Abstract
Algorithms compute myocardial blood flow (MBF) from dynamic PET data for each of 17 left ventricular (LV) segments, with global MBF obtained by averaging segmental values. This study was undertaken to compare MBF values with and without the basal-septal segments. Methods: Data were examined retrospectively for 196 patients who underwent rest and regadenoson-stress 82Rb PET/CT scans for evaluation of known or suspected coronary artery disease. MBF data were acquired in gated list mode, and rebinned to isolate the first pass dynamic portion. Coronary vascular resistance (CVR) was computed as mean arterial pressure divided by MBF. MBF inhomogeneity was computed as the ratio of standard deviations to mean MBF. Relative perfusion scores were obtained using 82Rb -specific normal limits applied to polar maps of myocardial perfusion generated from myocardial equilibrium portions of PET data. MBF and CVR values from 17 and 14 segments were compared. Results: Mean MBF’s were lower for 17- than 14-segment means for rest (0.78±0.50 versus 0.85±0.54 ml/g/min, paired t-test p<0.0001) and stress (1.50±0.88 versus 1.67±0.96 ml/g/min, p<0.0001). Bland-Altman plots of MBF differences versus means exhibited non-zero intercept (-0.04±0.01, P = 0.0004) and significant correlation (r = -0.64, P < 0.0001), with slopes significantly different from 0.0 (P < 0.0001) of -7.2±0.6% and -8.3±0.7% for rest and stress MBF. 17-segment CVR’s were higher than 14-segment CVR’s for rest (159±86 versus 147±81 mm Hg/ml/g/min, paired T-test P < 0.0001) and stress CVR (85±52 versus 76±48 mm Hg/ml/g/min, P < 0.0001). MBF inhomogeneity correlated significantly (P < 0.0001) with summed perfusion scores, but values were significantly more strongly correlated for 14- than 17-segment values for rest (r = 0.67 versus r = 0.52, P = 0.02) and stress (r = 0.69 versus r = 0.47, P = 0.001). When basal segements were included in MBF determinations, perfusion inhomogeneity was greater both for rest (39±10% versus 31±10%, P < 0.0001) and stress (42±12% versus 32±11%, P < 0.0001). Conclusion: Averaging 17- versus 14-segments leads to systematic 7-8% lower MBF calculations, higher CVR’s, and greater computed inhomogeneity. Consideration should be given to excluding basal-septal segments from standard global MBF determination.