Residual Water Signal Research Articles

Application of a 1H brain MRS benchmark dataset to deep learning for out-of-voxel artifacts

Abstract Neural networks are potentially valuable for many of the challenges associated with MRS data. The purpose of this manuscript is to describe the AGNOSTIC dataset, which contains 259,200 synthetic 1H MRS examples for training and testing neural networks. AGNOSTIC was created using 270 basis sets that were simulated across 18 field strengths and 15 echo times. The synthetic examples were produced to resemble in vivo brain data with combinations of metabolite, macromolecule, residual water signals, and noise. To demonstrate the utility, we apply AGNOSTIC to train two Convolutional Neural Networks (CNNs) to address out-of-voxel (OOV) echoes. A Detection Network was trained to identify the point-wise presence of OOV echoes, providing proof of concept for real-time detection. A Prediction Network was trained to reconstruct OOV echoes, allowing subtraction during post-processing. Complex OOV signals were mixed into 85% of synthetic examples to train two separate CNNs for the detection and prediction of OOV signals. AGNOSTIC is available through Dryad, and all Python 3 code is available through GitHub. The Detection network was shown to perform well, identifying 95% of OOV echoes. Traditional modeling of these detected OOV signals was evaluated and may prove to be an effective method during linear-combination modeling. The Prediction Network greatly reduces OOV echoes within FIDs and achieved a median log10 normed-MSE of—1.79, an improvement of almost two orders of magnitude.

Multi-echo single-shot spectroscopy combined with simultaneous 2D model fitting for fast and accurate measurement of metabolite-specific concentrations and T2 relaxation times.

The purpose of the current study was to develop a novel single-voxel MR spectroscopy acquisition scheme to simultaneously determine metabolite-specific concentrations and transverse relaxation times within realistic clinical scan times. Partly truncated multi-TE data are acquired as an echo train in a single acquisition (multi-echo single-shot [MESS]). A 2D multiparametric model fitting approach combines truncated, low-resolved short TE data with fully sampled, highly resolved, longer TE data to yield concentration and T2 estimates for major brain metabolites simultaneously. Cramer-Rao lower bounds (CRLB) are used as a measure of performance. The novel scheme was compared with traditional multi-echo multi-shot methods. In silico, in vitro, and in vivo experiments support the findings. MESS schemes, requiring only 2 min 12s for the acquisition of three echo times, provide valid concentration and relaxation estimates for multiple metabolites and outperform traditional methods for simultaneous determinations of metabolite-specific T2 s and concentrations, with improvements ranging from 5% to 30% for T2 s and from 10% to 50% for concentrations. However, substantial unsuppressed residual water signals may hamper the method's reproducibility, as observed in an initial experiment setup that prioritizes short TEs with severely truncated acquisition for the benefit of signal-to-noise ratio (SNR). Nevertheless, CRLB have been confirmed to be well suited as design criteria, and within-session repeatability approaches CRLB when residual water is removed in postprocessing by exploiting longer and less truncated data recordings. MESS MRS combined with 2D model fitting promises comparable accuracy, increased precision, or inversely shorter experimental times compared with traditional approaches. However, the optimal design must be investigated as a trade-off between SNR, the truncation factor, and TE batch selections, all of which influence the robustness of estimations.

Water-suppression cycling 3-T cardiac 1 H-MRS detects altered creatine and choline in patients with aortic or mitral stenosis.

