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

Abstract

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 (rMRO₂ ) is a potentially valuable biomarker of kidney function. The key parameters required to determine rMRO₂ include the renal blood flow rate (RBF) in the feeding artery and oxygen saturation in the draining renal vein (SvO₂ ). However, there is currently no noninvasive method to quantify rMRO₂ in absolute physiologic units. Here, a new MRI pulse sequence, Kidney Metabolism of Oxygen via T₂ 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 T₂ -prepared balanced steady-state-free-precession (bSSFP) readout to measure RBF and SvO₂ in a single breath-hold period of 22 s, yielding rMRO₂ 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 SvO₂ were performed, and the method's sensitivity was evaluated with a high-protein meal challenge (N = 8). K-MOTIVE yielded the following metabolic parameters: T₂ = 157 ± 19 ms; SvO₂ = 92% ± 6%; RBF = 400 ± 110 mL/min; and rMRO₂ = 114 ± 117(μmol O₂ /min)/100 g tissue. Reproducibility studies of T₂ 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 rMRO₂ , which was corroborated by serum biomarkers. The K-MOTIVE sequence measures SvO₂ and RBF, the parameters necessary to quantify whole-organ rMRO₂ , in a single breath-hold. The present work demonstrates that rMRO₂ quantification is feasible with good reproducibility. rMRO₂ is a potentially valuable physiological biomarker.

Keywords: MOTIVE; T2-based oximetry; kidney; oxygen metabolism; renal oxygenation.