## Investigation of Choice for Acute Ischemic Stroke Confirmation **Key Point:** DWI-MRI is the gold standard for detecting acute ischemic stroke within the hyperacute window (first 24 hours), with sensitivity >90% even when conventional MRI and CT are normal. ### Why DWI-MRI is Superior **High-Yield:** DWI detects restricted water diffusion in ischemic brain tissue within **minutes** of stroke onset, whereas conventional CT/MRI may appear normal for hours. This is the most specific and sensitive test for acute cerebral infarction. **Clinical Pearl:** In this case, non-contrast CT was performed to rule out hemorrhage (mandatory before thrombolysis). Now that hemorrhage is excluded, DWI-MRI provides: - Confirmation of acute ischemia (appears hyperintense on DWI, hypointense on ADC map) - Identification of stroke territory and volume - Detection of multiple acute infarcts (cardioembolic source) - Prognostic information ### Comparison with Other Investigations | Investigation | Sensitivity in Acute Stroke | Timing | Clinical Role | |---|---|---|---| | **DWI-MRI** | >90% | Minutes | Gold standard for confirmation | | Non-contrast CT | ~15% | Minutes | Rules out hemorrhage | | CTA | Moderate | Minutes | Identifies large vessel occlusion | | Transcranial Doppler | Variable | Minutes | Assesses vessel patency, not diagnostic | | EEG | Not applicable | — | Not used for acute stroke diagnosis | **Mnemonic:** **DWI = Diffusion-Weighted Imaging = Detects Ischemia Immediately** ### Timing Consideration DWI-MRI can be performed rapidly (5–10 minutes) in stroke centers and should not delay thrombolytic therapy if clinical diagnosis is clear and hemorrhage has been excluded. It is confirmatory, not mandatory before treatment in the hyperacute window. [cite:Harrison 21e Ch 370] 
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