title: Two-dimensional spectroscopic imaging with combined free induction decay and long-TE acquisition (FID echo spectroscopic imaging, FIDESI) for the detection of intramyocellular lipids in calf muscle at 7 T.
abstract: The aim of this study was to introduce a two-dimensional chemical shift imaging (2D CSI) sequence, with simultaneous acquisition of free induction decay (FID) and long TEs, for the detection and quantification of intramyocellular lipids (IMCLs) in the calf at 7 T. The feasibility of the new 2D CSI sequence, which acquires FID (acquisition delay, 1.3 ms) and an echo (long TE) in one measurement, was evaluated in phantoms and volunteers (n = 5): TR/TE*/TE = 800/1.3/156 ms; 48 × 48 matrix; field of view, 200 × 200 × 20 mm(3) ; Hamming filter; no water suppression; measurement time, 22 min 2 s. The IMCL concentration and subcutaneous lipid contamination were assessed. Spectra in the tibialis anterior (TA), gastrocnemius (GM) and soleus (SOL) muscles were analyzed. The water signal from the FID acquisition was used as an internal concentration reference. In the spectra from subcutaneous adipose tissue (SUB) and bone marrow (BM), an unsaturation index (UI) of the vinyl-H (5.3 ppm) to methyl-CH3 ratio, and a polyunsaturation index (pUI) of the diallylic-H (2.77 ppm) to -CH3 ratio, were calculated. Long-TE spectra from muscles showed a simplified spectral pattern with well-separated IMCL for several muscle groups in the same scan. The IMCL to water ratio was largest in SOL (0.66% ± 0.23%), and lower in GM (0.37% ± 0.14%) and TA (0.36% ± 0.12%). UI and pUI for SUB were 0.65 ± 0.06 and 0.18 ± 0.04, respectively, and for BM were 0.60 ± 0.16 and 0.18 ± 0.08, respectively. The new sequence, with the proposed name 'free induction decay echo spectroscopic imaging' (FIDESI), provides information on both specific lipid resonances and water signal from different tissues in the calf, with high spectral and spatial resolution, as well as minimal voxel bleeding and subcutaneous lipid contamination, in clinically acceptable measurement times.
authors.affiliation: MR Centre of Excellence, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria; Department of NMR and MS, Faculty of Chemical and Food Technology, Slovak University of Technology, Bratislava, Slovakia.
authors.forename: Ivica
authors.initials: I
authors.lastname: Just Kukurova
authors.forename: Ladislav
authors.initials: L
authors.lastname: Valkovič
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bogner
authors.forename: Martin
authors.initials: M
authors.lastname: Gajdošík
authors.forename: Martin
authors.initials: M
authors.lastname: Krššák
authors.forename: Stephan
authors.initials: S
authors.lastname: Gruber
authors.forename: Siegfried
authors.initials: S
authors.lastname: Trattnig
authors.forename: Marek
authors.initials: M
authors.lastname: Chmelík
mesh_terms: D000328:Adult; D003401:Creatine / Q000378:metabolism; D005260:Female; D006801:Humans; D007866:Leg / Q000502:physiology*; D008055:Lipids / Q000032:analysis*; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009132:Muscles / Q000378:metabolism*; D019047:Phantoms, Imaging; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors; D055815:Young Adult
chemical_list: D008055:Lipids; D003401:Creatine
keywords: 1H chemical shift imaging (1H CSI); 7 T; calf; free induction decay (FID); intramyocellular lipid (IMCL); long TE