Severity of polycystic kidney disease revealed by multiparametric MRI

Abstract

Purpose: We aimed to compare multiple MRI parameters, including relaxation rates ( $R_1$ , $R_2$ , and $R_{1\rho }$ ), ADC from diffusion weighted imaging, pool size ratio (PSR) from quantitative magnetization transfer, and measures of exchange from spin-lock imaging ( $S_{\rho }$ ), for assessing and predicting the severity of polycystic kidney disease (PKD) over time.

Methods: Pcy/Pcy mice with CD1 strain, a mouse model of autosomal dominant PKD, were imaged at 5, 9, and 26 wk of age using a 7T MRI system. Twelve-week normal CD1 mice were used as controls. Post-mortem paraffin tissue sections were stained using hematoxylin and eosin and picrosirius red to identify histological changes.

Results: Histology detected segmental cyst formation in the early stage (week 5) and progression of PKD over time in Pcy kidneys. In $T_2$ -weighted images, small cysts appeared locally in cystic kidneys in week 5 and gradually extended to the whole cortex and outer stripe of outer medulla region from week 5 to week 26. Regional PSR, $R_1$ , $R_2$ , and $R_{1\rho }$ decreased consistently over time compared to normal kidneys, with significant changes detected in week 5. Among all the MRI measures, $R_2$ and $R_{1\rho }$ allow highest detectability to PKD, while PSR and $R_1$ have highest correlation with pathological indices of PKD. Using optimum MRI parameters as regressors, multiple linear regression provides reliable prediction of PKD progression.

Conclusion: $R_2$ , $R_1$ , and PSR are sensitive indicators of the presence of PKD. Multiparametric MRI allows a comprehensive analysis of renal changes caused by cyst formation and expansion.

Keywords: MRI; diffusion weighted imaging; magnetization transfer; polycystic kidney disease (PKD); relaxation; spin-lock.