Measurement of total cerebral blood flow in the monkey by external monitoring of cesium-131.

Abstract

A modification of the 42 K fractionation technique has been developed which permits rapid, repeated measurement of cerebral blood flow by external isotope monitoring without jugular or carotid puncture. 131 Cs, an isotope with distribution characteristics similar to those of 42 K, has been used in this study. Cerebral blood flow measurement involves determination of the peak cephalic activity of an intravenously injected bolus of 131 Cs by digital rate counting in a well-scintillation crystal that encloses the head. If the entire fraction of the isotopic bolus entering the head appears in the cerebral circulation before significant venous loss of 131 Cs begins, the ratio of peak cephalic activity to total injected activity will represent the cephalic portion of the cardiac output. Since cerebral capillaries are not very permeable to 131 Cs, activity remaining in the head after decay of peak cephalic activity will represent uptake by noncerebral cephalic tissue, and the peak activity can be corrected to yield only the cerebral cardiac output fraction. Total cerebral blood flow calculated from 131 Cs injection was compared with measured bilateral internal jugular flow obtained by cannulation of the jugular veins. In anesthetized rhesus monkeys, the average ratio (calculated flow/measured flow) was 1.05±0.06.