3. Which of the following are possible results of partial voluming?
1. decreased sharpness of edges
2. misleading CT numbers
3. improvement in resolution
B. 1 and 2
6. Which of the following has the highest patient dose assuming all other parameters are the same?
C. mA=150, rotation time=3 seconds
10. CT numbers _____ would appear black if a window width of 400 and a window level of -100 are used.
B. below -300
40. If a calcification iwth a CT number of +300 appears pure white on an image, which of the following could be the window width and window level selected?
1. window level = 0, window width = 500
2. window level = +300, window width = 500
3. window level = +100, window width = 1000
D. 1 only
1. Which of the following determinants of CT image quality is responsible for how grainy or speckled a CT image appears?
B. noise
23. Which of the following statements is FALSE?
1. magnification requires the raw data
2. increasing magnification increases resolution
3. magnification decreases the size of displayed anatomy
D. 1, 2 and 3
15. If a thin slice is used, which of the following would help reduce the apparent image noise?
B. increased mAs
25. A CT number Calibration Test should be performed:
A. daily
12. Which of the following is a reason to increase the pitch?
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
A. 1 and 2
4. Which of the following is FALSE about the spatial resolution of an image?
1. resolution is dependent on matrix size
2. resolution is dependent on reconstruction FOV
3. resolution is dependent on scanned FOV
B. 3 only
2. An increase in _____ will result in hardening of an x-ray beam
1. tissue density
2. tissue thickness
3. kVp
A. 1, 2 and 3
26. If the slice thickness is changed from 5 mm to 7 mm and all other parameters are held constant, _____ % more photons will be used in making the slice.
B. 40
2mm/5mm x 100%
7. Which of the following will result in an increased voxel size?
1. decreased reconstruction FOV
2. increased slice thickness
3. increased matrix
A. 2 only
11. If a reconstruction FOV of 32 cm and a 512x512 matrix are used, the pixel size is _____ mm.
A. 0.625 X 0.625
Pixel size is equal to reconstruction FOV divided by matrix--remember to convert to mm
39. Which of the following does NOT occur when reconstruction FOV is decreased?
1. spatial resolution is increased
2. pixel size is increased
3. noise in the image increases
C. 2 only
8. Which of the following is the converstion equation from CT number to Hounsfield unit?
C. CT number=Hounsfield unit
21. There are _____ total pixels in a 1024 x 1024 matrix.
C. more than 1 million
multiply 1024 x 1024
Which of the following occurs when slice thickness is reduced?
1. appearance of noise in the image increases
2. the nubmer of photons used in making the slice decreases
3. partial volume averaging decreases
C. 1, 2 and 3
14. Increasing _____ results in lowering the patient dose.
1. pitch
2. mAs
3. table increment
A. 1 and 3
29. ____ affects the CT number of water.
D. No imaging parameter
18. The smallest object that can be resolved if a reconstruction FOV of 24 cm and a 512 x 512 matrix are used is _____ mm.
C. .047
240 mm divided by 512
9. If the radiologist requires 2 mm thick contiguous slices through the pituitary, and 2.4 cm of coverage, _____ slices are necessary?
C. 12
Which of the following is NOT a result of reducing the reconstruction FOV?
1. improved spatial resolution
2. increased appearance of image noise
3. anatomical structures appear smaller
A. 3 only
19. Which of the following parameters affects the contrast of a CT image?
D. kVp
36. Which of the following parameters is responsible for partial volume averaging?
B. slice thickness
35. On MDCT, the final reconstructed slice thickness is determined by the:
B. number of rows of detectors and the size of the detectors wise attenuation data gets combined
37. The distance that the table travels between slices is called:
D. table increment
16. A set of images is reconstructed with a 150 mm reconstruction FOV. 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 second set of images is better than the first set
2. the apparent noise in the second set of images is more pronounced than the first set
3. the patient dose of the first set of images is higher than the second set
C. 1, 2 and 3
5. Which of the following is NOT directly proportional to mAs?
C. the mean energy of the x-ray photons leaving the tube
38. Which of the following parameters causes helical slices to be reconstructed so they overlap?
B. Reconstruction interval
28. Which of the following is the expected result of a CT number Calibration Test performed on a water phantom?
A. 0+/-3
34. On a conventional, or serial, CT scan, if we want 5 mm slices with 1 mm of overlap, the table increment should be _____mm.
