Comparison of liver T1 relaxation times without and with iron correction in pediatric autoimmune liver disease.

BACKGROUND: Magnetic resonance imaging (MRI) T1 relaxometry (mapping) has been reported as a quantitative biomarker of liver injury due to inflammation and fibrosis. OBJECTIVE: To assess the relationship between liver MRI T1 relaxometry measurements obtained using a modified Look-Locker inversion recovery (MOLLI) pulse sequence without and with iron (T2*) correction (cT1) in pediatric autoimmune liver disease. MATERIALS AND METHODS: This cross-sectional study was institutional review board-approved, with informed consent obtained. MRI was acquired at 1.5 T in patients participating in an autoimmune liver disease registry. T1 relaxometry was performed using a MOLLI sequence with a 5(3)3-s acquisition strategy. A multi-echo gradient echo sequence was used to measure liver T2*. Non-iron-corrected native T1 (ms), calculated as the mean of four slices through the mid-liver, was measured using T1 parametric maps generated off-line. A proprietary T2* correction (Perspectum Diagnostics, Oxford, UK), blinded to native T1 values, calculated cT1 values. The relationship between native T1 and cT1 measurements was assessed using Spearman rank correlation and Bland-Altman analyses. RESULTS: Forty-eight patients with a mean (standard deviation [SD]) age of 15.2 (4.1) years were included. Mean (SD) liver native T1 was 651.2 (123.9) ms and mean (SD) cT1 was 919.5 (86.8) ms, with excellent positive correlation between values (r=0.91 [95% confidence interval (CI): 0.85-0.95]; P<0.0001). Mean bias between native T1 and cT1 measurements was 268.3 ms (95% limits of agreement: 131.9-404.7 ms). CONCLUSION: There is excellent positive correlation between liver native T1 and cT1 measurements in pediatric patients with autoimmune liver disease. This relationship brings into question the need to perform T1 iron correction in this patient population. T1 and cT1 measurements are not interchangeable, however, due to considerable systematic bias with cT1 values being considerably higher.