Abstract: Abstract Different spatial structures that arise due to rotation around simple bonds without violating the integrity of the molecule (without breaking chemical bonds) are called conformations. 1H nuclear magnetic resonance (NMR) study of the spatial structure of calcium gluconate in the aqueous solution has been carried out. It was shown that molecules of calcium gluconate exist in the form of two conformations: zigzag 1-P and cyclic 3 G +. The results of homonuclear 2D 1H NMR spectroscopy indicate the predominantly zigzag conformation. It was found that the intermolecular hydrogen bonds are formed and the spatial structure of molecules changes at the increase in the solution concentration. The observed concentration behavior of the conformation of calcium gluconate is also associated with the presence of the intramolecular hydrogen bonds –O(C4)H··O(C2). PubDate: 2017-10-01
Abstract: Abstract Norm smoothing is commonly used in nuclear magnetic resonance (NMR) T2 inversion and the choice of a suitable regularization parameter is a key step for obtaining a satisfactory inversion result, which is usually achieved by repeating T2 inversion multiple times. However, a greater number of inversions result in a slower speed for the inversion process. In this paper, we propose a rapid norm smoothing T2 inversion method achieved using a new selection method for the regularization parameter. First, the singular value decomposition (SVD) method is used to calculate singular values of the kernel matrix to compress the echo train data. Subsequently, a suitable regularization parameter is calculated based on the signal-to-noise ratio (SNR) of the echo train and the maximum singular value of the kernel matrix, which avoids the repetitions of the T2 inversion. Finally, a rapid T2 inversion is obtained using the Butler–Reeds–Dawson (BRD) method. Numerical simulation and logging data inversion results show that the new method can rapidly provide reasonable T2 spectra for data with different SNRs and is insensitive to the amount of the compressed data. PubDate: 2017-10-01
Abstract: Abstract The study aimed to introduce a ferritin gene probe into a mouse melanoma model to facilitate longitudinal in vivo monitoring of malignant melanoma via magnetic resonance imaging (MRI), thus creating a new prognostic tool and pharmacodynamic resource. B16 cells transfected with the human ferritin heavy chain (hFTH) and human ferritin light chain (hFTL) were subcutaneously inoculated into the dorsal areas of C57BL/6J mice for xenograft models. These xenograft models of malignant melanoma were monitored using the 4.7-T MRI system. Axial slices were acquired at the xenograft site, using T2-weighted spin-echo and T2*-weighted gradient-echo sequences. In addition, the efficacy of anticancer drugs was evaluated in the xenograft models. The hFTH- and hFTL-transfected B16 cells had significantly lower signal intensities in T2- and T2*-weighted MRI images than did the control group (w/o ferritin transfection). This was grossly correlated with tumor progression and could be visualized. The oregonin and oregonin + dacarbazine (DTIC) treated groups showed greater survival rates than the control and DTIC-only groups. We have developed an effective MRI contrast enhancement method using a ferritin gene probe. It can be applied reliably to evaluate the efficacy of drugs in preclinical and clinical trials, greatly assisting the development of new chemotherapeutics. PubDate: 2017-10-01
Abstract: Abstract Fluid typing in reservoirs is currently based on longitudinal relaxation and/or diffusion contrast method, the latter represented by the dual-TE method which uses two types of Carr–Purcell–Meiboom–Gill (CPMG) echo trains with short and long echo spacings. In this paper, we describe a scheme to enhance efficiency of dual-TE method by combining it with multi-frequency CPMG. We took advantage of the echo spacing in the long-TE pulse sequence and interleaved a second sequence for a different slice in the gaps to obtain information from both slices. Verification experiments were performed with a surface coil in a gradient magnetic field. PubDate: 2017-10-01
Abstract: Abstract The present work involves a comprehensive study to provide a theoretical model of the internal magnetic field gradients, present in paramagnetic shale pores, to explain the main relaxation features observed by nuclear magnetic resonance transversal relaxation measurements. In the systematic analysis process of relaxation data it is necessary to know up to what extent the magnetic field gradients are generated by the logging tool and/or arise internally in the rock due to their paramagnetic impurities content. The physical model to explain the relaxation features is based on the calculation of field gradients in a planar pore with and without relaxatives walls. The results reproduce the features of the relaxation parameters in pores due to paramagnetic and tortuous walls. The mechanism that drives the relaxation process is governed by anomalous diffusion within micro-pores. These relaxation processes arise from the interactions between the protons, belonging to the liquid molecules and the pore walls, whose structure is characterized by both large tortuosity and abundance of paramagnetic impurities, giving rise to local strong time dependent magnetic field gradients. The theoretical results are compared with those obtained experimentally to validate the relaxation model. The experimental data were gathered from a sample belonging to the “Vaca Muerta” formation of the Neuquén basin, Argentina. PubDate: 2017-10-01
