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Background Myocardial perfusion imaging by positron emission tomography (PET-MPI) is the current gold standard for quantification of myocardial blood flow. F-18-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 F-18-flurpiridaz is feasible in mice. Methods Rest/stress PET-MPI was performed with F-18-flurpiridaz (0.6-3.0 MBq) in 27 mice aged 7-8 months. Regadenoson (0.1 mu g/g) was used for induction of vasodilator stress. Kinetic modeling was performed using a metabolite-corrected arterial input function. Image-derived myocardial F-18-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 center dot cm(-3)center dot min(-1), while myocardial volumes of distribution (V-T) were between 34.6 and 83.6 mL center dot cm(-3). Of note, myocardial F-18-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 F-18-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 F-18-flurpiridaz were virtually identical, suggesting that %ID/g F-18-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 F-18-flurpiridaz in mice, enabling high-throughput mechanistic CFR studies in rodents., Journal of Nuclear Cardiology, 30 (1), ISSN:1071-3581, ISSN:1532-6551

Alterations in brain cholesterol homeostasis have been broadly implicated in neurological disorders. Notwithstanding the complexity by which cholesterol biology is governed in the mammalian brain, excess neuronal cholesterol is primarily eliminated by metabolic clearance via cytochrome P450 46A1 (CYP46A1). No methods are currently available for visualizing cholesterol metabolism in the living human brain; therefore, a noninvasive technology that quantitatively measures the extent of brain cholesterol metabolism via CYP46A1 could broadly affect disease diagnosis and treatment options using targeted therapies. Here, we describe the development and testing of a CYP46A1-targeted positron emission tomography (PET) tracer, 18 F-CHL-2205 ( 18 F-Cholestify). Our data show that PET imaging readouts correlate with CYP46A1 protein expression and with the extent to which cholesterol is metabolized in the brain, as assessed by cross-species postmortem analyses of specimens from rodents, nonhuman primates, and humans. Proof of concept of in vivo efficacy is provided in the well-established 3xTg-AD murine model of Alzheimer’s disease (AD), where we show that the probe is sensitive to differences in brain cholesterol metabolism between 3xTg-AD mice and control animals. Furthermore, our clinical observations point toward a considerably higher baseline brain cholesterol clearance via CYP46A1 in women, as compared to age-matched men. These findings illustrate the vast potential of assessing brain cholesterol metabolism using PET and establish PET as a sensitive tool for noninvasive assessment of brain cholesterol homeostasis in the clinic.