Spectral Editing Technique Research Articles

IMG-21. PROSPECTIVE PREOPERATIVE DETERMINATION OF ISOCITRATE DEHYDROGENASE MUTATION IN GLIOMAS USING SPECTRAL EDITING MAGNETIC RESONANCE SPECTROSCOPY

BACKGROUNDGliomas are the most common malignant brain tumors in children and adults. A subset of these tumors harbour mutations in the enzyme isocitrate dehydrogenase (IDH) which produces the novel oncometabolite 2-hydroxyglutarate (2HG). In general, patients with an IDH mutant glioma have a longer survival—often necessitating more re-treatment sessions over the span of a patient’s life and surveillance monitoring for tumor recurrence. The need to non-invasively detect early evidence of tumor recurrence is therefore heightened in this unique subset of patients with extended survival. As magnetic resonance spectroscopy (MRS) has been demonstrated to measure biochemical components of intracranial tumors using MRI, we conducted a study in 58 pre-operative adult patients to determine if a diagnosis of IDH mutant glioma could be made confidently using imaging data.METHODSPatients underwent neuroimaging for diagnosis or preoperative planning on a 3 tesla MR scanner. A MEGA-PRESS spectral editing technique was employed. Imaging findings were directly compared to post-operative histopathologic diagnosis. RESUTLS: For all patients with gliomas from grade II to IV, detection of 2-HG with MEGA-PRESS sequence had a sensitivity between 48% and 81%, specificity between 60% and 100%, PPV between 53% and 100% and NPV between 77% and 85% depending on the CRLB threshold. Among the different metabolite ratios, a 2-HG/NAA ratio >0.034 had the highest sensitivity and specificity, 86% and 73% respectively.DISCUSSIONMagnetic resonance spectroscopy (MRS) is an underused advanced MR technique that deserves consideration in pediatric neuro-oncology given its utility in non-invasively detecting malignant gliomas.

Assessment of the triacylglycerol fraction of olive oil by 1D-NMR spectroscopy: exploring the usefulness of DEPT tool on the peak assignments of 13C NMR spectra

Nuclear magnetic resonance (NMR) spectroscopy has been extensively used to date for the analysis of olive oil samples and constitutes a valuable tool particularly for the study of the triacylglycerol fraction, which is the major fraction of olive oils. In this report, we demonstrate the usefulness of one-dimensional NMR spectroscopy (1H and 13C NMR) for the non-destructive analysis of the triacylglycerol fraction of olive oils. To achieve this goal, 13C spectral editing technique known as distortionless enhancement by polarization transfer (DEPT), namely 13C NMR DEPT 45, 13C NMR DEPT 90, 13C NMR DEPT 135 was used for the analysis of the triacylglycerol fraction of the olive oil sample owing to the simplification on peak assignments of 13C spectra. The suitability and usefulness of those DEPT experiments using different angle values in only one pulse sequence will be explored on the interpretation of 13C NMR spectra. In overall, DEPT tool improves the sensitivity of the analysis due to the enhancement in the signal-to-noise ratio, which is important for this type of analysis contributing to the characterization of olive oils.

Multi-vendor standardized sequence for edited magnetic resonance spectroscopy

Spectral editing allows direct measurement of low-concentration metabolites, such as GABA, glutathione (GSH) and lactate (Lac), relevant for understanding brain (patho)physiology. The most widely used spectral editing technique is MEGA-PRESS, which has been diversely implemented across research sites and vendors, resulting in variations in the final resolved edited signal. In this paper, we describe an effort to develop a new universal MEGA-PRESS sequence with HERMES functionality for the major MR vendor platforms with standardized RF pulse shapes, durations, amplitudes and timings.New RF pulses were generated for the universal sequence. Phantom experiments were conducted on Philips, Siemens, GE and Canon 3 T MRI scanners using 32-channel head coils. In vivo experiments were performed on the same six subjects on Philips and Siemens scanners, and on two additional subjects, one on GE and one on Canon scanners. On each platform, edited MRS experiments were conducted with the vendor-native and universal MEGA-PRESS sequences for GABA (TE = 68 ms) and Lac editing (TE = 140 ms). Additionally, HERMES for GABA and GSH was performed using the universal sequence at TE = 80 ms.The universal sequence improves inter-vendor similarity of GABA-edited and Lac-edited MEGA-PRESS spectra. The universal HERMES sequence yields both GABA- and GSH-edited spectra with negligible levels of crosstalk on all four platforms, and with strong agreement among vendors for both edited spectra. In vivo GABA+/Cr, Lac/Cr and GSH/Cr ratios showed relatively low variation between scanners using the universal sequence.In conclusion, phantom and in vivo experiments demonstrate successful implementation of the universal sequence across all four major vendors, allowing editing of several metabolites across a range of TEs.

