Evaluating Renal Fibrosis with R2* Histogram Analysis of the Whole Cortex in a Unilateral Ureteral Obstruction Model

The aim of this study was to use histogram analysis to assess the correlation between blood oxygen-level dependent magnetic resonance imaging (BOLD-MRI) and renal fibrosis induced by unilateral ureteral obstruction (UUO) in an animal model for a long experimental period.

The rabbits were randomly divided into a control group (n = 6) and a UUO group (n = 30). The rabbits in the UUO group underwent left ureteral obstruction surgery. BOLD-MRI examinations were performed at 2, 4, 6, and 8 weeks after ligation. After the examinations, nephrectomy was performed for histologic evaluation. Histogram analysis of the left renal cortex (C) R2* values was performed to measure the mean, median, 10th percentile, 90th percentile, skewness, and kurtosis for all kidneys. Masson trichrome staining was used to assess the percentage of fibrotic area.

The histogram R2* values of the mean, median, 10th percentile, and 90th percentile at week 2 were all lower than those at baseline. Over the course of UUO progression, there were statistical differences between the histogram R2* values at any other two time points, except between weeks 4 and 6, and weeks 6 and 8. A close correlation was found between the percentage of fibrotic area and R2* values (mean: F = 21.49, p = 0.0001, R² = 0.49, median: F = 30.07, p < 0.0001, R² = 0.58, 10th percentile: F = 31.02, p < 0.0001, R² = 0.59, 90th percentile: F = 24.13, p < 0.0001, R² = 0.52).

BOLD-MRI could reflect the formation and progression of renal fibrosis in a rabbit UUO model; however, the value of BOLD-MRI in the long-term evaluation of fibrosis is limited.