Abstract: Objective To explore the characteristics of blood oxygen level dependent (BOLD) magnetic resonance imaging (MRI) in healthy native kidneys. To investigate the relationship between BOLD-MRI and common physiological indexes. Methods Ninety patients who were ruled out chronic kidney diseases underwent BOLD-MRI with T2*-spoiled gradient recalled echo (T2*SPGR) sequence. BOLD images were analyzed on R2*map software to yield R2* pseudo-color map. Cortical and medullary R2* values were analyzed in bilateral kidneys and in different gender. Different regional R2* values in cortex and medulla were also analyzed. Physiological indices including age, body height and weight, body mass index (BMI), body surface area (BSA), estimated glomerular filtration rate (eGFR) was recorded. Correlation between R2* value and physiological indices were analyzed. Results Bilateral renal cortical R2* values were less than values in medulla. Female and male cortical R2* values were also less than corresponding values in medulla. In bilateral renal medullary region, R2* values in low pole was less than values in middle and upper pole (F =15.184 , P <0.001). Age positively correlated with R2* values in medulla(r =0.284, P =0.002). However, eGFR negatively correlated with medullary R2* value (r =-0.232, P =0.007). Conclusions BOLD MRI can directly visualize renal oxygenation. Oxygenation level discrepancy exists in different regions of renal parenchyma. In healthy kidneys, renal medullary oxygenation level attenuated when patient age increase and eGFR decrease.

Key words: renal cortex, renal medullar, blood oxygen level dependent, magnetic resonance, R2* value