LAUSR

PURPOSE To evaluate the influence of arm position on B1 and proton density fat fraction (PDFF) in the liver using chemical shift-encoded magnetic resonance imaging. MATERIALS AND METHODS Participants were 8 healthy volunteers without liver disease and 36 patients with presumed or proven fatty liver. We assessed two preliminary examinations in healthy subjects, i.e., arm position influence on B1 and the variability of the PDFF between two scans within a short period of time. To verify the changes in PDFF measurement, 36 patients with fatty liver were conducted to compare 2 different arm positions-the elevated arms and side arms positions. The measurement location was based on the Healey & Schroy classification. The Wilcoxon test was used to analyze the difference in B1 in between the elevated arms and side arms positions. The Bland-Altman analysis was used to assess the agreement between two measurements of PDFF: two same scans within a short period of time, and two scans with different arms positions. RESULTS B1 was significantly different in all segments except for medial segment. The variability of the PDFF between two scans within a short period of time was small in all segments. Some patients had large fluctuations in all segments, although the mean differences in PDFF were small. Upper and lower limits of agreement were 2.064% to 2.871% and - 2.430% to -1.462%, respectively. The relative difference in the rate of PDFF changes as the median (interquartile range [IQR]) in the lateral, medial, anterior, and posterior segments between both the arms positions were 0.0% (9.4), 1.1% (7.3), 1.5% (8.2) and - 0.2% (10.3), respectively. CONCLUSIONS Arm position can significantly affect B1 and PDFF in the liver. Although the absolute change in PDFF between arm positions was not so large, the difference in arm positions can cause large relative PDFF fluctuations.