MRI-based quantification of whole-organ renal metabolic rate of oxygen during free-breathing

Renal metabolic rate of oxygen (rMRO₂) reflects the kidney's metabolic efficiency, making it a potential biomarker for early-stage kidney disease. This study introduces an ungated, free-breathing MRI sequence in comparison to its breath-hold counterpart to noninvasively measure whole-organ rMRO₂.

Free-breathing (FB) K-MOTIVE sequence (kidney metabolism of oxygen via T₂ and interleaved velocity encoding) was developed to simultaneously measure renal blood flow rate (BFR) and T₂ of blood water using the conservation of mass. T₂ is converted to venous oxygen saturation (SvO₂) using a calibration curve. Compared to previous versions, FB K-MOTIVE minimizes respiratory motion artifacts by acquiring fully sampled velocity maps with spiral readout instead of partially collecting radial views at each T₂ weighting. Healthy participants (n = 15, 32 ± 9 years) were imaged at 3 T at the renal veins to quantify individual rMRO₂, and at the suprarenal and infrarenal inferior vena cava to indirectly quantify bilateral rMRO₂ (the total metabolism from both kidneys).

Renal venous blood was highly oxygenated (SvO₂ 91% ± 3%) and exhibited high BFR of 460 ± 90 mL/min per kidney. Further, total rMRO₂ of the two kidneys (160 ± 80 (μmol O₂/min)/100 g) was statistically comparable to the indirect bilateral rMRO₂ (250 ± 120 (μmol O₂/min)/100 g, p = 0.066). Using Lin's concordance correlation coefficient, there was good agreement between breath-hold and free-breathing acquisitions at the individual kidneys for SvO₂ (>0.75), BFR (>0.96), and rMRO₂ (>0.75).

FB K-MOTIVE is a feasible approach to estimate rMRO₂, yielding reproducible and physiologically plausible metabolic parameters. Free-breathing acquisition can enhance patient comfort by eliminating the need for breath-holding.