Influence of fat on hepatic T2 relaxation time estimation: a preliminary investigation

Abstract

To examine the in uence of fat content on hepatic T2 estimation through T2 mapping without and with fat suppression. MATERIALS AND METHODS:This prospective IRB-approved study included participants without known liver disease (controls), with hepatic steatosis (proton density fat fraction [PDFF] >6%), or with brotic (> 3kPa) liver from other chronic liver diseases. Imaging at 1.5T included a quantitative 3D chemical shift encoded six-echo radiofrequency spoiled gradient echo MRI sequence (mDIXON Quant) for PDFF estimation, nine-echo 2D gradient and spin echo (GRASE) for T2 estimation, and nine-echo 2D GRASE with fat suppression for water-speci c T2 (wT2) estimation.A single blinded observer traced a large freehand region-of-interest (ROI) in the right hepatic lobe on the T2 and wT2 maps, and a circular ROI on the PDFF map. Consistency and agreement of T2 and wT2 estimates were assessed using linear regression, intra-class correlation coe cients (ICC), and Bland-Altman analysis. Pearson's correlation evaluated the relationship between differences in hepatic T2 and wT2 estimates and PDFF. RESULTS:A total of 21 participants (7 controls, 9 with hepatic steatosis, 5 with other liver diseases) with a mean age of 18.4±4.7 years (range: 9-27 years; 9 males) were included. Estimated liver PDFF ranged from 2% to 34% (median 4%, IQR 7.5%). T2 estimates (57±7.3 ms [range: 44.5-70.5 ms]) were signi cantly longer (p=0.0085) compared to wT2 estimates (52.5±8 ms [range: 43-69.7 ms]) with moderate agreement (ICC = 0.57 [95% CI: 0.19 -0.80]).For participants with hepatic steatosis, T2 estimates were signi cantly longer than wT2 estimates (p=0.0063) with poor agreement (ICC=0.06 [95% CI: -0.59 -0.67]). Participants without hepatic steatosis showed comparable T2 and wT2 estimates (p=0.3577, p=0.3954) with excellent agreement (ICC = 0.99 [95% CI: 0.96 -0.99]). The relative bias of T2 to wT2 was very strongly correlated with PDFF (r 2 = 0.95), increasing by 0.8 ms (1.22%) for every 1% rise in PDFF. CONCLUSION:Liver fat content proportionally increases estimated T2, potentially confounding the quanti cation of changes in T2 that can be attributed to alteration in tissue water content.