Spatially Localized Two-Dimensional J-Resolved NMR Spectroscopy via Intermolecular Double-Quantum Coherences for Biological Samples at 7 T

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.

Fast quantification of fatty acid profile of intact fish by intermolecular double‐quantum coherence 1H‐NMR spectroscopy

“…Therefore, iDQC makes an appropriate supplement to extraction NMR when the samples are not suitable for extraction. With sensitivity improved, the iDQC method may be more practical for applications in in vivo and in situ NMR experiments in which samples are not allowed to spin, and the preliminary study of the whole fish on seven T MRI scanner by iDQC has been reported recently . The iDQC method may be more practical for applications in in vivo and in situ NMR experiments in which samples are not allowed to spin.…”

Two-Dimensional J-Resolved NMR Analyses of Fish and Its Products via Spatially Encoded Intermolecular Double-Quantum Coherences

“…In comparison with our previous work, also proposed for high-resolution 2D JRES spectra (Huang et al 2010;Huang et al 2014;Huang et al 2015;Tan et al 2015), all these studies and the UfiDQCJRES method in the present article are based on the iMQC and are modulated by the distant dipolar field effect for observed signals. The intermolecular single quantum coherence (iSQC)-JRES method (Huang et al 2010) was conducted by a conventional 3D acquisition mode, and its acquisition time depended on the range of chemical shift in the F1 dimension and the range of field inhomogeneity in the F2 dimension.…”

“…The acquisition efficiency of the iDQCJRES sequence depends on the half range of field inhomogeneity plus J coupling splitting in the F1 dimension and the range of J coupling splitting in the F2 dimension. Further applications of the iDQCJRES method were performed on a 7 T small animal magnetic resonance scanner (Tan et al 2015). The spatial encoding technique was employed in the DDFJRES method to further shorten the acquisition time.…”