Dynamic SPECT Measurement of Absolute Myocardial Blood Flow in a Porcine Model

Absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) provide incremental diagnostic and prognostic information over relative perfusion alone. Recent development of dedicated cardiac SPECT cameras with better sensitivity and temporal resolution make dynamic SPECT imaging more practical. In this study, we evaluate the measurement of MBF using a multipinhole dedicated cardiac SPECT camera in a pig model of rest and transient occlusion at stress using 3 common tracers: Tl-20, Tc-99m-tetrofosmin, and Tc-99m-sestamibi. Methods: Animals (n = 19) were injected at rest/stress with Tc-99m radiotracers (370/1,100 MBq) or Tl-201 (37/110 MBq) with a 1-h delay between rest and dipyridamole stress. With each tracer, microspheres were injected simultaneously as the gold standard measurement for MBF. Dynamic images were obtained for 11 min starting with each injection. Residual resting activity was subtracted from stress data and images reconstructed with CT-based attenuation correction and energy window-based scatter correction. Dynamic images were processed with kinetic analysis software using a 1-tissue-compartment model to obtain the uptake rate constant K-1 as a function of microsphere MBF. Results: Measured extraction fractions agree with those obtained previously using ex vivo techniques. Converting K1 back to MBF using the measured extraction fractions produced accurate values and good correlations with microsphere MBF: r = 0.75-0.90 (P < 0.01 for all). The correlation in the MFR was between r = 0.57 and 0.94 (P < 0.01). Conclusion: Noninvasive measurement of absolute MBF with stationary dedicated cardiac SPECT is feasible using common perfusion tracers.