Deck 9: Image Quality

Question 1

Total data acquisition time is determined by all of the following except:

A) scanning delay.
B) gantry speed.
C) helical pitch.
D) detector coverage.

Answer 1

scanning delay.

Question 2

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

Answer 2

Increase scan speed

Question 3

Which of the following is defined as the smallest object that can be visualized at a given contrast level and dose?

A) High-contrast visibility
B) Low-contrast visibility
C) High-contrast performance
D) Low-contrast performance

Answer 3

Low-contrast performance

Question 4

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

A) X-ray flux
B) CT scanner model
C) Physical limitations of the system
D) Reconstruction parameters

Question 5

What is a common disadvantage for prospective gating?

A) Reduction in X-ray dose to the patient
B) Fewer motion artifacts
C) Decreased scan time
D) Reliance on the regularity of the heart motion

Question 6

CT number uniformity can be affected by all of the following factors except:

A) scatter.
B) beam hardening.
C) linearity.
D) CT system stability.

Question 7

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 8

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 9

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

A) Modulation transfer function (MTF)
B) Point spread function
C) Spatial resolution
D) Reconstruction algorithm

Question 10

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

A) Attenuation ratio
B) Linearity
C) Reciprocity
D) Uniformity

Question 11

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 12

What term is in-plane resolution measured?

A) Line pairs/inch
B) Line pairs/centimeter
C) Line pairs/milliliter
D) Line pairs/foot

Question 13

All of the following factors affect in-plane spatial resolution except:

A) focal spot size.
B) detector cell size.
C) sampling frequency.
D) magnification.

Question 14

All of the following are operator-controlled factors that affect image noise except:

A) inherit filtration.
B) kilovoltage.
C) detector cell size.
D) tube current.

Question 15

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 16

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

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

Question 17

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

A) High-contrast resolution
B) Low-contrast resolution
C) Spatial resolution
D) Temporal resolution

Question 18

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 19

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 20

Cross-plane spatial resolution is traditionally described by the:

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

Question 21

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

Question 22

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

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

Question 23

How do beam-hardening artifacts appear on a CT image?

A) Bands
B) Shading
C) Streaks
D) Ghosting

Question 24

Linearity can be checked by a yearly calibration test.

Question 25

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

Question 26

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

Question 27

The fact that noise in the reconstructed images is no longer white describes which spectrum?

A) Noise power spectrum (NPS)
B) Reconstruction spectrum
C) Reformation spectrum
D) Temporal spectrum

Question 28

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

Question 29

Partial volume averaging occurs when linear attenuation coefficients for a voxel of tissue contains only one tissue type resulting in streaking artifacts within the CT image.

Question 30

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 31

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 32

Artifacts can have all of the following effects except:

A) degrade image quality.
B) affect the perceptibility of detail.
C) lead to misdiagnosis.
D) reduce patient radiation dose.

Question 33

Coverage is a method of reducing cardiac motion in CT imaging by synchronizing data acquisition and reconstruction with an electrocardiographic signal.

Question 34

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

Question 35

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 36

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

Question 37

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

Question 38

The averaging of all tissues in a voxel is:

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

Question 39

Metallic materials usually present as ____________ artifacts on the image.

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

Question 40

All of the following are major categories of artifacts except:

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