ASC Stroke Imaging & Diagnostics 3 — Questions and Answers
Question 1: A patient with acute stroke undergoes MR angiography. Which technique best evaluates collateral blood flow without contrast injection?
- Time-of-flight (TOF) MRA (Correct answer)
- Contrast-enhanced MRA
- Phase-contrast MRA
- Susceptibility-weighted angiography
Correct answer: Time-of-flight (TOF) MRA
TOF MRA relies on flow-related enhancement without contrast, making it ideal for assessing vessel patency and collateral flow when contrast is contraindicated.
Question 2: Which finding on susceptibility-weighted imaging (SWI) is characteristic of cerebral microangiopathy and increases hemorrhagic transformation risk after thrombolysis?
- Cortical vein thrombosis
- Cerebral microbleeds (CMBs) appearing as small hypointense foci (Correct answer)
- Dural sinus stenosis
- Cortical spreading depression artifact
Correct answer: Cerebral microbleeds (CMBs) appearing as small hypointense foci
Cerebral microbleeds appear as small hypointense foci on SWI due to hemosiderin deposits and signal an increased risk of hemorrhagic transformation after tPA.
Question 3: In a posterior circulation stroke, which imaging modality is most limited due to bone artifact and should be supplemented?
- MRI DWI
- CT perfusion
- Non-contrast CT (Correct answer)
- MR perfusion
Correct answer: Non-contrast CT
Non-contrast CT has significant limitations in the posterior fossa due to bone artifact, making MRI DWI the preferred modality for detecting posterior circulation ischemia.
Question 4: When interpreting an ASPECTS (Alberta Stroke Program Early CT Score), a score of 7 out of 10 means that how many regions show early ischemic changes?
- 3 regions (Correct answer)
- 7 regions
- 5 regions
- 2 regions
Correct answer: 3 regions
ASPECTS starts at 10 points and subtracts 1 point for each affected region; a score of 7 means 3 out of 10 MCA territory regions show early ischemic changes.
Question 5: Which vessel imaging finding best predicts poor collateral circulation and worse clinical outcome in proximal MCA occlusion?
- Absent pial collateral filling on CTA or DSA (Correct answer)
- Single hyperdense MCA sign on NCCT
- Gadolinium enhancement of the ischemic core
- Bilateral DWI lesions
Correct answer: Absent pial collateral filling on CTA or DSA
Absent or poor pial collateral filling on CTA or DSA correlates with rapid core expansion and is a strong predictor of poor outcome in proximal MCA occlusion.
Question 6: What does the 'DWI-FLAIR mismatch' pattern suggest about stroke onset timing?
- Stroke occurred more than 24 hours ago
- Stroke is likely within 4.5 hours of onset (wake-up or unknown onset) (Correct answer)
- Hemorrhagic transformation has occurred
- Bilateral watershed infarction is present
Correct answer: Stroke is likely within 4.5 hours of onset (wake-up or unknown onset)
DWI-FLAIR mismatch (DWI positive, FLAIR negative) indicates the stroke is likely within 4.5 hours, as FLAIR changes typically lag behind DWI by several hours.
Question 7: A carotid ultrasound shows a 75% stenosis by NASCET criteria. Which measurement method defines this calculation?
- Stenosis diameter divided by the common carotid diameter
- Residual lumen diameter divided by the distal normal ICA diameter (Correct answer)
- Plaque length divided by total vessel length
- Peak systolic velocity ratio of ICA to CCA
Correct answer: Residual lumen diameter divided by the distal normal ICA diameter
The NASCET method calculates stenosis as (1 - residual lumen / distal normal ICA lumen) × 100%, comparing the narrowest point to the normal vessel distal to the stenosis.
ASC Stroke Imaging & Diagnostics 3
A patient with acute stroke undergoes MR angiography.
Which technique best evaluates collateral blood flow without contrast injection?