A Study of the Safety, Imaging and Clinical Outcomes of THR-18 in Acute Stroke Subjects Treated With tPA

Inclusion Criteria: * Age 18 to 80 years, both inclusive. * Acute ischemic stroke, defined as an acute, focal, neurological deficit(s), secondary to an ischemic vascular event, which must include at baseline at least 1 of the following components as reflected by at least 1 point on items 9, 3 and 11 of the National Institutes of Health Stroke Scale (NIHSS), i.e. language dysfunction (aphasic disorder, excluding dysarthria), visual field defect (excluding monocular blindness), extinction and inattention. * NIHSS above 5 and below 18 for left and right hemisphere strokes. * Indication for the administration of intravenous tPA for acute stroke in accordance with tPA's authorized label for acute stroke. * Pre-stroke modified Rankin Scale score lower or equal to 2. * Ability to understand the requirements of the study and willing to provide written informed consent. In the event of incapacitated subjects, informed consent will be sought from a legally acceptable representative or by any other means as approved by the Ethics Committee. * No contraindication to i.v. administration of iodinated contrast agent Exclusion Criteria: * Contraindications for tPA administration because of an increased risk of bleeding * Known hypersensitivity to tPA or to iodinated contrast agents. * Neurological deficit that has led to stupor or coma (NIHSS level of consciousness score above or equal to 2). * Stroke 90 days before screening/baseline assessments that is either confirmed or assumed to be in the same cerebral territory as is the current acute stroke. * Seizure any time between stroke symptoms onset and randomization. * Life expectancy below 1 month. * Serious illness, e.g. heart failure grade III or IV according to the New York Heart - Association functional classification, severe hepatic or renal failure. * Neurological or non-neurological disease that in the investigator's opinion may confound the assessment of the treatment's safety or biological effects. * Estimated creatinine clearance equal to or lower than 45 mL/min or dependency on renal dialysis. * Treatment of the qualifying stroke with intravenous heparin unless activated partial thromboplastin time prolongation is not more than 2 seconds above the upper limit of normal for local laboratory prior to study drug initiation. * Treatment of the qualifying stroke with a low molecular weight heparin or heparinoid. * Female of childbearing potential who is not willing to use adequate and effective birth control measures for the duration of the trial. * Positive urine pregnancy test at screening/baseline or lactating female. * Body weight (measured or estimated) above 100 kg. * Current drug or alcohol abuse.