations are usually 50 100 200 300 400 amp 600

8

Exposure Time

Should be kept as short as possible for most examinations To minimize the risk of patient motion

mA X s = mAs mAs controls OD

mAs determines the number of photons in the primary beam

9

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

mA

Determines the number of photons radiation quantity OD amp patient dose

Changing mA does not change the kinetic energy of e-

Available mA stations are usually 50 100 200 300 400 amp 600

8

Exposure Time

Should be kept as short as possible for most examinations To minimize the risk of patient motion

mA X s = mAs mAs controls OD

mAs determines the number of photons in the primary beam

9

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Exposure Time

Should be kept as short as possible for most examinations To minimize the risk of patient motion

mA X s = mAs mAs controls OD

mAs determines the number of photons in the primary beam

9

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Distance

Affects exposure of the IR because of the Inverse Square Law

SID largely determines the intensity of photons at the IR

Distance has no effect on radiation quality

10

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

INTENSITY IS SPREAD OUThellip

11

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Inverse Square Law Formula

Intensity 1

Intensity 2

Distance 2 - Squared

Distance 1 - Squared

12

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Direct Square Law

bull New mAs = New distance 2

Old mAs Old distance 2

13

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Focal-Spot Changes

14

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Tube voltage (kVp)

bull Determines the maximum energy in the beam

bull spectrum and affects the quality of the output spectrum

bull Efficiency of x-ray production is directly related to tube voltage

15

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Influencing factors kVp

15 rule 15 kVp = doubling of exposure to the film

15 kVp = halving of exposure to the film

15 rule will always change the contrast of the image because kV is the primary method of changing image contrast

Remember 15 change ( ) KVP has the same effect as

doubling or frac12 the MAS on density

16

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

kVp Changes

bull The kVp setting must be changed by at least 4 to produce visual changes an image

17

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

4 kVp Changes

18

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Radiographic Technique

Technique charts are based on the ldquoaverage patientrdquo

The thicker the part the more x-radiation is required to penetrate Calipers should be used

Keep in mind not only the measurement but the type of tissue you need to penetrate (fat vs muscle)

19

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Technique

In general Soft tissue = low kVp and high mAs

Extremity (soft tissue amp bone) = low kVp

Chest (high subject contrast) = high kVp Abdomen (low subject contrast) = middle kVp

20

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Pathology

Can appear with increased radiolucency or radiopacity

Some pathology is destructive causing tissue to be radiolucent

Others can be additive causing tissue to be radiopaque

21

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Technique selection ndash Fixed kVp For each anatomic part there is an optimum

kVp

mAs is varied based on part thickness or pathological condition

22

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Image Quality

Bushong Ch 16

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Objectives

bull Image Quality ndash Factors

bull Geometric Factors

bull Subject Factors

bull Artifacts

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Image Quality

bull Is the exactness of the representation of the patientrsquos anatomy

bull 3 major factors affecting image quality that is under the control of the technologist Image Receptor selectionuse Geometric factors amp Subject factors

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Judging Image Quality

bull The most important characteristic of radiographic quality are Spatial Resolution Contrast Resolution Noise amp Artifacts

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Main Factors Affecting Recorded Detail

bull kVp amp mAsbull Motionbull Object

Unsharpnessbull SID (Source to

Image Distance)bull OID (Object to

Image Distance)

bull Material Unsharpness Film Screen Combo

bull Focal Spot Size bull MTF (modulation

transfer function)

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Recorded Detail

bull Other names- detail-sharpness of detail-definition-resolution-degree of noise- visibility of detail

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Resolution

bull Is the ability to image two separate objects and visually distinguish one from the other

bull Spatial resolution is the ability to image small objects that have high subject contrast Ex bone-soft tissue interface breast calcifications calcified lung nodule

bull Conventional radiography has excellent spatial resolution

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

RESOLUTION TEST

TOOLS

LINE PAIRS MM

Depicts how well you can see the differences in structures

More lines=more detail

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Measuring Resolution for an x-ray imaging system

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

SMPTE Test Pattern

bull In 1985 the Society of Motion Picture and Television Engineers (SMPTE) published a recommended practice (RP-122)

bull Specifications for Medical Diagnostic Imaging Test Patterns for Television Monitors and Hard-copy Cameras

