What mode of MRI do you order for acute cerebral vascular accident (CVA)?

MRI Protocol for Acute Cerebrovascular Accident (CVA)

For acute stroke evaluation, order MRI brain without contrast including diffusion-weighted imaging (DWI), FLAIR, and gradient-echo (GRE) or susceptibility-weighted imaging (SWI) sequences, which can be completed in approximately 10 minutes and provides superior sensitivity compared to CT for detecting acute ischemia. 1, 2, 3

Core MRI Sequences Required

Diffusion-Weighted Imaging (DWI)

• DWI is the single most sensitive and specific technique for demonstrating acute infarction within minutes of onset, with 91% sensitivity and 95% specificity within 6 hours compared to CT's 61% sensitivity and 65% specificity 1, 2
• DWI detects cerebral ischemia with 77% sensitivity in the first 3 hours versus only 16% for CT, and remains superior up to 12 hours after symptom onset 3, 4, 5
• This sequence is established as more useful than non-contrast CT for diagnosing acute ischemic stroke within 12 hours 5

FLAIR (Fluid-Attenuated Inversion Recovery)

• FLAIR is the best method for showing abnormal fluid accumulations and detects 91% of ischemic lesions 1
• This sequence helps identify chronic lacunar infarcts and white matter disease 3

Gradient-Echo (GRE) or Susceptibility-Weighted Imaging (SWI)

• GRE/SWI excludes intracranial hemorrhage with superior sensitivity compared to CT and detects acute, subacute, and chronic hemorrhage 1, 2
• These sequences identify microhemorrhages indicating amyloid angiopathy, hypertension, and other vascular diseases 2
• The presence of a small number of microbleeds is not a contraindication to IV tPA within the 3-hour window 3

Additional Vascular Imaging

When to Add MRA

• For patients who are candidates for endovascular therapy, add MRA head and neck to the initial MRI protocol 1, 2
• The preferred approach combines non-contrast MRA of the head with contrast-enhanced MRA of the neck 1, 3
• MRA can be performed without contrast using time-of-flight technique to assess intracranial vasculature for stenosis or occlusion 3
• Vascular imaging should be obtained during initial evaluation if endovascular therapy is contemplated, even within the 3-hour window, provided it does not delay IV tPA administration 2

DWI and PWI Can Identify Large Vessel Occlusion

• DWI and perfusion-weighted imaging (PWI) alone accurately identify anterior circulation large vessel occlusions with 95.9% sensitivity and 98.4% specificity, potentially eliminating the need for MRA in hyperacute scenarios 6
• The combined yield of PWI and DWI identifies cerebral ischemic lesions in approximately 51% of TIA patients 7

Contrast Administration Strategy

Contrast is NOT indicated for initial acute stroke MRI evaluation 3

• MRI findings of both acute and chronic ischemic changes can be depicted without IV contrast 3
• There is insufficient evidence to support MRI with contrast for initial stroke evaluation 3
• If MRA of the neck is performed, contrast-enhanced imaging provides superior visualization of the carotid bifurcation and extracranial vessels 3

Timing Considerations

Within 4.5-Hour Window

• The primary goal is rapid exclusion of hemorrhage—either non-contrast CT or MRI is appropriate 2, 3
• Do not delay IV tPA while waiting for MRI if non-contrast CT is immediately available and shows no contraindications 3
• Imaging should be completed and interpreted within 45 minutes of emergency department arrival 3

Beyond 6-Hour Window

• Add perfusion imaging (PWI) to identify salvageable tissue (ischemic penumbra) versus irreversibly infarcted core 1, 2
• Multimodal imaging with perfusion assessment is essential for treatment selection in extended time windows 2
• MR diffusion/perfusion mismatch or MRA-DWI mismatch identifies patients likely to benefit from reperfusion therapy in the 3-6 hour window 8

Critical Pitfall to Avoid

Focusing solely on parenchymal imaging without vascular imaging may miss large vessel occlusions requiring endovascular therapy, representing a critical missed opportunity for potentially life-saving intervention 2

• For endovascular therapy candidates, vascular imaging is strongly recommended during initial evaluation 2
• The presence of large vessel occlusion significantly influences treatment decisions and prognosis 2