Cardiac proton spectroscopy (1H‐MRS) is widely used to quantify lipids. Other metabolites (e.g. creatine and choline) are clinically relevant but more challenging to quantify because of their low concentrations (approximately 10 mmol/L) and because of cardiac motion. To quantify cardiac creatine and choline, we added water‐suppression cycling (WSC) to two single‐voxel spectroscopy sequences (STEAM and PRESS). WSC introduces controlled residual water signals that alternate between positive and negative phases from transient to transient, enabling robust phase and frequency correction. Moreover, a particular weighted sum of transients eliminates residual water signals without baseline distortion. We compared WSC and the vendor's standard ‘WET’ water suppression in phantoms. Next, we tested repeatability in 10 volunteers (seven males, three females; age 29.3 ± 4.0 years; body mass index [BMI] 23.7 ± 4.1 kg/m2). Fat fraction, creatine concentration and choline concentration when quantified by STEAM‐WET were 0.30% ± 0.11%, 29.6 ± 7.0 μmol/g and 7.9 ± 6.7 μmol/g, respectively; and when quantified by PRESS‐WSC they were 0.30% ± 0.15%, 31.5 ± 3.1 μmol/g and 8.3 ± 4.4 μmol/g, respectively. Compared with STEAM‐WET, PRESS‐WSC gave spectra whose fitting quality expressed by Cramér‐Rao lower bounds improved by 26% for creatine and 32% for choline. Repeatability of metabolite concentration measurements improved by 72% for creatine and 40% for choline. We also compared STEAM‐WET and PRESS‐WSC in 13 patients with severe symptomatic aortic or mitral stenosis indicated for valve replacement surgery (10 males, three females; age 75.9 ± 6.3 years; BMI 27.4 ± 4.3 kg/m2). Spectra were of analysable quality in eight patients for STEAM‐WET, and in nine for PRESS‐WSC. We observed comparable lipid concentrations with those in healthy volunteers, significantly reduced creatine concentrations, and a trend towards decreased choline concentrations. We conclude that PRESS‐WSC offers improved performance and reproducibility for the quantification of cardiac lipids, creatine and choline concentrations in healthy volunteers at 3 T. It also offers improved performance compared with STEAM‐WET for detecting altered creatine and choline concentrations in patients with valve disease.

Calibration-free regional RF shims for MRS.

Achieving a desired RF transmit field ( ) in small regions of interest is critical for single-voxel MRS at ultrahigh field. Radio-frequency (RF) shimming, using parallel transmission, requires mapping and optimization, which limits its ease of use. This work aimed to generate calibration-free RF shims for predefined target regions of interest, which can be applied to any participant, to produce a desired absolute magnitude (| |). The RF shims were found offline by joint optimization on a database comprising maps from 11 subjects, considering regions of interest in occipital cortex, hippocampus and posterior cingulate, as well as whole brain. The | | achieved was compared with a tailored shimming approach, and MR spectra were acquired using tailored and calibration-free shims in 4 participants. Global and local 10g specific-absorption-rate deposition were estimated using Duke and Ella dielectric models. There was no difference in the mean | | produced using calibration-free versus tailored RF shimming in the occipital cortex (p=.15), hippocampus (p=.5), or posterior cingulate (p=.98), although differences were observed in the RMS error | |. Spectra acquired using calibration-free shims had similar SNR and low residual water signal. Under identical power settings, specific-absorption-rate deposition was lower compared with operating in quadrature mode. For example, the total head specific absorption rate was around 35% less for the occipital cortex. This work demonstrates that static RF shims, optimized offline for small regions, avoid the need for mapping and optimization for each region of interest and participant. Furthermore, power settings may be increased when using calibration-free shims, to better take advantage of RF shimming.

Robust Metabolite Quantification from J-Compensated 2D 1H-13C-HSQC Experiments.

The spectral resolution of 2D H-C heteronuclear single quantum coherence (H-C-HSQC) nuclear magnetic resonance (NMR) spectra facilitates both metabolite identification and quantification in nuclear magnetic resonance-based metabolomics. However, quantification is complicated by variations in magnetization transfer, which among others originate mainly from scalar coupling differences. Methods that compensate for variation in scalar coupling include the generation of calibration factors for individual signals or the use of additional pulse sequence schemes such as quantitative HSQC (Q-HSQC) that suppress the JCH-dependence by modulating the polarization transfer delays of HSQC or, additionally, employ a pure-shift homodecoupling approach in the H dimension, such as Quantitative, Perfected and Pure Shifted HSQC (QUIPU-HSQC). To test the quantitative accuracy of these three methods, employing a 600 MHz NMR spectrometer equipped with a helium cooled cryoprobe, a Latin-square design that covered the physiological concentration ranges of 10 metabolites was used. The results show the suitability of all three methods for the quantification of highly abundant metabolites. However, the substantially increased residual water signal observed in QUIPU-HSQC spectra impeded the quantification of low abundant metabolites located near the residual water signal, thus limiting its utility in high-throughput metabolite fingerprinting studies.

Correcting frequency and phase offsets in MRS data using robust spectral registration.

