Direct comparison of [13N]ammonia and [15O]water estimates of perfusion with quantification of regional myocardial blood flow by microspheres.

Abstract

BACKGROUND Both [13N]ammonia and [15O]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. [13N]ammonia- and [15O]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 [13N]ammonia with and without arterial metabolite correction and with a single-tissue-compartment model for [15O]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 [13N]ammonia (with metabolite correction) was obtained (y = 3 + 0.78x, r = 0.94). The correlation with microspheres was slightly better with [15O]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 [13N]ammonia and [15O]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.

Microvascular Function in Viable Myocardium After Chronic Infarction Does Not Influence Fractional Flow Reserve Measurements

“…In the present study, RFR was measured with H 2 15 O PET. In infarcted areas, H 2 15 O-PET provides perfusion data only on tissue that is capable of exchanging water rapidly-a property of viable myocardium (7)(8)(9). Myocardial blood flow in nonperfusable (scar) tissue is negligible.…”

“…The first issue can be addressed by using H 2 15 O PET to measure myocardial flow. H 2 15 O PET provides perfusion data only on the viable myocardium within an infarcted region (7)(8)(9). Because flow is expressed per milliliter of perfusable (viable) tissue, the smaller amount of viable myocardium within the infarcted area is accounted for and, thus, comparison of blood flow between the infarcted and reference myocardial areas is possible.…”

Quantification of myocardial blood flow will reform the detection of CAD

“…These two tracers have been found to be equivalent for quantifying myocardial perfusion. 16 There are, however, some obvious differences between these two tracers. 13 N-ammonia is extracted from blood with an extraction fraction lower than 100% and the extraction is inversely related to the perfusion (Figure 1).…”

Myocardial perfusion reserve in adults with cyanotic congenital heart disease

“…Hyperemic values were divided by basal measurements to calculate perfusion reserves. In animal studies, the accuracy of the PET measurements has been determined relative to measurements obtained with simultaneously administered radioactive microspheres (4,6,8,32,38). The 95% confidence limits are about Ϯ0.33 ml ⅐ min Ϫ1 ⅐ g Ϫ1 for the LV measurements and Ϯ0.57 ml ⅐ min Ϫ1 ⅐ g Ϫ1 for the RV measurements.…”