Effect of Fat Composition on Allylic Proton Transverse Relaxation and J-Coupling Evolution at 9.4 T

Transverse (T₂) relaxation and J-coupling evolution of oleic, linoleic, and linolenic acid allylic protons are investigated at 9.4 T as an indirect means of assessing fat composition. We hypothesize that the relative proximity of one allylic proton group to the methyl end of the fatty acid impacts the measures. A Point RESolved Spectroscopy (PRESS) sequence was used for apparent (includes J-coupling effects) T₂ estimation. Spectra were acquired from oleic, linoleic, and linolenic acid, from edible oils, and from intraperitoneal adipose tissue of two groups of mice (n = 4 per group) randomized to a high or low ω-3 diet. Apparent T₂ values of 62, 106, and 220 ms were obtained for oleic, linoleic, and linolenic acid allylic protons, respectively. For oils containing negligible linolenic acid, apparent T₂ values correlated with linoleic acid contribution to total unsaturation (R² = 1). For oils containing linolenic acid, a correlation with linolenic acid contribution to total unsaturation was found (R² = 0.91). In animal experiments, the mean allylic apparent T₂ in the group fed the high ω-3 diet was 72.3 ms compared to 66.1 ms measured from the low ω-3 diet group. Signal yield with an echo time (TE) of 130 ms results in an inverse correlation with relative linolenic acid content (R² = 0.99) for the oils.