Spectral editing at ultra-fast magic-angle-spinning in solid-state NMR: facilitating protein sequential signal assignment by HIGHLIGHT approach.

This study demonstrates a novel spectral editing technique for protein solid-state NMR (SSNMR) to simplify the spectrum drastically and to reduce the ambiguity for protein main-chain signal assignments in fast magic-angle-spinning (MAS) conditions at a wide frequency range of 40-80 kHz. The approach termed HIGHLIGHT (Wang et al., in Chem Comm 51:15055-15058, 2015) combines the reverse (13)C, (15)N-isotope labeling strategy and selective signal quenching using the frequency-selective REDOR pulse sequence under fast MAS. The scheme allows one to selectively observe the signals of "highlighted" labeled amino-acid residues that precede or follow unlabeled residues through selectively quenching (13)CO or (15)N signals for a pair of consecutively labeled residues by recoupling (13)CO-(15)N dipolar couplings. Our numerical simulation results showed that the scheme yielded only ~15% loss of signals for the highlighted residues while quenching as much as ~90% of signals for non-highlighted residues. For lysine-reverse-labeled micro-crystalline GB1 protein, the 2D (15)N/(13)Cα correlation and 2D (13)Cα/(13)CO correlation SSNMR spectra by the HIGHLIGHT approach yielded signals only for six residues following and preceding the unlabeled lysine residues, respectively. The experimental dephasing curves agreed reasonably well with the corresponding simulation results for highlighted and quenched residues at spinning speeds of 40 and 60 kHz. The compatibility of the HIGHLIGHT approach with fast MAS allows for sensitivity enhancement by paramagnetic assisted data collection (PACC) and (1)H detection. We also discuss how the HIGHLIGHT approach facilitates signal assignments using (13)C-detected 3D SSNMR by demonstrating full sequential assignments of lysine-reverse-labeled micro-crystalline GB1 protein (~300 nmol), for which data collection required only 11 h. The HIGHLIGHT approach offers valuable means of signal assignments especially for larger proteins through reducing the number of resonance and clarifying multiple starting points in sequential assignment with enhanced sensitivity.

In vivo GABA T2 determination with J‐refocused echo time extension at 7 T

A method to measure the T2 relaxation time of GABA with spectral editing techniques is proposed. Spectral editing techniques can be used to unambiguously extract signals of low concentration J-coupled spins such as γ-aminobutyric acid (GABA) from overlapping resonances such as creatine and macromolecules. These sequences, however, generally have fixed and relatively long echo times. Therefore, for the absolute quantification of the edited spectrum, the T2 relaxation time must be taken into account. To measure the T2 relaxation time, the signal intensity has to be obtained at multiple echo times. However, on a coupled spin system such as GABA this is challenging, since the signal intensity of the target resonances is modulated not only by T2 decay but also by the J-coupling, which strongly influences the shapes and amplitudes of the edited signals, depending on the echo time. Here, we propose to refocus the J-modulation of the edited signal at different echo times by using chemical shift selective refocusing. In this way the echo time can be arbitrarily extended while preserving the shape of the edited signal. The method was applied in combination with the MEGA-sLASER editing technique to measure the in vivo T2 relaxation time of GABA (87 ± 11 ms, n = 10) and creatine (109 ± 8 ms, n = 10) at 7 T. The T1 relaxation time of these metabolites in a single subject was also determined (GABA, 1334 ± 158 ms; Cr, 1753 ± 12 ms). The T2 decay curve of coupled spin systems can be sampled in an arbitrary fashion without the need for signal shape correction. Furthermore, the method can be applied with any spectral editing technique. The shortest echo time of the method is limited by the echo time of the spectral editing technique.

