Effect of carbon-11-acetate recirculation on estimates of myocardial oxygen consumption by PET

Mono- and biexponential fitting of myocardial ¹¹C-acetate kinetics does not account for the effect of recirculating ¹¹C activity following intravenous injection of the tracer. A tracer kinetic model comprising two and three compartments was developed to describe intravascular and myocardial ¹¹C-acetate kinetics defined by PET. This model approach including a correction for ¹¹C-metabolites in blood was validated by correlating the model parameter estimates with directly measured oxygen consumption (MVO₂) in 11 closed-chest dog experiments over a wide range of cardiac work. The model parameter k2 closely correlated with oxygen consumption (r = 0.94). This approach was subsequently applied to human studies and k2-related to rate-pressure product (PRP). In comparison to conventional monoexponential fitting of ¹¹C-acetate tissue kinetics, the model approach improved the correlation coefficients of scintigraphic MVO₂ estimates and PRP values from 0.61 to 0.91. Thus, analysis of myocardial ¹¹C-acetate and clearance kinetics with a tracer kinetic model corrects for recirculating ¹¹C-activity and may provide more consistent estimates of myocardial oxygen consumption.