title: Localized 2D COSY sequences: Method and experimental evaluation for a whole metabolite quantification approach.
abstract: Two-dimensional spectroscopy offers the possibility to unambiguously distinguish metabolites by spreading out the multiplet structure of J-coupled spin systems into a second dimension. Quantification methods that perform parametric fitting of the 2D MRS signal have recently been proposed for resolved PRESS (JPRESS) but not explicitly for Localized Correlation Spectroscopy (LCOSY). Here, through a whole metabolite quantification approach, correlation spectroscopy quantification performances are studied. The ability to quantify metabolite relaxation constant times is studied for three localized 2D MRS sequences (LCOSY, LCTCOSY and the JPRESS) in vitro on preclinical MR systems. The issues encountered during implementation and quantification strategies are discussed with the help of the Fisher matrix formalism. The described parameterized models enable the computation of the lower bound for error variance--generally known as the Cramér Rao bounds (CRBs), a standard of precision--on the parameters estimated from these 2D MRS signal fittings. LCOSY has a theoretical net signal loss of two per unit of acquisition time compared to JPRESS. A rapid analysis could point that the relative CRBs of LCOSY compared to JPRESS (expressed as a percentage of the concentration values) should be doubled but we show that this is not necessarily true. Finally, the LCOSY quantification procedure has been applied on data acquired in vivo on a mouse brain.
authors.affiliation: Université de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Claude Bernard Lyon 1, France.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Martel
authors.affiliation: Université de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Claude Bernard Lyon 1, France.
authors.forename: K
authors.initials: K
authors.lastname: Tse Ve Koon
authors.affiliation: Aix-Marseille Université, CRMBM, CNRS UMR, 7339 Marseille, France.
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Fur
authors.affiliation: Université de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Claude Bernard Lyon 1, France. Electronic address: helene.ratiney@creatis.insa-lyon.fr.
authors.forename: Hélène
authors.initials: H
authors.lastname: Ratiney
mesh_terms: D000465:Algorithms; D000818:Animals; D016477:Artifacts; D001923:Brain Chemistry; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism; D016014:Linear Models; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D055442:Metabolome; D051379:Mice; D008810:Mice, Inbred C57BL; D013113:Spin Labels; D013788:Thalamus / Q000737:chemistry
chemical_list: D013113:Spin Labels; D019344:Lactic Acid
keywords: 2D MRS quantification; Cramér Rao lower bounds; Fisher information formalism; JPRESS; LCOSY