Noninvasive Quantification of Myocardial Blood Flow in Humans

Abstract

Background [ 13 N]Ammonia has been validated in dog studies as a myocardial blood flow tracer. Estimates of myocardial blood flow by [ 13 N]ammonia were highly linearly correlated to those by the microsphere and blood sample techniques. However, estimates of myocardial blood flow with [ 13 N]ammonia in humans have not yet been compared with those by an independent technique. This study therefore tested the hypothesis that the [ 13 N]ammonia positron emission tomographic technique in humans gives estimates of myocardial blood flow comparable to those obtained with the [ 15 O]water technique. Methods and Results A total of 30 pairs of positron emission tomographic flow measurements were performed in 30 healthy volunteers; 15 volunteers were studied at rest and 15 during adenosine-induced hyperemia. Estimates of average and of regional myocardial blood flow by the [ 13 N]ammonia and the [ 15 O]water approaches correlated well ( y =0.02+1.02 x , r =.99, P <.001, SEE=0.023 for average and y =0.06+1.00 x , r =.97, P <.001, SEE=0.025 for regional values) over a flow range of 0.45 to 4.74 mL·min −1 ·g −1 . At rest, mean myocardial blood flow was 0.64±0.09 mL·min −1 ·g −1 for [ 13 N]ammonia and 0.66±0.12 mL·min −1 ·g −1 for [ 15 O]water ( P =NS). For adenosine-induced hyperemia, mean myocardial blood flow was 2.63±0.75 mL·min −1 ·g −1 for [ 13 N]ammonia and 2.73±0.77 mL·min −1 ·g −1 for [ 15 O]water ( P =NS). The coefficient of variation as an index of the observed heterogeneity of myocardial blood flow averaged, for [ 13 N]ammonia, 9±4% at rest and 12±7% during stress and, for [ 15 O]water, 14±11% at rest and 16±9% during stress. The coefficients of variation for [ 15 O]water were significantly higher than those for [ 13 N]ammonia ( P =.004 at rest and P =.03 during stress). Conclusions The two approaches yield comparable estimates of myocardial blood flow in humans, which supports the validity of the [ 13 N]ammonia method in human myocardium previously shown only in animals. However, the [ 15 O]water approach reveals a greater heterogeneity (presumably method-related), which might limit the accuracy of sectorial myocardial blood flow estimates in humans.