components of image quality & radiographic artifacts

Components of Components of Image Quality Image Quality

& & Radiographic Radiographic

ArtifactsArtifacts

Radiologic Technology ARadiologic Technology ASpring 2010 Spring 2010 FinalFinal

X-ray Exposure FactorsX-ray Exposure Factors

Radiographic Density & ContrastRadiographic Density & Contrast

Components of Components of Image Quality Image Quality

Radiographic ArtifactsRadiographic Artifacts

Review Chapter 7Review Chapter 7

Primary radiation exits the tubePrimary radiation exits the tube

Interacts with various densities in the body Interacts with various densities in the body

Photons may be absorbedPhotons may be absorbed

Scattered Scattered

Passed through without any interference Passed through without any interference to the cassette or image receptor (IR)to the cassette or image receptor (IR)

How well we can see something on the imageHow well we can see something on the image

Image detail Image detail is affected by:is affected by:

Photographic Photographic PropertiesProperties

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X-ray Exposure FactorsX-ray Exposure Factors

TECHNIQUE SELECTION:TECHNIQUE SELECTION: Radiographer selects the Radiographer selects the Kilovoltage peak Kilovoltage peak (kVp)(kVp) Milliamperage (mA) & time (s)Milliamperage (mA) & time (s) Milliamperage x time = Milliamperage x time = mAsmAs

(milliamperage multiplied by a set (milliamperage multiplied by a set time measured in seconds)time measured in seconds)

Kilovoltage PeakKilovoltage Peak kVpkVp One kilovolt = 1000 voltsOne kilovolt = 1000 volts

The amount of voltage The amount of voltage selected for the x-ray tube.selected for the x-ray tube.

Range 30 to 150 kVpRange 30 to 150 kVp

kVp controls __________ ?kVp controls __________ ?

MilliamperageMilliamperage One milliampere (mA) = one One milliampere (mA) = one

thousandth of an ampere.thousandth of an ampere.

The amount of current supplied to The amount of current supplied to the x-ray tubethe x-ray tube

How many x-rays will be produced How many x-rays will be produced

Range 10 to 1200 mARange 10 to 1200 mA

TimeTime

In secondsIn seconds

How long x-rays will be producedHow long x-rays will be produced

0.001 to 6 seconds0.001 to 6 seconds

Milliampere SecondsMilliampere Seconds Technologists think in terms of Technologists think in terms of mAsmAs

Calculated by mA x secondsCalculated by mA x seconds

Ex: 100mA X 0.2s = 20 mAsEx: 100mA X 0.2s = 20 mAs

How many x-rays will be produced and How many x-rays will be produced and for how long.for how long.

Modern x-ray machines only allow Modern x-ray machines only allow control of control of

mAsmAs controls _______________ ? controls _______________ ?

Factors Affecting Factors Affecting DensityDensity Primary control factor:Primary control factor:

Influencing factors:Influencing factors:

Primary Controlling Primary Controlling Factor of DensityFactor of Density

1.1. mAs mAs

2.2. mA = AMOUNT of electrons sent mA = AMOUNT of electrons sent across the tube combined with TIME across the tube combined with TIME (S) = mAs(S) = mAs

3.3. mAs controls DENSITY on radiograph mAs controls DENSITY on radiograph primary function of mAs is DENSITYprimary function of mAs is DENSITY

Imagine this…Imagine this… If the mA station is changed from 200 to If the mA station is changed from 200 to

400 mA, twice as many electrons will 400 mA, twice as many electrons will flow from the cathode to the anode.flow from the cathode to the anode.

From 10 mA to 1000 mA = 100 x moreFrom 10 mA to 1000 mA = 100 x more

mA controls mA controls how manyhow many electrons are electrons are coming at the targetcoming at the target

mAs is a combination of mAs is a combination of how manyhow many and and for for how longhow long (seconds)(seconds)

10 mA 1000 mA

Changing Mas – Changes DensityChanging Mas – Changes Density + 25 % + 50 % + 25 % + 50 % masmas

Influencing Factor Influencing Factor on Density:on Density:

kVpkVp more energy = more photons passing though more energy = more photons passing though

tissue & striking the imagetissue & striking the image

____________ = ____________ = doubling of exposure to the filmdoubling of exposure to the film

_____________ = _____________ = halving of exposure to the filmhalving of exposure to the film

_____ rule will also change the contrast of _____ rule will also change the contrast of the image because kV is the primary the image because kV is the primary method of changing image contrast.method of changing image contrast.

Remember : Remember : ___ change ( ___ change ( ) KVP has the same effect ) KVP has the same effect

as doubling or ½ the MAS on densityas doubling or ½ the MAS on density

Change in kVpChange in kVp kVp controls the energy level of the kVp controls the energy level of the

electrons and subsequently the energy electrons and subsequently the energy of the x-ray photons.of the x-ray photons.