An algorithm for retrospective correction of frequency and phase offsets in MRS data is presented. The algorithm, termed robust spectral registration (rSR), contains a set of subroutines designed to robustly align individual transients in a given dataset even in cases of significant frequency and phase offsets or unstable lipid contamination and residual water signals. Data acquired by complex multiplexed editing approaches with distinct subspectral profiles are also accurately aligned. Automated removal of unstable lipid contamination and residual water signals is applied first, when needed. Frequency and phase offsets are corrected in the time domain by aligning each transient to a weighted average reference in a statistically optimal order using nonlinear least-squares optimization. The alignment of subspectra in edited datasets is performed using an approach that specifically targets subtraction artifacts in the frequency domain. Weighted averaging is then used for signal averaging to down-weight poorer-quality transients. Algorithm performance was assessed on one simulated and 67 in vivo pediatric GABA-/GSH-edited HERMES datasets and compared with the performance of a multistep correction method previously developed for aligning HERMES data. The performance of the novel approach was quantitatively assessed by comparing the estimated frequency/phase offsets against the known values for the simulated dataset or by examining the presence of subtraction artifacts in the in vivo data. Spectral quality was improved following robust alignment, especially in cases of significant spectral distortion. rSR reduced more subtraction artifacts than the multistep method in 64% of the GABA difference spectra and 75% of the GSH difference spectra. rSR overcomes the major challenges of frequency and phase correction.

Adsorbed and free hydrocarbons in unconventional shale reservoir: A new insight from NMR T1-T2 maps

Abstract Characterizing free and adsorbed hydrocarbon is crucial for the resources assessment and mobility evaluation of shale oil plays. The complex feature of hydrogen-bearing components in shale reservoirs requires new analytical methods to study the occurrences of different states of hydrocarbons. In this study, forty core samples from five shale oil research wells in the Jiyang Depression of China were analyzed using various analytical tools including nuclear magnetic resonance (NMR) T1-T2 mapping, Leco total organic carbon (TOC) analysis, routine and special programmed Rock-Eval pyrolysis, solvent extraction and fractionation, as well as mercury injection capillary pressure (MICP) experiments. Additional experiments were conducted on a powdered shale for NMR T1-T2 maps under four states: as-received, after being dried at 110 °C, after special programmed pyrolysis to 350 °C, and after solvent extraction. The results showed that residual water signals in the NMR T1-T2 map disappeared after being dried at 110 °C. Free oil signals decreased dramatically when the sample was thermally treated to 350 °C, while adsorbed oil signals decreased sharply after solvent extraction. A good accordance was observed between the organic hydrogen T2 spectra and three modes of Rock-Eval pyrograms, representing free hydrocarbons, adsorbed hydrocarbons, and hydrocarbons from kerogen/bitumen decomposition. A positive correlation was also found between the intensity of NMR T1-T2 map signals and the free and adsorbed hydrocarbon contents from geochemical analysis. T2 cut-off values of adsorbed hydrocarbons and free hydrocarbons were determined to be 0.2 ms and 1 ms, respectively. Core samples with a high oil saturation index, porosity, and relative content of hydrocarbons display a low T1/T2 ratio indicative of a high shale oil mobility. As a complementary method to the Rock-Eval analysis, NMR T1-T2 mapping is a non-destructive technique for the characterization of adsorbed and free hydrocarbons at the core scale with limited sample preparation. The results of this study are helpful for NMR characterization of shale reservoirs.

Improved volumetric myelin imaging in human brain using 3D dual echo inversion recovery-prepared UTE with complex echo subtraction.

Inversion recovery-based UTE (IR-UTE) sequences have been proposed to directly image myelin with extremely short (~0.3 ms). In this study, we demonstrate the feasibility of complex echo subtraction to improve 3D IR-UTE imaging of myelin in white matter of the brain in vivo. In IR-UTE imaging, long T2 components in white matter (i.e., water) are suppressed using an adiabatic inversion recovery preparation pulse. Dual echo UTE data acquisition and magnitude echo subtraction are used to suppress the residual white matter and gray matter signals, providing high myelin contrast. Complex echo subtraction may further improve the myelin contrast byreducing the residual long T2 water signal contamination caused by regional T1 variations. To verify the efficacy of the complex subtraction technique, in vivo experiments were performed with 5 non-symptomatic healthy volunteers and 5 multiple sclerosis patients on a 3T clinical MR system. Signal enhancement between the complex subtraction and the magnitude subtraction was introduced to evaluate the improvement. The complex subtraction improved myelin contrast over the magnitude subtraction in both healthy and patient groups, with more fine myelin structures being revealed. The foci of the demyelinated lesion were more clearly detected by complex subtraction. An average signal enhancement of up to 135.9% was achieved with the complex subtraction over the magnitude subtraction. The complex echo subtraction improves 3D IR-UTE morphologic imaging of myelin in white matter of the brain.