Abstract: Abstract Self-calibrating GRAPPA operator gridding (SC-GROG) is a method by which non-Cartesian (NC) data in magnetic resonance imaging (MRI) are shifted to the Cartesian k-space grid locations using the parallel imaging concept of GRAPPA operator. However, gridding with SC-GROG becomes computationally expensive and leads to longer reconstruction time when mapping a large number of NC samples in MRI data to the nearest Cartesian grid locations. This work aims to accelerate the SC-GROG for radial acquisitions in MRI, using massively parallel architecture of graphics processing units (GPUs). For this purpose, a novel implementation of GPU-accelerated SC-GROG is presented, which exploits the inherent parallelism in gridding operations. The proposed method employs the look-up-table (LUT)-based optimized kernels of compute unified device architecture (CUDA), to pre-calculate all the possible combinations of 2D-gridding weight sets and uses appropriate weight sets to shift the NC signals from multi-channel receiver coils at the nearest Cartesian grid locations. In the proposed method, LUTs are implemented to avoid the race condition among the CUDA kernel threads while shifting various NC points to the same Cartesian grid location. Several experiments using 24-channel simulated phantom and (12 and 30 channel) in vivo data sets are performed to evaluate the efficacy of the proposed method in terms of computation time and reconstruction accuracy. The results show that the GPU-based implementation of SC-GROG can significantly improve the image reconstruction efficiency, typically achieving 6× to 30× speed-up (including transfer time between CPU and GPU memory) without compromising the quality of image reconstruction. PubDate: 2017-10-01
Abstract: Abstract Anderson–Weiss–Kubo model of magnetic resonance is reconsidered to bridge the existing gaps in its applications for solutions of fundamental problems of spin dynamics and theory of master equations. The model considers the local field fluctuations as one-dimensional normal random process. We refine the conditions of applicability of perturbation theory to calculate the spin depolarization and phase relaxation. A counterexample is considered to show that in the absence of temporal fluctuations of local fields, perturbation theory is not applicable even qualitatively. It is shown that for slow fluctuations, the behavior of the longitudinal magnetization is simply related to the correlation function of the local field. Quasi-adiabatic losses are estimated. PubDate: 2017-10-01
Abstract: Abstract This paper proposes a new method to determine the permeability of tight sandstone using characteristic parameters of the nuclear magnetic resonance (NMR) transverse relaxation time (T 2) distribution. First, the Swanson parameters (T s ) and Capillary–Parachor parameters (T cp) are calculated as the percolation characteristic parameters (T c) of NMR T 2 distribution. The logarithmic mean (T lm), arithmetic mean (T am), and harmonic mean (T hm) are calculated as the pore structure characteristic parameters (T m) of NMR T 2 distribution. T x , the transverse relaxation time when the value of Y-axis is x% in the normalized accumulated T 2 distribution curve accumulated from long relaxation time part to short relaxation time part, is selected as a characteristic parameter of pore size distribution. Second, different T c, T m, T x , and NMR porosity (T por) values are selected to establish single-, double-, three-, and four- parameter models for estimating permeability. An analysis of the relationships between calculated permeabilities of different models and measured permeability in tight sandstone rocks indicated that the four-parameter model based on T cp, T 40, T am, and T por was the best model. Moreover, this model was superior to the calibrated Timur model and the calibrated SDR model for calculating permeability in tight sandstone reservoirs. PubDate: 2017-10-01
Abstract: Abstract Forbidden transitions are not observed in the continuous-wave electron paramagnetic resonance (EPR) spectrum nor in the free induction decay because, unlike allowed transitions, their coherences have no observable magnetic moment and are spectroscopically silent. Yet, the paramagnetic relaxation described by Redfield theory can cause coherence transfer between any types of transitions. Coherence transfer between allowed transitions is now known to cause noticeable changes in EPR spectra, but coherence transfer involving forbidden transitions has long been considered to be negligible because those coherences are silent and unseen. However, our simulations of a simple model system indicate that coherence transfer with silent transitions can introduce new features into EPR spectra. The EPR-silent coherence of a forbidden transition can be transferred to an allowed transition by paramagnetic relaxation. A silent coherence can have consequences felt in the EPR spectrum. PubDate: 2017-09-21
