Noninvasive Quantification of Myocardial Blood Flow in Humans

BACKGROUND: 13NAmmonia has been validated in dog studies as a myocardial blood flow tracer. Estimates of myocardial blood flow by 13Nammonia were highly linearly correlated to those by the microsphere and blood sample techniques. However, estimates of myocardial blood flow with 13Nammonia in humans have not yet been compared with those by an independent technique. This study therefore tested the hypothesis that the 13Nammonia positron emission tomographic technique in humans gives estimates of myocardial blood flow comparable to those obtained with the 15Owater 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 hypermia. Estimates of average and of regional myocardial blood flow by the 13Nammonia and the 15Owater approaches correlated well (y = 0.02 + 1.02x, r = .99, P < .001 SEE = 0.023 for average and y = 0.06 + 1.00x, 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 13Nammonia and 0.66 +/- 0.12 mL.min-1.g-1 for 15Owater (P = NS). For adenosine-induced hyperemia, mean myocardial blood flow was 2.63 +/- 0.75 mL.min-1.g-1 for 13Nammonia and 2.73 +/- 0.77 mL.min-1.g-1 for 15Owater (P = NS). The coefficient of variation as an index of the observed heterogeneity of myocardial blood flow averaged, for 13Nammonia, 9 +/- 4% at rest and 12 +/- 7% during stress and, for 15Owater, 14 +/- 11% at rest and 16 +/- 9% during stress. The coefficients of variation for 15Owater were significantly higher than those for 13Nammonia (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 13Nammonia method in human myocardium previously shown only in animals. However, the 15Owater approach reveals a greater heterogeneity (presumably method-related), which might limit the accuracy of sectorial myocardial blood flow estimates in humans.