Local cerebral blood volume determined by three dimensional reconstruction of radionuclide scan data

Abstract

A method was developed to determine in man absolute values of local cerebral blood volume (LCBV) localized throughout the brain in 3 dimensions and presented in a cross sectional picture format. Previously, absolute values of LCBV have been determined in vivo by stimulated X ray fluorescence, but these determinations have been limited to one point in the brain at a time. All other previous estimates of LCBV by external emission counting have been contaminated by the significant contribution of blood in the overlying scalp and cranium. In the authors' method, a transverse section scan is made after the injection of 99Tc(m) labeled red blood cells into a peripheral vein. Data processing then gives a point to point estimate of absolute radionuclide concentration analogous to an autoradiograph. After the concentration of blood activity is determined, counting data are converted to a 2 dimensional map of LCBV representing a cross section at a known level of the brain. In a series of 5 baboons, the following equation was obtained for the regression plane that relates LCBV in the center of the brain to arterial carbon dioxide tension [P(a)CO2] and mean arterial blood pressure (MABP): LCBV = 2.88 + 0.049P(a)CO2 - 0.013MABP. In patients, LCBV values ranged from 2 to 4 ml/100 g depending on location; higher values corresponded to regions of cerebral cortex. Differences in blood volumes of focal brain lesions were also quantified.