DHA Diagnostic Imaging & Radiology 4 — Questions and Answers
Question 1: Which MRI sequence is most sensitive for detecting acute cerebral ischemia within the first few hours of onset?
- T1-weighted imaging
- Diffusion-weighted imaging (DWI) (Correct answer)
- FLAIR imaging
- T2-weighted imaging
Correct answer: Diffusion-weighted imaging (DWI)
DWI detects restricted diffusion caused by cytotoxic edema in acute ischemia, making it positive within minutes of stroke onset.
Question 2: On a chest X-ray, the 'silhouette sign' is caused by:
- Pneumothorax adjacent to the heart border
- Air-space consolidation obliterating a normally visible border (Correct answer)
- Pleural effusion layering in the costophrenic angle
- Cardiomegaly displacing lung tissue
Correct answer: Air-space consolidation obliterating a normally visible border
The silhouette sign occurs when two structures of equal radiodensity are in contact, causing loss of the normal visible interface between them.
Question 3: Which imaging modality is the gold standard for evaluating the rotator cuff for full-thickness tears?
- Plain radiography
- CT arthrography
- MRI (Correct answer)
- Ultrasound
Correct answer: MRI
MRI provides excellent soft tissue contrast and multiplanar imaging, making it the gold standard for rotator cuff tear assessment.
Question 4: A 'target sign' on bowel ultrasound typically indicates:
- Bowel perforation
- Intussusception (Correct answer)
- Appendicitis
- Volvulus
Correct answer: Intussusception
The target sign on transverse ultrasound view represents layers of bowel wall telescoping into itself in intussusception.
Question 5: What is the primary advantage of using gadolinium-based contrast agents in MRI over iodinated contrast in CT?
- Lower cost
- No risk of nephrogenic systemic fibrosis
- Significantly lower risk of anaphylaxis (Correct answer)
- Better bone detail
Correct answer: Significantly lower risk of anaphylaxis
Gadolinium-based agents have a significantly lower rate of severe anaphylactic reactions compared to iodinated CT contrast agents.
Question 6: On mammography, which feature is MOST suspicious for malignancy?
- Round mass with circumscribed margins
- Coarse calcifications
- Irregular mass with spiculated margins (Correct answer)
- Smooth-walled cyst
Correct answer: Irregular mass with spiculated margins
Spiculated margins on mammography are highly associated with malignancy due to desmoplastic reaction pulling surrounding tissue inward.
Question 7: The 'double bubble' sign on abdominal X-ray in a neonate is characteristic of:
- Hirschsprung disease
- Ileal atresia
- Duodenal atresia (Correct answer)
- Meconium ileus
Correct answer: Duodenal atresia
Duodenal atresia produces two air-filled bubbles representing the stomach and proximal duodenum, with no distal bowel gas.
DHA Diagnostic Imaging & Radiology 4
Which MRI sequence is most sensitive for detecting acute cerebral ischemia within the first few hours of onset?