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

SMPTE Test Pattern

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Focal spot size of the cathode

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Line-focus principle

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Modulation Transfer Function

bull The ability of a system to record available spatial frequencies

bull The sum of the components in a recording system cannot be greater than the system as a whole

bull When any componentrsquos function is compromised because of some type of interference the overall quality of the system is affected

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Contrast Resolution

bull Is the ability to distinguish anatomic structures of similar subject contrast Ex liver-spleen gray matter-white matter

bull Magnetic Resonance Imaging has the highest contrast resolution

bull Computed Tomography is excellent as well

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

MRI CT

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

The contrast of an object is expressed relative to its surrounding background

That is what determines its visibility

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Radiographic Contrast

bull Is the product of image receptor contrast and subject contrast

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

ldquoNoiserdquo

bull Borrowed from electrical engineering

bull Audio noise = hum or flutter heard from a stereo

bull Video noise = ldquosnowrdquo on a TV

bull Radiographic noise = random fluctuation on the OD of the image

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy

image - MORE COMMON IN CR SYSTEMS

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Radiographic noise

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Radiographic Noise

bull Four components

bull Film graininess structure mottle quantum mottle amp scatter radiation

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Radiographic Noise

bull Film graininess ndash distribution amp size of the silver halide grains in the emulsion

bull Structure mottle ndash speed of the intensifying screen Phosphor size amp DQECE

bull Not under the control of the technologist

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Image Noise

bull Speckled background on the imagebull Caused when fast screens and high kVp

techniques are used Noise reduces image contrast

bull The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)

bull The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Quantum Mottle

bull An image produced with just a few x-rays will have more quantum mottle

bull The use of very fast intensifying screens or not enough mAs or kVp will increase quantum mottle

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Quantum mottle

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Screen Speed

bull Efficiency of a screen in converting x-rays to light is Screen Speed

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Speed

bull Fast image receptorsndash Noise Spatial resolutionndash Contrast resolution

bull Slow image receptorsndash Noise Spatial resolutionndash Contrast resolution

ndash See pg 274 for answers

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Speed

bull Low noise = fast or slow speed

bull High contrast resolution = fast or slow speed

bull Reduced spatial resolution = fast or slow speed

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

PARALLAX ndasheach emulsion has an image

single image overlaped edges edge sharp less sharp

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Other Film FactorsCharacteristic Curve

bull Is used to describe the relationship between OD and radiation exposure

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

What is the useful OD range

Characteristic curveof radiographic film

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

The latitude of an image receptor is the exposure range over which it responds with diagnostically

useful OD

bull Depending on the manufacturing characteristics

radiographic film will respond differently to

radiation exposure

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

FS vs Digital Dynamic Range

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Unexposed film

bull Appears like a frosted glass window

bull ODs of unexposed film are due to base density and fog density

bull Base density ndash tint added to the base to reduce eye strain and crossover Has a densitometer value of approximately 01

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

CROSSOVER

bull Reducing crossover by adding a dye to the base

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Unexposed film

bull Fog Density ndash inadvertent exposure of film during storage chemical contamination improper processing radiation exposure etc

bull Fog density contributes to reduction of radiographic contrast

bull Fog density should not exceed 01

bull Base + fog OD = 01 to 03

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

2 principal characteristics of any image are Spatial amp Contrast Resolution

bull Spatial resolution ndash Resolution is the ability to image two separate

objects and visually distinguish one from the otherndash Spatial resolution is the ability to image small

objects that have high subject contrast (eg bone-soft tissue interface calcified lung nodules)

ndash Determined by focal-spot size and other factors that contribute to blur

ndash Diagnostic x-ray has excellent spatial resolution It is measured in line pairs per mm

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Other factors affecting the finished radiograph

bull The concentration of processing chemicals

bull The degree of chemistry agitation during development

bull Development time

bull Development temperature

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Image Quality in Digital

Matrix size is determined by

bull Receptor size (Field of View FOV)

bull Pixel size

bull CR - Sampling frequency

bull DR - DEL size

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Spatial Resolution determined by

