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Jun Shen - One of the best experts on this subject based on the ideXlab platform.
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Signal enhancement of glutamine and glutathione by single-step Spectral Editing.
Journal of magnetic resonance (San Diego Calif. : 1997), 2020Co-Authors: Maria Ferraris Araneta, Milalynn Victorino, Jun ShenAbstract:Abstract A single-step Spectral Editing approach using an always-on Editing pulse was proposed to enhance the signals of strongly coupled spins. Specifically, a single-step Spectral Editing sequence with an always-on Editing pulse applied at 2.12 ppm was used to enhance glutamine (Gln) and glutathione (GSH) signals at TE = 56 ms on a 7 T scanner. Density matrix simulations demonstrated that the current method (TE = 56 ms) led to large signal enhancement of at least 61% for Gln and 51% for GSH compared to a previous single-step method (TE = 106 ms). Monte Carlo simulations showed that the current method reduced noise-originated variations by 31% for Gln and 26% for GSH compared to a previous three-step Spectral Editing method from which the present method was derived.
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Effects of carrier frequency mismatch on frequency-selective Spectral Editing.
Magma (New York N.Y.), 2018Co-Authors: Maria Ferraris Araneta, Christopher Johnson, Jun ShenAbstract:OBJECTIVES This study sought to investigate the effects of carrier frequency mismatch on Spectral Editing and its correction by frequency matching of basis functions. MATERIALS AND METHODS Full density matrix computations and Monte-Carlo simulations based on magnetic resonance spectroscopy (MRS) data collected from five healthy volunteers at 7 T were used to analyze the effects of carrier frequency mismatch on Spectral Editing. Relative errors in metabolite quantification were calculated with and without frequency matching of basis functions. The algorithm for numerical computation of basis functions was also improved for higher computational efficiency. RESULTS We found significant errors without frequency matching of basis functions when carrier frequency mismatch was generally considered negligible. By matching basis functions with the history of frequency deviation, the mean errors in glutamate, glutamine, γ-aminobutyric acid, and glutathione concentrations were reduced from 3.90%, 1.85%, 11.53%, and 3.43% to 0.18%, 0.34%, 0.40%, and 0.51%, respectively. CONCLUSION Matching basis functions to frequency deviation history was necessary even when frequency deviations during frequency-selective Spectral Editing were fairly small. Basis set frequency matching significantly improved accuracy in the quantification of glutamate, glutamine, γ-aminobutyric acid, and glutathione concentrations.
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Simultaneous measurement of glutamate, glutamine, GABA, and glutathione by Spectral Editing without subtraction.
Magnetic resonance in medicine, 2018Co-Authors: Maria Ferraris Araneta, Chris R. Johnson, Jun ShenAbstract:PURPOSE To simultaneously measure glutamate, glutamine, γ-aminobutyric acid (GABA), and glutathione using Spectral Editing without subtraction at 7T. METHODS A novel Spectral Editing approach was proposed to simultaneously measure glutamate, glutamine, GABA, and glutathione using a TE of 56 ms at 7T. By numerical optimization of sequence timing in the presence of an Editing pulse, the 4 metabolites all form relatively intense pseudo singlets with maximized peak amplitudes and minimized peak linewidths in 1 of the 3 interleaved spectra. For measuring glutamate, glutamine, and glutathione, the Editing pulse targets the H3 protons of these metabolites near 2.12 parts per million. Both GABA H2 and H4 resonances are fully utilized in Spectral fitting. RESULTS Concentration levels (/[total creatine]) of glutamate, glutamine, GABA, and glutathione from an 8 mL voxel in the pregenual anterior cingulate cortex of 5 healthy volunteers were found to be 1.26 ± 0.13, 0.33 ± 0.06, 0.13 ± 0.03, and 0.27 ± 0.03, respectively, with within-subject coefficient of variation at 3.2%, 8.2%, 7.1%, and 10.2%, respectively. The total scan time was less than 4.5 min. CONCLUSIONS The proposed new technique does not require data subtraction. The 3 major metabolites of the glutamatergic and GABAergic systems and the oxidative stress marker glutathione were all measured in 1 short scan with high precision.
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Retrospective correction of frequency drift in Spectral Editing: The GABA Editing example.
