ARRT Radiation Safety 3 — Questions and Answers
Question 1: During a CT-guided biopsy procedure, which measure BEST reduces radiation exposure to the interventional CT technologist?
- Standing at the gantry opening throughout the procedure
- Using fluoroscopy-like CT intermittently and stepping back during exposures (Correct answer)
- Wearing a lead apron only when the patient is being positioned
- Reducing tube current to zero between acquisitions
Correct answer: Using fluoroscopy-like CT intermittently and stepping back during exposures
Intermittent CT fluoroscopy combined with stepping away from the gantry during exposures significantly reduces occupational dose during interventional procedures.
Question 2: Which regulatory body sets the annual occupational effective dose limit of 50 mSv in the United States?
- FDA
- NRC and Agreement States (Correct answer)
- ARRT
- CDC
Correct answer: NRC and Agreement States
The Nuclear Regulatory Commission (NRC) and Agreement State regulations set the 50 mSv/year occupational effective dose limit (10 CFR 20).
Question 3: An automatic exposure control (AEC) system in CT adjusts which parameter in real time?
- Gantry rotation speed
- Tube current (mA) based on patient attenuation (Correct answer)
- Detector row width
- Reconstruction kernel
Correct answer: Tube current (mA) based on patient attenuation
CT AEC (tube current modulation) automatically adjusts mA based on patient size and attenuation to maintain consistent image quality at optimal dose.
Question 4: What is the recommended gonadal shielding practice for most routine CT examinations of the abdomen and pelvis?
- Always shield gonads with bismuth shields placed directly on the skin
- Gonadal shielding is not routinely recommended because it can degrade image quality and obscure anatomy (Correct answer)
- Place lead gonadal shields inside the bore before every scan
- Use shadow shielding on all patients regardless of scan region
Correct answer: Gonadal shielding is not routinely recommended because it can degrade image quality and obscure anatomy
Current ACR and AAPM guidance (2019) recommends against routine gonadal shielding in CT because it degrades image quality, increases dose, and gonads are rarely in the primary beam.
Question 5: Which scan parameter change will REDUCE patient dose while keeping all other factors constant?
- Increasing mAs from 200 to 300
- Decreasing scan length from 40 cm to 30 cm (Correct answer)
- Decreasing pitch from 1.5 to 0.75
- Increasing rotation time from 0.5 s to 1.0 s
Correct answer: Decreasing scan length from 40 cm to 30 cm
Reducing scan length directly reduces the total volume irradiated and therefore lowers DLP and patient dose.
Question 6: In CT, iterative reconstruction (IR) algorithms primarily allow dose reduction by:
- Eliminating beam hardening artifacts entirely
- Producing diagnostic-quality images at lower mAs settings than filtered back projection (Correct answer)
- Increasing spatial resolution without any dose penalty
- Reducing the number of detector rows required
Correct answer: Producing diagnostic-quality images at lower mAs settings than filtered back projection
Iterative reconstruction models image noise mathematically, allowing lower mAs protocols to produce acceptable image quality compared to filtered back projection.
Question 7: A pregnant patient requires urgent abdominal CT. What is the approximate threshold fetal dose below which deterministic effects (e.g., malformations) are considered negligible?
- 5 mGy
- 50 mGy (Correct answer)
- 100 mGy
- 500 mGy
Correct answer: 50 mGy
Below approximately 50 mGy, deterministic effects such as malformations or growth retardation are not expected; however, stochastic risk remains and dose should be minimized.
ARRT Radiation Safety 3
During a CT-guided biopsy procedure, which measure BEST reduces radiation exposure to the interventional CT technologist?