[Continuous measurement of regional cerebral blood flow using krypton-81 m (author's transl)]

In order to obtain sequential change of cerebral blood flow using the intracarotid 81mKr infusion method, we devised a new method by using the radiation from cervical internal carotid artery as the concentration of radioisotope in the blood perfused to the brain. Under continuous intracarotid injection of 81mKr, the radio activity obtained from the surface of the skull is proportional to the cerebral blood flow. However, since the method depends upon the infusion of a given volume of radioisotope per unit of time into the internal carotid artery, changes in the blood flow through the internal carotid artery result in changes in the concentration of radioisotope perfused to the brain. Under such conditions, the radioactivity obtained from the surface of the skull does not indicate the changes in blood flow. In such a case, the value obtained from the radioactivity (count rate) in the ROI of the brain divided by concentration of radioisotope in the blood perfused to the brain indicates the changes in cerebral blood flow. Our attention was drawn to the fact that the radioactivity measured from a constant area of the cervical internal carotid artery per unit of time is an indicator of the blood concentration of radioisotope following in the internal carotid artery, provided that, there are no changes in the size of lumen of internal carotid artery. According to this method devised by us, it had been possible to follow extremely short period changes in cerebral blood flow following CO2 inhalation, change of blood pressure (autoregulation) and administration of various drugs.