Abstract: Abstract Parallel magnetic resonance imaging (MRI) (pMRI) uses multiple receiver coils to reduce the MRI scan time. To accelerate the data acquisition process in MRI, less amount of data is acquired from the scanner which leads to artifacts in the reconstructed images. SENSitivity Encoding (SENSE) is a reconstruction algorithm in pMRI to remove aliasing artifacts from the undersampled multi coil data and recovers fully sampled images. The main limitation of SENSE is computing inverse of the encoding matrix. This work proposes the inversion of encoding matrix using Jacobi singular value decomposition (SVD) algorithm for image reconstruction on GPUs to accelerate the reconstruction process. The performance of Jacobi SVD is compared with Gauss–Jordan algorithm. The simulations are performed on two datasets (brain and cardiac) with acceleration factors 2, 4, 6 and 8. The results show that the graphics processing unit (GPU) provides a speed up to 21.6 times as compared to CPU reconstruction. Jacobi SVD algorithm performs better in terms of acceleration in reconstructions on GPUs as compared to Gauss–Jordan method. The proposed algorithm is suitable for any number of coils and acceleration factors for SENSE reconstruction on real time processing systems. PubDate: 2017-09-21
Abstract: Abstract The development of electron paramagnetic resonance (EPR) and magnetic resonance imaging (MRI) over six decades is sketched with an emphasis on the contributions of James S. Hyde. For twenty years starting three years after the first commercial EPR spectrometer was shipped by Varian, he led commercial EPR developments, and then for more than forty years, he led development of instrumentation and biomedical applications of EPR at the Medical College of Wisconsin. It was there that he also made major contributions to MRI, and especially functional MRI. PubDate: 2017-09-21
Abstract: Abstract The use of pressure is an advantageous approach to the study of protein structure and dynamics, because it can shift the equilibrium populations of protein conformations toward higher energy states that are not of sufficient population to be observable at atmospheric pressure. Recently, the Hubbell group at the University of California, Los Angeles, reintroduced the application of high pressure to the study of proteins by electron paramagnetic resonance (EPR) spectroscopy. This methodology is possible using X-band EPR spectroscopy due to advances in pressure intensifiers, sample cells, and resonators. In addition to the commercial availability of the pressure generation and sample cells by Pressure Biosciences Inc., a five-loop–four-gap resonator required for the initial high-pressure EPR spectroscopy experiments by the Hubbell group, and those reported here, was designed by James S. Hyde and built and modified at the National Biomedical EPR Center. With these technological advances, we determined the effect of pressure on the essential periplasmic lipopolysaccharide (LPS) transport protein from Escherichia coli, LptA, and one of its binding partners, LptC. LptA unfolds from the N-terminus to the C-terminus, binding of LPS does not appreciably stabilize the protein under pressure, and monomeric LptA unfolds somewhat more readily than oligomeric LptA upon pressurization to 2 kbar. LptC exhibits a fold and relative lack of stability upon LPS binding similar to LptA, yet adopts an altered, likely monomeric, folded conformation under pressure with only its C-terminus unraveling. The pressure-induced changes likely correlate with functional changes associated with binding and transport of LPS. PubDate: 2017-09-21
Abstract: Abstract The dielectric tube resonator (DTR) for electron paramagnetic resonance spectroscopy is introduced. It is defined as a metallic cylindrical TE011 microwave cavity that contains a dielectric tube centered on the axis of the cylinder. Contour plots of dimensions of the metallic cylinder to achieve resonance at 9.5 GHz are shown for quartz, sapphire, and rutile tubes as a function of wall thickness and average radius. These contour plots were developed using analytical equations and confirmed by finite-element modeling. They can be used in two ways: design of the metallic cylinder for use at 9.5 GHz that incorporates a readily available tube such as a sapphire tube intended for NMR and design of a custom procured tube for optimized performance for specific sample-size constraints. The charts extend to the limiting condition where the dielectric fills the tube. However, the structure at this limit is not a dielectric resonator due to the metal wall and does not radiate. In addition, the uniform field (UF) DTR is introduced. Development of the UF resonator starting with a DTR is shown. The diameter of the tube remains constant along the cavity axis, and the diameter of the cylindrical metallic enclosure increases at the ends of the cavity to satisfy the uniform field condition. This structure has advantages over the previously developed UF TE011 resonators: higher resonator efficiency parameter Λ, convenient overall size when using sapphire tubes, and higher quality data for small samples. The DTR and UF DTR structures fill the gap between free space and dielectric resonator limits in a continuous manner. PubDate: 2017-09-18
