Evaluation Of Kidney Oxygen Bioavailability And Pathology In Acute Renal Failure By BOLD And DW MRI

OBJECTIVETo assess the kidney oxygen bioavailability and pathologic state in acute renal failure using blood oxygen level dependent (BOLD) and Diffusion-weighted (DW) magnetic resonance (MR) imaging.MATERIALS AND METHODSStudy protocol was approved by local ethics committee; informed 20 healthy volunteers and 21 patients who had acute renal failure were selected for this study. The patients included 18 patients with oliguric renal failure,2 patients with functionality renal failure, and 1 patient with nonoliguric acute renal failure. All the subjects received renal functio MR examination. BOLD MR imaging with 16 gradient-recalled-echoes on a 1.5-T scanner was performed. R2*(1/sec) values of the cortex and medulla and R2* ratio of the medulla to cortex (R2* ratio of M/C) of the renal were recorded respectively. DW MR imaging with single echo-planar imaging (EPI) was performed. The images were in an axial view included 5 slices with renal hilum. Then the Apparent Diffusion Coefficient (ADC) values of kidneys were measured with different diffusion sensitivity gradient factors (b values). Statistical analysis was performed, and a p value≤0.05 was considered statistically significant.RESULTS The R2* values of the medulla were higher than that of the cortex in volunteers (medulla:17.64±1.86/sec, cortex:13.73±0.49/sec. P＜0.00). The R2* ratio of M/C in the volunteers was 1.28±0.06. The R2* values of the medulla (13.31±4.28/sec) and cortex (12.25±2.418/sec) and the R2* ratio of M/C (1.01) were lower than that in volunteers (P<0.05,).3 patients with functionality renal failure and nonoliguric acute renal failure had higher R2* values in cortex and medulla and higher R2* ratio of M/C than volunteers.Patients with acute renal failure had significantly lower ADC (P<0.05) than did normal function patients with all the different b values (b=200,400,600,800, 1000s/mm2).CONCLUSIONBOLD MRI as a noninvasive tool described the changes of renal oxygen status in patients with acute renal failure. Decreases in R2* values of cortex and medulla simultaneously suggest lower oxygen bioavailability in acute renal failure. Decreases in the R2* ratio of M/C suggest the disappearance of a steep cortico-medullary gradient of oxygen.DW MR imaging is a non-invasive method to assess the pathologic changes in kidneys.