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 T₂ 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 T₂ values. In phantoms, rewinding J‐coupling evolution resulted in 198%, 64%, 44%, 20% and 15% higher T₂ 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. T₂ 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 T₂ 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 T₂ values is not negligible. The linoleic and oleic acid T₂ results indicate that T₂ measures of lipids with standard MRS techniques are dependent on lipid composition. Copyright © 2015 John Wiley & Sons, Ltd.