28. Which of the following may reduce the out-of-field artifact?
A. increasing the scan field-of-view
8. A cone beam artifact may look like stars:
B. coming from structures around the edge of the image
36. Which of the following affects beam hardening?
1. the types of tissues the beam passes through
2. the thickness of the tissues traversed by the beam
3. the energies of the photons in the beam
B. 1, 2 and 3
10. A CT artifact is:
C. an anomaly in the CT image
16. Which of the following would desplay the greatest amount of partial volume artifact?
C. a 10 mm slice from a 20 slice study
29. Which of the following is a result of reducing the slick thickness to reduce partial volume effects?
1. increased appearance of noise
2. increased spatial resolution
3. decreased anatomical coverage with the same number of slices
C. 1, 2 and 3
20. Which of the following is a possible manifestation of beam hardening?
1. CT number inaccuracies
2. streaks in the image
3. cupping artifact
A. 1, 2 and 3
38. Which of the following would result if the filter at the aperture of the x-ray tube removed even more low energy x-ray photons?
B. beam hardening artifact would decrease
21. What is the cause for the cupping artifact?
D. the tissues of the body attenuate low energy photons
13. Which of the following would make noise in the image appear less noticeable?
1. increased window widths
2. increased mAs
3. increased slice thickness
A. 1, 2 and 3
22. Which of the following may be the cause of two parallel lines seen on a localizer image?
A. two faulty detector elements
30. How would we expect metal to affect the appearance of a localizer image?
A. the metal object will be represented by high CT numbers and there will be no streaks
40. Why must we choose a scan field-of-view which is larger than the anatomy to be scanned?
1. to achieve the highest spatial resolution
2. to minimize partial volume artifacts
3. to avoid out-of-field artifacts
C. 3 only
32. Which of the following may be the cause of a metal artifact?
1. earrings
2. a zipper
3. dental fillings
D. 1, 2 and 3
11. Beam hardening refers to:
1. the increase in the number of photons reaching the detectors
2. the increase in the number of low energy photons reaching the detectors
3. the increase in the average energy of the photons that reach the detectors
C. 3 only
37. Which of the following might increase the possibility of motion artifacts occuring?
C. using no straps or pads so that the patient feels comfortable and unrestricted
31. What is the cause of cone beam artifacts?
A. the use of a standard filtered back projection reconstruction when the x-ray beam is more than 20 mm thick
23. Which of the following would reduce the partial volume effect?
C. decreased slice thickness
19. Which of the following would increase the severity of the edge gradient effect?
1. a scanner with a small detector aperture
2. a scanner with a low data sampling rate
3. using thin slices
C. 2 only
1. Which of the following affects the severity of metal artifacts?
1. the quantity, composition and shape of the metal
2. the slice thickness
3. the number of data sampling points
A. 1, 2 and 3
18. Which of the following would eliminate a ring artifact?
B. recalibration of the detector elements
6. _____ in the image is a possible manifestation of patient motion
1. Ghosting
2. Blurring
3. Streaks
C. 1, 2 and 3
4. CT x-ray tue arcing can occur because of _____ the x-ray tube.
1. impurities in the oil outside
2. tungsten gas inside
3. tungsten solids in the oil inside
A. 1 and 2
If an algorithm to correct for the cupping artifact is applied too aggressively to the data for a head image, the _____ of the image would be too bright.
1. top and bottom
2. center
3. edges
C. 2 only
2. Which of the following may occur if the patient's arms are placed at their sides during a chest exam if the scan field-of-view is 33 cm?
1. beam hardening
2. out-of-field artifact
3. cone beam artifact
A. 1 and 2
12. Which of the following could allow for a reduction of partial volume artifact while not increasing the appearance of the noise in the image?
C. decreasing slice thickness while increasing mAs
9. A variation in which of the following will affect the hardening of an x-ray beam?
1. tissue density
2. tissue thickness
3. kVp
C. 1, 2 and 3
26. In which direction are streaks from the edge gradient effect oriented?
A. parallel to the direction of the sharp density defference interface
7. On a CT image of the brain a cupping artifact would appear brighter:
B. at the periphery of the brain
33. Which of the following may be a result of partial volume averaging?
1. decreased sharpness of edges
2. inaccurate CT numbers
3. ghosting of tissue boundaries
B. 1 and 2
14. The service engineer should be notified about which of the following?
1. frequent bad streaks on the inferior slices of head scans
2. a consistent circle on the images
3. frequent bad streaks throughout the entire image
C. 2 and 3
35. How would the artifact from a faulty detector element appear on a localizer image?
D. a line parallel to the long axis of the patient table
39. Which of the following is TRUE as the slice thickness is decreased?
A. partial volume artifacts and edge gradient artifacts decrease
25. A(n) _____ artifact is a streak artifact which arises from a high spatial frequency interface between tissues with a great diference in density.
C. edge gradient
24. Which of the following would decrease the effects of beam hardening artifacts?
1. increased kVp
2. increased mAs
3. increased scan time
D. 1 only
27. Which of the following strategies would NOT help us differentiate possible pathology from a partial volume artifact?
1. inspection of adjacent slices
2. collect additional thinner slices through suspicious region
3. rescan and decrease pitch (without changing slice thickness)
D. 3 only
15. Which of the following strategies minimizes beam hardening artifact from dense contrast media?
1. the contrast solution can be diluted
2. the scan can be performed with a slight delay
3. the scan can be performed in the opposite direction
D. 1, 2 and 3
34. Tube arcing might cause _____ on the images.
D. an increased appearance of noise
5. Which of the following will have the least likelihood of producing edge gradient artifacts?
B. thin slices with full scan
17. Which of the following strategies will minimize metal artifacts?
1. remove as much metal from the patient as possible
2. orient slices such that the metal is avoided if possible
3. inspect the localizer for any metal on the patient and remove any metal or avoid imaging it as much as possible
D. 1, 2 and 3
Which of the following will help reduce edge gradient effect?
1. move structure causing artifact
2. reposition patient
3. increase data sampling
4. use thinner slices
B. 1, 2, 3, and 4
3. A(n) ____ artifact can be created when attempting to correct for a cupping artifact by applying a correction algorithm too agressively to the data for a head image. This results in the ___ of the image appearing too bright.
