Deck 9: Image Quality

Question 1

Which of the following can be used to compare the performance of different computed tomography systems?

A)modulation transfer function
B)point spread function
C)spatial resolution
D)reconstruction algorithm

Answer 1

modulation transfer function

Question 2

Scatter-induced artifacts can be corrected with algorithms by carefully measuring or estimating the scatter distribution in the projection.

Answer 2

True

Question 3

Because the computed tomography acquisition and reconstruction process is band limited, the reconstructed image of a bar pattern is a blurred version of the original object.

Answer 3

True

Question 4

Although factors affecting resolution are largely determined by computed tomography manufacturers, operators do have a great deal of control.

Question 5

Which of the following describes the scanner's ability to resolve closely placed objects that are significantly different in the background?

A)low-contrast resolution
B)high-contrast resolution
C)accuracy
D)noise

Question 6

Low-contrast resolution can be measured with phantoms that contain low-contrast objects of different sizes.

Question 7

Which theory states that the sampling interval (pixel size) has to be sufficiently small to support the reconstruction and visualization of small objects?

A)Hounsfield
B)McCormack
C)Nyquist
D)Kernel

Question 8

To sharpen the image, a convolution process (a ramp filter) is applied to modify the frequency contents of the projection before back-projection.

Question 9

If the field of view is 30 cm with a matrix size of 512 * 512, what is the pixel size?

A)0.50 mm
B)0.58 mm
C)0.60 mm
D)0.68 mm

Question 10

Linearity can be checked by a yearly calibration test.

Question 11

A small focal spot size or lower tube current will result in:

A)decreased sampling frequency
B)decreased detector cell size
C)higher spatial resolution
D)lower spatial resolution

Question 12

In computed tomography, artifacts can arise from a number of sources, including the patient, inappropriate selection of protocols, reconstruction process, and problems relating to the equipment.

Question 13

All of the following can be described as image quality parameters except:

A)high-contrast spatial resolution
B)low-contrast spatial resolution
C)noise
D)reconstruction parameters

Question 14

One of the disadvantages of computed tomography over conventional radiography is its ability to observe low-contrast objects whose density is slightly different from the background.

Question 15

In-plane resolution is measured in terms of: I. line pairs/centimeter
II) line pairs/millimeter
III) line pairs/inch

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 16

To sharpen the image, a(n) ___________ process is applied to modify the frequency contents of the projection before back-projection.

A)convolution
B)accuracy
C)resolution
D)noise

Question 17

Pixel size is determined by:

A)matrix size/field of view
B)field of view/matrix size
C)field of view * matrix size
D)field of view + matrix size

Question 18

Which of the following factors affects in-plane spatial resolution? I. focal spot size
II) detector cell size
III) sampling frequency

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 19

As a result of volumetric computed tomography, the scatter-to-primary ratio decreases.

Question 20

Cross-plane spatial resolution is traditionally described by the:

A)shallow angled slice ramp
B)slice-sensitivity profile
C)Cat phan phantom
D)full-width-at-half-max

Question 21

On an image, partial volume artifacts will appear as: I. bands
II) shading
III) streaks

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 22

In general, a high-resolution reconstruction kernel produces a(n) ______________ noise level.

A)increased
B)decreased
C)shorter
D)longer

Question 23

Which of the following is not a source of image noise?

A)x-ray flux
B)computed tomography scanner model
C)physical limitations of the system
D)reconstruction parameters

Question 24

All of the following can cause shading artifacts except:

A)beam hardening
B)off-focal radiation
C)improper sampling of data
D)partial volume averaging

Question 25

Artifacts can: I. degrade image quality
II) affect the perceptibility of detail
III) lead to misdiagnosis

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 26

Metallic materials usually present as ____________ artifacts on the image.

A)streaks
B)shading
C)ring
D)band

Question 27

Total data acquisition time is determined by: I. gantry speed
II) helical pitch
III) detector coverage

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 28

What refers to an increase in the mean energy of the x-ray beam as it passes through the patient?

A)beam hardening
B)attenuation
C)scatter radiation
D)partial volume

Question 29

What types of artifacts can arise from insufficient projection sampling or from insufficient view sampling?

A)aliasing artifacts
B)burst artifacts
C)ring artifacts
D)shading artifacts

Question 30

Partial volume artifacts can be reduced with _____________ slice acquisitions and computer algorithms.

A)faster
B)shorter
C)thicker
D)thinner

Question 31

Which of the following refers to the relationship of computed tomography numbers to the linear attenuation coefficients of the object to be imaged?

A)attenuation ratio
B)linearity
C)reciprocity
D)uniformity

Question 32

Which of the following operator-controlled factors affects image noise? I. kilovoltage
II) slice thickness
III) detector cell size

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 33

Which of the following describes an object whose thickness is significantly smaller than the slice thickness of the system?

A)Dirac delta function
B)slice-sensitivity profile
C)Nyquist function
D)Hounsfield function

Question 34

Which of the following is defined as the smallest object that can be visualized at a given contrast level and dose? I. high-contrast detectability
II) low-contrast detectability
III) low-contrast performance

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 35

The fact that noise in the reconstructed images is no longer white describes: I. noise power spectrum
II) Wiener spectrum
III) reconstruction spectrum

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 36

What is the most straightforward way to reduce or eliminate the motion of an object?

A)increase scan speed
B)decrease scan speed
C)increase slice thickness
D)decrease slice thickness

Question 37

All of the following are major categories of artifacts except:

A)streaks
B)shading
C)rings and bands
D)noise

Question 38

Both voluntary and involuntary motion appears as ____________ that are usually tangential to the high-contrast edges of the moving part.

A)streaks
B)shading
C)bands
D)rings

Question 39

The averaging of all tissues in a voxel is:

A)beam-hardening averaging
B)reconstruction averaging
C)partial volume averaging
D)streaking averaging

Question 40

What is an indication of a computed tomography system's ability to freeze motions of the scanned object?

A)high-contrast resolution
B)low-contrast resolution
C)spatial resolution
D)temporal resolution