Regional Cerebral Blood Flow in Man Determined by the Initial Slope of the Clearance of Intra-arterially Injected l33Xe

Abstract

The regional cerebral blood flow can be calculated from the initial slope of the logarithmically displayed clearance curve following intra-arterial injection of133Xe (rCBFinitial). The relationship between this parameter and the values resulting from stochastic (height over area) and compartmental analyses is extensively discussed. Experimental results demonstrate the theoretically expected close relationship between rCBFinitialand flow of gray substance (rCBFinitial20% to 30% lower than Fg). It is shown how the cerebral clearance curve (normally biexponential) with low flow values becomes gradually monoexponential. Thus only flow of gray substance changes, whereas flow of white substance is independent of CBF∞. CBF10was shown to overestimate CBF∞with about 15% independent of the flow level. Correlation between CBFinitialand CBF10was linear (r=0.98) at CBF10values above 20 ml/100 gm/min.The CBFinitialnormal value is found to be 64±9 ml/100 gm/min, and the interchannel coefficient of variation is 8.2%. A correction for remaining radioactivity from previous measurements is described. Using this, no significant difference was found between repeated resting state measurements.The CBFinitial-Paco2relationship was found to be best described as exponential. In a group of patients with various intracranial diseases, 1 mm Hg change in Paco2resulted in 4% change of CBFinitialquite independent of the CBFinitiallevel.