Mosby CT Review Exam: Image Production | Complete Solutions (Answered)
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CT Image Production
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CT Image Production
Mosby CT Review Exam: Image Production | Complete Solutions (Answered) 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 Pre-detector collimation and post-patient collima...
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
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
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.
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
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.
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
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
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
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.
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
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?
1. 360-degree circular detector arrays are used.
2. Data are collected only during translation.
3. Was used in first- and second-generation CT scanners.
A. 2 only
, B. 3 only
C. 1 and 2 only
D. 2 and 3 only
The first- and second-generation CT scanners used a translate-rotate method of data
acquisition. The x-ray tube and detector(s) translated across the patient's head,
recording transmission measurements. The entire system then rotated 1 degree. This
process of translation-rotation then repeated itself for a total of 180 degrees. First- and
second-generation CT scanners used anywhere from 2 to 30 detectors.
Which of the following terms accurately describes the type of x-ray beam used in a
third-generation CT scanner?
A. Pencil beam
B. Fan beam
C. Nutating beam
D. Electron beam
The third-generation CT scanner uses a fan beam projected onto a wide detector array.
The third-generation CT x-ray beam is commonly mistaken for the "pencil beam" used
with only two detectors in the first-generation CT scanner.
Which of the following technologic advances has led to the development of spiral/helical
CT scanning?
A. 1 only
B. 1 and 2 only
C. 1 and 3 only
D. 1, 2, and 3
Spiral/helical CT scanners are a recent development in computed tomography
technology. The advents of slip-ring technology and improvements in x-ray tube design
have made this innovation possible. Slip-rings have taken the place of the cumbersome
cables previously used to transmit the CT signal and supply power to the tube and
detectors. This development enables the tube and detectors to rotate continuously
around the patient, acquiring data in the form of a helix. The longer exposure times of
up to 60 seconds require extremely efficient x-ray tubes with enormous heat capacities.
For a given CT acquisition, the calculated mAs applied to each reconstructed slice may
be referred to as the:
A. effective mAs.
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