Long TE STEAM and PRESS for estimating fat olefinic/methyl ratios and relative ω-3 fat content at 3T.

Abstract

Fat olefinic/methyl ratios provide a measure of fat unsaturation. The methyl resonance linewidth is altered with the presence of ω-3 fat. To optimize stimulated echo acquisition mode (STEAM) and point resolved spectroscopy (PRESS) echo times (TE) at 3T to 1) improve olefinic/methyl ratios and 2) enable relative ω-3 fat content assessment. Technical development on phantoms and healthy volunteers. Nine edible oils and four healthy volunteers (tibial bone marrow). STEAM (mixing time = 20 msec) and PRESS sequences at 3T. High-resolution oil spectra at 16.5T. 3T STEAM and PRESS olefinic/methyl ratios as a function of TE were compared to 16.5T measures for the oils, and to a literature-deduced value for tibial bone marrow. Oil methyl linewidths were calculated at each TE to investigate correlation with expected ω-3 fatty acid content. Percent differences were calculated between oil olefinic/methyl ratios obtained at 3T and 16.5T. Linear regression R2 values measured correlation of methyl linewidth to ω-3 content. STEAM, TE = 120 msec, resulted in average oil olefinic/methyl ratios that differ by about -4.8% compared to high-resolution ratios. Tibial bone marrow olefinic/methyl ratios differ by -1.8% compared with literature-obtained ratios. PRESS, TE = 180 msec, resulted in oil ratios that differ by 7.8% and tibial bone marrow ratios that differ by 0.2%. A TE of 160 msec for both STEAM and PRESS enabled relative levels of oil ω-3 fatty acid content to be estimated (R2 values ≥0.9). STEAM, TE = 120 msec (mixing time = 20 msec), and PRESS, TE = 180 msec, optimally estimated olefinic/methyl ratios. STEAM and PRESS, TE = 160 msec, enable relative oil ω-3 fatty acid estimation from methyl linewidths. 1 Technical Efficacy Stage 1 J. Magn. Reson. Imaging 2017.