Quantification of whole-organ individual and bilateral renal metabolic rate of oxygen

Renal metabolic rate of oxygen (rMRO₂ ) is a potentially important biomarker of kidney function. The key parameters for rMRO₂ quantification include blood flow rate (BFR) and venous oxygen saturation (SvO₂ ) in a draining vessel. Previous approaches to quantify renal metabolism have focused on the single organ. Here, both kidneys are considered as one unit to quantify bilateral rMRO₂ . A pulse sequence to facilitate bilateral rMRO₂ quantification is introduced.

To quantify bilateral rMRO₂ , measurements of BFR and SvO₂ are made along the inferior vena cava (IVC) at suprarenal and infrarenal locations. From the continuity equation, these four parameters can be related to derive an expression for bilateral rMRO₂ . The recently reported K-MOTIVE pulse sequence was implemented at four locations: left kidney, right kidney, suprarenal IVC, and infrarenal IVC. A dual-band variant of K-MOTIVE (db-K-MOTIVE) was developed by incorporating simultaneous-multi-slice imaging principles. The sequence simultaneously measures BFR and SvO₂ at suprarenal and infrarenal locations in a single pass of 21 s, yielding bilateral rMRO₂ .

SvO₂ and BFR are higher in suprarenal versus infrarenal IVC, and the renal veins are highly oxygenated (SvO₂  >90%). Bilateral rMRO₂ quantified in 10 healthy subjects (8 M, 30 ± 8 y) was found to be 291 ± 247 and 349 ± 300 (μmolO₂ /min)/100 g, derived from K-MOTIVE and db-K-MOTIVE, respectively. In comparison, total rMRO₂ from combining left and right was 329 ± 273 (μmolO₂ /min)/100 g.

The present work demonstrates that bilateral rMRO₂ quantification is feasible with fair reproducibility and physiological plausibility. The indirect method is a promising approach to compute bilateral rMRO₂ when individual rMRO₂ quantification is difficult.