Fast and accurate quantification using Genetic Algorithm optimized 1H-13C refocused constant-time INEPT

Using Genetic Algorithm, a global optimization method inspired by nature’s evolutionary process, we have improved the quantitative refocused constant-time INEPT experiment (Q-INEPT-CT) of Mäkelä et al. (JMR 204 (2010) 124–130) with various optimization constraints. The improved ‘average polarization transfer’ and ‘min–max difference’ of new delay sets effectively reduces the experimental time by a factor of two (compared with Q-INEPT-CT, Mäkelä et al.) without compromising on accuracy. We also discuss a quantitative spectral editing technique based on average polarization transfer.

Negative Correlation between Brain Glutathione Level and Negative Symptoms in Schizophrenia: A 3T 1H-MRS Study

BackgroundGlutathione (GSH), a major intracellular antioxidant, plays a role in NMDA receptor-mediated neurotransmission, which is involved in the pathophysiology of schizophrenia. In the present study, we aimed to investigate whether GSH levels are altered in the posterior medial frontal cortex of schizophrenic patients. Furthermore, we examined correlations between GSH levels and clinical variables in patients.Methods and FindingsTwenty schizophrenia patients and 16 age- and gender-matched normal controls were enrolled to examine the levels of GSH in the posterior medial frontal cortex by using 3T SIGNA EXCITE 1H-MRS with the spectral editing technique, MEGA-PRESS. Clinical variables of patients were assessed by the Global Assessment of Functioning (GAF), Scale for the Assessment of Negative Symptoms (SANS), Brief Psychiatric Rating Scale (BPRS), Drug-Induced Extra-Pyramidal Symptoms Scale (DIEPSS), and five cognitive performance tests (Word Fluency Test, Stroop Test, Trail Making Test, Wisconsin Card Sorting Test and Digit Span Distractibility Test). Levels of GSH in the posterior medial frontal cortex of schizophrenic patients were not different from those of normal controls. However, we found a significant negative correlation between GSH levels and the severity of negative symptoms (SANS total score and negative symptom subscore on BPRS) in patients. There were no correlations between brain GSH levels and scores on any cognitive performance test except Trail Making Test part A.ConclusionThese results suggest that GSH levels in the posterior medial frontal cortex may be related to negative symptoms in schizophrenic patients. Therefore, agents that increase GSH levels in the brain could be potential therapeutic drugs for negative symptoms in schizophrenia.

In vivo MRS markers of response to CHOP chemotherapy in the WSU-DLCL2 human diffuse large B-cell lymphoma xenograft.

To identify 1H-MRS molecular biomarkers of early clinical therapeutic response in non-Hodgkin's lymphoma, an in vivo longitudinal study was performed on human non-Hodgkin's diffuse large B-cell lymphoma xenografts (WSU-DLCL2) grown in the flanks of female SCID mice. 31P-MRS measurements, which have been demonstrated to be prognostic clinical indices of response (Arias-Mendoza et al. Acad. Radiol. 2004; 11: 368-376) but which provide lower spatial resolution, were included for comparison. The animals received CHOP (cyclophosphamide, hydroxydoxorubicin, oncovin and prednisone) chemotherapy for three 1-week cycles, resulting in stable disease based on tumor volume. Localization of total choline and phosphorus metabolites in vivo was achieved with stimulated echo acquisition mode and image selected in vivo spectroscopy sequences, respectively. Significant decreases in lactate were detected by the selective multiple quantum coherence spectral editing technique after the first cycle of CHOP, whereas total choline and the phosphomonoester/nucleoside triphosphate ratio did not change until the third cycle. Ex vivo extract MRS of tumors corroborated the in vivo results. Histological staining with antibodies to Ki67 revealed a decrease in proliferation rate in CHOP-treated tumors that coincided with the decrease in lactate. This study demonstrates the utility of lactate as an early proliferation-sensitive indicator of therapeutic response in a mouse model of non-Hodgkin's lymphoma and serves as a basis for future clinical implementation of these methods.

