Comparison of Quantitative and Semiquantitative MT-MRI for Detection of Interstitial Fibrosis in Kidney Transplant Recipients

OBJECTIVES: To evaluate the efficacy of quantitative magnetization transfer (qMT) in quantifying interstitial fibrosis in kidney transplantation (KT) recipients, and to assess its dependence on MRI field strength (1.5T vs 3.0T), in comparison to conventional magnetization transfer imaging (MTI) performed at both 600 Hz and 1000 Hz offset frequencies. MATERIALS AND METHODS: This cross-sectional study involved 20 patients, 4 to 10 years post-KT, and 31 healthy volunteers (HV). Using 3.0T-MRI, we assessed KT and HV kidneys using MTI, qMT, blood oxygenation-level-dependent (BOLD), and diffusion-weighted imaging (DWI), and at 1.5T-MRI, we also assessed in KT renal fibrosis with MTI and qMT. In addition, we measured fibrogenic cytokine levels in KT and HV using ELISA and assessed fibrosis and cytokine expression in KT biopsy samples. RESULTS: KT showed renal dysfunction and higher circulating collagen-IV, MCP-1, IL-6, and NGAL than HV. At 3.0T-MRI, both the qMT index f and the MTI index magnetization-transfer ratio (MTR) measured at either 1000 Hz or 600 Hz demonstrated greater KT cortex and medulla fibrosis compared with HV, whereas DWI and BOLD signals showed no difference. Cortical and medullary MTI-MTR-600 Hz and f -qMT were comparable between 1.5T and 3.0T-MRI, whereas MTI-MTR-1000 Hz was not. Inter- and intra-observer reproducibility of qMT and MTR showed consistently high reliability across the cortex and medulla. Histologic cortical fibrosis in KT [11.12% (8.02, 15.32)] correlated directly with f -qMT at 3.0T-MRI (Spearman, P < 0.0001) but not at 1.5T-MRI, and correlated modestly with cortical and medullary MTR at 600 Hz and 1000 Hz at 1.5T but not at 3.0T-MRI. In addition, f correlated with years post-KT. CONCLUSIONS: Both MTI-600 Hz at 1.5T-MRI and qMT at 3.0T-MRI are promising noninvasive tools for evaluating kidney allograft fibrosis, and the choice between them may depend on machine availability. Furthermore, their fidelity between 1.5T and 3.0T-MRI may facilitate clinical translation by affording comparison of renal fibrosis measured on different MRI machines.