A change from 72 kVp will produceA change from 72 kVp will producex-rays with a lower energy than atx-rays with a lower energy than at82 kVp82 kVp

Difference between a ball traveling 72 Difference between a ball traveling 72 mph and 82 mph (how much energy did mph and 82 mph (how much energy did it take to throw the ball at the rates?)it take to throw the ball at the rates?)

+ 15% kvp - 15% + 15% kvp - 15% kvpkvp

Radiolucent vs. Radiolucent vs. RadiopaqueRadiopaque

___________ materials allow ___________ materials allow x-ray photons to pass x-ray photons to pass through easily (soft tissue).through easily (soft tissue).

____________________ materials are materials are not easily penetrated by x-not easily penetrated by x-rays (bones)rays (bones)

Creating the ImageCreating the Image

Transmission (no Transmission (no interaction)interaction)– Responsible for dark Responsible for dark

areasareas Scatter (grays) – Scatter (grays) –

produces no produces no diagnostic infodiagnostic info

Absorption Absorption (photoelectric (photoelectric effect)effect)– Responsible for light Responsible for light

areasareas

ImagesImages

____________ = THE AMOUNT OF ____________ = THE AMOUNT OF BLACKENING “DARKNESS” ON BLACKENING “DARKNESS” ON THE RADIOGRAPH (mAs)THE RADIOGRAPH (mAs)

____________ – THE DIFFERENCES ____________ – THE DIFFERENCES BETWEEN THE BLACKS TO THE BETWEEN THE BLACKS TO THE WHITES (kVp)WHITES (kVp)

Why you see what you Why you see what you see…see… The films or images have different levels of The films or images have different levels of

density – different shades of graydensity – different shades of gray

X-rays show different features of the body in X-rays show different features of the body in various shades of gray. various shades of gray.

The gray is darkest in those areas that do not The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass absorb X-rays well – and allow it to pass throughthrough

The images are lighter in dense areas (like The images are lighter in dense areas (like bones) that absorb more of the X-rays.bones) that absorb more of the X-rays.

Image ProductionImage Production __________________________ – The beam of photons, – The beam of photons,

B4 it interacts with the pt’s body.B4 it interacts with the pt’s body. __________________________ – The resulting beam – The resulting beam

that is able to exit from the patient.that is able to exit from the patient. __________________________ – Radiation that – Radiation that

interacts with matter & only interacts with matter & only continues in a different direction – not continues in a different direction – not useful for image production.useful for image production.

__________________________ – Primary radiation that – Primary radiation that is changed (partially absorbed) as it is changed (partially absorbed) as it travels through the pt.travels through the pt.

Patient Body Size Patient Body Size and and

PathologyPathology

3 Different Body Habitus3 Different Body HabitusHypersthenic Sthenic HyposthenicHypersthenic Sthenic Hyposthenic

Thank you to the 3 men in my life ! DCharman

Dr. Charman, Eric Guzman, Adam Guzman

Density and ImagesDensity and Images

Goal: Producing optimal radiographsGoal: Producing optimal radiographs

DENSITYDENSITY

Too dark Too light

Controlling Factor ofControlling Factor ofContrastContrast

Controlling Factor of Controlling Factor of ContrastContrast

Kilovolts to anode side – kVpKilovolts to anode side – kVp

Kilovolts controls how fast the Kilovolts controls how fast the electrons are sent across the tubeelectrons are sent across the tube

_______ – controls CONTRAST on _______ – controls CONTRAST on imagesimages

Producing optimal radiographsContrast Scale

Long scale short scale

Scale of Contrast?Scale of Contrast? Which one is “better” Which one is “better” How does the kVp affect these How does the kVp affect these images?images?

Short Scale vs. Long Short Scale vs. Long ScaleScale

Beam Restriction Beam Restriction and and GridsGrids

ScatterScatter

– Creates fogCreates fog– Lowers contrast (more grays)Lowers contrast (more grays)

Increases as: Increases as:

Effects of collimation Effects of collimation (beam restriction) on (beam restriction) on scatterscatter

Collimate to Collimate to area of interest area of interest -reduces -reduces scatter and scatter and radiation dose radiation dose to the patientto the patient

GridsGrids

A device with lead strips that is A device with lead strips that is placed between the patient and placed between the patient and the cassettethe cassette

Used on larger body parts to Used on larger body parts to reduce the number of scattering reduce the number of scattering photons from reaching the imagephotons from reaching the image

