T_1ρ mapping for assessment of renal allograft fibrosis

Background: There is an unmet need for noninvasive methods to diagnose and stage renal allograft fibrosis. Purpose: To investigate the utility of T_1ρ measured with MRI for the assessment of fibrosis in renal allografts. Study Type: Institutional Review Board (IRB)-approved prospective. Subjects: Fifteen patients with stable functional allograft (M/F 9/6, mean age 56 years) and 12 patients with allograft dysfunction and established fibrosis (M/F 6/6, mean age 51 years). Field Strength/Sequence: T_1ρ imaging at 1.5T using a custom-developed sequence. Assessment: Average T_1ρ in the cortex and medulla was quantified and T_1ρ repeatability (expressed by the coefficient of variation [CV]) was measured in four patients. Statistical Tests: Differences in T_1ρ values between the 2 groups were assessed using Mann–Whitney U-tests. Diagnostic performance of T_1ρ for differentiation between functional and fibrotic allografts was evaluated using receiver operating characteristic (ROC) analysis. Spearman correlations of T_1ρ with Masson's trichrome-stained fractions and serum estimated glomerular filtration rate (eGFR) were assessed. Results: Higher T_1ρ repeatability was found for cortex compared with medulla (mean CV T_1ρ cortex 7.4%, medulla 13.3%). T_1ρ values were significantly higher in the cortex of fibrotic vs. functional allografts (111.8 ± 17.2 msec vs. 99.0 ± 11.0 msec, P = 0.027), while there was no difference in medullary T_1ρ values (122.6 ± 20.8 msec vs. 124.3 ± 20.8 msec, P = 0.789). Cortical T_1ρ significantly correlated with Masson's trichrome-stained fractions (r = 0.515, P = 0.044) and eGFR (r = –0.546, P = 0.004), and demonstrated an area under the curve (AUC) of 0.77 for differentiating between functional and fibrotic allografts (sensitivity and specificity of 75.0% and 86.7%, using threshold of 106.9 msec). Data Conclusion: Our preliminary results suggest that T_1ρ is a potential imaging biomarker of renal allograft fibrosis. These results should be verified in a larger study. Level of Evidence: 1. Technical Efficacy: Stage 1. J. Magn. Reson. Imaging 2019;50:1085–1091.