1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Sampling Frequency

bull The sampling frequency is the rate at

bull which the laser extracts the image data

bull from the plate

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Signal Sampling Frequency Good sampling under sampling

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Nyquist Frequency

bull The Nyquist Frequency will be frac12 of thebull sampling frequencybull A plate that is scanned using a sampling

frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency

bull The Nyquist Frequency allows the determination of the spatial resolution for a given sampling frequency

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Geometric Factors

bull Producing high quality radiographs Technologists must maximize geometric conditions

bull Three principal geometric conditions affect radiographic quality Magnification Distortion amp Focal-spot blur

bull Review table 16-4 pg 295 for summary

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Object Unsharpness

bull Main problem is trying to image a 3-D object on a 2-D film

bull Human body is not straight edges and sharp angles

bull We must compensate for object unsharpness with factors we can control focal spot size SID amp OID

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Magnification

bull All image on the radiograph are larger than the object they represent

bull For most exams minimizing magnification is desired There are a few exams where some magnification can be helpful

bull TUBE CLOSE TO THE PART (SID)bull PART FAR FROM THE CASSETTE (OID)

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Minimizing Magnification

bull Large SID use as large a source-to-image receptor distance as possible

bull Small OID place the object as close to the Image receptor as possible

bull In terms of recorded detail and magnification the best image is produced with a small OID and a large SID

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Size Distortion amp SID

bull Major influences SID amp OID

bull As SID magnification bull Standardized SIDrsquos allow radiologist to

assume certain amt of magnification factors are present

bull Must note deviations from standard SID

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away ndash the less magnified uarrSID darr MAGNIFICATION

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

SID

bull Shine a flashlight on a 3-D object shadow borders will appear ldquofuzzyrdquo

-On a radiograph called Penumbrabull Penumbra (fuzziness) obscures true

border ndash umbrabull Farther the flashlight from object =

sharper borders Same with radiography

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

OIDObject to Image Distance

bull The closer the object to the film the sharper the detail

bull OID penumbra sharpness bull OID penumbra sharpness bull Structures located deep in the body

radiographer must know how to position to get the object closest to the film

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Size Distortion amp OID

bull If source is kept constant OID will affect magnification

bull As OID magnification bull The farther the object is from the film the

more magnification

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away ndash the more magnified

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Minimal magnification small OID

Magnification - large OID

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

40rdquo SID VS 72rdquo SID

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Magnification Factor

source-to-image receptor distance

bull MF = source-to-object distancendash SOD difficult to measure accurately

usually an estimated value

SID

bull MF = SOD

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Finding SOD

bull SID ndash OID = SOD

bull SID = 100 cm

bull OID = 7 cm

bull What is the SOD

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Finding magnification of the heart on a lateral CXR

bull SID ndash OID = SOD

bull SID = 72 inches

bull OID = 8 inches (estimated)

bull What is the SOD

bull What is the Mag Factor

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Distortion

bull Misrepresentation of the true size or shape of an object

-MAGNIFICATION (size distortion)

-TRUE DISTORTION (shape distortion)

bull Shape distortion unequal magnification of different portions of the same object

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Shape Distortion

bull Depends on

bull Object thickness

bull Object position

bull Object shape

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Object Thickness

bull Thick objects have more OID and are more distorted than thinner structures

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Object Position

bull If the object plane and the image plane are parallel the image is not distorted

bull CR perpendicular

to the part

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Position Distortion

bull Foreshortened = anatomy at an incline to the CR displays smaller than true size

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

D amp E = shape distortion

(foreshortening of part)

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Position Distortion

bull Elongation anatomy at an incline and lateral to the central axisndash Could be

foreshortened as well

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Elongation Foreshortened Normal

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Position Distortion

bull Spatial distortion = anatomy positioned at various OIDs but superimposed only one can be seen

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Position Distortion ndash Irregular Anatomy

bull Anatomy or objects can cause considerable distortion when imaged off the central axis

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Focal-Spot Blur

bull Dependent on the size of the effective focal spot

bull Smaller the effective focal spot = less blur and better spatial resolution

bull Focal-spot blur is the most important factor in determining spatial resolution