NMR in biomedicine, 2017Co-Authors: Jan Willem Van Der Veen, Stefano Marenco, Karen Faith Berman, Jun ShenAbstract:GABA levels can be measured using proton MRS with a two-step Editing sequence. However due to the low concentration of GABA, long acquisition time is usually needed to achieve sufficient SNR to detect small differences in many psychiatric disorders. During this long scan time the frequency offset of the measured voxel can change because of magnetic field drift and patient movement. This drift will change the frequency of the Editing pulse relative to that of metabolites, leading to errors in quantification. In this article we describe a retrospective method to correct for frequency drift in Spectral Editing. A series of reference signals for each metabolite was generated for a range of frequency offsets and then averaged together based on the history of frequency changes over the scan. These customized basis sets were used to fit the in vivo data. Our results demonstrate the effectiveness of the correction method and the remarkable robustness of a GABA Editing technique with a top hat Editing profile in the presence of frequency drift.
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Spectral Editing for in vivo 13C magnetic resonance spectroscopy
Journal of magnetic resonance (San Diego Calif. : 1997), 2011Co-Authors: Yun Xiang, Jun ShenAbstract:In vivo detection of carboxylic/amide carbons is a promising technique for studying cerebral metabolism and neurotransmission due to the very low RF power required for proton decoupling. In the carboxylic/amide region, however, there is severe Spectral overlap between acetate C1 and glutamate C5, complicating studies that use acetate as an astroglia-specific substrate. There are no known in vivo MRS techniques that can Spectrally resolve acetate C1 and glutamate C5 singlets. In this study, we propose to Spectrally separate acetate C1 and glutamate C5 by a two-step J-Editing technique after introducing homonuclear (13)C-(13)C scalar coupling between carboxylic/amide carbons and aliphatic carbons. By infusing [1,2-(13)C(2)]acetate instead of [1-(13)C]acetate the acetate doublet can be Spectrally edited because of the large separation between acetate C2 and glutamate C4 in the aliphatic region. This technique can be applied to studying acetate transport and metabolism in brain in the carboxylic/amide region without Spectral interference.
Klaus Schmidt-rohr - One of the best experts on this subject based on the ideXlab platform.
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Multinuclear solid-state NMR of complex nitrogen-rich polymeric microcapsules: Weight fractions, Spectral Editing, component mixing, and persistent radicals.
Solid state nuclear magnetic resonance, 2020Co-Authors: Shichen Yuan, Pu Duan, Damien Berthier, Géraldine Leon, Horst Sommer, Jean-yves De Saint-laumer, Klaus Schmidt-rohrAbstract:Abstract The molecular structure of a crosslinked nitrogen-rich resin made from melamine, urea, and aldehydes, and of microcapsules made from the reactive resin with multiple polymeric components in aqueous dispersion, has been analyzed by 13C, 13C{1H}, 1H–13C, 1H, 13C{14N}, and 15N solid-state NMR without isotopic enrichment. Quantitative 13C NMR spectra of the microcapsules and three precursor materials enable determination of the fractions of different components. Spectral Editing of non-protonated carbons by recoupled dipolar dephasing, of CH by dipolar DEPT, and of C–N by 13C{14N} SPIDER resolves peak overlap and helps with peak assignment. It reveals that the N- and O-rich resin “imitates” the spectrum of polysaccharides such as chitin, cellulose, or Ambergum to an astonishing degree. 15N NMR can distinguish melamine from urea and guanazole, NC=O from COO, and primary from secondary amines. Such a comprehensive and quantitative analysis enables prediction of the elemental composition of the resin, to be compared with combustion analysis for validation. It also provides a reliable reference for iterative simulations of 13C NMR spectra from structural models. The conversion from quantitative NMR peak areas of structural components to the weight fractions of interest in industrial practice is derived and demonstrated. Upon microcapsule formation, 15N and 13C NMR consistently show loss of urea and aldehyde and an increase in primary amines while melamine is retained. NMR also made unexpected findings, such as imbedded crystallites in one of the resins, as well as persistent radicals in the microcapsules. The crystallites produce distinct sharp lines and are distinguished from liquid-like components by their strong dipolar couplings, resulting in fast dipolar dephasing. Fast 1H spin–lattice relaxation on the 35-ms time scale and characteristically non-exponential 13C spin–lattice relaxation indicate persistent radicals, confirmed by EPR. Through 1H spin diffusion, the mixing of components on the 5-nm scale was documented.