Water removal in MR spectroscopic imaging with L2 regularization.

An L2-regularization based postprocessing method is proposed and tested for removal of residual or unsuppressed water signals in proton MR spectroscopic imaging (MRSI) data recorded from the human brain at 3T. Water signals are removed by implementation of the L2 regularization using a synthesized water-basis matrix that is orthogonal to metabolite signals of interest in the spectral dimension. Simulated spectra with variable water amplitude and in vivo brain MRSI datasets were used to demonstrate the proposed method. Results were compared with two commonly-used postprocessing methods for removing water signals. The L2 method yielded metabolite signals that were close to true values for the simulated spectra. Residual/unsuppressed water signals in human brain short- and long-echo time MRSI datasets were efficiently removed by the proposed method allowing good quality metabolite maps to be reconstructed with minimized contamination from water signals. Significant differences of the creatine signal were observed between brain long-echo time MRSI without and with water saturation, attributable to the previously described magnetization transfer effect. With usage of a synthesized water matrix generated based on reasonable prior knowledge about water and metabolite resonances, the L2 method is shown to be an effective way to remove water signals from MRSI of the human brain.

Tailored spiral in-out spectral-spatial water suppression pulses for magnetic resonance spectroscopic imaging.

To develop short water suppression sequences for 7 T magnetic resonance spectroscopic imaging, with mitigation of subject-specific transmit RF field ( B1+) inhomogeneity. Patient-tailored spiral in-out spectral-spatial saturation pulses were designed for a three-pulse WET water suppression sequence. The pulses' identical spatial subpulses were designed using patient-specific B1+ maps and a spiral in-out excitation k-space trajectory. The subpulse train was weighted by a spectral envelope that was root-flipped to minimize peak RF demand. The pulses were validated in in vivo experiments that acquired high resolution magnetic resonance spectroscopic imaging data, using a crusher coil for fast lipid suppression. Residual water signals and MR spectra were compared between the proposed tailored sequence and a conventional WET sequence. Replacing conventional spectrally-selective pulses with tailored spiral in-out spectral-spatial pulses reduced mean water residual from 5.88 to 2.52% (57% improvement). Pulse design time was less then 0.4 s. The pulses' specific absorption rate were compatible with magnetic resonance spectroscopic imaging TRs under 300 ms, which enabled spectra of fine in plane spatial resolution (5 mm) with good quality to be measured in 7.5 min. Tailored spiral in-out spectral-spatial water suppression enables efficient high resolution magnetic resonance spectroscopic imaging in the brain. Magn Reson Med 79:31-40, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Parameter optimization for reproducible cardiac 1 H-MR spectroscopy at 3 Tesla.

To optimize data acquisition parameters in cardiac proton MR spectroscopy, and to evaluate the intra- and intersession variability in myocardial triglyceride content. Data acquisition parameters at 3 Tesla (T) were optimized and reproducibility measured using, in total, 49 healthy subjects. The signal-to-noise-ratio (SNR) and the variance in metabolite amplitude between averages were measured for: (i) global versus local power optimization; (ii) static magnetic field (B0 ) shimming performed during free-breathing or within breathholds; (iii) post R-wave peak measurement times between 50 and 900 ms; (iv) without respiratory compensation, with breathholds and with navigator triggering; and (v) frequency selective excitation, Chemical Shift Selective (CHESS) and Multiply Optimized Insensitive Suppression Train (MOIST) water suppression techniques. Using the optimized parameters intra- and intersession myocardial triglyceride content reproducibility was measured. Two cardiac proton spectra were acquired with the same parameters and compared (intrasession reproducibility) after which the subject was removed from the scanner and placed back in the scanner and a third spectrum was acquired which was compared with the first measurement (intersession reproducibility). Local power optimization increased SNR on average by 22% compared with global power optimization (P = 0.0002). The average linewidth was not significantly different for pencil beam B0 shimming using free-breathing or breathholds (19.1 Hz versus 17.5 Hz; P = 0.15). The highest signal stability occurred at a cardiac trigger delay around 240 ms. The mean amplitude variation was significantly lower for breathholds versus free-breathing (P = 0.03) and for navigator triggering versus free-breathing (P = 0.03) as well as for navigator triggering versus breathhold (P = 0.02). The mean residual water signal using CHESS (1.1%, P = 0.01) or MOIST (0.7%, P = 0.01) water suppression was significantly lower than using frequency selective excitation water suppression (7.0%). Using the optimized parameters an intrasession limits of agreement of the myocardial triglyceride content of -0.11% to +0.04%, and an intersession of -0.15% to +0.9%, were achieved. The coefficient of variation was 5% for the intrasession reproducibility and 6.5% for the intersession reproducibility. Using approaches designed to optimize SNR and minimize the variation in inter-average signal intensities and frequencies/phases, a protocol was developed to perform cardiac MR spectroscopy on a clinical 3T system with high reproducibility. J. Magn. Reson. Imaging 2016;44:1151-1158.

