Renal diffusion and BOLD MRI in experimental diabetic nephropathy

Purpose: To investigate the possibility of using combined blood oxygen level-dependent (BOLD) imaging and diffusion-weighted imaging (DWI) to detect pathological and physiological changes in renal tissue damage of the kidney induced by chronic renal hyperfiltration. Materials and Methods: The apparent diffusion coefficient (ADC) and the T-2* value within the inner compartments of the kidneys of 17 rats with diabetes mellitus were compared with the results obtained from a control group (N 16). The influence of dynamic changes of the renal function on the blood-oxygen saturation was evaluated by comparing the T-2* values before and after the active reduction of tubular transport by furosemide injection. Results: All compartments of the diabetic kidney showed significantly (P < 0.05) lower T-2*-values compared to the control group. In particular, the very low values in the outer stripe (OS) of the outer medulla (OM) (T-2*-normal: 69.4 +/- 10.9 msec; T-2*-diabetic: 51.4 +/- 13.9 msec) indicated either hypoxia due to hyperfiltration, or renal blood volume changes. Diffusion imaging of the same area showed significantly lower ADC values (ADC-normal: 1.45 +/- 0.26; ADC-edema: 1.19 +/- 0.25 [10(-9)m(2)/s]) that correlated with pathological findings on histopathology. The injection of 1 furosemide significantly (P < 0.05) increased T-2* in all compartments of both populations while the ADC remained unchanged. Conclusion: BOLD-contrast imaging appears to be able to depict tissue at risk from ischemia by revealing information I about the balance between tubular workload and delivery of oxygen, and thus may reflect a measure of the reserve capacity. The diffusion measurements apparently reveal complementary information. Although ADC imaging is not sensitive to the current energy metabolism, it appears tore-flect the pathological changes within the tissue. Therefore, I ADC measurements may be a sensitive indicator of the severity of ischemic lesions.