MICC PRACTICE TEST CH.3

Question 1

Which of the following determinants of CT image quality is responsible for how grainy or speckled a CT image appears?
A. Resolution.
B. Linearity.
C. Noise.
D. Contrast.

Answer 1

C - Noise.

Question 2

An increase in __________ will result in hardening of an X-ray beam.
A. Tissue density.
B. Tissue thickness.
C. kVp.
D. All of the above.

Answer 2

D - All of the above.

Question 3

Which of the following are possible results of partial voluming?
1. Decreased sharpness of edges.
2. Misleading CT numbers.
3. Improvement in resolution.

(CHOOSE ONE OR MORE CORRECT ANSWER(S)).

Answer 3

1 and 2 only.

Question 4

Which of the following is FALSE about spatial resolution of an image?
1. Resolution is dependent on matrix size.
2. Resolution is dependent on construction FOV.
3. Resolution is dependent on scanned FOV.

A. 1 only.
B. 2 only.
C. 3 only.
D. 1, 2, and 3.

Answer 4

C - 3 only.

Question 5

Which of the following is NOT directly proportional to mAs?
A. The mean energy of the X-ray photons leaving the tube.
B. The number of X-ray photons leaving the X-ray tube.
C. X-ray tube heating.
D. Dose to the patient.

Answer 5

A - the mean energy of the X-ray photons leaving the tube.

Question 6

Which of the following has the highest pt dose assuming all other parameters are the same?
A. MA = 200, rotation time = 2 secs.
B. MA = 200, rotation time = 1 secs.
C. MA = 150, rotation time = 3 secs.
D. MA = 400, rotation time = 1 secs.

Answer 6

C

Question 7

Which of the following will result in an increased voxel size?
A. Decreased reconstruction FOV.
B. Increased slice thickness.
C. Increased matrix.
D. B and C only.
E. A, B, and C.

Answer 7

B - increased slice thickness.

Question 8

Which of the following is the conversion equation for CT number of Hounsfield Unit?
A. CT number = 0.5 x HU.
B. CT number = (HU)2
C. CT number = HU.
D. CT number = 2 x HU.

Answer 8

C - CT number = HU.

Question 9

If the radiologist requires 2 mm thick contiguous slices through the pituitary and 2.4 cm of coverage, __________ slices are necessary?
A. 8.
B. 10.
C. 12.
D. 13.

Answer 9

C - 12.

24/2 = the number of slices necessary in order to cover the area.

Question 10

CT numbers ____________ would appear black if a WW of 400 and a WL of -100 are used.
A. Above +200.
B. Below -300.
C. Below -200.
D. Above +100.

Answer 10

B - Below -300.

Question 11

If a reconstruction FOV of 32 cm and a 512x512 matrix are used, the pixel size is ___________ mm.
A. 0.35 x 0.35.
B. 0.625 x 0.625.
C. 1.6 x 1.6.
D. 3.25 x 3.25

Answer 11

B - 0.625

320 mm + 512 (FOV).

Question 12

Which of the following is a reason to increase the pitch? (PICK ONE OR MORE ANSWERS)
1. A greater volume of anatomy can be covered in a given time.
2. A given volume of anatomy can be covered faster.
3. Radiation dose to the patient can be increased.

Answer 12

1 and 2 only.

Question 13

Which of the following would be used to better visualize low contrast resolutions?
A. Decreased mAs.
B. Sharp reconstruction filter.
C. Narrow window width.
D. All of the above.

Answer 13

C - Narrow window width.

Question 14

Increasing __________ results in lowering the pt dose.
A. Pitch.
B. MAs.
C. Table increment.
D. A & C only
E. A & B only

Answer 14

D - A & C

Table increment is the distance the pt table moves b/t serial scans. increasing table increment causes fewer photons to be used to cover the region of interest = lowers pt dose.

Pitch = distance the pt table moves during one complete rotation of the X-ray tube during a helical scan. Increasing pitch = lower pt dose.

Question 15

If a thin slice is used, which of the following would help reduce the apparent image noise?
A. Reduced reconstruction field of view.
B. Increased matrix.
C. Increased mAs.
D. Increased kVp.

Answer 15

C - Increased mAs.

