OPtimizing REperfusion by Intra-Arterial ThRomboLysis as Adjunct to Endovascular Treatment for Medium Vessel Occlusion

Inclusion Criteria: 1. Aged 18 years or older. 2. Clinical diagnosis of acute ischemic stroke. 3. CT angiography (CTA) or MR angiography (MRA) confirmed primary isolated medium vessel occlusion (i.e. an occlusion of the co-/non-dominant M2, the M3/M4 segment of the MCA, the A1/A2/A3 segment of the ACA, or the P1/P2/P3 segment of the PCA). 4. Baseline NIHSS ≥6. 5. Treatment (arterial puncture) can be initiated 5.1 Within 6 hours of last known well (LKW) OR 5.2 Within 6 to 24 hours of LKW AND evidence of salvageable brain tissue on CT perfusion or perfusion-diffusion MRI (ischemic core volume \<50mL, hypo-perfused tissue volume to ischemic core volume ratio \>1.4, mismatch volume \>10mL). Hypo-perfused tissue is defined as Tmax \>6s on CT perfusion or perfusion MRI. Ischemic core is defined as rCBF \<30% on CT perfusion or ADC \<620μm2/s on diffusion MRI. 6. Signed informed consent. Exclusion Criteria: 1. Evidence of intracranial hemorrhage. 2. Pre-stroke mRS score ≥ 2. 3. Rapidly improving symptoms, in the judgment of the managing clinician that the improvement is likely to result in the patient having an NIHSS score of \<6 at randomization. 4. The intervention procedure is unlikely to be completed as assessed by the investigator. 5. Suspected cerebral vasculitis, septic embolization, or vascular occlusion due to infective endocarditis. 6. Suspected arterial dissection. 7. Severe allergy to contrast agents (non-mild rash allergy) or absolute contraindication to iodine contrast. 8. Known genetic or acquired bleeding disposition or anticoagulant factors deficiency. 9. Coagulation disorder with INR \>1.7 or use of new oral anticoagulants within 48 hours prior to symptom onset. 10. Platelet count \<50×10\^9/L. 11. Any active or recent bleeding (gastrointestinal, urinary tract bleeding, etc.), or previous parenchymal organ surgery or biopsy in the last 1 month. 12. Systolic blood pressure \>185 mmHg or diastolic blood pressure \>110 mmHg, refractory to treatment. 13. Known severe renal insufficiency with glomerular filtration rate \<30 ml/min or blood creatinine \>220 μmol/L (2.5 mg/dl). 14. Radiological confirmed evidence of mass effect or intracranial tumour (except small meningioma). 15. Anticipated life expectancy \<6 months due to advanced disease (e.g., malignancy, severe cardiopulmonary disease, etc.). 16. Women who are pregnant or breastfeeding. 17. Participation in other clinical trials. 18. Any condition that, in the judgment of the investigator, makes the patient unsuitable for this study or where this study may impose a significant risk to the patient (e.g., inability to understand and/or comply with study procedures and/or follow-up due to psychiatric disorders, cognitive or emotional impairment).