A New Way to Use Solid‐State Carbon‐13 Nuclear Magnetic Resonance Spectroscopy to Study the Sorption of Organic Compounds to Soil Organic Matter

Several solid-state 13C nuclear magnetic resonance (NMR) techniques were used to characterize soil organic matter spiked with 13C-labeled organic compounds spanning a range of hydrophobicities (benzoic acid, benzophenone, naphthalene, phenanthrene, and palmitic acid). The chemical shifts of NMR resonances of the sorbed species were shifted by up to 3 ppm relative to those of the neat compounds. Sorption also resulted in increased resonance linewidth for the compounds containing a single 13C label, indicating the presence of a range of different chemical environments at the sites of sorption. On the other hand, sorption decreased the linewidth of the resonance of naphthalene, which was uniformly 13C-labeled. This was attributed to the removal of intermolecular 13C-13C dipolar coupling. Heterogeneity of the organic matter was demonstrated using the spectral editing technique proton spin relaxation editing (PSRE), which enabled the identification and quantification of charcoal-rich domains characterized by rapid rates of proton spin-lattice relaxation in the static frame (T1H), and humic domains characterized by slow rates of T1H relaxation. Furthermore it was demonstrated that the sorbed 13C-labeled molecules "inherit" the T1H "signature" of the organic matrix in their immediate vicinity. Thus PSRE on the spiked soils enabled evaluation of the relative affinity of the two domain types for the sorbate molecules. The charcoal-rich domains were shown to have a twofold to tenfold greater affinity for the organic compounds, with greater differences found for the more hydrophobic compounds.

Investigation of the Role of Structural Domains Identified in Sedimentary Organic Matter in the Sorption of Hydrophobic Organic Compounds

The role of composition and structure of sedimentary organic matter (SOM) in the sorption of hydrophobic organic compounds (HOCs) was investigated by spiking 13C-labeled phenanthrene onto six estuarine sediments known to vary in SOM content and character. After equilibration and HF treatment, 13C NMR cross polarization and stable carbon isotope analyses indicated that the amount of desorption-resistant phenanthrene was related to aromatic carbon content. Application of the 13C NMR spectral editing technique proton spin relaxation editing (PSRE) demonstrated that all samples consisted of a rapidly relaxing and a slowly relaxing component, further evidence that SOM can be described as a structurally heterogeneous sorbent. Further, comparison of corresponding control and spiked PSRE subspectra revealed that, for each of the six sediments, desorption-resistant phenanthrene had become associated almost exclusively with the rapidly relaxing component. In only two of the sediments were there even small amounts of phenanthrene discernible in the slowly relaxing component, which is signficant as it was not always true that aromatic carbon was concentrated exclusively in the rapidly relaxing phase. The implication of these findings is that not all aromatic fractions have the same affinity for phenanthrene and that some fractions may indeed have little affinity at all. These results were interpreted as indicative that rapidly relaxing aromatic carbon associated with either sediment-associated charcoal or diagenetic organic matter plays a controlling role in the sorption of HOCs. However, the exact manner in which this rapidly relaxing aromatic phase relates to models presented elsewhere remains unclear.

Uncovering hidden in vivo resonances using editing based on localized TOCSY

A novel single-shot spectral editing technique for in vivo proton NMR is proposed to recover resonances of low-concentration metabolites obscured by very strong resonances. With this new method, editing is performed by transferring transverse magnetization to J-coupled spins from selected coupling partners using a homonuclear Hartmann-Hahn polarization transfer with adiabatic pulses. The current implementation uses 1D-TOCSY with single-voxel localization based on LASER to recover the H1 proton of beta-glucose at 4.63 ppm from under water and the lactate methyl resonances from beneath a strong lipid signal. The method can be extended to further spin systems where conventional editing methods are difficult to perform.

Quantitative solid‐state 13C NMR spectroscopy of organic matter fractions in lowland rice soils

