Determinations of renal oxygenation by blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) in chronic kidney disease (CKD) patients have given heterogeneous results, possibly due to the lack of a reproducible method to analyse BOLD-MRI. It therefore remains uncertain whether patients with CKD have a reduced renal tissue oxygenation. We developed a new method to analyse BOLD-MRI signals and applied it to CKD patients and controls.
MRI was performed under standardized conditions before and 15 min after IV furosemide in 104 CKD patients, 61 hypertensives and 42 controls. MR images were analysed with the new twelve-layer concentric objects method (TLCO) that divides renal parenchyma in 12 layers of equal thickness. The mean R2* value of each layer was reported, along with the change in R2* between successive layers, as measured by the slope steepness of the relevant curve.
Inter-observer variability was 2.3 ± 0.9%, 1.9 ± 0.8% and 3.0 ± 2.3% in, respectively, controls, moderate and severe CKD. The mean R2* of the outer (more cortical) layers was significantly higher in CKD, suggesting lower cortical oxygenation as compared with controls. In CKD patients, the response to furosemide was blunted in the inner (more medullary) layers, and the R2* slope was flatter. In multivariable regression analysis, the R2* slope correlated positively with estimated glomerular filtration rate (eGFR) in patients with an eGFR <90 mL/min/1.73 m2 (P < 0.001).
Using the new TLCO method, we confirm the hypothesis that renal cortical oxygenation is reduced in CKD in humans, and that the level of cortical oxygenation correlates with CKD severity.