Deck 12: CT Physics and Instrumentation

Question 1

In an x-ray tube, of the energy applied to the system, the percentage of x-rays that exit is

A)1%.
B)10%.
C)50%.
D)99%.

Answer 1

1%.

Question 2

In an x-ray tube, when the milliamperes (mA) are increased:

A)Bremsstrahlung and characteristic x-rays increase.
B)Bremsstrahlung and characteristic x-rays decrease.
C)Bremsstrahlung x-rays increases and characteristic x-rays decrease.
D)Bremsstrahlung x-rays decrease and characteristic x-rays increase.

Answer 2

Bremsstrahlung and characteristic x-rays increase.

Question 3

In an x-ray tube, a low kVp results in

A)high-energy Bremsstrahlung x-rays.
B)low-energy Bremsstrahlung x-rays.
C)fewer Bremsstrahlung x-rays.
D)an increase in tungsten characteristic x-rays.

Answer 3

low-energy Bremsstrahlung x-rays.

Question 4

Which of the following may be used to reduce streaking artifacts when scanning anatomy with high-density objects?

A)Bow-tie filter
B)Adaptive detector array
C)Thinner collimation
D)Decreased kVp

Question 5

A general rule is that a 15% increase in kVp results in

A)a 15% increase in mAs.
B)doubling the mAs.
C)a 15% reduction in mAs.
D)no affect on mAs.

Question 6

Energies required for typical PET/CT studies of the body will be in the range of

A)20 to 30 kVp.
B)40 to 75 kVp.
C)80 to 140 kVp.
D)145 to 160 kVp.

Question 7

Important technical developments that define current helical CT systems include all of the following EXCEPT

A)continuous reduction in radiation of the x-ray tube.
B)continuous-motion gantry using slip-ring technology.
C)continuous motion of the imaging table.
D)continuous data transfer from the detector array.

Question 8

Collimators in CT scanning are used to do all of the following EXCEPT

A)limit the beam size.
B)reduce scattered x-rays.
C)define slice thickness.
D)offset the alignment of the tube and detector array to optimize the beam location.

Question 9

In x-ray tubes, the types of reactions that produce x-rays include

A)Bremsstrahlung and scatter.
B)Bremsstrahlung and characteristic.
C)characteristic and scatter.
D)characteristic and refraction.

Question 10

What is the purpose of administering a contrast agent for a CT procedure?

A)Reduce patient dose for longer scans that require thinner slicers
B)Reduce streaking artifacts when scanning high-density objects
C)Reduce attenuating properties of tissues with wide variances in density
D)Enhance detection of lesions and aid in defining normal structures

Question 11

In helical CT, pitch is defined as

A)the ratio of the patient's movement through the gantry during one 360-degree beam rotation relative to the beam collimation.
B)the total time for a patient to move through the gantry during a CT scan.
C)the ratio of the beam collimation relative to the mAs for a CT scan.
D)the coordination of a patient's possible movement,
E)g., breathing, during the CT scan relative to slice thickness.

Question 12

What is a reconstruction kernel?

A)A unit of data in a reconstructed CT image
B)The entire data set used to produce reconstructed images in CT
C)A measurement used to determine the data set used for CT reconstruction
D)An algorithm that defines the clinical application and amount of image smoothing applied in the reconstruction

Question 13

All of the following are true about the kVp setting EXCEPT

A)it selects the maximum possible energy of the x-ray beam.
B)it defines the fraction of photons that will reach the detectors.
C)it affects the radiation exposure to the patient.
D)it increases beam hardening.

Question 14

Computed tomography (CT) scanning accomplishes all of the following EXCEPT

A)minimal superimposition of tissues.
B)improved contrast resolution.
C)reduction of radiation dose compared to conventional radiography.
D)differentiation of tissue densities.

Question 15

Using a higher mA

A)results in an increase in image noise.
B)results in an increase in contrast resolution.
C)results in a decrease in dose to the patient.
D)shortens the imaging time for the patient.

Question 16

The purpose of using a filter in CT scanning is

A)to absorb the very-low-energy x-rays.
B)to act as an upper level discriminator.
C)to act as a window.
D)To attenuate the high-energy x-rays.

Question 17

Which of the following restricts the width and shapes the beam to the area of interest for a single rotation of the tube and detectors around the patient?

A)Prepatient collimators
B)Postpatient collimators
C)Pitch
D)Rotation speed

Question 18

In a CT scanner, the oil bath that may surround the rotating anode tubes serves to

A)make the tubes rotate more quickly.
B)make the tubes rotate more smoothly.
C)cool the tubes.
D)provide efficient conduction of the current.

Question 19

In an x-ray tube, a high kVp results in

A)low-energy Bremsstrahlung x-rays.
B)a decrease in tungsten characteristic x-rays.
C)an increase in tungsten characteristic x-rays.
D)fewer Bremsstrahlung x-rays.

Question 20

In an x-ray tube, the anode, for the most part, is most commonly constructed from

A)tungsten.
B)lead.
C)rhenium.
D)silver.

Question 21

Thin collimation has an advantage because it results in faster scanning time.

Question 22

A disadvantage to having image overlap on CT images is the possibility of artificially creating small lesions.

Question 23

The slice thickness that may be reconstructed can be up to half as thin as the collimator width.

Question 24

What is the CT number for water?

A)0
B)10
C)100
D)1000

Question 25

In high-performance CT scanners, the speed of the data transfer from the detector array determines the maximum resolution.