Assessment of myocardial perfusion by dynamic N-13 ammonia PET imaging: Comparison of 2 tracer kinetic models

Background. Measurement of myocardial blood flow (MBF) by dynamic nitrogen 13 ammonia (NH3) positron emission tomography (PET) uses tracer kinetic modeling to analyze time-activity curves. We compared 2 commonly used models with 2 compartments (2C) and 3 compartments (3C) for quantification of MBF and coronary flow reserve (CFR). Methods and Results. Seventy-seven patients underwent NH3 PET at rest and during hyperemia. Time-activity curves for blood pool and myocardial segments were obtained from short-axis images of dynamic sequences. Model fitting of the 2C and 3C models was performed to estimate regional MBF. MBF values calculated by 2C and 3C models were 0.98 +/- 0.31 mL (.) min(-1) (.) g(-1) and 1.11 +/- 0.37 mL (.) min(-1) (.) g(-1), respectively, at rest (P <.0001) and 2.79 +/- 1.18 mL (.) min(-1 .) g(-1) and 2.46 +/- 1.02 mL (.) min(-1) - g(-1), respectively, during hyperemia (P <.01), resulting in a CFR of 3.02 +/- 1.31 and 2.39 +/- 1.15 (P <.0001), respectively. Significant correlation was observed between the 2 models for calculation of resting MBF (r = 0.78), hyperemic MBF (r = 0.68), and CFR (r = 0.68). Conclusion. Measurements of MBF and CFR by 2C and 3C models are significantly related. However, quantification of MBF and CFR significantly differs between the methods. This difference needs to be considered when normal values are established or when measurements obtained with different methods need to be compared.