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Mosby CT Review Exam: ImageProduction
Which of the following reduces the scatter radiation reaching the detectors?
A. Post-patient collimation
B. Pre-patient collimation
C. Pre-detector collimation
D. Both a and c - correct answer ✔✔D. Both a and c
Pre-detector collimation and post-patient collimation are synonymous. Both terms describe a device
designed to remove scatter radiation before it reaches the detector.
Which of the following is the primary interaction between x-ray photons and tissue during computed
tomography?
A. Bremsstrahlung
B. Characteristic
C. Compton effect
D. Coherent scatter - correct answer ✔✔C. Compton effect
Owing to the high-energy beam used in CT, the Compton effect is the predominant interaction between
x-ray and matter. CT scanners use between 120 and 140 kVp, yielding x-ray energies with averages
between 70 and 80 keV.
The process by which electrons are produced at the cathode of a CT x-ray tube is known as:
A. rectification.
B. anode heel effect.
,C. thermionic emission.
D. isotropic emission. - correct answer ✔✔C. thermionic emission.
When the cathode of an x-ray tube is heated, electrons are released through the process of thermionic
emission. It is these electrons that are then accelerated toward the anode for x-ray production.
The assignment of different generations to CT scanners is based on the configuration of the:
A. patient and gantry.
B. tube and detectors.
C. anode and cathode.
D. tube and collimators - correct answer ✔✔B. tube and detectors.
CT scanners are often placed into one of several different "generations." The differences in generations
are based on the relationship of the tube and detectors and the position of each during data acquisition.
When one is using a third-generation CT scanner, it is important that reference detectors positioned at
the peripheral portions of the detector array be exposed to:
A. homogeneous radiation.
B. unattenuated radiation.
C. monochromatic radiation.
D. remnant radiation. - correct answer ✔✔B. unattenuated radiation.
Reference detectors are used to measure incident radiation intensity. This information is used by the
computer during the calculation of the linear attenuation coefficient. If the patient is placed incorrectly
within the gantry, the reference detectors may be partially blocked, causing an out-of-field artifact.
In 1979, the scientists __________ and __________ shared the Nobel Prize for their research in
computed tomography.
,A. Watson and Crick
B. Olendorf and Hounsfield
C. Hounsfield and Cormack
D. Hounsfield and Ambrose - correct answer ✔✔C. Hounsfield and Cormack
Dr. Godfrey Hounsfield and Dr. Allan Cormack shared the Nobel Prize for their work on the development
of computed tomography in 1979.
The type of compensating filter used at the x-ray tube of a CT scanner is called a:
A. kernel.
B. water bath.
C. bow-tie filter.
D. wedge filter - correct answer ✔✔C. bow-tie filter.
The bow-tie filter used at the x-ray tube of a CT scanner absorbs a larger amount of radiation at the
periphery of the patient, where the part thickness is reduced. The center of the patient is placed at the
center of the filter, where the largest amount of radiation is allowed to pass through. The use of this type
of filter attempts to compensate for the differences in thickness of the often oval-shaped patient.
The interaction between x-ray and matter that is responsible for the production of the scatter radiation
absorbed by the patient and detectors is:
A. Compton effect.
B. bremsstrahlung.
C. photoelectric.
D. characteristic - correct answer ✔✔A. Compton effect.
In the Compton interaction, an x-ray photon ejects an outer-shell electron of an atom. The photon loses
some of its energy in the collision and then continues on in a different, scattered direction. This
interaction is the major source of the scatter radiation involved in the formation of the CT image.
, The types of detectors used in computed tomography are:
1. Gas ionization
2. Stimulable phosphor
3. Scintillation
A. 1 only.
B. 3 only.
C. 1 and 3 only.
D. 2 and 3 only. - correct answer ✔✔C. 1 and 3 only.
The types of detectors used in computed tomography are scintillation and gas ionization detectors. Both
operate by measuring the amount of transmitted radiation passed through the patient and transmitting
this information to the computer for image reconstruction. Newer MDCT systems utilize solid-state
scintillation detectors exclusively.
Which of the following is used in gas ionization CT detectors?
A. Neon
B. Xenon
C. Helium
D. Nitrogen - correct answer ✔✔B. Xenon
Gases with high atomic numbers, such as xenon, are used in ionization-type CT detector systems. The
high atomic number of the xenon gas (Z = 54) increases the incidence of interaction with x-ray photons,
thus improving the efficiency of the detector.
Which of the following statements concerning the translate-rotate mode of CT data acquisition is/are
correct?
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