Cerebral blood flow measured by NMR indicator dilution in cats

We developed techniques to assess the utility of a nuclear magnetic resonance (NMR) indicator for cerebral blood flow studies in cats, using Freon-22 for the first candidate. A PIN-diode-switched NMR experiment allowed the acquisition of an arterial as well as a cerebral fluorine-19 signal proportional to concentration vs. tune in a 1.89 T magnet. Mean±SD blood:brain partition coefficients for Freon-22 were estimated at 0.93±0.08 for gray matter and 0.77±0.12 for white matter. Using maximum-likelihood curve fitting, estimates of mean±SD resting cerebral blood flow were 50±19 ml/100 g-min for gray matter and 5.0±2.0 ml/100 g-min for white matter. Hypercapnia produced the expected increases in gray and white matter blood flow. The physiologic effects of Freon-22, including an increase in cerebral blood flow itself with administration of 40% by volume, may limit its use as an indicator. Nevertheless, the NMR techniques described demonstrate the feasibility of fluorine-19-labeled compounds as cerebral blood flow indicators and the promise for their use in humans.