In acute ischemic stroke with large vessel occlusion, mechanical thrombectomy is recommended within up to 24 hours in select patients per perfusion imaging; sooner is better.

• A. CT perfusion imaging
• B. Non-contrast CT
• C. CTA
• D. MRI with diffusion

Answer: (A)

The key idea is using perfusion imaging to identify brain tissue that is still salvageable, so thrombectomy can be offered even if the patient presents later, up to 24 hours from onset in select cases with a favorable mismatch pattern.

CT perfusion provides rapid, quantitative maps of the brain’s perfusion status, giving two crucial pieces: the infarct core (irreversibly damaged tissue) and the penumbra (vulnerable but potentially salvageable tissue). By comparing these, clinicians can determine whether there is a meaningful amount of tissue at risk that could be saved with reperfusion. This makes it the most practical and widely available method for selecting patients for extended-window thrombectomy, aligning with trial data that show benefit when a favorable core–penumbra mismatch is present.

Non-contrast CT can rule out hemorrhage and show early ischemic changes, but it does not assess tissue viability. CTA shows the vessel occlusion but not how much tissue can be saved. MRI with diffusion can measure core and perfusion as well, but it is less accessible and slower in many emergent settings, making CT perfusion the preferred initial perfusion imaging tool in acute stroke workflow. The emphasis remains that earlier treatment yields better outcomes, but CT perfusion specifically enables the extended-window decision by defining salvageable tissue.