FRCR MCQ 3 — Questions and Answers
Question 1: Which statement best describes the radiation weighting factor (wR) for neutrons of 1 MeV energy?
- wR = 20, reflecting high relative biological effectiveness (Correct answer)
- wR = 1, same as X-rays
- wR = 5, intermediate between X-rays and alpha particles
- wR = 2, reflecting moderate tissue penetration
Correct answer: wR = 20, reflecting high relative biological effectiveness
Fast neutrons (around 1 MeV) have a radiation weighting factor of 20, reflecting their high linear energy transfer and relative biological effectiveness compared to X-rays.
Question 2: On gadolinium-enhanced MRI of the liver, which feature best distinguishes a haemangioma from a metastasis?
- Peripheral nodular enhancement with progressive centripetal fill-in (Correct answer)
- Rim enhancement without central fill-in
- Homogeneous early arterial enhancement
- T1 hyperintensity on pre-contrast images
Correct answer: Peripheral nodular enhancement with progressive centripetal fill-in
Haemangiomas show characteristic peripheral nodular enhancement on early post-contrast phases with progressive centripetal fill-in on delayed images, following blood pool kinetics.
Question 3: In nuclear medicine, which radionuclide is used for myocardial perfusion imaging with the longest physical half-life among common agents?
- Thallium-201 (T½ = 73 hours) (Correct answer)
- Technetium-99m (T½ = 6 hours)
- Fluorine-18 (T½ = 110 minutes)
- Rubidium-82 (T½ = 76 seconds)
Correct answer: Thallium-201 (T½ = 73 hours)
Thallium-201 has a physical half-life of approximately 73 hours, which is the longest among commonly used myocardial perfusion imaging agents.
Question 4: A CT of the neck shows a cystic mass at the angle of the mandible that displaces the carotid vessels posteriorly. What is the most likely diagnosis?
- Second branchial cleft cyst (Correct answer)
- First branchial cleft cyst
- Thyroglossal duct cyst
- Cystic schwannoma
Correct answer: Second branchial cleft cyst
Second branchial cleft cysts are the most common branchial anomalies, typically appearing as cystic masses at the anteromedial border of the sternocleidomastoid, displacing the carotid vessels.
Question 5: Which feature on mammography is most suspicious for malignancy?
- Spiculated mass with architectural distortion (Correct answer)
- Round well-circumscribed mass with smooth margins
- Cluster of round/punctate calcifications
- Asymmetric fibroglandular density without distortion
Correct answer: Spiculated mass with architectural distortion
A spiculated mass with architectural distortion has a very high positive predictive value for malignancy and warrants tissue sampling (BI-RADS 5).
Question 6: In a patient with suspected acute ischaemic stroke, DWI shows restricted diffusion in the left MCA territory. Which additional sequence best identifies the ischaemic penumbra?
- MR perfusion (PWI) — the PWI-DWI mismatch represents salvageable tissue (Correct answer)
- T2-weighted FLAIR — identifies early infarct core
- MR angiography — shows arterial occlusion site only
- T1 post-contrast — shows blood-brain barrier breakdown
Correct answer: MR perfusion (PWI) — the PWI-DWI mismatch represents salvageable tissue
The DWI-PWI mismatch (perfusion deficit larger than diffusion core) represents potentially salvageable ischaemic penumbra and guides thrombolysis or thrombectomy decisions.
Question 7: Which of the following best describes the Doppler waveform normally seen in the hepatic veins?
- Triphasic waveform with two retrograde phases reflecting cardiac transmitted pulsatility (Correct answer)
- Monophasic low-resistance waveform
- High-resistance biphasic waveform
- Continuous non-pulsatile forward flow
Correct answer: Triphasic waveform with two retrograde phases reflecting cardiac transmitted pulsatility
Normal hepatic veins show a triphasic waveform with two antegrade and one retrograde phase, reflecting transmitted cardiac pulsatility from the right heart.
FRCR MCQ 3
Which statement best describes the radiation weighting factor (wR) for neutrons of 1 MeV energy?