Abstract
Background and PurposeMagnetic resonance spectroscopy (MRS) constitutes a mainstream technique for characterizing biological samples. Benefiting from the separation of chemical shifts and J couplings, spatially localized two-dimensional (2D) J-resolved spectroscopy (JPRESS) shows better identification of complex metabolite resonances than one-dimensional MRS does and facilitates the extraction of J coupling information. However, due to variations of macroscopic magnetic susceptibility in biological samples, conventional JPRESS spectra generally suffer from the influence of field inhomogeneity. In this paper, we investigated the implementation of the localized 2D J-resolved spectroscopy based on intermolecular double-quantum coherences (iDQCs) on a 7 T MRI scanner.Materials and MethodsA γ-aminobutyric acid (GABA) aqueous solution, an intact pig brain tissue, and a whole fish (Harpadon nehereus) were explored by using the localized iDQC J-resolved spectroscopy (iDQCJRES) method, and the results were compared to those obtained by using the conventional 2D JPRESS method.ResultsInhomogeneous line broadening, caused by the variations of macroscopic magnetic susceptibility in the detected biological samples (the intact pig brain tissue and the whole fish), degrades the quality of 2D JPRESS spectra, particularly when a large voxel is selected and some strongly structured components are included (such as the fish spinal cord). By contrast, high-resolution 2D J-resolved information satisfactory for metabolite analyses can be obtained from localized 2D iDQCJRES spectra without voxel size limitation and field shimming. From the contrastive experiments, it is obvious that the spectral information observed in the localized iDQCJRES spectra acquired from large voxels without field shimming procedure (i.e. in inhomogeneous fields) is similar to that provided by the JPRESS spectra acquired from small voxels after field shimming procedure (i.e. in relatively homogeneous fields).ConclusionThe localized iDQCJRES method holds advantage for recovering high-resolution 2D J-resolved information from inhomogeneous fields caused by external non-ideal field condition or internal macroscopic magnetic susceptibility variations in biological samples, and it is free of voxel size limitation and time-consuming field shimming procedure. This method presents a complementary way to the conventional JPRESS method for MRS measurements on MRI systems equipped with broad inner bores, and may provide a promising tool for in vivo MRS applications.
Highlights
Magnetic resonance spectroscopy (MRS) is a powerful tool for investigating chemical compositions and elucidating molecular structures
We investigated the implementation of the localized 2D J-resolved spectroscopy based on intermolecular double-quantum coherences on a 7 T magnetic resonance imaging (MRI) scanner
High-Resolution 2D J-Resolved MRS Applications to Biological Samples procedure is similar to that provided by the JPRESS spectra acquired from small voxels after field shimming procedure
Summary
Magnetic resonance spectroscopy (MRS) is a powerful tool for investigating chemical compositions and elucidating molecular structures. The intrinsic magnetic susceptibility variations in biological samples generally lead to inhomogeneous line broadening in 1D PRESS spectra, even severe overlapping of spectral peaks. By separating chemical shifts and J couplings into two different frequency dimensions, the localized two-dimensional (2D) J-resolved spectroscopy (JPRESS) is designed by adding an indirect spectral dimension in the original 1D PRESS to alleviate the spectral congestion [9, 10]. The JPRESS method remains sensitive to field inhomogeneity caused by macroscopic magnetic susceptibility variations in biological samples, especially in the investigations of large voxels that include different components. Benefiting from the separation of chemical shifts and J couplings, spatially localized two-dimensional (2D) J-resolved spectroscopy (JPRESS) shows better identification of complex metabolite resonances than one-dimensional MRS does and facilitates the extraction of J coupling information. We investigated the implementation of the localized 2D J-resolved spectroscopy based on intermolecular double-quantum coherences (iDQCs) on a 7 T MRI scanner
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