Clinical Measurement of Brain Uptake of Radioisotope

Abstract

During the course of some studies of cerebral circulation using γ-emitting radioisotopes injected intravenously we were interested in following the passage through the brain of a γ-emitting radioisotope deposited abruptly into the right heart. Ideally the indicator that passes through the brain would remain entirely intravascular. Because of its extremely rapid renal excretion the substance we felt most desirable was o-iodinated sodium hippurate. We were interested in how well this material remained intravascular in the brain. As a consequence of this interest we developed the technique to be described. Our early experience with labeled hippurate has been described.¹ Technique The technique consists of giving a small amount of γ-emitting radioisotope intravenously and following the total cranial content as the blood level falls. Initially the entire cranial content will be in the circulating blood pool and none in the noncirculating tissues. By subtracting the blood contribution to the total