The Imaging Compass: Navigating Reperfusion in Acute Ischemic Stroke

The management of acute ischemic stroke has shifted from rigid time-based protocols to imaging-driven, tissue-based reperfusion strategies. Non-contrast CT and CT angiography remain the indispensable frontline for rapid triage, particularly in community and low-resource settings. However, magnetic resonance imaging (MRI) provides unique biological information that complements CT-based assessment: Diffusion-weighted imaging (DWI) detects cellular ischemia within minutes without contrast; DWI-fluid-attenuated inversion recovery (FLAIR) mismatch serves as a tissue clock for unknown-onset stroke; susceptibility-weighted imaging (SWI) aids thrombus characterization; and MRI resolves the posterior fossa without beam-hardening artifact. Low-field portable MRI further extends these capabilities to the bedside where conventional scanners are unavailable. This review examines four convergent trends within this transition: expanding thrombectomy to large-core infarction, extending thrombolysis through tissue-based selection, advancing recanalization in posterior-circulation stroke while defining boundaries for medium- and distal-vessel occlusions, and simplifying imaging workflows through fast MRI protocols, quantitative CT biomarkers, and artificial intelligence (AI). Landmark trials have established that treatment benefit is determined by tissue viability rather than clock time, while recent negative trials define critical boundaries beyond which intervention may cause harm. We critically appraise how CT and MRI are integrated hierarchically across these scenarios, and how emerging fast MRI and quantitative biomarkers may reshape future selection paradigms. EVIDENCE LEVEL: 3-4. TECHNICAL EFFICACY: 3.