FRCR MCQ 4 — Questions and Answers
Question 1: Which of the following is the correct definition of the mean glandular dose (MGD) in mammography?
- The average dose absorbed by the glandular tissue of the breast, excluding skin dose (Correct answer)
- The surface entrance dose measured at the skin surface
- The dose to the entire breast volume including fat and skin
- The dose delivered per frame in tomosynthesis
Correct answer: The average dose absorbed by the glandular tissue of the breast, excluding skin dose
Mean glandular dose (MGD) is the primary dosimetric quantity in mammography, representing the average absorbed dose to glandular tissue, which is the radiation-sensitive component of the breast.
Question 2: A 35-year-old woman presents with haematuria. Ultrasound shows an echogenic renal mass with no acoustic shadowing. What is the most likely diagnosis?
- Angiomyolipoma (Correct answer)
- Renal cell carcinoma
- Oncocytoma
- Renal abscess
Correct answer: Angiomyolipoma
Angiomyolipomas are typically echogenic on ultrasound due to their fat content, and absence of acoustic shadowing helps distinguish them from calculi.
Question 3: On plain radiograph, which pattern of periosteal reaction is most suggestive of an aggressive bone lesion?
- Codman's triangle (interrupted periosteal reaction at the tumour margins) (Correct answer)
- Dense solid periosteal reaction
- Undulating periosteal reaction
- Lobulated periosteal new bone
Correct answer: Codman's triangle (interrupted periosteal reaction at the tumour margins)
Codman's triangle represents periosteum lifted and broken at the tumour margin, indicating aggressive growth that outpaces periosteal healing capacity.
Question 4: Which statement about the inverse square law as applied to X-ray imaging is correct?
- Doubling the distance from the source reduces radiation intensity to one-quarter (Correct answer)
- Doubling the distance from the source halves the radiation intensity
- The intensity is proportional to the square of the distance
- The inverse square law does not apply in the diagnostic X-ray energy range
Correct answer: Doubling the distance from the source reduces radiation intensity to one-quarter
The inverse square law states that intensity is inversely proportional to the square of the distance, so doubling the distance reduces intensity to 1/4 (1/2² = 1/4).
Question 5: In a patient with portal hypertension, which ultrasound finding directly confirms the diagnosis?
- Reversal of flow (hepatofugal) in the portal vein on Doppler (Correct answer)
- Splenomegaly with a span greater than 12 cm
- Ascites in the hepatorenal space
- Dilated intrahepatic bile ducts
Correct answer: Reversal of flow (hepatofugal) in the portal vein on Doppler
Hepatofugal (away from the liver) flow in the portal vein on Doppler ultrasound is a direct haemodynamic sign of severe portal hypertension with portosystemic shunting.
Question 6: A CT shows a 'double bubble' sign in a neonate. What is the most likely diagnosis?
- Duodenal atresia (Correct answer)
- Pyloric stenosis
- Midgut volvulus
- Hirschsprung's disease
Correct answer: Duodenal atresia
The double bubble sign on AXR or CT represents a distended stomach and proximal duodenum separated by the pylorus, pathognomonic of duodenal atresia.
Question 7: Which pattern of enhancement on dynamic contrast-enhanced MRI of the breast is most suspicious for malignancy?
- Rapid initial enhancement with washout on delayed phases (type III kinetics) (Correct answer)
- Slow progressive enhancement (type I kinetics)
- Intermediate initial rise with plateau on delayed phases (type II kinetics)
- No enhancement after gadolinium administration
Correct answer: Rapid initial enhancement with washout on delayed phases (type III kinetics)
Type III (washout) kinetics — rapid early enhancement followed by signal decrease on delayed images — is most suspicious for malignancy due to tumour neoangiogenesis.
FRCR MCQ 4
Which of the following is the correct definition of the mean glandular dose (MGD) in mammography?