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Background: Selection of optimal tracer activity for 82Rb PET is based on a trade-off between necessary count-statistics in the late static phase and detector saturation in the early blood-pool phase. Administered tracer activity recommended in prescribing information differs substantially from recommendations in current literature. The present study examines the effect on both absolute myocardial blood flow (MBF), myocardial flow reserve (MFR) and relative myocardial perfusion imaging (MPI) of reducing dose.Methods: Forty patients were scanned twice on a PMT-based PET/CT (GE D690): At recommended activity (1110 MBq) and at either 740 or 370 MBq. MBF, MFR, total perfusion deficit (TPD) and ejection fractions (EF) were quantified. Results were compared using linear regression and Bland–Altman plots.Results: Linear correlation between MBF at 1110 MBq at either reduced activity had an R2 > 0.98. A small bias (± 5%-9%) was observed with opposite signs for 1110/740 and 1110/370. Limits of agreement for MBF were larger for 1110/370. MFR had a lower linear correlation (R2 = 0.96), but wide limits of agreement especially for 1110/370. TPD and EF correlated well at 1110/740 (R2 = 0.96 and 0.99, respectively), but large scatter was observed for 1110/370.Conclusion: Reduction of the tracer activity to 740 MBq, significantly reduced dead-time correction factors, while still producing reliable static and gated images. However, despite large dead-time at 1110 MBq, no systematic bias on absolute MBF was observed compared to reduced activities.

BACKGROUND To define the relationship between regional coronary vasodilator capacity and myocardial circumferential strain at rest in normal weight overweight and obese individuals with normal global left ventricular function. METHODS AND RESULTS Myocardial blood flow at rest and during pharmacologic vasodilation was measured with (13)N ammonia PET/CT in mL/g/minute in normal weight control (CON n = 12) overweight (OW n = 10) and obese individuals (OB n = 10). In addition resting myocardial function was evaluated as circumferential strain (?c ) by MRI. Global myocardial flow reserve (MFR) did not differ significantly between CON and OW (2.98 ± 0.96 vs 2.70 ± 0.66 P = .290) whereas it declined significantly in OB (1.98 ± 1.04 P = .030). Further global ?c () was comparable between CON OW and OB ( 0.24 ± 0.03 0.23 ± 0.02 and 0.23 ± 0.04) but it was lowest in OB when normalized to the rate pressure product (N?c: 0.31 ± 0.06 0.32 ± 0.05 and 0.26 ± 0.08). When MFR of the three major coronary territories was correlated with corresponding ?c a positive association was observed in CON (r = 0.36 P = .030) in OW (r = 0.54 P = .002) and also in OB when relating N?c to coronary vascular resistance during pharmacologic vasodilation (r = 0.46 P = .010). CONCLUSIONS Higher coronary vasodilator capacity is related to corresponding regional circumferential strain at rest in non obese individuals while this is also observed for reduced MFR in obesity.