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Aromatic Spectral Editing techniques for magic-angle-spinning solid-state NMR spectroscopy of uniformly (13)C-labeled proteins.
Solid state nuclear magnetic resonance, 2015Co-Authors: Jonathan K. Williams, Klaus Schmidt-rohr, Mei HongAbstract:The four aromatic amino acids in proteins, namely histidine, phenylalanine, tyrosine, and tryptophan, have strongly overlapping (13)C chemical shift ranges between 100 and 160ppm, and have so far been largely neglected in solid-state NMR determination of protein structures. Yet aromatic residues play important roles in biology through π-π and cation-π interactions. To better resolve and assign aromatic residues' (13)C signals in magic-angle-spinning (MAS) solid-state NMR spectra, we introduce two Spectral Editing techniques. The first method uses gated (1)H decoupling in a proton-driven spin-diffusion (PDSD) experiment to remove all protonated (13)C signals and retain only non-protonated carbon signals in the aromatic region of the (13)C spectra. The second technique uses chemical shift filters and (1)H-(13)C dipolar dephasing to selectively detect the Cα, Cβ and CO cross peaks of aromatic residues while suppressing the signals of all aliphatic residues. We demonstrate these two techniques on amino acids, a model peptide, and the microcrystalline protein GB1, and show that they significantly simplify the 2D NMR spectra and both reveal and permit the ready assignment of the aromatic residues' signals.
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Characterization of a nitrogen-rich fulvic acid and its precursor algae from solid state NMR
Organic Geochemistry, 2007Co-Authors: Jingdong Mao, Rose M. Cory, Diane M. Mcknight, Klaus Schmidt-rohrAbstract:Abstract A nitrogen-rich fulvic acid (FA) from Pony Lake, a coastal pond in Antarctica, was investigated using advanced solid state nuclear magnetic resonance (NMR) techniques and compared with the precursor algal material. A significant fraction of non-protonated alkyl carbons, some bonded to nitrogen, was detected; most must be humification products, since they were undetectable in the lake algae. The corresponding branched alkyl structures account for 25–50% of carbon in the FA. Spectral Editing detected methylenes (20% of all C) and ethyl groups attached to a branch point. COOH groups are also enriched (∼10% of all C); 15N NMR and Spectral Editing of CH and CN groups indicates peptides (∼1/4 of all C, ∼2/5 of all N), but the 15N NMR spectrum also exhibits bands up- and downfield from the peptide signal; these must be associated with a 157 ppm sp2-hybridized carbon bonded to three heteroatoms, of which at least two are N, according to 13C{14N} SPIDER (saturation pulse induced dipolar exchange with recoupling) NMR. This component, possibly a degradation product of penguin guano, accounts for nearly half the N. OCH, O–CH–O and OCH2 moieties, typically found in sugar rings, were identified using Spectral Editing (∼12% of all C). The quantitative 13C spectrum shows an aromaticity of 8%; many of the aromatic carbons are bonded to N. 1H–13C NMR with 1H spin diffusion shows that most components are within 1 nm from non-polar alkyl segments, which excludes polysaccharide or aromatic domains. Overall, the structural differences between the algal precursor and the FA are striking.
Mei Hong - One of the best experts on this subject based on the ideXlab platform.
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Aromatic Spectral Editing techniques for magic-angle-spinning solid-state NMR spectroscopy of uniformly (13)C-labeled proteins.
Solid state nuclear magnetic resonance, 2015Co-Authors: Jonathan K. Williams, Klaus Schmidt-rohr, Mei HongAbstract:The four aromatic amino acids in proteins, namely histidine, phenylalanine, tyrosine, and tryptophan, have strongly overlapping (13)C chemical shift ranges between 100 and 160ppm, and have so far been largely neglected in solid-state NMR determination of protein structures. Yet aromatic residues play important roles in biology through π-π and cation-π interactions. To better resolve and assign aromatic residues' (13)C signals in magic-angle-spinning (MAS) solid-state NMR spectra, we introduce two Spectral Editing techniques. The first method uses gated (1)H decoupling in a proton-driven spin-diffusion (PDSD) experiment to remove all protonated (13)C signals and retain only non-protonated carbon signals in the aromatic region of the (13)C spectra. The second technique uses chemical shift filters and (1)H-(13)C dipolar dephasing to selectively detect the Cα, Cβ and CO cross peaks of aromatic residues while suppressing the signals of all aliphatic residues. We demonstrate these two techniques on amino acids, a model peptide, and the microcrystalline protein GB1, and show that they significantly simplify the 2D NMR spectra and both reveal and permit the ready assignment of the aromatic residues' signals.