B. 4
30. Which of the following parameters allows adjacent slices to be overlapped without increasing the dose to the patient?
A. Reconstruction interval
31. Which of the following can be changed retrospectively?
1. the slick thickness from an MDCT helical scan
2. the slick overlap from a single-row detector scanner helical scan
3. the slick thickness from a single-row detector scanner helical scan
A. 1 and 2
20. Which of the following values for pitch would stretch the x-ray helix the most?
D. 1.5
17. The _____ determines how penetrating the x-ray beam will be.
D. kVp
32. Which of the folling would be used in a high resolution study of the temporal bones?
1. reduced slick thickness
2. reduced reconstruction FOV
3. sharp reconstruction filter
B. 1, 2 and 3
13. Which of the following would be used to better visualize low contrast resolution?
1. decreased mAs
2. sharp reconstruction filter
3. narrow window width
D. 3 only
22. For a given distance of coverage, which of the following is TRUE?
1. as reconstruction FOV increases, patient dose increases
2. as pitch increases, patient dose decreases
3. as slice thickness increases, patient dose decreases
A. 2 and 3
27. ____ the window _____ will make the image appear darker so that bony structures can be evaluated.
C. Increasing, level
_______ refers to the precision of a measurement with respect to time.
A. temporal resolution
_______ is a measure of the size of the smallest object that can be visualized in an image.
D. spatial resolution
______ is the ability to differentiate small differences in density on the image.
B. contrast resolution
What percentage of tissue densities can CT defferentiate?
A. 0.5 %
Spatial resolution can be affected by geometric factors such as:
1. focal spot size
2. detector aperature size
3. focal spot to patient distance
4. patient to detector distance
A. 1, 2, 3, and 4
What developements led to the improvement of spatial resolution?
1. helical scanning
2. multi-detector scanners
3. retrospective ECG
A. 1, 2, and 3
An image will appear more ______ when there are fewer photons contributing to the pixels.
Noisy or grainy
What is represented by the CT number -1000
C. air
What is represented by the CT number -80
D. fat
What is represented by the CT number 0
A. water
What is represented by the CT number 30 to 80
D. soft tissues
What is represented by the CT number 100 to 1000
D. calcification
As CT numbers increase, the shades of gray become______.
A. lighter
As CT numbers decrease, the shades of gray become_____.
C. darker
mAs does not affect which of the following.
1. patient dose
2. image contrast
3. spatial resolution
A. 2 and 3 only
Pitch = Table Movement / Slice Thickness. If the pitch is 2 and the patient tables moves 4mm, what is the slice thickness.
A. 2 mm
2 = 4/X
x = 2
The dose to the patient increases during which of the following overlapping.
a. conventional
b. helical
a. conventional
Window width does what to the CT image?
a. adjusts how contrasty the image appears
b. adjusts the brightness the image appears
a. adjusts how contrasty the image appears
Window level does what to the CT image?
a. adjusts how contrasty the image appears
b. adjusts the brightness the image appears
b. adjusts the brightness the image appars
What kind of window width increases the displayed contrast of an image?
a. narrow
b. wide
a. narrow
What kind of window width decreased the displayed contrast of an image?
a. narrow
b. wide
b. wide
A wide window width is good for what kind of imaging?
B. lungs
A narrow window width is good for what kind of imaging?
B. brain soft tissues
What kind of window level makes the image appear brighter?
a. low
b. high
a. low
What kind of window level makes the image appear darker?
a. low
b. high
b. high
24. Compared to a CT scan protocol without iterative reconstruction applied, when using iterative reconstruction the scan parameter most likely to be reduced is:
C. mAs
33. The ability to scan a moving organ without seeing motion artifacts on the images is an example of an exam performed with high: