Rest/stress myocardial perfusion imaging by positron emission tomography with 18 F-Flurpiridaz: A feasibility study in mice.

Background: Myocardial perfusion imaging by positron emission tomography (PET-MPI) is the current gold standard for quantification of myocardial blood flow. ¹⁸ F-flurpiridaz was recently introduced as a valid alternative to currently used PET-MPI probes. Nonetheless, optimum scan duration and time interval for image analysis are currently unknown. Further, it is unclear whether rest/stress PET-MPI with ¹⁸ F-flurpiridaz is feasible in mice.
Methods: Rest/stress PET-MPI was performed with ¹⁸ F-flurpiridaz (0.6-3.0 MBq) in 27 mice aged 7-8 months. Regadenoson (0.1 µg/g) was used for induction of vasodilator stress. Kinetic modeling was performed using a metabolite-corrected arterial input function. Image-derived myocardial ¹⁸ F-flurpiridaz uptake was assessed for different time intervals by placing a volume of interest in the left ventricular myocardium.
Results: Tracer kinetics were best described by a two-tissue compartment model. K ₁ ranged from 6.7 to 20.0 mL·cm ^-3 ·min ^-1 , while myocardial volumes of distribution (V _T ) were between 34.6 and 83.6 mL·cm ^-3 . Of note, myocardial ¹⁸ F-flurpiridaz uptake (%ID/g) was significantly correlated with K ₁ at rest and following pharmacological vasodilation for all time intervals assessed. However, while Spearman's coefficients (r _s ) ranged between 0.478 and 0.681, R ² values were generally low. In contrast, an excellent correlation of myocardial ¹⁸ F-flurpiridaz uptake with V _T was obtained, particularly when employing the averaged myocardial uptake from 20 to 40 min post tracer injection (R ² ≥ 0.98). Notably, K ₁ and V _T were similarly sensitive to pharmacological vasodilation induction. Further, mean stress-to-rest ratios of K ₁ , V _T , and %ID/g ¹⁸ F-flurpiridaz were virtually identical, suggesting that %ID/g ¹⁸ F-flurpiridaz can be used to estimate coronary flow reserve (CFR) in mice.
Conclusion: Our findings suggest that a simplified assessment of relative myocardial perfusion and CFR, based on image-derived tracer uptake, is feasible with ¹⁸ F-flurpiridaz in mice, enabling high-throughput mechanistic CFR studies in rodents.
(© 2022. The Author(s).)