GRID NO GRIDGRID NO GRIDCONTROLS CONTRASTCONTROLS CONTRAST

Basic Grid Basic Grid ConstructionConstruction

1.1. Radiopaque lead stripsRadiopaque lead strips

2.2. Separated by radiolucent interspace Separated by radiolucent interspace material - Typically aluminummaterial - Typically aluminum

3.3. Allow primary radiation to reach the Allow primary radiation to reach the image receptor (IR)image receptor (IR)

4.4. Absorb most scattered radiationAbsorb most scattered radiation

5.5. Primary disadvantage of grid use Primary disadvantage of grid use 1.1. Grid lines on filmGrid lines on film

GRIDSGRIDS

Grid is placedGrid is placedbetween patient (behind between patient (behind table or upright bucky) & table or upright bucky) & cassettecassette

Grids absorb scatter –Grids absorb scatter –prevents it from reaching prevents it from reaching the imagethe image

GRID

STOPS

SCATTER

With Grid No Grid

GEOMETRIC PropertiesGEOMETRIC Properties Recorded DetailRecorded Detail

DISTORTIONDISTORTION– __________________________

MagnificationMagnification

– __________________________ Elongation Elongation ForeshorteningForeshortening

RECORDED DETAILRECORDED DETAIL

RECORDED DETAILRECORDED DETAILThe degree of sharpness The degree of sharpness in an object’s borders in an object’s borders and structural details.and structural details.

How “clear” the object How “clear” the object looks on the radiographlooks on the radiograph

Recorded DetailRecorded Detail

The degree of sharpness in an object’s The degree of sharpness in an object’s borders and structural details.borders and structural details.

Other names:Other names:

1.1.

2.2.

3.3.

4.4.

RESOLUTION TEST

TOOLS

LINE PAIRS/ MM

Depicts how well you can see the differences in structures

More lines=more detail

Factors that affectFactors that affectRecorded DetailRecorded Detail

1.1. Geometric unsharpnessGeometric unsharpness

2.2. OID SID SIZE SHAPEOID SID SIZE SHAPE

3.3. Motion unsharpness (blurring)Motion unsharpness (blurring)

4.4. Intensifying Screens Intensifying Screens

5.5. Film Speed / CompositionFilm Speed / Composition

6.6. Film – Screen contactFilm – Screen contact

7.7. Kvp & Mas (density / visibility)Kvp & Mas (density / visibility)

MOTION MOTION

AKAAKA

BlurringBlurring

MotionMotion Can be voluntary or _____________Can be voluntary or _____________

Best controlled by short exposure Best controlled by short exposure timestimes

Use of careful _______________ to the pt.Use of careful _______________ to the pt.

Suspension of pt. respirationSuspension of pt. respiration

_____________________ devices_____________________ devices

Decrease Motion Decrease Motion UnsharpnessUnsharpness Instruct patient not to move or Instruct patient not to move or

breathbreath

Use Immobilization devicesUse Immobilization devices

Use Short exposure timesUse Short exposure times

Lock equipment in placeLock equipment in place

Object UnsharpnessObject Unsharpness

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

Human body is not straight edges and Human body is not straight edges and sharp angles.sharp angles.

We must compensate for object We must compensate for object unsharpness with factors we can unsharpness with factors we can control: focal spot size, SID & OIDcontrol: focal spot size, SID & OID

SID SID Source to Image DistanceSource to Image Distance

The greater the source X-ray tube) The greater the source X-ray tube) to image (cassette) distance, the to image (cassette) distance, the greater the image sharpness.greater the image sharpness.

Standard distance = 40 in. most Standard distance = 40 in. most examsexams

Exception = Chest radiography 72 Exception = Chest radiography 72 in.in.

SIDSID Shine a flashlight on a 3-D object, Shine a flashlight on a 3-D object,

shadow borders will appear “fuzzy” shadow borders will appear “fuzzy” -On a radiograph called -On a radiograph called

PenumbraPenumbra

Penumbra (fuzziness) obscures Penumbra (fuzziness) obscures true border – true border – umbraumbra

Farther the flashlight from object = Farther the flashlight from object = sharper borders. Same with sharper borders. Same with radiography.radiography.

OIDOIDObject to Image DistanceObject to Image Distance The closer the object to the film, the The closer the object to the film, the

sharper the detail.sharper the detail.

OID OID , penumbra , penumbra , sharpness , sharpness OID OID , penumbra , penumbra , sharpness , sharpness

Structures located deep in the body, Structures located deep in the body, radiographer must know how to position radiographer must know how to position to get the object closest to the film.to get the object closest to the film.