SummarySpin counting on solid‐state 13C cross‐polarization (CP) nuclear magnetic resonance (NMR) spectra of two humic fractions isolated from tropical lowland soils showed that only 32–81% of potential 13C NMR signal was detected. The observability of 13C NMR signal (Cobs) was higher in the mobile humic acid (MHA) than in the calcium humate (CaHA) fraction, and increased with increasing intensity of irrigated rice cropping. NMR observability appeared to be related to the nature of the organic carbon, with phenol‐ and methoxyl‐rich samples having the higher values of Cobs. The Bloch decay (BD) technique provided more quantitatively reliable 13C NMR spectra, as evidenced by values of Cobs in the range 91–100% for seven of the eight humic fractions studied. The BD spectra contained considerably more aryl and carbonyl signal, and less O–alkyl and alkyl signal, with the greatest differences between CP and BD spectra observed for the samples with low Cobs(CP). The causes of low CP observability were investigated using the spectral editing technique RESTORE ( REstoration of Spectra via TCH and T One Rho (T1ρH) Editing). Rapid T1ρH relaxation was found to be primarily responsible for the under‐representation of carbonyl carbon, whereas inefficient cross‐polarization was primarily responsible for the under‐representation of aryl carbon in CP spectra. Proton NMR relaxation rates T1H and T1ρH were found to correlate with other NMR properties and also with cropping management. Non‐uniform rates of T1H relaxation in two of the CaHA fractions enabled the generation of proton spin relaxation editing subspectra.

Ring-chain tautomerism in solid-phase erythromycin A: evidence by solid-state NMR

Chemical shift modeling, utilizing the DFT B3LYP/D95** method, provides the spectral assignment of the 35 visible 13C resonances from the solid-phase erythromycin A dihydrate. A new resonance at 110.8 ppm is observed in the high-resolution 13C CP/MAS spectrum upon the application of heat or sample desiccation. With the use of the dipolar-dephasing spectral editing technique, this resonance is identified as a hemiketal carbon and the alternative hypothesis, a conformational change to the anomeric carbon of the desosamine sugar, is ruled out. Hence, the formation of a cyclic hemiketal in erythromycin A while in the solid phase is proven by solid-state NMR. The principal components of the 13C chemical-shift tensor corresponding to this hemiketal are reported. This is the first measurement of hemiketal 13C principal values. The δ 11 and δ 22 components are unique compared to anomeric carbon values reported in the literature.

Efficient CH-group selection and identification in 13C solid-state NMR by dipolar DEPT and 1H chemical-shift filtering.

A new spectral-editing technique for solid-state nuclear magnetic resonance (NMR), based principally on the different dipolar-dephasing properties of CH and CH(2) multiple-quantum (MQ) coherence, yields pure C-H spectra with overall efficiencies of up to 14%. The selection is based on dephasing of methylene heteronuclear MQ coherence by the second proton and can be considered essentially as a solid-state, slow-magic-angle-spinning version of the distortionless enhancement by polarization transfer (DEPT) experiment. A short dipolar transfer and inverse gated decoupling suppress quaternary-carbon resonances, and T(1)-filtering reduces methyl signals. Applications to amorphous polymers with long, flexible sidegroups demonstrate excellent suppression of the signals of partially mobile methylene groups, consistent with simulations and superior to existing methods. CH selection in various model compounds and a humic acid confirms the robust nature and good sensitivity of the technique. Distinction of NCH and CCH groups, which have overlapping (13)C chemical-shift ranges, is achieved by combining dipolar DEPT with (1)H isotropic-chemical-shift filtering. In the humic acid, this permits unequivocal assignment of the methine resonance near 53 ppm to NCH groups.

NMR of a Phospholipid: Modules for Advanced Laboratory Courses

A laboratory project is described that builds upon the NMR experience undergraduates receive in organic chemistry with a battery of NMR experiments that investigate egg phosphatidylcholine (egg PC). This material, often labeled in health food stores as lecithin, is a major constituent of mammalian cell membranes. The NMR experiments may be used to make resonance assignments, to study molecular organization in model membranes, to test the effects of instrumental parameters, and to investigate the physics of nuclear spin systems. A suite of modular NMR exercises is described, so that the instructor may tailor the laboratory sessions to biochemistry, instrumental analysis, or physical chemistry. The experiments include solution-state one-dimensional (1D) 1H, 13C, and 31P experiments; two-dimensional (2D) TOtal Correlated SpectroscopY (TOCSY); and the spectral editing technique of Distortionless Enhancement by Polarization Transfer (DEPT). To demonstrate the differences between solution and solid-state NMR spectroscopy and instrumentation, a second set of experiments generates 1H, 13C, and 31P spectra of egg PC dispersed in aqueous solution, under both static and magic-angle spinning conditions.

