A non-invasive method of diagnosing and treating vessel occlusion and, in particular, small vessel occlusion by using transcranial Doppler ultrasound scanning. The method can be used for all forms of small vessel ischaemia, including all sub-types of ischaemic stroke, ischaemia secondary to primary intracerebral hemorrhage and intracerebral tumour, diagnosis and treatment is carried out by the identification of abnormal signals during ultrasound intonation.