Renal Oxygenation Characteristics in Healthy Native Kidneys: Assessment with Blood Oxygen Level-Dependent Magnetic Resonance Imaging.

Objective: To explore the characteristics of blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) in healthy native kidneys.

Methods: Seventy-nine patients without chronic kidney disease underwent BOLD-MRI with T2* spoiled gradient recalled echo sequences. BOLD images were analyzed using R2*map software to produce an R2* pseudo-color map. Cortical and medullary R2* values were analyzed in both kidneys and in both sexes. Different regional R2* values in the cortex and medulla were also analyzed. Physiological indices including age, height, weight, body mass index, body surface area, and estimated glomerular filtration rate (eGFR) were recorded. Correlations between R2* value and physiological indices were determined.

Results: Renal cortical R2* values were lower than values in the medulla (p < 0.001). Female and male cortical R2* values were also lower than the corresponding values in the medulla (p < 0.001). Renal medullary R2* values in the lower renal pole were lower than values in the middle and upper poles (p = 0.001). Age was positively correlated with R2* values in the medulla (r = 0.32, p = 0.004). eGFR was negatively correlated with both cortical R2* values (r = -0.26, p = 0.02) and medullary R2* values (r = -0.29, p = 0.009).

Conclusions: BOLD-MRI can directly visualize renal oxygenation. There was variation in the oxygenation of different regions of the kidney. Renal cortical and medullary oxygenation in healthy kidneys decreased with patient age. eGFR also decreased with patient age.