MRI-PHYSIOL-NIRS: an integrated platform to study kidney oxygenation.

The kidney always operates close to hypoxia, a pathological condition of O2-shortage, due to its unique relationship between blood flow and oxygen demand. Renal hypoxia is central to kidney diseases, where progressive loss of renal function ultimately can no longer sustain life. Magnetic resonance imaging (MRI) can assess renal oxygenation non-invasively in vivo via the relaxation times T2* and T2, which reflect deoxygenated hemoglobin, but are influenced by several physiological confounders. We developed MRI-PHYSIOL-NIRS, a platform integrating MRI with ground-truth probes that directly measure tissue oxygenation in rat kidneys (PHYSIOL), and near-infrared spectroscopy (NIRS) to estimate oxygenation-related parameters to dissect the relationship between MRI-based measures and true tissue oxygenation. Using aortic occlusion and hyperoxia interventions within the MRI scanner, we investigated correlations between non-invasive MRI-based oxygenation measures and true tissue oxygenation. These results demonstrate the potential for entirely MRI-based measurement of renal oxygenation in health and disease, with ultimate application in patients.