A 62-year-old man with hypertension and diabetes presents to the emergency department with acute onset left-sided weakness and speech difficulty of 2 hours duration. Non-contrast CT head is normal. Which investigation is most appropriate to confirm acute ischemic stroke and guide thrombolytic therapy?

## Investigation of Choice for Acute Ischemic Stroke Confirmation **Key Point:** DWI-MRI is the gold standard for detecting acute ischemic stroke within the first few hours when conventional CT and standard MRI sequences are still normal. ### Why DWI-MRI is Superior Diffusion-weighted imaging detects restricted water diffusion in ischemic tissue within **minutes** of symptom onset, making it: - The most sensitive (88–100%) and specific (86–100%) modality for acute ischemia - Positive even when conventional CT and T2-weighted MRI are negative - Capable of identifying the **exact location and volume** of infarcted tissue - Essential for thrombolytic decision-making within the therapeutic window ### Timing of Imaging Findings | Modality | Time to Positivity | Sensitivity in Acute Phase | |----------|-------------------|---------------------------| | **DWI-MRI** | **Minutes (5–30 min)** | **88–100%** | | Conventional CT | Hours (6–24 h) | 10–20% (early ischemic changes subtle) | | CT perfusion | Minutes (but less specific) | Detects hypoperfusion, not infarction | | CTA | Minutes (for vessel occlusion) | Identifies large vessel occlusion | | Conventional angiography | Hours | Gold standard for vessel anatomy but invasive | **Clinical Pearl:** In this patient with a normal non-contrast CT at 2 hours post-onset, DWI-MRI is the single best test to: 1. Confirm acute ischemic stroke 2. Exclude stroke mimics (migraine, Todd's paralysis, seizure) 3. Identify salvageable penumbra (mismatch between DWI and perfusion-weighted imaging) 4. Guide thrombolytic or thrombectomy decisions **High-Yield:** DWI positivity persists for 1–2 weeks, whereas conventional CT remains normal for 6–24 hours in acute ischemia. This makes DWI the investigation of choice in the hyperacute phase (0–6 hours). **Mnemonic:** **DWI = Diffusion Wins In acute ischemia** — it detects water restriction (cytotoxic edema) before any other imaging modality. ### Role of Other Modalities - **CTA:** Used to identify **large vessel occlusion (LVO)** and guide thrombectomy candidacy, but does NOT confirm infarction; often done **alongside** DWI-MRI - **Conventional angiography:** Invasive; reserved for therapeutic intervention (thrombectomy), not diagnosis - **PET:** No role in acute stroke diagnosis; used for chronic stroke assessment of viability