CT Review

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CT assigned number for LDPE

+-90 HU

CT assigned number for air

-1000

CT assigned number for water

0

CT assigned number for bone

1000

CT assigned number for acrylic

120HU

What generation of CT is Single ray pencil beam Single detector

1st

360 linear interpolation requires how many rotations to reconstruct a slice

2

What generation of CT is Linear scan and rotate (6 scans, 30° rotations)

2nd

What generation of CT is Single projection fan-shaped beam (permitting whole body scanning) Up to 30 detectors 10-90 second scan time

2nd and 3rd

What generation of CT is 360° rotation of x-ray tube and detectors Crude dynamic capabilities

3rd

What generation of CT is Single projection fan-shaped beam 360° ring of stationary detectors

3rd

What generation of CT is 2-10 second scan time 360° Rotation of x-ray tube Dynamic capabilities

4th

What generation of CT is 50 msec imaging

5th

What generation of CT is Annular targets

5th

What generation of CT is Cardiac Imaging

5th

What generation of CT is Electron beam scanners Stationary tube

5th

What generation of CT is Computer controlled table movement through gantry bore

6th

What generation of CT is Continuous scanning throughout entire examination

6th

What generation of CT is Helical/Spiral Imaging 360° ring of stationary detectors 360° rotation of x-ray tube

6th

What generation of CT is Multiple projection fan-shaped beam

6th

0.5 mm section thickness

7th

>10k detector elements

7th

>20 simultaneous contiguous detectors

7th

Multidetector CT (MDCT)

7th

≈12-15 sec procedure time (body region scan time)

7th

CT assigned number for teflon

990

What is a two-dimensional square of data called?

A Pixel

When slice thickness is decreased, image noise: a) Increases b) Decreases c) Does neither

A inc

What effect does slice thickness have on the radiation dose?

A thinner slice will deliver a higher dose

Which of these factors will increase the radiation dose to the patient? A) decreasing pitch B) increasing slice thickness C) decreasing the display field

A) decreasing pitch

What generation of CT is 4.5-5 minute scan time

A. First Generation

What generation of CT is Linear scan and rotate: 180 scans, 1°rotations

A. First Generation

_____ is the ability of an imaging system to demonstrate small changes in tissue contrast

Contrast resolution or tissue resolution to image objects 2 to 3 mm in size that vary slightly in density from the environment in which they are located

Factors to increase spatial resolution ___ focal spot size ____ slice thickness (assuming mAs is increased to compensate for loss of radiation reaching the detectors) ____ the number of detectors ____ matrix size ____ pixel size

Decreasing focal spot size Decreasing slice thickness (assuming mAs is increased to compensate for loss of radiation reaching the detectors) Increasing the number of detectors Increasing matrix size Decreasing pixel size

What generation of CT is Head Scan Only

First Generation

All the measurements obtained from the detector array are called

Scan Data or Raw Data

Creator of CT

Sir Godfrey Newbold Hounsfield

The ability to represent small objects and differentiate between closely spaced objects is called

Spatial resolution

FOV (field of view)

The diameter of image reconstruction

With what type of scanner are ring artifacts more commom? y?

Third generation scanners each detector views an anulus (ring) of anatomy during the examination

Voxel

Tissue volume; determined by multiply the pixel size by the thickness of the CT image slice Voxel size (mm3)=pixel size (mm2) x slice thickness (mm)

Plane that correlates to the slice thickness, or depth, of a CT slice?

Z Axis

True or False: Today, helical scanner possess a function of pitch; pitch is a ration of slice thickness to interval (the rate at which the table advances. a) True b) False

b) False

Which of the following accurately describes the relationship between patient dose and pitch? a) if pitch increases, patient dose increases b) if pitch increases, patient dose decreases c) if pitch decreases, patient dose decreases d) if pitch decreases, patient dose remains unchanged

b) if pitch increases, patient dose decreases

window level

brightness

Which of the following is defined as the ability to distinguish details in objects of different densities a small distance apart? a) contrast resolution b) cross field uniformity c) spatial resolution d) interpolation

c) spatial resolution

window width

contrast

When the FOV is increased for a fixed matrix size the size of each pixel is ______ When matrix size is increased for a fixed FOV pixel size is

increased proportionately; smaller Pixel size = FOV/Matrix Size

A grid formed from rows and columns of pixels is called

matrix

Spatial resolution is measured using

modulation transfer function (MTF)

what type of artifact occurs when an off-centre obj projects partly into scan plane A. partial volume artifact B. photon starvation

partial volume artifact

caused by low signal reaching detectors for particular projections use of thin slices make this more likely to occur

photon starvation

Linear attenuation coefficient

reflects the degree to which the x-ray intensity is reduced by a material

due to erros in individual detector calibration

ring artifacts

due to helical interpolation

shading artifacts

The mechanism in some CT scanners that allows the x-ray tube to rotate continually in the same direction is called

slip-ring

To magnify in CT you must Choose a ___ display field of view (DFOV)

smaller

due to inconsistency in a small group of readings (partial vol, photon starvation, metal artifacts, patient movement)

streaking artifact

pitch equation

table travel per rotation/ nominal slice width

DFOV (displayed field of view)

the actual viewing of the image on the monitor.

Density and contrast can be manipulated by the computer using

window level and width control

Scanned patient information is stored as

"raw" data


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