Comparison of T1 Mapping and T1rho Values with Conventional Diffusion-weighted Imaging to Assess Fibrosis in a Rat Model of Unilateral Ureteral Obstruction

Rationale and Objectives: The aim of this study was to investigate the potential of magnetic resonance imaging (MRI) T1 mapping and T1 relaxation time in the rotating frame (T1rho) for assessment of renal fibrosis in a rat model of unilateral ureteral obstruction (UUO). Materials and Methods: UUO was created in 36 rats. Six rats were scanned at each of the six time points (on days 0, 1, 3, 5, 10, and 15 after UUO). The contralateral kidneys were examined as controls. Hematoxylin-eosin, Masson's trichrome, and alpha-smooth muscle actin (alpha-SMA) antibody staining assays were performed. MRI data obtained with a 3.0T scanner were analyzed with alpha-SMA expression and Masson's staining. Results: The T1 relaxation times and T1 rho values increased, and the mean apparent diffusion coefficient (ADC) values decreased with time after UUO. Simple regression analysis indicated that the mean ADCs, T1 relaxation times, and T1rho values had strong correlations with the a-SMA expression levels (R-2 = 0.34, R-2 = 0.66, R-2 = 0.71, respectively; P < .001) and positive Masson's staining (R-2 = 0.38, R-2 = 0.67, R-2 = 0.65, respectively; P < .001). Conclusions: The T1 mapping and T1rho parameters had better correlations with a-SMA expression and Masson's staining than ADC values.