Cerebral functional imaging has been greatly improved over the last ten years by the development of noninvasive techniques using radioactive elements emitting gamma radiation. Depending on the radioactive tracer used, these single photon emission computed tomography (SPECT) techniques provide either simple imaging of the distribution of local blood flows (99m Tc or 131 I labelled molecules) or quantitative imaging of the cerebral regional blood flow (133 Xe). Because of the rapidity of these techniques and the possibility of performing repeated examinations associated with dynamic test, quantitative measurement of cerebral blood flow with 133 Xe constitutes a value investigation for cerebral ischaemia by defining the site of the lesions, the distant consequences, the haemodynamic disturbances and their course over time. It has an even more important place in the preoperative assessment of stenoses and thromboses of the supra-aortic vessels and intracranial vessels: the study of the haemodynamic reserve by induced vasodilatation (injection of acetazolamide or acetazolamide test) provides valuable information necessary for the decision to perform a revascularisation procedure. In the future, 133 Xe SPECT will certainly be useful for determining the prognosis of an ischaemic cerebral vascular accident by means of very early examinations and to demonstrate the efficacy of new treatments for cerebral ischaemia by means of repeated examinations.