Modified Spectral Editing Methods for 13C CP/MAS Experiments in Solids

The spectral editing approach of Zilm and coworkers utilizes polarization, polarization inversion, and spin depolarization methods for enhancing or suppressing NMR spectral lines in solids. The proposed pulse sequences allow nonprotonated C, CH, CH2, and CH3 types of carbon resonances to be separated from one another and identified accordingly. The former method tentatively separates the nonprotonated C and CH3 peaks with a cutoff shift of 35 ppm. This shift is a reasonable demarcation shift for a preponderance of organic molecules, but exceptions do exist that could constitute a serious drawback in a few instances. The new approach separates the nonprotonated C and CH3 carbon peaks unequivocally using modified pulse sequences similar to those of Zilm. Further, both the CH only and CH2 only spectra, respectively, can be acquired directly from combining so called (+) and (−) sequences using different spectral delay periods and pulse parameters. The (+) and the (−) pulse sequences produce signals for the nonprotonated and methyl carbons that have essentially the same amplitude but opposite phases. These spectra, combined with the previously reported CH3 and nonprontonated C only spectra, offer a complete spectral editing technique for solid samples. Examples of these spectral editing methods are provided for 3-methylglutaric acid, fumaric acid monoethyl ester, and two complex natural products: methyl o-methylpodocarpate and 10-deacetylbaccatin III.

A localized double-quantum filter for in vivo detection of taurine.

Noninvasive detection of taurine, an important amino acid involved in numerous physiological processes, by in vivo (1)H magnetic resonance (MR) spectroscopy is complicated by severe overlap of the taurine resonances with those of a number of other metabolites. Unambiguous differentiation of the taurine resonances requires spectral editing. In this study, the development of a localized spectral editing technique based on double-quantum filtering optimized for in vivo detection of taurine is described. The sequence recovers the taurine signal while substantially eliminating overlapping resonances and provides excellent three-dimensional spatial localization. The performance of the sequence is demonstrated both in phantoms and in rat brain in vivo. Magn Reson Med 42:454-460, 1999.

Structure analysis of allyl polymers by high resolution 1H and 13C NMR spectroscopy

1H and 13C NMR spectra of poly allyl acetate, prepared in bulk with initiator benzoyl peroxide, were measured and analysed using spectral editing technique, DEPT, and two-dimensional NMR techniques, COSY and HMQC. Peaks due to end groups resulting from initiation and chain transfer, and triad structures of the main chain were assigned, and an ambiguity in previous assignment corrected. The assignment of the peaks in the spectra of poly(allyl acetate) was extended to the spectra of poly(CR39) prepared after 10% conversion. The peaks were used to estimate different end groups in the polymer structure and degree of polymerization of both polymers. Spectra were also used to estimate cyclization in poly(CR39).

Structural Investigation of the First Stages of Pyrolysis of Si-C-O Preceramic Polymers Containing Si–H Bonds

The polymer-to-glass transformation in the Si-C-O system usually involves cross-linking reactions at the C sites, which transform for example ≡Si–\(\underline {\text{C}} \)H3 sites into \(\underline {\text{C}} \)(Si)4 sites, leading to the formation of a silicon oxycarbide network. Identification of the various C sites that form during pyrolysis under inert atmosphere is rather difficult from 13C MAS-NMR spectra, due to strong overlap of resonance lines, which prevents an accurate determination of the chemical shift values. This paper reports on the use of a spectral editing technique called Inversion Recovery Cross Polarization (IRCP), which, when combined with Cross Polarization (CP) technique, allows us to identify and quantify the formation of Si-\(\underline {\text{C}} \)H2-Si bridges during the early stages of the pyrolytic transformation of a polysiloxane containing Si–CH3 and Si–H groups. Several Si-C-O systems characterized by the same initial number of Si–CH3 bonds but with increasing number of Si–H bonds, have been investigated by MAS-NMR as well as thermogravimetric analysis coupled with mass spectrometry (TG/MS). The Si—H bonds play clearly an active role in the insertion of C atoms within the silica network.

CP/MAS [formula omitted] spectral editing of dried pine leaves

The recently developed CP/MAS 13 C spectral editing technique is applied to the study of the structure of the dried Australian pine leaves. Subspectra of quaternary carbon C, methenyl CH, methylene CH 2 and methyl CH 3 for Australian pine leaves have been obtained. Simple formulae for spectral editing are proposed.