Study Guide 8

Which of the following may reduce the out-of-field artifact?
A. increasing the scan field-of-view
B. reducing the slice thickness
C. reducing the reconstruction field-of-view
D. increasing the matrix

A cone beam artifact may look like stars:
A. from all structures with high CT numbers
B. coming from structures around the edge of the image
C. coming from con-shaped structures
D. at the center of the image

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

A CT artifact is:
A. a parameter used to control the brightness of the image
B. used to time the injection of contrast media
C. an anomaly in the CT image
D. always a reason to call for repair of the CT scanner

Which of the following would desplay the greatest amount of partial volume artifact?
A. a 5 mm slice from a 40 slice study
B. a 5 mm slice from a 20 slice study
C. a 10 mm slice from a 20 slice study
D. a, b and c would experience the same amount of partial volume artifact

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

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
B. 3 only
C. 1 only
D. 2 only

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?
A. beam hardening artifact would increase
B. beam hardening artifact would decrease
C. partial volume artifact would increase
D. partial volume artifact would decrease

What is the cause for the cupping artifact?
A. the interface between tissues with different densities causes the high energy photons to be absorbed
B. the mean energy of the photons that comprise the x-ray beam is lowered
C. the central tissues are not penetrated by the x-ray beam
D. the tissues of the body attenuate low energy photons

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
B. 1 only
C. 3 only
D. 2 only

Which of the following may be the cause of two parallel lines seen on a localizer image?
A. two faulty detector elements
B. cone beam artifact
C. a problem with the reconstruction algorithm
D. tube arcing

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
B. the entire image will appear blurry
C. streaks will emenate from the metal object in the image
D. the CT numbers of the tissues in the image will be misrepresented

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

Which of the following may be the cause of a metal artifact?
1. earrings
2. a zipper
3. dental fillings
A. 1 only
B. 3 only
C. 2 only
D. 1, 2 and 3

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

Which of the following might increase the possibility of motion artifacts occuring?
A. using a helical scanning technique to acquire the necessary slices in a single breath-hold (assuming the patient can refrain from breathing for the required time)
B. explaining the procedure to the patient
C. using no straps or pads so that the patient feels comfortable and unrestricted
D. immobilizing the patient

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
B. faulty detector elements
C. inefficient x-ray tubes used on multi-row detector scanners
D. hardening of the x-ray beam on multi-row detector scanners

Which of the following would reduce the partial volume effect?
A. decreased matrix
B. increased reconstruction field-of-view
C. decreased slice thickness
D. increased mAs

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

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
B. 3 only
C. 1 only
D. 2 only

Which of the following would eliminate a ring artifact?
A. removal of metal
B. recalibration of the detector elements
C. decreased matrix
D. increased mAs

_____ in the image is a possible manifestation of patient motion
1. Ghosting
2. Blurring
3. Streaks
A. 3 only
B. 2 only
C. 1, 2 and 3
D. 1 only

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

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

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
B. 1 only
C. 2 only
D. 3 only

Which of the following could allow for a reduction of partial volume artifact while not increasing the appearance of the noise in the image?
A. increasing slice thickness while increasing mAs
B. decreasing slice thickness while decreasing mAs
C. decreasing slice thickness while increasing mAs
D. increasing slice thickness while decreasing kVp

A variation in which of the following will affect the hardening of an x-ray beam?
1. tissue density
2. tissue thickness
3. kVp
A. 1 only
B. 3 only
C. 1, 2 and 3
D. 2 only

In which direction are streaks from the edge gradient effect oriented?
A. parallel to the direction of the sharp density defference interface
B. perpendicular to the direction of the sharp density difference interface
C. radially outward from the center of the image
D. in a herringbone pattern across the image

On a CT image of the brain a cupping artifact would appear brighter:
A. in the center of the brain
B. at the periphery of the brain
C. at the anterior and posterior aspects of the brain
D. immediately around dense structures

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

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

How would the artifact from a faulty detector element appear on a localizer image?
A. a line perpendicular to the long axis of the patient table
B. a circle in the center of the image
C. it depends on the orientation in which the localizer image is performed
D. a line parallel to the long axis of the patient table

Which of the following is TRUE as the slice thickness is decreased?
A. partial volume artifacts and edge gradient artifacts decrease
B. partial volume artifacts increase while edge gradient artifacts decrease
C. partial volume artifacts and edgte gradient artifacts increase
D. partial volume artifacts decrease while edge gradient artifacts increase

A(n) _____ artifact is a streak artifact which arises from a high spatial frequency interface between tissues with a great diference in density.
A. ring
B. cone beam
C. edge gradient
D. tube arcing

Which of the following would decrease the effects of beam hardening artifacts?
1. increased kVp
2. increased mAs
3. increased scan time
A. 3 only
B. 1 and 2
C. 2 only
D. 1 only

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

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

Tube arcing might cause _____ on the images.
A. an appear of a cirlce or ring
B. shading and inaccurate CT numbers
C. star-like artifacts at the edges
D. an increased appearance of noise

Which of the following will have the least likelihood of producing edge gradient artifacts?
A. thin slices iwth partial scan
B. thin slices with full scan
C. thick slice with full scan
D. thick slices with partial scan

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