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

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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.

Study Type

Technical development on phantoms and healthy volunteers.


Nine edible oils and four healthy volunteers (tibial bone marrow).

Field Strength/Sequence

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.

Statistical Tests

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).

Data Conclusion

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.

Data Conclusion

Level of Evidence: 1

Data Conclusion

Technical Efficacy Stage 1

Data Conclusion

J. Magn. Reson. Imaging 2017.

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