Clinical Application Of Renal Blood Oxygenation Level-dependent MR Imaging Of Diabetic Nephropathy:a Preliminary Study

Objective:To explore the characteristics of blood oxygen level-dependent magnetic resonance imaging (BOLD MRI) and renal oxygenation in patient with type 2 diabetic nephropathy. To investigate the relationship between R2* values and cystatin C (Cys C)、estimated glomerular filtration rate (eGFR).Methods:Twenty one patients with type 2 diabetes mellitus (T2DM) were inrolled in the study between March 2014 and March 2015 from the inpatient department of Endocrinology. All patients were diagnosed as type 2 diabetes mellitus by specialists according to the criteria of American diabetes Association (ADA) in 1999. Out of them 13 patients were having simple diabetes without any other complications, and their renal functional indexes were normal. Other eight patients were clinically diagnosed as diabetic kidney disease (DKD). Within a week prior to the MR imaging study, a sample of blood were taken from all of the patients for a serial tests including serum cystatin C (Cys C), serum creatinine (SCr), and the estimated glomerular filtration rate (eGFR) was calculated based on the SCr level according to the Modification of Diet in Renal Disease (MDRD) formula. Addition to the patients with T2DM,20 healthy volunteers matched for age and gender and without history of diabetes or renal disease also enrolled in the study. The prospective study was approved by the local ethics committee and written informed consent was obtained from all subjects after detailed explanations. Kidney BOLD MRI studies were performed on a 3.0T MR scanner (Achieva TX, Philips Healthcare) using multiple T2*-weighted gradient echo sequence with an eight-channel flexible body matrix coil. The medullary R2* and cortical R2* values were extracted and quantified on BOLD MRI. To understand the difference of the renal oxygenation between the cortex and the medulla, R2* values were compared in each group using paired samples t-test. Furthermore, one-way ANOVA as multiple comparisons was used to assess the difference of the medullary R2* and cortical R2* values among the two patient groups and controls. P<0.05 was considered to indicate a statistically significant difference. Besides, in the two patient groups, the relationships between R2* values and cystatin C (Cys C)、estimated glomerular filtration rate (eGFR) were assessed using Pearson correlation coefficient.Results:All of the subjects could successfully complete the kidney BOLD MR scan. The images of all the subjects were finally analyzed. Analysis of R2* values confirmed a significant difference between the cortex and medulla in all the three groups. The cortical R2* values were significantly lower than the medullary R2* values, largely due to the higher concentrations of deoxyhemoglobin in the medulla (P<0.001). The cortical R2* values in DKD group were significantly higher than that in the other two groups (,P<0.05), while there were no significant differences of the cortical R2* values between simple DM and the control groups (P>0.05). The comparison between controls and diabetes showed that the medullary R2* values were significantly increased in diabetes (P<0.05). Interestingly, compared with simple DM group, the medullary R2* values were significantly decreased in DKD group (P<0.05). In simple DM group, the medullary R2* values was positively correlated with eGFR and Cys C (P<0.05), respectively. No significant correlation was found between the cortical R2* values with eGFR and Cys C (P>0.05). In DKD group, the medullary R2* values was positively correlated with Cys C (P<0.05), while negatively with eGFR (P<0.05), and so was the cortical R2* values. The correlation coefficient between the cortical R2* values and Cys C was the highest.Conclusion:BOLD MRI is a noninvasive procedure that can sensitively monitor and reliably assess intrarenal oxygenation in healthy controls, as well as patients with type 2 diabetes and its nephropathy. Our findings suggest that the renal medulla functions in relative hypoxia under physiologic conditions, the renal medulla in type 2 diabetes and the cortex and medulla in DKD were also in a state of hypoxia. We speculate that the changes in the cortical and medullary R2* values may reflect the alteration in renal function.