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Focal Spot Size

bull Smaller x-ray beam width will produce a sharper image

bull Fine detail = small focal spot (ie small bones)

bull General radiography uses large focal spot

bull Beam from penlight size flashlight vs flood light beam

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

ANODE

ANODE

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Focal spot size ndash determined by filament in cathode amp surface area used at anode

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Focal-spot blur is caused by the effective size of the focal spot which is larger to the

cathode side of the image

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Focal-spot blur is small when the object-to-image receptor distance (OID) is small

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Image QualitySubject Factors

bull Patient thickness

bull Effective atomic number

bull Object shape

bull Subject contrast

bull Tissue mass density

bull kVp

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Object shape

Objects with structurehaving a form that coincides with thex-ray beam has maximum detail

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Patient Motion

bull Can be voluntary or involuntary

bull Best controlled by short exposure times

bull Use of careful instructions to the pt

bull Suspension of pt respiration

bull Immobilization devices

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Blurring of image due to patient movement during exposure

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions

Questions

• PRIME FACTORS
• PRIME FACTORS
• Slide 6
• Slide 7
• Inverse Square Law Formula
• Direct Square Law
• Focal-Spot Changes
• Tube voltage (kVp)
• Influencing factors kVp
• kVp Changes
• 4 kVp Changes
• Image Quality
• Objectives
• Image Quality
• Judging Image Quality
• PowerPoint Presentation
• Main Factors Affecting Recorded Detail
• Slide 29
• Recorded Detail
• Slide 31
• Slide 32
• Slide 33
• Resolution
• Slide 35
• Measuring Resolution for an x-ray imaging system
• Slide 37
• Slide 38
• SMPTE Test Pattern
• SMPTE Test Pattern
• Focal Spot Size
• Focal spot size of the cathode
• Line-focus principle
• Modulation Transfer Function
• Contrast Resolution
• MRI CT
• Slide 47
• The contrast of an object is expressed relative to its surrounding background That is what determines its visibility
• Radiographic Contrast
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• ldquoNoiserdquo
• QUANTUM MOTTLE Not enough PHOTONS ndash can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS
• Radiographic noise
• Radiographic Noise
• Slide 58
• Image Noise
• Quantum Mottle
• Quantum mottle
• Slide 62
• Slide 63
• Screen Speed
• Speed
• Slide 66
• PARALLAX ndash each emulsion has an image single image overlaped edges edge sharp less sharp
• Other Film Factors Characteristic Curve
• What is the useful OD range
• Slide 70
• The latitude of an image receptor is the exposure range over which it responds with diagnostically useful OD
• Slide 72
• FS vs Digital Dynamic Range
• Unexposed film
• CROSSOVER
• Slide 76
• Slide 77
• 2 principal characteristics of any image are Spatial amp Contrast Resolution
• Other factors affecting the finished radiograph
• Slide 80
• Image Quality in Digital
• Slide 82
• Slide 83
• Slide 84
• Spatial Resolution determined by
• Slide 86
• Sampling Frequency
• Slide 88
• Signal Sampling Frequency Good sampling under sampling
• Nyquist Frequency
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Slide 95
• Slide 96
• Geometric Factors
• Object Unsharpness
• Magnification
• Minimizing Magnification
• Size Distortion amp SID
• Slide 102
• SID
• Slide 104
• Slide 105
• OID Object to Image Distance
• Size Distortion amp OID
• Slide 108
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• 40rdquo SID VS 72rdquo SID
• Slide 115
• Magnification Factor
• Finding SOD
• Finding magnification of the heart on a lateral CXR
• Distortion
• Slide 120
• Shape Distortion
• Object Thickness
• Slide 123
• Object Position
• Position Distortion
• D amp E = shape distortion (foreshortening of part)
• Slide 127
• Elongation Foreshortened Normal
• Slide 129
• Position Distortion ndash Irregular Anatomy
• Focal-Spot Blur
• Slide 132
• Slide 133
• Slide 134
• Slide 135
• Focal-spot blur is caused by the effective size of the focal spot which is larger to the cathode side of the image
• Focal-spot blur is small when the object-to-image receptor distance (OID) is small
• Image Quality Subject Factors
• Object shape
• Patient Motion
• Slide 141
• Slide 142
• Slide 143
• Slide 144
• Questions