RAPID MEASUREMENT OF REGIONAL CEREBRAL BLOOD-FLOW IN THE BABOON USINGO-15-LABELED WATER AND DYNAMIC POSITRON EMISSION TOMOGRAPHY

The sensitivity and reproducibility of rapid measurements of regional cerebral flow (rCBF) using a bolus injection of (H2O)-O-15 and dynamic positron emission tomography (PET) were investigated in anaesthetised baboons. The cerebrovascular reactivity to changes in arterial pCO2 w as used as an experimental support. PET data were acquired over 4 min following a single bolus intravenous injection of (H2O)-O-15, while ar terial blood was withdrawn for continuous activity counting. Images we re reconstructed with a dynamic sequence of 45 x 2s + 15 x 10s, includ ing a correction for decay. Regional values of CBF were derived from n on-linear least-squares fits of the time activity curves using a four- parameter two-compartment model. The results obtained with a four-para meter fitting method were compared with those obtained with two other rapid estimation methods, first fitting two parameters only, CBF and p artition coefficient (p), and secondly autoradiography (with p fixed a t 0.95 ml brain ml blood-1). Twelve regions of interest were analysed. The values for the basal CBF obtained from 13 measurements in two bab oons were close to published values obtained with other techniques. Re producibility checks showed a mean variation of 9.7 per cent. The CBF measurements performed in hypercapnic conditions gave results similar to published data in other animal species, showing a 4.5 +/- 0.9 per c ent increase in CBF per mm Hg paCO2. The results obtained with the thr ee estimation techniques were closely correlated. The dynamic bolus (H 2O)-O-15 method appeared to be suitable for high blood flow measuremen ts.