ACCURACY OF STABLE XENON CT MEASUREMENTS OF REGIONAL CEREBRAL BLOOD-FLOW - EFFECT OF EXTRAPOLATED ESTIMATES OF BRAIN BLOOD PARTITION-COEFFICIENTS

Stable Xe/computed tomographic (Xe/CT) measurements of regional brain-blood partition coefficients of Xenon (.lambda.) and of regional cerebral blood flow (rCBF) is reported for animal models of stroke and for patients with a variety of neurological diseases. The uncertainty in reported measurements of .lambda. and rCBF was estimated using computer simulations based on Kety''s blood flow equation. Anesthetized baboons were scanned repeatedly for 30-60 min while inhaling an 80:20% Xe-O2 mixture and the resulting CT enhancement values for user-defined regions of interest were used to define a mathematical function with which to fit simulated CT enhancement data. In computer simulation studies, extrapolated and fit values of .lambda. for the same dataset were used to calculate rCBF and the calculated flow values were compared. Computer simulations for heterogeneous (gray-white matter) regions indicate that better estimates of flow are obtained by fitting .lambda. than by using extrapolated values of .lambda. to calculate flow, although, paradoxically, better estimates of .lambda. are obtained by extrapolation than by fitting .lambda.