Kinetic analysis of the novel myocardial PET imaging agent, ¹⁸F-FPTP, in a rat myocardial infarction model

Objectives (¹⁸F-fluoropentyl)triphenylphosphonium salt (¹⁸F-FPTP) is a promising myocardial PET imaging agent that highly accumulates in cardiomyocytes with the similar uptake mechanism to ^99mTc-sestamibi (Kim et al., JNM, 2012). The aim of this study was to establish the kinetic model of ¹⁸F-FPTP and compare the estimated kinetic parameters between normal and acute myocardial infarction (MI) regions.

Methods Eight-week old male rats (n=12) underwent left coronary artery ligation. Dynamic animal PET images were acquired for 20 min after injection of ¹⁸F-FPTP (37 Mbq). Summed PET (1-18 min) and co-registered CT images were used for drawing ROIs on left ventricle, MI, and normal myocardial regions. Two-compartment model (K₁ and k₂; 2C2P) and three-compartment models with irreversible uptake (K₁-k₃; 3C3P) were compared in terms of goodness-of-fit for time-activity curves (TACs; 10- and 20-min duration) in the myocardium. Blood volume fraction (V_p) term was included in the curve fitting.

Results The 2C2P was the most suitable model for describing ¹⁸F-FPTP in both the MI and normal myocardium (3C3P yielded equivalent K₁ and k₂ values to the 2C2P model and almost zero k₃ values). The average K₁, k₂, V_p and K₁/k₂ obtained from the 2C2P curve fitting on 20-min TACs in normal myocardium were 4.4, 1.4, 0.44 and 3.2, respectively. Those in MI region were 0.9, 1.3, 0.34 and 0.7. The parameters obtained using 10- and 20-min TACs were well correlated (K₁/k₂: slope = 0.99, r = 0.99).

Conclusions The results demonstrate that the fast kinetics of ¹⁸F-FPTP enable the quantitative analysis of this tracer using only 10-min data with two-tissue compartment model. Normal and MI regions in rat were well discriminated based on the kinetic parameters for ¹⁸F-FPTP uptake (K₁) and distribution volume (K₁/k₂). Therefore, ¹⁸F-FPTP will be useful for the quantitative assessment of myocardial function using PET.