Hyperpolarized [1-(13)C]-acetate Renal Metabolic Clearance Rate Mapping

(11)C-acetate is a positron emission tomography (PET) tracer of oxidative metabolism, whereas hyperpolarized (13)C-acetate can be used in magnetic resonance imaging (MRI) for investigating specific metabolic processes. The aims of this study were to examine if the kinetic formalism of (11)C-acetate PET in the kidneys is comparable to that of (13)C-acetate MRI, and to compare the dynamic metabolic information of hyperpolarized (13)C-acetate MRI with that obtained with (11)C-acetate PET. Rats were examined with dynamic hyperpolarized (13)C-acetate MRI or (11)C-acetate PET before and after intravenous injection of furosemide, a loop diuretic known to alter both the hemodynamics and oxygen consumption in the kidney. The metabolic clearance rates (MCR) were estimated and compared between the two modalities experimentally in vivo and in simulations. There was a clear dependency on the mean transit time and MCR for both (13)C-acetate and (11)C-acetate following furosemide administration, while no dependencies on the apparent renal perfusion were observed. This study demonstrated that hyperpolarized (13)C-acetate MRI is feasible for measurements of the intrarenal energetic demand via the MCR, and that the quantitative measures are correlated with those measured by (11)C-acetate PET, even though the temporal window is more than 30 times longer with (11)C-acetate.