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RT 255 CCross Sectional Anatomy

Week 1

FINAL

4-13-09

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Name the Sectional PlanesA

B

C

D

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Oblique and Transverse

Used for imaging of heart.

Commonly used in MR and sonography

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Axial (Transverse) Planes

– 1– 2– 3– 4– 5– 6

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Axial Scout

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Axial (cross sectional)

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Sagittal Plane

• 1

• 2

• 3

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Sagittal Scout

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Sagittal

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Coronal Plane

• 1

• 2

• 3

• 4

• 5

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Coronal

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Coronal

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Name the Imaging Plane

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17

18

19

20

21

22

23

24

25

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Both Radiation: Why CT vs. Radiography

• Superimposition

• Contrast Resolution– Less scatter

• One exposure

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Similar to Radiography

• Radiopaque are white– Bone– Prosthesis

• Lower density images are gray– Fat – Muscles– Organs

• Very low density are black– Air

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Hounsfield Units

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Fundamentals of CT

Cross sectional

Tube rotates around patientDetectors measures

primary data

Primary data sent to computerCalculated according to algorithmData assembled into a

matrix

Each sectional slice is displaced on cathode ray tube

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Generations of Scanners

• First generation– 1– 2– 3– 4

• Second generation– 1– 2– 3– 4

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Third Generation

• Rotate/ rotate

• More than 750 detectors

• 1-10 seconds

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Fourth Generation

• Rotate only

• Fixed detectors

• More detectors

• Higher dose to PT

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Technical Aspects

• Remnant radiation is collected– 1– 2

• Electrical signal digitized– Each signal assigned a number

• Signals combined to form digital image– Field of View (FOV) determines amount of data to be

displayed on monitor

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Breakdown of the Digital Image

• Array of numbers– 1

• Pixel– 1– 2

• Voxel– 1– 2– 3

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System Components

• Computer– Operators console

• Gantry

• Table

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Computer

• Four basic functions

– 1. – 2– 3– 4

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Data Acquisition

• Tech chooses various parameters

– 1– 2– 3– 4

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Image Reconstruction

• Digitizes raw data

• Computer performs mathematical computations on a temporary storage system– Host computer has limited storage capacity

• Reconstruction takes a few seconds

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Long term Storage

• After reconstruction it is transferred to another storage medium

• Those temporary images on the host computer are archived separately as an independent study that can be retrieved later

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Image display

• Can be viewed on a video monitor

• Tech and doctor can communicate with host computer to view images

• Can manipulate images– 1– 2

– Image resolution lost with reconstruction in other planes

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Gantry• Circular

• Aperture is the hole PT goes in

• Houses– Detector, slip ring, generator and x-ray tube

• Tube similar to x-ray tube– Must withstand higher amounts of heat

• Can be tilted 30 degrees forward and back

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Table• Automated device linked to gantry &

computer

• Moves in increments – According to protocol

• Made of wood or low density carbon composite

• Has a weight limit

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Control Console

• Where the tech controls the scanner

• Has a keyboard, display monitor & mouse

• Allows tech to control– 1. – 2– 3– 4

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Image Manipulation

• Windowing– 1.

• Window width– 1– 2– 3

• Window level– 1– 2

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Windowing

Window width 400

Window level 35

Window width 2200

Window level 400

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Factors Affecting Image Quality

• Spatial resolution

• Contrast resolution

• Noise

• Artifacts

• Patient factors

• Scan times

• Scan diameter

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Spatial Resolution

• What happens to resolution with smaller phosphor crystals in standard film screen systems?

• Is a function of pixel size– Smaller: better detail

• Thinner slices: increased detail

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Contrast Resolution and Noise

• Ability to distinguish adjacent tissue

• In CT it is better than in conventional x-ray– Less scatter

• Appears as graininess

• Low noise is smooth to the eye

• High noise is blotchy and spotty

• As noise increases contrast resolution decreases

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Artifacts

• Streak artifacts– Metallic objects,

pacemakers, and prosthesis

• High concentration barium

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Patient Factors

• Motion

• Size of patient

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Image Quality under Tech Control

• Slice thickness

• Scan time

• Scan diameters

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Diagnostic Applications• Most common anatomy examined is

– Head, chest and abdomen

• Exam of choice for:– Head trauma– CVA

• Also useful for:– Infarctions– Hemorrhage– Disk herniations– Craniofacial fractures and tumors– Cancers– Hydrocephalus– Degenerative diseases– Inflammatory infections– Congenital disorders

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Use of Contrast Media

• Can be administered orally, rectally and intravenously

• IV usually non-ionic contrast

• BA and Hypaque used for abdomen and GI studies.– 2% concentration BA– Low concentration (hypaque)

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Special Features

• Dynamic scanning

• CT angiography (CTA)

• Spiral/helical CT

• Multi-slice Spiral/helical CT

• 3 D imaging

• Radiation therapy treatment

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Dynamic Scanning and CTA

• After contrast administration

• Sequential scanning times as different structures enhance

• CTA: – 1– 2– 3

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CTA

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CTA

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Spiral / Helical CT and Multi-slice Spiral/ Helical CT

• Single row of detectors

• Gantry rotates around PT as table moves

• Scans a volume instead of slices

• Better detail

• Fast scan times– For peds and combative

patients

• Multiple rows of detector arrays

• A four row scanner would scan 4 times faster

• Improced spatial resolution

• LG areas of body can be done with one breath hold

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Spiral and Multi-slice Spiral

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3D Imaging

• Postprocessing technique

• Takes 2D raw data and constructs a 3D image

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3D imaging

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3D Imaging

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Radiation Therapy Planning

• Gives volumetric and depth calculation ability

• Allows for one CT instead of the 3 they used to do

• Flat board used instead of curved couch

• Dose to normal tissue is minimized

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RAD Therapy and CT

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RAD Therapy and CT

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CT and Radiation Dose

• CT doses are higher than conventional radiography

• A lower pitch results in a higher dose– More overlap

• Thinner slices also result in a higher dose

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CT vs. MRI

• MRI exhibits better low contrast than CT

• Higher cost and takes longer

• Cannot do with metal

• CT demonstrates bone better than MRI

• Faster, so preferred for some PT’s– Small gantry– Wide aperture

• Less costly

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The Future of CT

• Has significantly increased in the past 5 years

• Higher quality images increase accuracy of diagnosis and treatment

• Cost effective

• Will continue to be a diagnostic tool