Feasibility of susceptibility weighted imaging in the evaluation of renal fibrosis induced by unilateral ureteral obstruction in white rabbits

Abstract

Objective: To evaluate the feasibility of susceptibility weighted imaging (SWI) to reflect the progression of renal fibrosis (RF) induced by unilateral ureteral obstruction (UUO) in rabbits. Methods: Total of 32 New Zealand white rabbits (aged 4-5 months) were used to establish the UUO model (RF group) and were divided into 4 subgroups (including RF-2W group, RF-4W group , RF-6W group and RF-8W group) according to the duration of obstruction(2, 4, 6 and 8 weeks). Another 8 rabbits, underwent sham operation, were used as the control group (Sham group). T2 weighted imaging (T(2)WI) and SWI sequences were performed on the rabbits at 2, 4, 6 and 8 weeks after UUO, respectively. Rabbits were sacrificed and specimens were obtained after MR examination, then hematoxylin&eosin staining and Masson staining were performed to explore the renal tubular injury and interstitial fibrosis. The relationship between the relative signal-to-noise ratio(rSNR)measured on the SWI fusion maps and the degree of renal fibrosis was analyzed. Analysis of variance was used to compare the difference of rSNRs among 5 groups. Results: The rSNRs of the inner medulla gradually decreased over time, the rSNRs of Sham group, RF-2W group, RF-4W group, RF-6W group and RF-8W group was 2.29±0.18, 1.73±0.30, 1.67±0.08, 1.42±0.28, 1.12±0.15, respectively (F=25.876, P<0.01). In RF-2W group, the rSNRs of the outer medulla and cortex increased when compared with those in the Sham group, then they decreased gradually over time in the other groups (F=5.230, 7.621, both P<0.05). The pathological results demonstrated that the morphology of renal tubules in Sham group was normal and no apoptosis or necrosis was seen in the tubular epithelial cells. In the RF-2W group, the main pathological manifestations included renal tubules dilatation, tubular epithelial cell degeneration or necrosis and the infiltration of inflammatory cell. In Masson staining, lots of blue areas were present in the interstitial. As the obstruction time prolonged, the renal tubular collapse, inflammatory cells and fibroblasts increased significantly. Meanwhile blue area also increased significantly in Masson staining. Conclusion: SWI can be used as a noninvasive method to evaluate the pathological progression of fibrosis in the rabbit UUO model.