Liver tissue characterization in competitive student athletes by quantitative mri: Normal values

Background: MRI imaging biomarkers can non-invasively characterize liver tissue potentially allowing early diagnosis and treatment. Proton density fat fraction (PDFF), R2∗, and T1 and T2 times are relevant biomarkers measuring fat (PDFF), iron content (R2∗), inflammation, and fibrosis (T1, T2). This study takes advantage of the MRI screening program that was established at our institution for myocarditis in competitive athletes recovering from COVID-19. The purpose of this project was to establish hepatic reference values for these biomarkers for the specific population of young competitive adult athletes. Methods: This retrospective study was HIPAAcompliant and IRB approved. Clinical cardiac MRI exams of competitive student athletes recovering from COVID-19 acquired between 01/2020 and 04/2021 at 1.5T or 3T were screened. 3D confounder-corrected PDFF and R2∗ maps were obtained over the entire liver in the axial plane, while T1 and T2 maps obtained through the heart in the double oblique short axis view also visualized large portions of the left lobe of the liver. PDFF, R2∗, T1 and T2 Maps were analyzed with OsiriX (pixmeo SARL, Switzerland). In PDFF and R2∗ maps, the largest possible ROIs were placed in each Couinaud segment avoiding vessels, bile ducts, and artifacts. In T1 and T2 maps, the largest possible ROI was placed in each slice that included the liver. For each patient and map, the mean value of the liver ROIs was recorded. Results were compared between field strengths and sex using t-test. Results: 105 athletes matched the inclusion criteria (35 female, 19±1 years, BMI 26±5 kg/m). One patient was excluded due to clinical and imaging findings of COVID-associated myocarditis. 10 subjects had an elevated PDFF between 5.1% and 11.3%, one athlete had a mild iron overload (R2∗= 136 s-1 at 1.5T). Gender- and field strength-specific results are compiled in Table 1. PDFF, R2∗, and T1 values differed significantly between field strengths. T1 and T2 times differed significantly between gender at 3T and 1.5T, respectively. Conclusion: We generated gender- and field strength-specific reference values for hepatic T1, T2, PDFF and R2∗ in young athletes. Our results are consistent with published normal values for adults, with PDFF and T1 at the lower end of published values. The prevalence of pathologic hepatic fat and iron content was low. Significant differences in BMI and skewed gender distribution may limit the generalizability of our results. We will address this issue in a larger future study.