Fat-separated T1 mapping for liver function analysis on gadoxetic acid-enhanced MR imaging: 2D two-point Dixon Look-Locker inversion recovery sequence for differentiation of Child-Pugh class B/C from Child-Pugh class A/chronic liver disease.

Abstract

Background: T1 relaxation time is a tissue-specific parameter that correlates with liver fibrosis, and can be a valuable tool for detecting and staging of liver disease. However, T1 can be affected by histological factors such as fat, so it is necessary to study the effects of hepatic steatosis when assessing liver function and fibrosis. The purpose of this study is to investigate the fat separation effect of T1 mapping using Dixon watermap Look-Locker inversion recovery (LLIR) in the assessment of liver function on gadoxetic acid (GA)-enhanced magnetic resonance imaging (MRI).

Methods: A total of 226 patients who underwent 3T MRI, including a 2D Dixon fat-separated LLIR T1 mapping, were included retrospectively. Two independent readers measured pre- and post-contrast T1 relaxation times (preT1 and postT1) on composite and watermap T1, and reproducibility was evaluated. The correlation of T1 parameters with biochemical and imaging biomarkers of liver function were assessed on both composite and Dixon watermap images; T1 parameters included averaged preT1, postT1 values, changes between pre- and post-T1liver (deltaT1) and adjusted T1liver (postT1liver - T1spleen/T1spleen). And the diagnostic performance of T1 parameters for Child-Pugh (CP) class was also evaluated.

Results: Inter- and intra-reader reproducibility showed almost perfect agreement [intraclass correlation coefficient (ICC) 0.929-0.999]. Watermap preT1 (r=-0.125, P=0.068) and watermap deltaT1 (r=0.055, P=0.414) showed loss of correlation with fat fraction (FF) compared with preT1 and deltaT1. Albumin, total bilirubin (TB), hepatobiliary enhancement grade, and R2* (1/T2*), were significantly associated with watermap T1, eliminating the effect of FF. Area under the curve (AUC) of preT1, watermap preT1, deltaT1, postT1, watermap adjusted T1, and adjusted T1 were 0.681 [standard error (SE) 0.114], 0.748 (SE 0.098), 0.921 (SE 0.033), 0.951 (SE 0.018), 0.950 (SE 0.018), and 0.973 (SE 0.013) respectively, for differentiating patient with CP class B/C from CP-A/chronic liver disease (CLD).

Conclusions: T1 values using Dixon watermap LLIR eliminated the confounding effect of fat and showed the correlation with serological and imaging markers of liver function. Adjusted T1, watermap adjusted T1, and postT1 showed the highest diagnostic performance in differentiating CP class B/C from CP-A/CLD.