Quantitative measurements of cerebral blood flow in volume imaging PET scanners

Quantitative measurements of cerebral blood flow (CBF) are performed in a volume imaging PET scanner by means of moderate activity infusions. In equilibrium infusions, activations are measured by scanning over 10 minutes with 16 minute activations. Typical measured whole brain CBF values are 37±8 ml/min/100 g, close to the value of 42 ml/min/100 g reported by other groups using this method. For ramped infusions, scanning over 4 minutes with 5 minute activations results in whole brain CBFs of 49±9 ml/min/100 g, close to the Kety and Schmidt value of 50 ml/min 100 g. Both equilibrium and ramped infusion methods have been used to study face and word memory in human subjects. Both methods were able to detect significant activations in regions implicated in human memory. We conclude that precise quantitation of regional CBF is achieved using both methods, and that ramped infusions also provide accurate measures of CBF. In addition a simplified protocol for ramped infusion studies has been developed. In this method the whole brain tissue time activity curve generated from dynamic scanning is replaced by an appropriately scaled camera coincidence countrate curve. The resulting whole brain CBF values are only 9% different from the dynamic scan and fit results. Regional CBFs (rCBF) may then be generated from the summed image (4.25 minutes) using a count density vs flow lookup table