Methods for measurement of cerebral blood flow.

Difficulties in measuring total and regional cerebral flow have hindered advances in knowledge concerning the regulation of the cerebral circulation. Now, however, we can accurately measure total and regional cerebral blood flow with the labeled microsphere method. With this method, flow to cerebral and non-cerebral tissues in the head can be completely separated, and by using microspheres labeled with different radionuclides, six measurements can be obtained in each experiment. A disadvantage of the microsphere method is that flow is not monitored continuously. Therefore, transient changes in flow (less than 20 seconds) cannot be measured accurately, and it is difficult to determine the time course of changes in cerebral blood flow in response to a given stimulus. A new method, simultaneous measurements of velocity and diameter in a pial artery, complements the microsphere approach. With this new method, nearly continuous, accurate measurements of cerebral blood flow are obtainable. Now that several methods for measuring cerebral blood flow are available and appear to be valid, knowledge concerning the regulation of cerebral blood flow should advance more rapidly.