Simplified quantification of myocardial flow reserve with flurpiridaz F 18: Validation with microspheres in a pig model

The novel PET flow tracer flurpiridaz F 18 shows high myocardial extraction and slow washout. flurpiridaz F 18 PET data analysis with tracer kinetic modeling provides accurate absolute myocardial blood flow (MBF) measurements but requires in-scanner injection and complex processing. We evaluated the hypothesis that myocardial retention and standardized uptake values (SUVs) based on late uptake provide accurate estimates of myocardial flow reserve (MFR) and, thus, might allow simplified quantification after tracer injection outside the scanner. Methods: Nine pigs had dynamic PET scans after repeated injections of flurpiridaz F 18 at rest and combined adenosine and dobutamine stress. flurpiridaz F 18 PET with a 3-compartment model and coinjected radioactive microspheres were used to delineate MBF. These quantitative measurements were compared with myocardial retention (%/min) and SUV of flurpiridaz F 18 after summing data over 5-10, 5-12, 5-15, 10-15, and 10-20 min after tracer injection. Results: MBF ranged from 0.5 to 2.8 mL/min/g. There was a good correlation between both flurpiridaz F 18 retention and SUVs from = to 12 min after injection and MBF measured using 3-compartment model- or microsphere-derived MBF (r = 0.73, P < 0.05, and r = 0.68, P < 0.05, respectively, for retention; r = 0.88, P < 0.001, and r 5 0.92, P < 0.001, respectively, for SUV). At later time points, retention and SUV underestimated stress microsphere flow (at 10- 20 min: R = 0.41, P = not significant, and r = 0.46, P = not significant, respectively, for retention; r = 0.41, P = not significant, and r = 0.65, P < 0.05, respectively, for SUV). When measured 5-12 min after injection, there was a close agreement between MFR measured with either flurpiridaz F 18 retention or SUV and MFR measured using microspheres (mean difference, 20.08 ± 0.36 and 20.18 ± 0.25, respectively). Conclusion: Myocardial retention and SUVs of the ¹⁸F-labeled flow tracer flurpiridaz F 18 accurately reflect the MFR. These simplified analysis methods may facilitate the combination of quantitative assessment of perfusion reserve and rapid clinical imaging protocols.