DHA Diagnostic Imaging & Radiology 4

Question 1

Which MRI sequence is most sensitive for detecting acute cerebral ischemia within the first few hours of onset?

Accepted Answer

Diffusion-weighted imaging (DWI)

Answer

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:

Accepted Answer

Air-space consolidation obliterating a normally visible border

Answer

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?

Accepted Answer

MRI

Answer

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:

Accepted Answer

Intussusception

Answer

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?

Accepted Answer

Significantly lower risk of anaphylaxis

Answer

Gadolinium-based agents have a significantly lower rate of severe anaphylactic reactions compared to iodinated CT contrast agents.

DHA - Dubai Health Authority Practice Test