The aim of this thesis is to review the scientific literature on possibilities of reperfusion therapies for patients who present with unknown time of stroke onset, and those with stroke onset beyond the conventional 4.5-6 hour time window. Beyond the conventional time window, the eligibility of patients for intravenous thrombolysis or mechanical endovascular thrombectomy, the two main therapeutic procedures, is decided based on the concept of penumbral imaging. Penumbral imaging identifies patients with hypoperfused but viable brain tissue, who could possibly benefit from reperfusion. On the other hand, clock-based DWI-FLAIR magnetic resonance imaging can detect stroke that has occurred within 4.5 hours in patients with unknown time of onset, including patients who awaken with stroke. The introduction of penumbral imaging and MRI-based tissue clocking as imaging biomarkers for stroke has revolutionized stroke therapy, potentially allowing for personalized treatment of eligible stroke patients.