This is a randomized, placebo controlled, double-blind phase 3 clinical study to evaluate the efficacy and safety of transcranial ultrasound (TUS) using the Sonolysis Headframe as an adjunctive therapy to intravenous (IV) tissue plasminogen activator (tPA) therapy in subjects with acute ischemic stroke that initially present at non-endovascular (EVT) treating hospitals that have established transport services in place to transfer subjects to hospitals capable of performing EVT.

The primary objective of this study is to assess the safety and efficacy of TUS using the Sonolysis Headframe in combination with systemic tPA (Treatment group) compared to systemic tPA alone (Control group) in subjects with acute ischemic stroke.

Number of Subjects Required:

Lead-in Phase: 40 subjects in the U.S.; Primary Phase: 556 total enrolled subjects (278 per arm)

Number of Study Centers:

Lead-in Phase: Up to 20 Institutions in U.S.; Primary Phase: Up to 70 Institutions worldwide

Inclusion Criteria:

1. Subjects with acute ischemic stroke
2. Subjects that initially present at non-EVT treating hospitals that have established transport services in place to transfer subjects to hospitals capable of performing EVT
3. Males or females 18 - 80 years of age
4. Subjects presenting within time window for IV tPA treatment approved by local regulatory authorities but no more than 4.5 hours from onset of symptoms
5. No signs of intracranial bleeding on assessment by non-contrast CT
6. Subjects that in the opinion of the treating physician require treatment with full dose of IV tPA (0.9mg/kg) as standard of care per institutional standards
7. SBP ≤ 185 mmHg and DBP ≤ 105 mmHg at baseline or after treatment of hypertension with medications prior to tPA bolus
8. Pre-morbid mRS of 0-1
9. Arterial occlusion in the middle cerebral artery (MCA) M1 or proximal M2, intracranial carotid T, anterior cerebral artery (ACA) A1, basilar, proximal posterior cerebral artery (PCA) P1 or intracranial tandem lesions in these locations visible on CT angiography (CTA)
10. Provision of informed consent as demonstrated by the subject's signature or by the signature of the subject's authorized legal representative on the Informed Consent Form in accordance with all local and national regulations and no later than 15 minutes after standard of care tPA administration

Exclusion Criteria:

1. Tandem lesions where one lesion is extracranial (carotid or vertebral artery)
2. ASPECTS score < 6 on non contrast CT or ischemic changes that in the opinion of the investigator would be medically inappropriate for reperfusion therapy
3. Poor collateral circulation defined as minimal or no pial collaterals in >50% of the ischemic territory
4. Expected time between activation of Sonolysis Headframe and initiation of EVT < 90 minutes
5. Pregnant or breast feeding women, clinical signs of pericarditis, sepsis or any other serious medical illness likely to interact with treatment, confounding preexistent neurological or psychiatric disease or test values that, in the opinion of the investigator, pose significant risk to the subject and warrant exclusion from the study
6. Impaired renal function defined as eGFR < 60 mL/min/1.73 m2
7. No permanent address or phone number
8. Any investigational drug <14 days prior to study participation
9. Subjects with known allergy to x-ray contrast material
10. Subjects with any standard contraindication for intravenous tPA therapy as per local or national guidelines

Blinding is achieved through operator entry of a randomization variable obtained from IWRS at the time of enrollment and randomization. This randomization variable (A or B), the meaning of which is blinded to the operator, is entered into the control box and determines the mode of the device as either active insonation or sham insonation.