Effect of J coupling on 1.3‐ppm lipid methylene signal acquired with localised proton MRS at 3 T

The purpose of this work was to investigate the effect of J ‐coupling interactions on the quantification and T 2 determination of 1.3‐ppm lipid methylene protons at 3 T. The response of the 1.3‐ppm protons of hexanoic, heptanoic, octanoic, linoleic and oleic acid was measured as a function of point‐resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM) TE. In addition, a narrow‐bandwidth refocusing PRESS sequence designed to rewind J ‐coupling evolution of the 1.3‐ppm protons was applied to the five fatty acids, to corn oil and to tibial bone marrow of six healthy volunteers. Peak areas were plotted as a function of TE, and data were fitted to monoexponentially decaying functions to determine M o (the extrapolated area for TE = 0 ms) and T 2 values. In phantoms, rewinding J ‐coupling evolution resulted in 198%, 64%, 44%, 20% and 15% higher T 2 values for heptanoic, octanoic, linoleic and oleic acid, and corn oil, respectively, compared with those obtained with standard PRESS. The narrow‐bandwidth PRESS sequence also resulted in significant changes in M o , namely −77%, −22%, 28%, 23% and 28% for heptanoic, octanoic, linoleic and oleic acid, and corn oil, respectively. T 2 values obtained with STEAM were closer to the values measured with narrow‐bandwidth PRESS. On average, in tibial bone marrow (six volunteers) rewinding J ‐coupling evolution resulted in 21% ± 3% and 9 % ± 1% higher M o and T 2 values, respectively. This work demonstrates that the consequence of neglecting to consider scalar coupling effects on the quantification of 1.3‐ppm lipid methylene protons and their T 2 values is not negligible. The linoleic and oleic acid T 2 results indicate that T 2 measures of lipids with standard MRS techniques are dependent on lipid composition. Copyright © 2015 John Wiley & Sons, Ltd.