T1ρ 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.