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

The farther away – the more magnified

DistortionDistortion Misrepresentation of the true size Misrepresentation of the true size

or shape of an objector shape of an object

– ________________________________– size distortionsize distortion

– ________________________________– shape distortionshape distortion

MAGNIFICATIONMAGNIFICATION

TUBE CLOSE TO THE PART (SID)TUBE CLOSE TO THE PART (SID)

PART FAR FROM THE CASSETTE PART FAR FROM THE CASSETTE (OID)(OID)

http://http://www.coursewareobjects.com/www.coursewareobjects.com/objects/mroimaging_v1/mod04i/objects/mroimaging_v1/mod04i/0416a.htm0416a.htm

Size Distortion & OIDSize Distortion & OID

If source is kept constant, OID will If source is kept constant, OID will affect magnificationaffect magnification

As OID As OID , magnification , magnification

The farther the object is from the The farther the object is from the film, the more magnification film, the more magnification

•In terms of recorded detail and magnification the best image is produced with a

•______ OID & _____ SID

Minimal magnification small OID

Magnification - large OID

Size Distortion & SIDSize Distortion & SID Major influences: SID & OIDMajor influences: SID & OID

As SID As SID , magnification , magnification

Standardized SID’s allow Standardized SID’s allow radiologist to assume certain amt. radiologist to assume certain amt. of magnification factors are of magnification factors are presentpresent

Must note deviations from Must note deviations from standard SIDstandard SID

SHAPE DISTORTIONSHAPE DISTORTION

ElongationElongation

and and

ForeshorteningForeshortening

Shape DistortionShape Distortion

Misrepresentation of the shape of Misrepresentation of the shape of an objectan object

Controlled by alignment of the Controlled by alignment of the beam, part (object), & image beam, part (object), & image receptorreceptor

Influences: Central ray angulation Influences: Central ray angulation & body part rotation& body part rotation

Image DistortionImage Distortion

When the part to be imaged – When the part to be imaged – does not lay parallel with the IR does not lay parallel with the IR (cassette)(cassette)

If the Central Ray is not If the Central Ray is not perpendicular to the part perpendicular to the part – CR should be at right angle with the CR should be at right angle with the

cassettecassette

Central Ray AngulationCentral Ray Angulation Body parts are not always 90 Body parts are not always 90

degrees from one anotherdegrees from one another

Central ray angulation is used to Central ray angulation is used to demonstrate certain details that demonstrate certain details that can be hidden by superimposed can be hidden by superimposed body parts.body parts.

Body part rotation or obliquing the Body part rotation or obliquing the body can also help visualize body can also help visualize superimposed anatomy.superimposed anatomy.

Central RayCentral Ray Radiation beam diverges from the tube Radiation beam diverges from the tube

in a pyramid shape.in a pyramid shape.

Photons in the center travel along a Photons in the center travel along a straight line – straight line – central raycentral ray

Photons along the beam’s periphery Photons along the beam’s periphery travel at an angletravel at an angle

When central ray in angled, image When central ray in angled, image shape is distorted.shape is distorted.

Focal Spot SizeFocal Spot Size

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

Fine detail = small focal spot (i.e. small Fine detail = small focal spot (i.e. small bones)bones)

General radiography uses large focal General radiography uses large focal spotspot

Beam from penlight size flashlight vs. Beam from penlight size flashlight vs. flood light beamflood light beam

ANODE

ANODE

FOCAL SPOT ANGLEFOCAL SPOT ANGLE

SMALLER ANGLE – SMALLER BEAM AT PATIENT

http://www.xray2000.co.uk/

Artifacts - TypesArtifacts - Types

Processing ArtifactsProcessing Artifacts

Exposure ArtifactsExposure Artifacts

Handling & Storage Handling & Storage ArtifactsArtifacts

Processing ArtifactsProcessing Artifacts

Emulsion pickoffEmulsion pickoff Chemical fogChemical fog Guide-shoe marksGuide-shoe marks Water marksWater marks Chemical spotsChemical spots Guide-shoe & roller scratchesGuide-shoe & roller scratches

Exposure ArtifactsExposure Artifacts

MotionMotion Improper patient positionImproper patient position Wrong screen-film matchWrong screen-film match Poor film/screen contactPoor film/screen contact Double exposureDouble exposure Warped cassetteWarped cassette Improper grid positionImproper grid position

ArtifactArtifact

Handling & Storage Handling & Storage ArtifactsArtifacts Light fogLight fog Radiation fogRadiation fog StaticStatic Kink marksKink marks ScratchesScratches Dirty cassettesDirty cassettes

??

??

Pt clothing

PATHOLOGY NOT PATHOLOGY NOT ARTIFACTARTIFACT

Name &Name & cause causeof this?of this?

Evaluating ImagesEvaluating Images

What do you think?What do you think?

Does this show good detail?Does this show good detail? Is all of the anatomy present?Is all of the anatomy present? How is the density / contrast?How is the density / contrast?