Quantification of Regional Myocardial Blood Flow in Vivo with H215O

Using H215O (half-life = 2.1 min) we demonstrated that a modification of the tissue autoradiographic approach permitted quantitation of myocardial blood flow in open-chest dogs by direct assay of myocardial tissue and that noninvasive estimation with positron-emission tomography (PET) delineated relative myocardial blood flow in intact dogs. In open-chest anesthetized dogs, the single-pass extraction fraction of H215O averaged 96 +/- 5% at flows of 80 to 100 ml/100 g/min. This high extraction fraction did not differ significantly over the range of 12 to 238 ml/100 g/min. Myocardial blood flow calculated after a 60 sec intravenous infusion of H215O and direct analysis of tissue correlated well with results obtained with microspheres (r = .94, n = 9 dogs). Subsequently the approach was adapted for preliminary use with PET. Estimation of myocardial content of radiolabeled H2O after intravenous infusion of 20 to 30 mCi of H215O was corrected for vascular pool radioactivity with the use of tomographic data obtained after administration of C15O by inhalation to label red blood cells. Tomograms obtained in vivo in six dogs with either normal or reduced regional blood flow correlated closely with the tomographically detectable distribution of 68Ga-labeled microspheres (r = .93) and with postmortem microsphere distribution (r = .95). The technique accurately reflects myocardial blood flow. With the use of PET, rapid sequential noninvasive estimation of relative regional myocardial blood flow has been demonstrated that should ultimately permit improved objective assessment of nutritional blood flow in patients in response to medical and surgical interventions designed to augment perfusion.