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Computed Tomography (CT) > CT Image Appearance > Flashcards

Flashcards in CT Image Appearance Deck (44)
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1

The resolution of a CT scanner is often expressed in terms of...

"Line pairs"

2

How can you determine spatial resolution?

Centimeter divided by lines (in a line pair)

3

What can we adjust to affect resolution?

Pixel size
Slice thickness
Reconstruction filter

4

What factor would make an image appear more noisy?

Insufficient number of photons contributing to the pixels

5

What are some factors that influence parameter selection?

Contrast
Resolution
Noise
Dose

6

Why would applying a noise-reducing algorithm during image reconstruction be a preferred method?

Can minimize the dose without compromising the image quality

7

What determines the number of x-ray photons produced by the CT x-ray tube?

mA

8

What happens when you increase the mAs / kVp?

Dose increases while noise decreases

9

What determines the maximum energy of the x-ray photons produced by the CT x-ray tube?

kVp

10

What does it mean when you increase the kVp?

Increases the photon's ability to penetrate the tissues of the patient's body

11

Which parameter controls the contrast in a CT image?

kVp

12

On single-row detector scanners, slice thickness is partially defined by:

The size of the focal spot in the CT x-ray tube

13

On single-row detectors, the acquired slice thickness is equal to:

The collimated x-ray beam thickness (as well as the final image thickness)

14

What does the acquired slice thickness indicate?

Which rows of detectors are being used to measure the photons

15

What are the two slice thickness parameters?

Acquired slice thickness
Reconstructive ("effective") slick thickness

16

What does the reconstructive ("effective") slice thickness indicate?

The thickness of the final image

17

On multi-row detector scanners, the final slice thickness must be equal to or greater than:

The acquired slice thickness

18

What happens when you increase the slice thickness?

Decreases noise
Increases amount of anatomy being covered

19

The result of a decrease in resolution due to slices that are too thick:

Partial voluming

20

If you increase the slice thickness while covering the same anatomical region, what happens to the radiation dose to the patient?

May decrease

21

How can you achieve contiguous slices?

The table increment must be equal to the slice volume

22

What does selecting a value for the pitch specify?

How compressed or stretched the path of the x-ray beam takes on a helical scan

23

On a single-row detector, what is the pitch equal to?

Movement of the patient table in one gantry rotation divided by the slick thickness

24

On a multi-row detector, what is the pitch equal to?

Movement of the patient table in one gantry divided by total slice volume or thickness of a single slice

25

A pitch that is increased / decreased results in a _____ / _____ helix

Stretched / Compressed

26

What are some reasons to increasing the pitch?

Greater anatomical coverage in less time
Faster scan for trauma patients
Appropriate contrast timing during a CTA study
Decrease dose to the patient

27

How is the radiation dose to the patient related to the pitch?

Reducing the pitch increases dose to the patient

28

Reconstruction interval may be modified and the new value may be applied through:

Retrospective reconstruction

29

If the reconstruction interval is equal to the reconstructed slice thickness, the reconstructed slice thickness will be:

Contiguous

30

If the reconstruction interval is less than the reconstructed slice thickness, the reconstructed slice thickness will be:

Overlapped