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

PURPOSE

Renal metabolic rate of oxygen (rMRO) 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 rMRO.

METHODS

Free-breathing (FB) K-MOTIVE sequence (kidney metabolism of oxygen via T and interleaved velocity encoding) was developed to simultaneously measure renal blood flow rate (BFR) and T of blood water using the conservation of mass. T is converted to venous oxygen saturation (SvO) 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 T weighting. Healthy participants (n = 15, 32 ± 9 years) were imaged at 3 T at the renal veins to quantify individual rMRO, and at the suprarenal and infrarenal inferior vena cava to indirectly quantify bilateral rMRO (the total metabolism from both kidneys).

RESULTS

Renal venous blood was highly oxygenated (SvO 91% ± 3%) and exhibited high BFR of 460 ± 90 mL/min per kidney. Further, total rMRO of the two kidneys (160 ± 80 (μmol O/min)/100 g) was statistically comparable to the indirect bilateral rMRO (250 ± 120 (μmol O/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 SvO (>0.75), BFR (>0.96), and rMRO (>0.75).

CONCLUSION

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