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Spectral Editing of two-dimensional magic-angle-spinning solid-state NMR spectra for protein resonance assignment and structure determination
Journal of Biomolecular NMR, 2012Co-Authors: K. Schmidt-rohr, K. J. Fritzsching, S. Y. Liao, Mei HongAbstract:Several techniques for Spectral Editing of 2D ^13C–^13C correlation NMR of proteins are introduced. They greatly reduce the Spectral overlap for five common amino acid types, thus simplifying Spectral assignment and conformational analysis. The carboxyl (COO) signals of glutamate and aspartate are selected by suppressing the overlapping amide N–CO peaks through ^13C–^15N dipolar dephasing. The sidechain methine (CH) signals of valine, lecuine, and isoleucine are separated from the overlapping methylene (CH_2) signals of long-chain amino acids using a multiple-quantum dipolar transfer technique. Both the COO and CH selection methods take advantage of improved dipolar dephasing by asymmetric rotational-echo double resonance (REDOR), where every other π-pulse is shifted from the center of a rotor period t_r by about 0.15 t_r. This asymmetry produces a deeper minimum in the REDOR dephasing curve and enables complete suppression of the undesired signals of immobile segments. Residual signals of mobile sidechains are positively identified by dynamics Editing using recoupled ^13C–^1H dipolar dephasing. In all three experiments, the signals of carbons within a three-bond distance from the selected carbons are detected in the second Spectral dimension via ^13C spin exchange. The efficiencies of these Spectral Editing techniques range from 60 % for the COO and dynamic selection experiments to 25 % for the CH selection experiment, and are demonstrated on well-characterized model proteins GB1 and ubiquitin.
Arend Heerschap - One of the best experts on this subject based on the ideXlab platform.
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echo time independent signal modulations using press sequences a new approach to Spectral Editing of strongly coupled ab spin systems
Journal of Magnetic Resonance, 2005Co-Authors: Giulio Gambarota, Dennis W.j. Klomp, M Van Der Graaf, Robert V Mulkern, Arend HeerschapAbstract:Abstract In clinical MR spectroscopy, double spin-echo point resolved spectroscopy (PRESS) sequences are routinely used for volume selection. For strongly coupled AB spin systems under PRESS excitation, the dependence of the signal on the echo time TE has been thoroughly investigated, whereas less attention has been paid to the signal modulation which occurs at constant TE with varying interpulse delays. A substantial TE-independent J modulation is here predicted from analytical solutions of the Liouville equation and density matrix simulations, and verified with experiments on citrate at 1.5 and 3 T. It is also shown that this modulation effect could be exploited for Editing of strongly coupled AB resonances or for removal of singlets in spectra—by means of difference spectroscopy—just using a standard PRESS sequence. The applicability in vivo of this new Spectral Editing approach is also demonstrated, with selective detection of citrate resonances in the human prostate. This novel approach has the advantages of being simple, and directly applicable on standard clinical MR scanners, provided that the exact behavior of the resonance is known.
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Echo-time independent signal modulations using PRESS sequences: a new approach to Spectral Editing of strongly coupled AB spin systems.
Journal of magnetic resonance (San Diego Calif. : 1997), 2005Co-Authors: Giulio Gambarota, Dennis W.j. Klomp, Robert V Mulkern, M. Van Der Graaf, Arend HeerschapAbstract:In clinical MR spectroscopy, double spin-echo point resolved spectroscopy (PRESS) sequences are routinely used for volume selection. For strongly coupled AB spin systems under PRESS excitation, the dependence of the signal on the echo time TE has been thoroughly investigated, whereas less attention has been paid to the signal modulation which occurs at constant TE with varying interpulse delays. A substantial TE-independent J modulation is here predicted from analytical solutions of the Liouville equation and density matrix simulations, and verified with experiments on citrate at 1.5 and 3T. It is also shown that this modulation effect could be exploited for Editing of strongly coupled AB resonances or for removal of singlets in spectra-by means of difference spectroscopy-just using a standard PRESS sequence. The applicability in vivo of this new Spectral Editing approach is also demonstrated, with selective detection of citrate resonances in the human prostate. This novel approach has the advantages of being simple, and directly applicable on standard clinical MR scanners, provided that the exact behavior of the resonance is known.
