To measure the intrarenal acetate turnover in response to furosemide using hyperpolarized [1-¹³C]-acetate.Ten female adult Wistar rats (256.0±7.0 g) were included. Blood glucose levels were measured as 7.1±0.7 mmol/L from the tail capillary blood with a Contour blood glucose meter. Tail vein catheterization was performed for administration of hyperpolarized [1-¹³C]-acetate and furosemide. The animal was anaesthetized with 3% sevoflurane in oxygen as breathing gas. [1-¹³C]-acetate was polarized in a SpinLab (GE Healthcare). MRI measurements were performed on a 3 T GE HDx scanner (GE Healthcare) equipped with a hydrogen/carbon-RF quadrature transmit/receive-coil (GE Healthcare). A dynamic (120 sec, 1 image/sec) sequence was initiated at start of [1-¹³C]-acetate injection. A second dynamic scan was performed 20 min after an iv bolus of furosemide (10 mg/ml). Regions-of-interests of left and right kidney parenchyma were manually segmented in order to measure the mean renal activity-curve, and a region inside the abdominal aorta was used to obtain the arterial input curve (AIF). The AIF was then fitted by a gamma variate function (using the nonlinear Levenberg-Marquardt method) for the initial 30 sec after [1-¹³C]-acetate injection to account for recirculation. Next, graphical analysis, by means of the Patlak plot, was used to estimate the intracellular [1-¹³C]-acetate conversion rate (k) in units of min^-1, using the approximation that the intracellular pharmacokinetics of acetate is considered being monocompartmental and irreversible¹.Hyperpolarized [1-¹³C]-acetate (fig. 1) accumulated in both kidneys following arterial filling. The acetate turnover or rate constants increased from 2.64 ± 0.78 min^-1 to 4.19 ± 1.50 min^-1 (paired t-test: p = 0.0021) after administration of furosemide (fig. 2).The rate constants in rat kidneys found in this study was two orders of magnitude larger than those reported with radioactive carbon-11 acetate measured by PET by Juillard et al¹. This discrepancy may be explained by the general allometric (log-scale) differences in size and metabolism between pigs and rats. This explanation is supported by the rate constants found in rat myocardium, demonstrating carbon-11 acetate rate constants around 1.5 min^{-1 2}. The increased conversion rate of [1-¹³C]-acetate following furosemide supports the view that this diuretic drug decreases the intrarenal oxygen consumption (reduction in the sodium reabsorption), thus increasing the cortical blood perfusion.This study demonstrated the potential of hyperpolarized [1-¹³C]-acetate MRI as a novel method of assessing renal oxidative metabolism via acetate turnover mapping.