T1 and T2 temperature dependence of female human breast adipose tissue at 1.5 T: groundwork for monitoring thermal therapies in the breast

The T1 and T2 temperature dependence of female breast adipose tissue was investigated at 1.5 T in order to evaluate the applicability of relaxation-based MR thermometry in fat for the monitoring of thermal therapies in the breast. Relaxation times T1 , T2 and T2TSE (the apparent T2 measured using a turbo spin echo readout sequence) were measured in seven fresh adipose breast samples for temperatures from 25 to 65 °C. Spectral water suppression was used to reduce the influence of the residual water signal. The temperature dependence of the relaxation times was characterized. The expected maximum temperature measurement errors based on average calibration lines were calculated. In addition, the heating-cooling reversibility was investigated for two samples. The T1 and T2TSE temperature (T) dependence could be fitted well with an exponential function of 1/T. A linear relationship between T2 and temperature was found. The temperature coefficients (mean ± inter-sample standard deviation) of T1 and T2TSE increased from 25 °C (dT1/dT = 5.35 ± 0.08 ms/°C, dT2TSE/dT = 3.82 ± 0.06 ms/°C) to 65 °C (dT1 /dT = 9.50 ± 0.16 ms/°C, dT2TSE/dT = 7.99 ± 0.38 ms/°C). The temperature coefficient of T2 was 0.90 ± 0.03 ms/°C. The temperature-induced changes in the relaxation times were found to be reversible after heating to 65 °C. Given the small inter-sample variation of the temperature coefficients, relaxation-based MR thermometry appears to be feasible in breast adipose tissue, and may be used as an adjunct to proton resonance frequency shift (PRFS) thermometry in aqueous tissue (glandular + tumor).

Application of ICA to realistically simulated (1)H-MRS data.

Introduction1H-MRS signals from brain tissues capture information on in vivo brain metabolism and neuronal biomarkers. This study aims to advance the use of independent component analysis (ICA) for spectroscopy data by objectively comparing the performance of ICA and LCModel in analyzing realistic data that mimics many of the known properties of in vivo data.MethodsThis work identifies key features of in vivo 1H-MRS signals and presents methods to simulate realistic data, using a basis set of 12 metabolites typically found in the human brain. The realistic simulations provide a much needed ground truth to evaluate performances of various MRS analysis methods. ICA is applied to collectively analyze multiple realistic spectra and independent components identified with our generative model to obtain ICA estimates. These same data are also analyzed using LCModel and the comparisons between the ground-truth and the analysis estimates are presented. The study also investigates the potential impact of modeling inaccuracies by incorporating two sets of model resonances in simulations.ResultsThe simulated fid signals incorporating line broadening, noise, and residual water signal closely resemble the in vivo signals. Simulation analyses show that the resolution performances of both LCModel and ICA are not consistent across metabolites and that while ICA resolution can be improved for certain resonances, ICA is as effective as, or better than, LCModel in resolving most model resonances.ConclusionThe results show that ICA can be an effective tool in comparing multiple spectra and complements existing approaches for providing quantified estimates.

Diffusion-weighted line-scan echo-planar spectroscopic imaging technique to reduce motion artifacts in metabolite diffusion imaging.