Dennis W.j. Klomp - One of the best experts on this subject based on the ideXlab platform.
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Efficient Spectral Editing at 7 T: GABA detection with MEGA-sLASER.
Magnetic resonance in medicine, 2011Co-Authors: A. Andreychenko, Vincent O. Boer, Catalina S. Arteaga De Castro, Peter R. Luijten, Dennis W.j. KlompAbstract:At high field (7 T) Spectral Editing of γ-aminobutyric acid with MEGA-point-resolved spectroscopy is inefficient due to the large chemical shift displacement error. In this article, a new pulse sequence is designed which has minimal chemical shift displacement error to perform an efficient Spectral Editing of the γ-aminobutyric acid 3.0 ppm resonance at 7 T. The sequence consists of the conventional MEGA Editing pulses and a semi-localized by adiabatic selective refocusing sequence. Phantom and in vivo measurements demonstrated an efficient detection of γ-aminobutyric acid. Using ECG triggering, excellent in vivo performance of the MEGA-semi-localized by adiabatic selective refocusing (MEGA-sLASER) provided well-resolved γ-aminobutyric acid signals in 27 mL volumes in the human brain at an echo time of 74 ms within a relatively short acquisition time (5 min). Furthermore, the high efficiency of the MEGA-sLASER was demonstrated by acquiring small volumes (8 mL) at an echo time of 74 ms, as well as long echo time measurements (222 ms in 27 mL volume).
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echo time independent signal modulations using press sequences a new approach to Spectral Editing of strongly coupled ab spin systems
Journal of Magnetic Resonance, 2005Co-Authors: Giulio Gambarota, Dennis W.j. Klomp, M Van Der Graaf, Robert V Mulkern, Arend HeerschapAbstract:Abstract In clinical MR spectroscopy, double spin-echo point resolved spectroscopy (PRESS) sequences are routinely used for volume selection. For strongly coupled AB spin systems under PRESS excitation, the dependence of the signal on the echo time TE has been thoroughly investigated, whereas less attention has been paid to the signal modulation which occurs at constant TE with varying interpulse delays. A substantial TE-independent J modulation is here predicted from analytical solutions of the Liouville equation and density matrix simulations, and verified with experiments on citrate at 1.5 and 3 T. It is also shown that this modulation effect could be exploited for Editing of strongly coupled AB resonances or for removal of singlets in spectra—by means of difference spectroscopy—just using a standard PRESS sequence. The applicability in vivo of this new Spectral Editing approach is also demonstrated, with selective detection of citrate resonances in the human prostate. This novel approach has the advantages of being simple, and directly applicable on standard clinical MR scanners, provided that the exact behavior of the resonance is known.
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Echo-time independent signal modulations using PRESS sequences: a new approach to Spectral Editing of strongly coupled AB spin systems.
Journal of magnetic resonance (San Diego Calif. : 1997), 2005Co-Authors: Giulio Gambarota, Dennis W.j. Klomp, Robert V Mulkern, M. Van Der Graaf, Arend HeerschapAbstract:In clinical MR spectroscopy, double spin-echo point resolved spectroscopy (PRESS) sequences are routinely used for volume selection. For strongly coupled AB spin systems under PRESS excitation, the dependence of the signal on the echo time TE has been thoroughly investigated, whereas less attention has been paid to the signal modulation which occurs at constant TE with varying interpulse delays. A substantial TE-independent J modulation is here predicted from analytical solutions of the Liouville equation and density matrix simulations, and verified with experiments on citrate at 1.5 and 3T. It is also shown that this modulation effect could be exploited for Editing of strongly coupled AB resonances or for removal of singlets in spectra-by means of difference spectroscopy-just using a standard PRESS sequence. The applicability in vivo of this new Spectral Editing approach is also demonstrated, with selective detection of citrate resonances in the human prostate. This novel approach has the advantages of being simple, and directly applicable on standard clinical MR scanners, provided that the exact behavior of the resonance is known.
