Cerebral blood flow xenon-133.

The technique of using the intra-arterial clearance method with the diffusible, inert gas 133Xe to measure rCBF has been well established over the past 30 years. By using this method, equations for calculation of rCBF are not very complicated. Because 133Xe is a low gamma emitter and small doses are used, the risk of radiation exposure to the patient and to medical personnel is quite small. Given this fact, it is less harmful than cerebral angiography which requires higher doses of radiation and much larger volumes of injected contrast media. The primary limitation is the "look-through" phenomenon in which the calculated rCBF might not truly represent areas (lesions) of low flow. The magnitude of change or level of rCBF, however, can have an important neurologic meaning. The assessment of collateral flow either during balloon occlusion study or during carotid surgery is of very important clinical value in the interest of the patient's well-being.