Metabolite diffusion is expected to provide more specific microstructural and functional information than water diffusion. However, highly accurate measurement techniques have still not been developed, especially for reducing motion artifacts caused by cardiac pulsation and respiration. We developed a diffusion-weighted line-scan echo-planar spectroscopic imaging (DW-LSEPSI) technique to reduce such motion artifacts in measuring diffusion-weighted images (DWI) of metabolites. Our technique uses line-scan and echo-planar techniques to reduce phase errors induced by such motion during diffusion time. The phase errors are corrected using residual water signals in water suppression for each acquisition and at each spatial pixel specified by combining the line-scan and echo-planar techniques. We apply this technique to a moving phantom and a rat brain in vivo to demonstrate the reduction of motion artifacts in DWI and apparent diffusion coefficient (ADC) maps of metabolites. DW-LSEPSI will be useful for investigating a cellular diffusion environment using metabolites as probes.

Identifying Key Amino Acid Residues That Affect α-Conotoxin AuIB Inhibition of α3β4 Nicotinic Acetylcholine Receptors

α-Conotoxin AuIB is a selective α3β4 nicotinic acetylcholine receptor (nAChR) subtype inhibitor. Its analgesic properties are believed to result from it activating GABAB receptors and subsequently inhibiting CaV2.2 voltage-gated calcium channels. The structural determinants that mediate diverging AuIB activity at these targets are unknown. We performed alanine scanning mutagenesis of AuIB and α3β4 nAChR, homology modeling, and molecular dynamics simulations to identify the structural determinants of the AuIB·α3β4 nAChR interaction. Two alanine-substituted AuIB analogues, [P6A]AuIB and [F9A]AuIB, did not inhibit the α3β4 nAChR. NMR and CD spectroscopy studies demonstrated that [F9A]AuIB retains its native globular structure, so its activity loss is probably due to loss of specific toxin-receptor residue pairwise contacts. Compared with AuIB, the concentration-response curve for inhibition of α3β4 by [F9A]AuIB shifted rightward more than 10-fold, and its subtype selectivity profile changed. Homology modeling and molecular dynamics simulations suggest that Phe-9 of AuIB interacts with a two-residue binding pocket on the β4 nAChR subunit. This hypothesis was confirmed by site-directed mutagenesis of the β4-Trp-59 and β4-Lys-61 residues of loop D, which form a putative binding pocket. AuIB analogues with Phe-9 substitutions corroborated the finding of a binding pocket on the β4 subunit and gave further insight into how AuIB Phe-9 interacts with the β4 subunit. In summary, we identified critical residues that mediate interactions between AuIB and its cognate nAChR subtype. These findings might help improve the design of analgesic conopeptides that selectively "avoid" nAChR receptors while targeting receptors involved with nociception.

Identification of Key Residues Essential for the Structural Fold and Receptor Selectivity within the A-chain of Human Gene-2 (H2) Relaxin

Human gene-2 (H2) relaxin is currently in Phase III clinical trials for the treatment of acute heart failure. It is a 53-amino acid insulin-like peptide comprising two chains and three disulfide bonds. It interacts with two of the relaxin family peptide (RXFP) receptors. Although its cognate receptor is RXFP1, it is also able to cross-react with RXFP2, the native receptor for a related peptide, insulin-like peptide 3. In order to understand the basis of this cross-reactivity, it is important to elucidate both binding and activation mechanisms of this peptide. The primary binding mechanism of this hormone has been extensively studied and well defined. H2 relaxin binds to the leucine-rich repeats of RXFP1 and RXFP2 using B-chain-specific residues. However, little is known about the secondary interaction that involves the A-chain of H2 relaxin and transmembrane exoloops of the receptors. We demonstrate here through extensive mutation of the A-chain that the secondary interaction between H2 relaxin and RXFP1 is not driven by any single amino acid, although residues Tyr-3, Leu-20, and Phe-23 appear to contribute. Interestingly, these same three residues are important drivers of the affinity and activity of H2 relaxin for RXFP2 with additional minor contributions from Lys-9, His-12, Lys-17, Arg-18, and Arg-22. Our results provide new insights into the mechanism of secondary activation interaction of RXFP1 and RXFP2 by H2 relaxin, leading to a potent and RXFP1-selective analog, H2:A(4-24)(F23A), which was tested in vitro and in vivo and found to significantly inhibit collagen deposition similar to native H2 relaxin.

