DIRECT COMPARISON OF [N-13] AMMONIA AND [O-15]WATER ESTIMATES OF PERFUSION WITH QUANTIFICATION OF REGIONAL MYOCARDIAL BLOOD-FLOW BY MICROSPHERES

Background. Both [N-13]ammonia and [O-15]water have been used to quantify myocardial blood flow with positron emission tomography using appropriate tracer kinetic models. A direct comparison of the two tracers with radioactive microspheres has not been performed in the same experimental preparation. Methods and Results. The two tracers have been tested for myocardial blood flow quantification in closed-chest dogs with circumflex coronary stenosis or permanent occlusion at rest and during adenosine-induced hyperemia. [N-13] ammonia- and [O-15]water-derived myocardial blood flow values have been compared with radiolabeled microspheres. Validation studies consisted of simultaneous measurements of blood flow with positron emission tomography and microspheres over a wide range of flow values. Blood pool and regional tissue activity curves were fitted with a three-compartment model for [N-13]ammonia with and without arterial metabolite correction and with a single-tissue-compartment model for [O-15]water. A correction for finite-resolution effect before the fit was also applied. In large regions of interest (5 cm3), a good correlation between the microsphere method and [N-13]ammonia (with metabolite correction) was obtained (y=3+0.78x, r=0.94). The correlation with microspheres was slightly better with [O-15]water (y=-3+0.89x, r=0.97). Similar correlations were achieved in smaller regions of interest (1 cm3) as well as in akinetic segments and in central infarct regions. Conclusions. Positron emission tomography with appropriate tracer kinetic models using [N-13] ammonia and [O-15]water provides an accurate quantitative method for measuring regional myocardial blood flow over a wide range of flow values in normally contracting or akinetic canine myocardium in the absence and in the presence of infarction.