A Method for the Estimation of Regional Cerebral Blood Flow §

Over the past years the nitrous oxide absorption method proposed by Kety and Schmidt12 has achieved wide application for the estimation of the blood flow through the cerebral tissue as a whole. However, histological evidence indicates a great variability in the relative vascularity of the several portions of the brain. Thus, for the most part, the white matter is relatively poorly supplied with blood vessels, while the gray matter, on the other hand, is very vascular. Some indication of the variable distribution of blood flow through the brain has been obtained by use of the so-called Gibbs needle Stromuhr."" Another approach to the measurement of local blood flow is the observation of the pial blood -essels through windows' or through the somewhat more satisfactory lucite calvarium.17 At best, these methods estimate the caliber of the pial blood vessels, but actually give little information about the blood flow through these small blood vessels. Recently Kety' has reported on a highly sensitive method for simultaneous measurement of blood flow through all regions of the brain. This method involves equilibration of cerebral tissue with a radioactive gas brought to the brain by the normal circulation; from the relative concentration of gas in the several areas of the brain, estimates of regional blood flow may be made. Since the animal must be sacrificed at the moment of the estimation of blood flow, this method cannot be used to follow progressive changes. The Kety isotope tissue clearance technique8 has been applied to a large variety of tissues." 2' 1, "8 Attempts to extend this method to cerebral circulation were made by Kety" who measured the rate of removal of Na24, and of an isotopically labeled gas, from various injection sites in the brain. The data did not satisfy him, however, and he has abandoned this approach. Boatman' measured the clearance of Na24, 1131, and P3204 from areas in the