Functional Characterization of the FoxE Iron Oxidoreductase from the Photoferrotroph Rhodobacter ferrooxidans SW2

Photoferrotrophy is presumed to be an ancient type of photosynthetic metabolism in which bacteria use the reducing power of ferrous iron to drive carbon fixation. In this work the putative iron oxidoreductase of the photoferrotroph Rhodobacter ferrooxidans SW2 was cloned, purified, and characterized for the first time. This protein, FoxE, was characterized using spectroscopic, thermodynamic, and kinetic techniques. It is a c-type cytochrome that forms a trimer or tetramer in solution; the two hemes of each monomer are hexacoordinated by histidine and methionine. The hemes have positive reduction potentials that allow downhill electron transfer from many geochemically relevant ferrous iron forms to the photosynthetic reaction center. The reduction potentials of the hemes are different and are cross-assigned to fast and slow kinetic phases of ferrous iron oxidation in vitro. Lower reactivity was observed at high pH and may contribute to prevent ferric iron precipitation inside or at the surface of the cell. These results help fill in the molecular details of a metabolic process that likely contributed to the deposition of precambrian banded iron formations, globally important sedimentary rocks that are found on every continent today.

Novel determination of the total phenolic content in crude plant extracts by the use of 1H NMR of the –OH spectral region

A novel method for the determination of the total phenolic content using 1H NMR spectroscopy in the –OH spectral region is presented. The use of DMSO- d 6, which is an aprotic and strongly hydrogen bonding solvent, allows the “appearance” of the relative sharp resonances of phenolic hydroxyl protons in the region of 8–14 ppm. The determination of the total phenolic –OH content requires three steps: (i) a 1D 1H NMR spectrum is obtained in DMSO- d 6; (ii) a subsequent 1D 1H NMR spectrum is recorded with irradiation of the residual water signal which results in the elimination or reduction of the phenolic –OH groups, due to proton exchange; and (iii) 1D 1H NMR spectra are recorded with the addition of a progressively increased amount of salt, NaHCO 3, which results in extensive linebroadening of the COOH resonances thus allowing the discrimination of the phenolic from the carboxylic acid signals. Integration, with respect to the internal standard TSP- d 4, of the signal resonances between 14 and 8 ppm in spectrum (i) which are either eliminated or reduced in intensity in steps (ii) and (iii) allows the quantitation of the total phenolic content. The method was applied to model compounds, a mixture of them and several extracts of natural products. The results of the proposed 1H NMR method were compared to the Folin-Ciocalteu (FC) reagent method. Additionally, since 1H NMR refers to the total phenolic hydroxyl protons, a reaction factor, A e, is proposed that corresponds to the hydroxyl reactivity. The 1H NMR method is rapid and accurate bearing the inherent advantages of the NMR spectroscopy and can be applied directly in complex extracts. Furthermore, it can be applied in a wide range of matrixes from crude plant extracts and food products to biological samples.

A novel phase and frequency navigator for proton magnetic resonance spectroscopy using water-suppression cycling.

Magnetic resonance spectroscopy is sensitive to movements, in part, because of motion-induced phase and frequency variations that lead to incoherent averaging. For in vivo proton magnetic resonance spectroscopy, the unsuppressed or under-suppressed water signal can be used to restore coherent averaging; however, this approach results in baseline distortions due to the large water peak. Therefore, a novel water-suppression cycling scheme was developed that alternates between positive and negative residual water signal. Using the residual water signal, the method allows for shot-to-shot phase and frequency correction of individual free induction decays and restoration of signal losses due to incoherent averaging, yet near-complete elimination of residual water. It is demonstrated that the residual water signal can be used to restore metabolite peaks in a brain spectrum from a subject who performed intentional head movements. The ability to correct phase and frequency fluctuations during subject motion is vital for use with adaptive motion correction approaches that ensure proper voxel positioning during head movements.

On the measurement of 15N–{ 1H} nuclear Overhauser effects. 2. Effects of the saturation scheme and water signal suppression

Measurement of steady-state 15N–{ 1H} nuclear Overhauser effects forms a cornerstone of most methods to determine protein backbone dynamics from spin-relaxation data, since it is the most reliable probe of very fast motions on the ps–ns timescale. We have, in two previous publications (J. Magn. Reson. 192 (2008) 302–313; J. Am. Chem. Soc. 131 (2009) 6048–6049) reevaluated spin-dynamics during steady-state (or “saturated”) and reference experiments, both of which are required to determine the NOE ratio. Here we assess the performance of several windowed and windowless sequences to achieve effective saturation of protons in steady-state experiments. We also evaluate the influence of the residual water signal due to radiation damping on the NOE ratio. We suggest a recipe that allows one to determine steady-state 15N–{ 1H} NOE’s without artifacts and with the highest possible accuracy.