• Rate of early recanalization on post-treatment MR or CT angiography. Recanalization is described using the tIMI classification. [ Designated as safety issue: Yes ]
  

• Rate of symptomatic intracerebral hemorrhage, mortality, Score on the modified Rankin scale [ Time Frame: 3 months ] [ Designated as safety issue: Yes ]
  

Proximal MCA occlusion is recognized using MR or CT angiography performed before inclusion. All patients are treated with alteplase according to current guidelines. In addition, patients randomized in the active group are continuously exposed to transcranial 2-MHz ultrasound for 1 hour combined with intravenous administration of microbubbles. Controls are only treated with alteplase. The ultrasound beam is positioned at the thrombus/blood flow interface using color-coded sonography. Galactose-based microbubbles are administered via continuous intravenous infusion over 40 min.

Early recanalization is assessed using MR or CT angiography 4 to 8 hours after symptom onset. The evaluation of angiograms is performed by 2 neuroradiologists blinded to group of randomization and clinical details. The primary outcome measure is the rate of early recanalization. Recanalization is assessed using the TIMI classification. Secondary endpoints include the rate of symptomatic intracerebral hemorrhage, mortality, and functional outcome on the modified Rankin scale at 3 months.