Question 16

A set of images is reconstructed with a 150 mm reconstruction FOBV. Keeping all other parameters constant, a second set of images is reconstructed with a 300 mm reconstruction FOV, and then magnified so that the anatomical structures in the first and second set appear the same size. Which of the following statements is FALSE?

1. The resolution of the 2nd set of images is better than the first.
2. The apparent noise in the 2nd set of images is more pronounced than the first set.
3. The pt dose of the first set of images is higher than the 2nd set.

Answer 16

All 3 are false.

Resolution would be reduced by a factor of two.
Larger FOV = less apparent noise.
Magnification has no affect on pt dose.

Question 17

The __________ determines how penetrating the x-ray beam will be.
A. kVp.
B. Rotation time.
C. MA.
D. Pitch.

Answer 17

A. KVP.

Question 18

The smallest object that can be resolved if a reconstruction FOV of 24 cm and a 512x512 matrix are used is __________ mm.
A. 0.47.
B. 1.00.
C. 2.13.
D. 3.57.

Answer 18

A. 0.47

240 mm / 512.

Question 19

Which of the following parameters affects the contrast of a CT image?
A. Reconstruction interval.
B. MAS.
C. KVP.
D. CT number.

Answer 19

C. KVP.

Question 20

Which of the following values for pitch would stretch the x-ray helix the most?
A. 1.5.
B. 1.0.
C. 0.8.
D. 0.5.

Answer 20

A. 1.5.

Pitch is the parameter that determines how stretched the x-ray helix is.
The greater the pitch value = the more stretched the helix.

Question 21

There are _________ total pixels in a 1024 x 1024 matrix.
A. 2048.
B. 524,288.
C. More than 1 million.
D. More than 2 million.

Answer 21

C. More than one million.

Question 22

For a given distance of coverage, which of the following is true? (Pick 1 or more answers)
1. as reconstruction FOV increases, pt doses increases.
2. as pitch increases, pt dose decrease.
3. as slice thickness increases, pt dose decreases.

Answer 22

2 & 3 only.

Pitch increases = pt is moved in faster = decreases dose.

Slice thickness increases = pt dose decreases.

FOV reconstruction has NO bearing on pt dose.

Question 23

True/false: Reconstruction FOV affects pt dose.

Answer 23

False, it has NO bearing on pt dose!

Question 24

Which of the following statements (pick 1 or more) is FALSE:
1. magnification requires the raw data.
2. Increasing magnification increases resolution.
3. Magnification decreases the size of the displayed anatomy.

Answer 24

1, 2, and 3.

Magnification does NOT utilize the raw data, only the image data!

Question 25

Compared to a CT scan protocol without iterative reconstruction applied, when using iterative reconstruction the scan parameter most likely to be reduced is:
A. mAs.
B. Matrix.
C. Pitch.
D. Scan field-of-view.

Answer 25

A. mAs. - Iterative reconstruction acts to REDUCE NOISE seen in the images. With less noise, the tube current may be reduced, resulting in less radiation dose to the pt (mAs).

Question 26

A CT Number Calibration Test should be performed:
A. Weekly.
B. Annually.
C. Monthly.
D. Daily.

Answer 26

D. Daily.

Question 27

If the slice thickness is changed from 5 mm to 7 m and all other parameters are held constant, _____% more photons will be used in making the slice.

Answer 27

40%.

We change the slickness by 2 mm thus the answer is 2 mm divided by 5 mm x 100%.

Question 28

_____ the window _____ will make the image appear darker so that bony structures can be evaluated.

Answer 28

Increasing; level.

Question 29

Which of the following is the expected result of a CT Number Calibration Test performed on a water phantom?
A. 0 +/- 3.
B. 0 +/- 5
C. 100 +/- 3
D. 1000 +/- 5.

Answer 29

A. 0 +/- 3.

Question 30

__________ affects the CT number of water.

Answer 30

No imaging parameter.

Question 31

Which of the following parameters allows adjacent slices to be overlapped without increasing the dose to the pt?
A. Reconstruction interval.
B. Slice thickness.
C. Table increments.
D. PItch.

Answer 31

A. Reconstruction interval.

• using this which is less than the slice thickness will generate overlapping slices with no additional dose to the pt.