Cerebral autoregulation can be assessed noninvasively by the use of Trans Cranial Doppler (TCD). This means using ultrasound probes over both sides of the head to measure changes in blood flow in one of the main brain arteries (the middle cerebral artery) in response to beat to beat changes dynamic cerebral autoregulation. However, the use of TCD may be limited by the absence of brain window and/or occlusion of the middle cerebral artery in the acute ischaemic stroke patients. Therefore, it is important to consider alternative sites to the middle cerebral artery to assess brain blood flow regulation, and our group has previously researched the use of the main neck artery (the internal carotid artery) site. In a healthy control population, brain blood flow regulation index (autoregulation index) estimated from the internal carotid artery is not statistically different from the middle cerebral artery. However, such comparisons have not been made in the acute ischaemic stroke population. This research will use noninvasive technique of Trans Cranial Doppler to look at blood flow regulation in the brain (cerebral autoregulation) in clotbusting therapy (thrombolysis) treated acute ischaemic stroke (AIS) patients at the initiation and completion of thrombolysis, and during acute, subacute and chronic phase post stroke onset, compared to those AIS patients who have similar age, sex and blood pressure but not treated with thrombolysis. This study will provide important data regarding peri-thrombolysis blood pressure management, an important and common clinical dilemma.