title: Ultrashort-TE stimulated echo acquisition mode (STEAM) improves the quantification of lipids and fatty acid chain unsaturation in the human liver at 7 T.
abstract: Ultrahigh-field, whole-body MR systems increase the signal-to-noise ratio (SNR) and improve the spectral resolution. Sequences with a short TE allow fast signal acquisition with low signal loss as a result of spin-spin relaxation. This is of particular importance in the liver for the precise quantification of the hepatocellular content of lipids (HCL). In this study, we introduce a spoiler Gradient-switching Ultrashort STimulated Echo AcqUisition (GUSTEAU) sequence, which is a modified version of a stimulated echo acquisition mode (STEAM) sequence, with a minimum TE of 6 ms. With the high spectral resolution at 7 T, the efficient elimination of water sidebands and the post-processing suppression of the water signal, we estimated the composition of fatty acids (FAs) via the detection of the olefinic lipid resonance and calculated the unsaturation index (UI) of hepatic FAs. The performance of the GUSTEAU sequence for the assessment of UI was validated against oil samples and provided excellent results in agreement with the data reported in the literature. When measuring HCL with GUSTEAU in 10 healthy volunteers, there was a high correlation between the results obtained at 7 and 3 T (R(2) = 0.961). The test-retest measurements yielded low coefficients of variation for HCL (4 ± 3%) and UI (11 ± 8%) when measured with the GUSTEAU sequence at 7 T. A negative correlation was found between UI and HCL (n = 10; p < 0.033). The ultrashort TE MRS sequence (GUSTEAU; TE = 6 ms) provided high repeatability for the assessment of HCL. The improved spectral resolution at 7 T with the elimination of water sidebands and the offline water subtraction also enabled an assessment of the unsaturation of FAs. This all highlights the potential use of this MRS acquisition scheme for studies of hepatic lipid composition in vivo.
authors: High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.|Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna, Austria.
authors: Martin
authors: M
authors: Gajdošík
authors: Department of Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany.|High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.
authors: Grzegorz L
authors: GL
authors: Chadzynski
authors: High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
authors: Gilbert
authors: G
authors: Hangel
authors: High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
authors: Vladimír
authors: V
authors: Mlynárik
authors: High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
authors: Marek
authors: M
authors: Chmelík
authors: High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.|Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Bratislava, Slovakia.
authors: Ladislav
authors: L
authors: Valkovič
authors: High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
authors: Wolfgang
authors: W
authors: Bogner
authors: High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.
authors: Rolf
authors: http://orcid.org/0000-0002-6137-9590
authors: R
authors: Pohmann
authors: Department of Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany.|High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.
authors: Klaus
authors: K
authors: Scheffler
authors: High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.|Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna, Austria.
authors: Siegfried
authors: S
authors: Trattnig
authors: High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.|Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria.
authors: Martin
authors: M
authors: Krššák
mesh_terms: D000328:Adult; D001834:Body Water; D003314:Corn Oil; D005231:Fatty Acids, Unsaturated / Q000032:analysis; D005260:Female; D006801:Humans; D008055:Lipids / Q000032:analysis*; D008099:Liver / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio
chemical_list: D005231:Fatty Acids, Unsaturated; D008055:Lipids; D003314:Corn Oil
keywords: 7T; MRS; lipids; liver; ultrashort TE; unsaturation