BACKGROUND: Omega-3 (n-3) fatty acids (FA) play and important role in neural development and other metabolic diseases such as obesity and diabetes. The knowledge about the in vivo content and distribution of n-3 FA in human body tissues is not well established and the standard quantification of FA is invasive and costly. PURPOSE: To detect omega-3 (n-3 CH3 ) and non-omega-3 (CH3 ) methyl group resonance lines with echo times up to 1200 msec, in oils, for the assessment of n-3 FA content, and the n-3 FA fraction in adipose tissue in vivo. STUDY TYPE: Prospective technical development. POPULATION: Three oils with different n-3 FA content and 24 healthy subjects. FIELD STRENGTH/SEQUENCE: Single-voxel MR spectroscopy (SVS) with a point-resolved spectroscopy (PRESS) sequence with an echo time (TE) of 1000 msec at 7 T. ASSESSMENT: Knowledge about the J-coupling evolution of both CH3 resonances was used for the optimal detection of the n-3 CH3 resonance line at a TE of 1000 msec. The accuracy of the method in oils and in vivo was validated from a biopsy sample with gas chromatography analysis. STATISTICAL TESTS: SVS data were compared to gas chromatography with the Pearson correlation coefficient. RESULTS: T2 relaxation times in oils were assessed as follows: CH2 , 65 ± 22 msec; CH3 , 325 ± 7 msec; and n-3 CH3 , 628 ± 34 msec. The n-3 FA fractions from oil phantom experiments (n = 3) were in agreement with chromatography analysis and the comparison of in vivo obtained data with the results of chromatography analysis (n = 5) yielded a significant correlation (P = 0.029). DATA CONCLUSION: PRESS with ultralong-TE can detect and quantify the n-3 CH3 signal in vivo at 7 T. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:71-82.

Division of Endocrinology and Metabolism Department of Internal Medicine 3 Medical University of Vienna Vienna Austria

High field MR Centre Department of Biomedical Imaging and Image guided Therapy Medical University of Vienna Vienna Austria

High field MR Centre Department of Biomedical Imaging and Image guided Therapy Medical University of Vienna Vienna Austria Christian Doppler Laboratory for Clinical Molecular MR Imaging Vienna Austria

High field MR Centre Department of Biomedical Imaging and Image guided Therapy Medical University of Vienna Vienna Austria Division of Endocrinology and Metabolism Department of Internal Medicine 3 Medical University of Vienna Vienna Austria Bernard and Irene Schwartz Center for Biomedical Imaging Department of Radiology New York University School of Medicine New York New York

High field MR Centre Department of Biomedical Imaging and Image guided Therapy Medical University of Vienna Vienna Austria Division of Endocrinology and Metabolism Department of Internal Medicine 3 Medical University of Vienna Vienna Austria Christian Doppler Laboratory for Clinical Molecular MR Imaging Vienna Austria

High field MR Centre Department of Biomedical Imaging and Image guided Therapy Medical University of Vienna Vienna Austria Institute of Experimental Endocrinology Biomedical Research Center Slovak Academy of Sciences Bratislava Slovakia

Institute of Experimental Endocrinology Biomedical Research Center Slovak Academy of Sciences Bratislava Slovakia

MR Unit Department of Diagnostic and Interventional Radiology Institute for Clinical and Experimental Medicine Prague Czech Republic

National Institute of Mental Health Klecany Czech Republic MR Unit Department of Diagnostic and Interventional Radiology Institute for Clinical and Experimental Medicine Prague Czech Republic

University Clinic for Trauma Surgery Medical University of Vienna Vienna Austria

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