Computed Tomography Test CT Radiation Safety and Dosimetry 1 — Questions and Answers
Question 1: Which unit is used to express the effective radiation dose received by a patient during a CT scan?
- Millisievert (mSv) (Correct answer)
- Milligray (mGy)
- Roentgen (R)
- Rad
Correct answer: Millisievert (mSv)
Millisievert (mSv) is the SI unit used to express effective dose, which accounts for the biological effect of radiation on different tissues.
Question 2: What does the term CTDI stand for in CT radiation dosimetry?
- Computed Tomography Dose Index (Correct answer)
- CT Diagnostic Imaging
- Computed Tomography Density Index
- CT Dose Interval
Correct answer: Computed Tomography Dose Index
CTDI (Computed Tomography Dose Index) is a standardized measure of radiation dose output from a CT scanner for a single rotation.
Question 3: Which principle of radiation protection states that doses should be kept as low as reasonably achievable?
- ALARA (Correct answer)
- BERT
- LNT
- NCRP
Correct answer: ALARA
ALARA (As Low As Reasonably Achievable) is the guiding principle for minimizing radiation exposure to patients and staff.
Question 4: Increasing the mAs in CT by a factor of 4 will have what effect on image noise?
- Reduce noise by 50% (Correct answer)
- Double the noise
- Eliminate noise entirely
- Quadruple the noise
Correct answer: Reduce noise by 50%
Since noise is proportional to 1/√mAs, quadrupling mAs reduces noise by half (√4 = 2).
Question 5: What is the primary purpose of using automatic exposure control (AEC) in CT?
- Adapt tube current to patient size and anatomy (Correct answer)
- Increase scan speed
- Improve spatial resolution
- Reduce contrast agent volume
Correct answer: Adapt tube current to patient size and anatomy
AEC (also called tube current modulation) automatically adjusts mA based on patient attenuation to optimize image quality while minimizing dose.
Question 6: Which CT parameter, when increased, directly increases patient radiation dose?
- mAs (Correct answer)
- Pitch (above 1.0)
- Detector row width
- FOV
Correct answer: mAs
Increasing mAs increases the number of X-ray photons produced, directly increasing the radiation dose delivered to the patient.
Computed Tomography Test CT Radiation Safety and Dosimetry 1
Which unit is used to express the effective radiation dose received by a patient during a CT scan?