Image Production CT
Which the following statements correctly describes the flow of electrons through an x-ray tube?
A. Cathode to anode
B. Anode to cathode
C. Positive to negative
D. target to a filament - correct answer ✔✔A. Cathode to anode
The cathode of the x-ray tube is the same as the filament, the source of electrons, which is negatively
charged. The anode is the target, which is positively charged. When a voltage (kVp) is applied, the
negatively charged electrons accelerate to the positively charged anode. Electron interactions in the
anode are responsible for x-ray production.
The specific process that accelerates electron in an x-ray tube is:
A. Evacuation of air in the envelope
B. Themionic emission
C. Application of a voltage
D. Bremsstrahlung electron interactions - correct answer ✔✔C. Application of a voltage
All options listed are valuable in the x-ray production process, but only the voltage actually causes
electrons to accelerate through the tube. A "voltage" is the same as the kilovoltage potential (kVp).
Increasing mA in CT has the effect of:
A. Increasing dose to the patient
B. Increasing exposure to the detector elements
C. Increasing the intensity of the beam
D. All answers listed are true - correct answer ✔✔D. All answers listed are true
,Increasing the mA results in more photons in the beam (intensity). This results in more dose to the
patient and more exposure to the detector elements.
An increase of which of the following exposure factors would increase the total number of x-ray photons
exposing the detectors?
1. mA
2. kVp
3. rotation time
A. 1 only
B. 2 only
C. 1 and 2 only
D. 1,2, and 3 - correct answer ✔✔D. 1,2, and 3
All options have the effect of increasing the total number of photons exposing the detectors. Increased
mA increases the total number of photons being produced. Increased kVp also increases the total
number of photons produced and increases the penetrating ability of those photons. Increased rotation
time, without changing the mA, results in a longer exposure (per rotation) and more total photons
exposing the detectors.
If mA is decreased by a factor of 2, how is the radiation dose to the patient changed? Assume all other
factors remain unchanged.
A. Dose is increased by a factor of 2
B. Dose is decreased by a factor of 2
C. Dose remains unchanged
D. Dose is decreased by a factor of 22 - correct answer ✔✔B. Dose is decreased by a factor of 2
The relationship between mA and dose is directly proportional and linear. If mA decreases by a certain
factor, dose will decrease by the same factor. In this question, dose decreased by a factor of 2 between
, mA decreased by a factor of 2. In other words,there are half as many photons interacting with the
patient and therefore the dose would also be half.
What technical change is expected to increase the penetrating ability of an x-ray beam?
A. Increased kVp
B. Increased mA
C. Increased rotation time
D. All of the above - correct answer ✔✔A. Increased kVp
The only technical change that results in higher energy photons is an increase in kVp. Increasing mA and
rotation time increase the number of photons, but not the energy of those photons.
If the rotation time of a scan is decreased, what other exposure parameter should be changed to
maintain the image quality?
A. Increase mA
B. Increase kVp
C. Decrease scan length
D. Decrease mA - correct answer ✔✔A. Increase mA
Rotation time and mA must be balanced to maintain the same total exposure. If one is increased, the
other must decrease. If one is decreased, the other must increase. This is the idea of mAs reciprocity.
A single "view" acquired during a CT scan is also called a:
A. Slice
B. Projection
C. Detector
D. Attenuation reading - correct answer ✔✔B. Projection
Which the following statements correctly describes the flow of electrons through an x-ray tube?
A. Cathode to anode
B. Anode to cathode
C. Positive to negative
D. target to a filament - correct answer ✔✔A. Cathode to anode
The cathode of the x-ray tube is the same as the filament, the source of electrons, which is negatively
charged. The anode is the target, which is positively charged. When a voltage (kVp) is applied, the
negatively charged electrons accelerate to the positively charged anode. Electron interactions in the
anode are responsible for x-ray production.
The specific process that accelerates electron in an x-ray tube is:
A. Evacuation of air in the envelope
B. Themionic emission
C. Application of a voltage
D. Bremsstrahlung electron interactions - correct answer ✔✔C. Application of a voltage
All options listed are valuable in the x-ray production process, but only the voltage actually causes
electrons to accelerate through the tube. A "voltage" is the same as the kilovoltage potential (kVp).
Increasing mA in CT has the effect of:
A. Increasing dose to the patient
B. Increasing exposure to the detector elements
C. Increasing the intensity of the beam
D. All answers listed are true - correct answer ✔✔D. All answers listed are true
,Increasing the mA results in more photons in the beam (intensity). This results in more dose to the
patient and more exposure to the detector elements.
An increase of which of the following exposure factors would increase the total number of x-ray photons
exposing the detectors?
1. mA
2. kVp
3. rotation time
A. 1 only
B. 2 only
C. 1 and 2 only
D. 1,2, and 3 - correct answer ✔✔D. 1,2, and 3
All options have the effect of increasing the total number of photons exposing the detectors. Increased
mA increases the total number of photons being produced. Increased kVp also increases the total
number of photons produced and increases the penetrating ability of those photons. Increased rotation
time, without changing the mA, results in a longer exposure (per rotation) and more total photons
exposing the detectors.
If mA is decreased by a factor of 2, how is the radiation dose to the patient changed? Assume all other
factors remain unchanged.
A. Dose is increased by a factor of 2
B. Dose is decreased by a factor of 2
C. Dose remains unchanged
D. Dose is decreased by a factor of 22 - correct answer ✔✔B. Dose is decreased by a factor of 2
The relationship between mA and dose is directly proportional and linear. If mA decreases by a certain
factor, dose will decrease by the same factor. In this question, dose decreased by a factor of 2 between
, mA decreased by a factor of 2. In other words,there are half as many photons interacting with the
patient and therefore the dose would also be half.
What technical change is expected to increase the penetrating ability of an x-ray beam?
A. Increased kVp
B. Increased mA
C. Increased rotation time
D. All of the above - correct answer ✔✔A. Increased kVp
The only technical change that results in higher energy photons is an increase in kVp. Increasing mA and
rotation time increase the number of photons, but not the energy of those photons.
If the rotation time of a scan is decreased, what other exposure parameter should be changed to
maintain the image quality?
A. Increase mA
B. Increase kVp
C. Decrease scan length
D. Decrease mA - correct answer ✔✔A. Increase mA
Rotation time and mA must be balanced to maintain the same total exposure. If one is increased, the
other must decrease. If one is decreased, the other must increase. This is the idea of mAs reciprocity.
A single "view" acquired during a CT scan is also called a:
A. Slice
B. Projection
C. Detector
D. Attenuation reading - correct answer ✔✔B. Projection
