MRI Modality for CVA Evaluation
Order MRI brain without contrast with diffusion-weighted imaging (DWI) sequences as the primary imaging modality for suspected cerebrovascular accident. 1
Primary Imaging Protocol
MRI brain without IV contrast including DWI is the preferred diagnostic imaging modality and should be performed within 24 hours of symptom onset. 1 This recommendation comes directly from American Heart Association and National Stroke Association guidelines for acute cerebral ischemia evaluation.
Key Sequences to Include:
- Diffusion-weighted imaging (DWI) - This is the critical sequence that detects acute ischemic changes within hours of stroke onset 1
- T2 FLAIR - Helps distinguish lacunar infarcts from perivascular spaces and detects white matter disease 1
- Gradient echo or susceptibility-weighted imaging (SWI) - Detects microhemorrhages and helps differentiate hemorrhagic from ischemic stroke 1
Vascular Imaging Add-On
Add MRA head without contrast (time-of-flight technique) to the same imaging session to evaluate for arterial occlusion, stenosis, or vascular malformation. 1, 2 The guidelines specifically recommend noninvasive imaging of cervicocephalic vessels as part of the routine stroke evaluation, and MRA can be easily obtained when brain MRI is performed. 1
Why MRA Matters:
- Identifies proximal vessel occlusions that may benefit from intervention 2
- Detects carotid stenosis requiring urgent treatment 1
- Can be performed without contrast using time-of-flight technique if contrast is contraindicated 1, 2
If MRI is Not Available
Use CT head without contrast as the alternative if MRI cannot be obtained within the appropriate timeframe. 1 While CT is less sensitive for acute infarcts, it effectively rules out hemorrhage and stroke mimics such as intracranial masses. 1
Common Pitfalls to Avoid
- Don't order MRI with contrast for initial stroke evaluation - The diagnostic information from DWI sequences does not require contrast administration 1
- Don't skip DWI sequences - Standard T1/T2 imaging alone is insufficient; DWI is what detects acute ischemia 1
- Don't delay imaging beyond 24 hours - Earlier imaging (ideally within 12 hours) provides better diagnostic and prognostic information 1, 3
- Don't rely on perfusion-weighted imaging (PWI) alone - While PWI can show the DWI/PWI mismatch suggesting penumbra, it overestimates tissue at risk and is not required for initial diagnosis 4, 5, 6
Clinical Context Considerations
For patients presenting within 6 hours of symptom onset where thrombolysis or thrombectomy is being considered, the imaging should be expedited and include both brain parenchymal assessment (DWI) and vascular assessment (MRA or CTA). 2
For patients with abnormal DWI showing acute cerebral infarction, this finding supports hospitalization and aggressive secondary stroke prevention measures. 1