MRI-based quantification of whole-organ renal metabolic rate of oxygen

During the early stages of diabetes, kidney oxygen utilization increases. The mismatch between oxygen demand and supply contributes to tissue hypoxia, a key driver of chronic kidney disease. Thus, whole-organ renal metabolic rate of oxygen (rMRO(2)) is a potentially valuable biomarker of kidney function. The key parameters required to determine rMRO(2) include the renal blood flow rate (RBF) in the feeding artery and oxygen saturation in the draining renal vein (SvO(2)). However, there is currently no noninvasive method to quantify rMRO(2) in absolute physiologic units. Here, a new MRI pulse sequence, Kidney Metabolism of Oxygen via T-2 and Interleaved Velocity Encoding (K-MOTIVE), is described, along with evaluation of its performance in the human kidney in vivo. K-MOTIVE interleaves a phase-contrast module before a background-suppressed T-2-prepared balanced steady-state-freeprecession (bSSFP) readout to measure RBF and SvO(2) in a single breath-hold period of 22 s, yielding rMRO(2) via Fick's principle. Variants of K-MOTIVE to evaluate alternative bSSFP readout strategies were studied. Kidney mass was manually determined from multislice gradient recalled echo images. Healthy subjects were recruited to quantify rMRO2 of the left kidney at 3-T field strength (N = 15). Assessments of repeat reproducibility and comparisons with individual measurements of RBF and SvO(2) were performed, and the method's sensitivity was evaluated with a highprotein meal challenge (N = 8). K-MOTIVE yielded the following metabolic parameters: T-2 = 157 +/- 19 ms; SvO(2) = 92% +/- 6%; RBF = 400 +/- 110 mL/min; and rMRO(2) = 114 +/- 117(mu mol O-2/min)/100 g tissue. Reproducibility studies of T-2 and RBF (parameters directly measured by K-MOTIVE) resulted in coefficients of variation less than 10% and intraclass correlation coefficients more than 0.75. The high-protein meal elicited an increase in rMRO(2), which was corroborated by serum biomarkers. The K-MOTIVE sequence measures SvO(2) and RBF, the parameters necessary to quantify whole-organ rMRO2, in a single breath-hold. The present work demonstrates that rMRO(2) quantification is feasible with good reproducibility. rMRO(2) is a potentially valuable physiological biomarker.