Quantification of Fatty Acids in Human Calf Adipose Tissue and Muscle by C MRS using J-refocused PRESS DEPT and ERETIC

Introduction Fatty acids serve as an important source of energy for muscular contraction and general metabolism [1]. Skeletal muscle fatty acid metabolism has been found in association with insulin resistance [2]. Compared to H MRS, which enables distinction of intramyocellular (IMCL) and extramyocellular (EMCL) lipids, in vivo C MRS offers a better separation of saturated and unsaturated fatty acid components and might allow for additional detection of omega-3, omega-6 and trans fatty acids, cholesterol and diglycerides [3]. Due to the intrinsic low sensitivity and large frequency dispersion of C MRS, previous investigations were limited to subcutaneous adipose tissue using surface coil [4] or half-volume coil [5] localization and only relative percentages of different fatty acid subgroups were assessed. In our work, a J-refocused proton PRESS localized DEPT sequence [6] is applied, to achieve reliably localized and SNR enhanced lipid signal detection by in vivo C MRS using a dual tuned volume coil, and combined with optically transmitted and inductively coupled ERETIC as a reference for absolute quantification [7]. The proposed method allows for the first time to assess fatty acid concentrations from two metabolically distinct tissue types: adipose tissue (here: calf tibial bone marrow) and skeletal muscle. Relative concentrations of different lipid compounds as well as their absolute molar concentrations are evaluated and compared among omnivores, vegetarians and vegans.