CT Image Appearance

Question 1

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

Answer 1

“Line pairs”

Question 2

How can you determine spatial resolution?

Answer 2

Centimeter divided by lines (in a line pair)

Question 3

What can we adjust to affect resolution?

Answer 3

Pixel size
Slice thickness
Reconstruction filter

Question 4

What factor would make an image appear more noisy?

Answer 4

Insufficient number of photons contributing to the pixels

Question 5

What are some factors that influence parameter selection?

Answer 5

Contrast
Resolution
Noise
Dose

Question 6

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

Answer 6

Can minimize the dose without compromising the image quality

Question 7

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

Answer 7

mA

Question 8

What happens when you increase the mAs / kVp?

Answer 8

Dose increases while noise decreases

Question 9

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

Answer 9

kVp

Question 10

What does it mean when you increase the kVp?

Answer 10

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

Question 11

Which parameter controls the contrast in a CT image?

Answer 11

kVp

Question 12

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

Answer 12

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

Question 13

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

Answer 13

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

Question 14

What does the acquired slice thickness indicate?

Answer 14

Which rows of detectors are being used to measure the photons

Question 15

What are the two slice thickness parameters?

Answer 15

Acquired slice thickness

Reconstructive (“effective”) slick thickness

Question 16

What does the reconstructive (“effective”) slice thickness indicate?

Answer 16

The thickness of the final image

Question 17

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

Answer 17

The acquired slice thickness

Question 18

What happens when you increase the slice thickness?

Answer 18

Decreases noise

Increases amount of anatomy being covered

Question 19

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

Answer 19

Partial voluming

Question 20

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

Answer 20

May decrease

Question 21

How can you achieve contiguous slices?

Answer 21

The table increment must be equal to the slice volume

Question 22

What does selecting a value for the pitch specify?

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

Stretched / Compressed

Question 26

What are some reasons to increasing the pitch?

Answer 26

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

Question 27

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

Answer 27

Reducing the pitch increases dose to the patient

Question 28

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

Answer 28

Retrospective reconstruction

Question 29

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

Answer 29

Contiguous

Question 30

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

Answer 30

Overlapped

Question 31

Increasing the reconstruction FOV will make the anatomy appear:

Answer 31

Smaller

Question 32

Increasing the reconstruction FOV will make the image appear:

Answer 32

Less noisy

Question 33

The size of a single pixel is equal to:

Answer 33

The reconstruction FOV divided by the number of pixels in the image matrix

Question 34

What happens when the image matrix increases?

Answer 34

Yield smaller pixels (better resolution)

Increases noise

Question 35

How is the degree of beam hardening determined?

Answer 35

By dense structures and travelling further through the tissues of the body

Question 36

Where may you might see beam hardening manifesting itself as a cupping artifact?

Answer 36

In the supratentorium of the brain

Question 37

What are ways in which you can minimize beam hardening artifacts?

Answer 37

Use correction algorithms
Using thin slices
Don’t scan through very dense contrast media

Question 38

What can be the result of a partial volume artifact?

Answer 38

Blurriness
Incorrect CT numbers
Missed pathology / false positives

Question 39

How can you minimize partial volume artifacts?

Answer 39

Using thinner slices

Question 40

A high window level will make the image appear:

Answer 40

Darker allowing more dense structures to be evaluated

Question 41

A low window level will make the image appear:

Answer 41

Brighter allowing less dense structures to be evaluated

Question 42

A display filter is applied directly to the _____ data.

Answer 42

Digital image

Question 43

Why would you not want to apply a display filter when taking ROI measurements?

Answer 43

Can vary the pixel values

False ROI readings

Question 44

Magnification is a post-processing technique applied to the ____ data.

Answer 44

Image