Absolute quantification of myocardial blood flow with H₂ ¹⁵O and 3-dimensional PET: An experimental validation

The purpose of this study was to assess a 3-dimensional (3D)-only PET scanner (ECAT EXACT3D) for its use in the absolute quantification of myocardial blood flow (MBF) using H₂ ¹⁵O. Methods: Nine large white pigs were scanned with H₂ ¹⁵O and C¹⁵O before and after partially occluding the circumflex (n = 4) or the left anterior descending (n = 5) coronary artery at rest and during hyperemia induced by intravenous dipyridamole. Radioactive microspheres labeled with either ⁵⁷Co or ⁴⁶Sc were injected during each of the H₂ ¹⁵O scans, which allowed comparison between microsphere and PET measurements of regional MBF. PET analyses of 3D acquisition data were performed using filtered backprojection reconstruction and region-of-interest definition by factor and cluster analysis techniques and single-compartment model quantification. Results: The Hanning filter applied in image reconstruction resulted in a left atrial blood volume recovery factor of 0.84 ± 0.06. Differences between repeated measurements of recovery were small (mean, -0.8%; range, -6.6% to 3.6%). In 256 paired measurements of MBF ranging from 0.05 to 4.4 mL · g-¹ · min^-1, microsphere and PET measurements were fairly well correlated. The mean difference between the 2 methods was -0.11 mL · g^-1 · min^-1 and the limits of agreement (+2 SD) were -0.82 and 0.60 mL · g^-1 · min^-1 (Bland-Altman plot). Conclusion: Dynamic measurements with H₂ ¹⁵O using a 3D-only PET tomograph provide reliable and accurate measurements of absolute regional MBF over a wide flow range. The 3D acquisition technique can reduce the radiation dose to the subject while maintaining adequate counting statistics.