Quantification of Subendocardial and Subepicardial Blood Flow Using ¹⁵O-Labeled Water and PET: Experimental Validation

Abstract

The purpose of this study was to assess the feasibility and accuracy of quantifying subendocardial and subepicardial myocardial blood flow (MBF) and the relative coronary flow reserves (CFR) using ¹⁵O-labeled water (H₂¹⁵O) and 3-dimensional–only PET. Methods: Eight pigs were scanned with H₂¹⁵O and ¹⁵O-labeled carbon monoxide (C¹⁵O) after partially occluding the circumflex (n = 3) or the left anterior descending (n = 5) coronary artery, both at rest and during hyperemia induced by intravenous dipyridamole. Radioactive microspheres were injected during each of the H₂¹⁵O scans. Results: In a total of 256 paired measurements of MBF, ranging from 0.30 to 4.46 mL·g⁻¹·min⁻¹, microsphere and PET MBF were fairly well correlated. The mean difference between the 2 methods was −0.01 ± 0.52 mL·g⁻¹·min⁻¹ with 95% of the differences lying between the limits of agreement of −1.02 and 1.01 mL·g⁻¹·min⁻¹. CFR was significantly reduced (P < 0.05) in the ischemic subendocardium (PET = 1.12 ± 0.45; microspheres = 1.09 ± 0.50; P = 0.86) and subepicardium (PET = 1.2 ± 0.35; microspheres = 1.32 ± 0.5; P = 0.39) in comparison with remote subendocardium (PET = 1.7 ± 0.62; microspheres = 1.64 ± 0.61; P = 0.68) and subepicardium (PET = 1.79 ± 0.73; microspheres = 2.19 ± 0.86; P = 0.06). Conclusion: Dynamic measurements using H₂¹⁵O and a 3-dimensional–only PET tomograph allow regional estimates of the transmural distribution of MBF over a wide flow range, although transmural flow differences were underestimated because of the partial-volume effect. PET subendocardial and subepicardial CFR were in good agreement with the microsphere values.