Measurement of intracranial blood volume by gamma camera emission tomography

Based on phantom and animal experiments a method is proposed for measuring the intracranial blood volume ( ICBV ) by gamma camera emission tomography. The intracranial radioactivity from 99mTc -tagged erythrocytes in intracranial vessels is measured with a gamma camera rotating around the head of the dog with a circulatory turn of 2-20 min. The radioactive counts from each cycle are pictorially displayed as 8-12 frontal sections through the head. On each section the intracranial space is delineated as the region of interest and counted separately. The sum of the intracranial counts of the various sections is an expression of the ICBV and linearly related to it. Accurate delineation of the intracranial space on each of the displayed slices is achieved by injection of a nondiffusible isotope ( 169Yb -DTPA) into the subarachnoid space at the end of each experiment. Scattered radiation is corrected for by a correction factor obtained from the phantom experiments. By means of special calibration procedures the measured ICBV , as expressed in counts may be transferred into volume units (ml). The present method seems to offer several advantages compared to earlier methods for measuring the ICBV .