Authors:A. Esmaeili; I. R. Vakhitov; I. V. Yanilkin; A. I. Gumarov; B. M. Khaliulin; B. F. Gabbasov; M. N. Aliyev; R. V. Yusupov; L. R. Tagirov Abstract: Abstract Magnetic anisotropies of 20 nm epitaxial film of palladium–iron alloy Pd0.92Fe0.08 grown on the (001) MgO substrate were studied. Ferromagnetic resonance (FMR) spectroscopy and vibrating sample magnetometry (VSM) were exploited to determine magnetic parameters of the film. It was found that the synthesized film reveals cubic anisotropy with tetragonal distortion. The simulated magnetic hysteresis loops, obtained utilizing the magnetic anisotropy constants taken from the FMR spectra analysis, agree well with those measured by VSM. PubDate: 2017-09-15 DOI: 10.1007/s00723-017-0946-1
Authors:A. N. Anisimov; V. A. Soltamov; E. N. Mokhov; P. G. Baranov; G. V. Astakhov; V. Dyakonov Abstract: Abstract A sharp variation of the near infrared photoluminescence intensity for spin-3/2 color centers in hexagonal (4H-, 6H-) and rhombic (15R-) SiC polytypes in the vicinity of level anticrossing (LAC) and cross-relaxation in an external magnetic field at room temperature are observed. This effect can be used for a purely all-optical sensing of the magnetic field with nanoscale spatial resolution. A distinctive feature of the LAC signal is a weak dependence on the magnetic field direction that allows monitoring of the LAC signals in the nonoriented systems, such as powder materials, without need to determine the nanocrystal orientation in the sensing measurements. Furthermore, an LAC-like signal is also observed for the spin color centers (NV centers) in diamond in low magnetic fields with only marginal dependence on the magnetic field direction. This effect is enabled to detect weak magnetic fields using nanodiamond samples in the form of disordered mixture. In addition, the optically detected magnetic resonance and LAC techniques are suggested to serve as a simple method to determine the local stress in nanodiamonds under ambient conditions. PubDate: 2017-09-14 DOI: 10.1007/s00723-017-0938-1
Authors:George A. Rinard; Richard W. Quine; Joseph McPeak; Laura Buchanan; Sandra S. Eaton; Gareth R. Eaton Abstract: Abstract A copper X-band (9.22 GHz) cross-loop resonator has been constructed for use with 4 mm sample tubes. The Q for the two resonators is 380 and 350, respectively. The resonator efficiency is about 1 G per square root of watt. Operation has been demonstrated with measurement of T 1 by saturation recovery for samples of coal and an immobilized nitroxide. PubDate: 2017-09-14 DOI: 10.1007/s00723-017-0945-2
Authors:Nikolay V. Anisimov; Olga S. Pavlova Abstract: Abstract The data of magnetic resonance imaging (MRI) studies include not only grayscale images, but also textual information associated with them —personal data about the patient, parameters of scanning and data processing, etc. This information is stored separately from graphic images. Therefore, the possibility for its correction and loss cannot be excluded. In this paper, the method of generation of marker information on diagnostic images is described. The marker information, as a textual analogue, is entered on the image during an MRI scan and becomes an integral part of the diagnostic material along with the images of anatomical structures. The method is realized by using the selective radiofrequency presaturation of non-scanable slices oriented perpendicularly to the scanned slices. It leads to the formation of bands of reduced signal in the areas of intersections of these slices on images. In this case, the band thicknesses are equal to the thicknesses of non-scanable slices. Different combinations of these bands (marker lines) are formed directly on images and can contain information about MRI studies. This information is determined not only by positions and angle orientations of bands, but also by their thickness, total brightness and brightness distribution in the transverse direction of these bands. The examples of introducing and positioning the marker information in conventional MRI studies are presented. PubDate: 2017-09-13 DOI: 10.1007/s00723-017-0944-3
Authors:L. V. Mingalieva; R. T. Galeev; A. A. Sukhanov; V. K. Voronkova; I. K. Budnikova; G. Novitchi Abstract: Abstract Dimers of Cr3+ ions in compounds [Fe(phen)3][Cr2(OH)(Ac)(nta)2]·6,25H2O (I) and [Fe(bpy)3][Cr2(OH)(Ac)(nta)2]·8H2O (II), temperature dependences of the electron paramagnetic resonance (EPR) spectra of which in the range of 300–12 К are characteristic for dimers with strong antiferromagnetic exchange interaction are studied by the EPR method in the X-band. The anisotropy of the spin–spin interaction is estimated from fitting spectra corresponding to the multiplet with S = 2 to model spectra. It is shown that the tensor of the anisotropic spin–spin interaction considerably differs from that of the dipole–dipole contribution. Signals from the multiplet with S = 1 were also separated for the compound II that made it possible to estimate the fine structure parameter of the Cr3+ ion. Features of the variation of the integral intensity of EPR spectra are observed at temperatures below 6 К for I and 7 К for II, which are explained by the decrease in the value of the isotropic exchange between chromium ions in dimers. Only the intensity of spectrum changes and its shape is completely preserved. PubDate: 2017-09-11 DOI: 10.1007/s00723-017-0937-2
Abstract: Abstract Calibrations are given to extract orientation order parameters from pseudo-powder electron paramagnetic resonance line shapes of 14N-nitroxide spin labels undergoing slow rotational diffusion. The nitroxide z-axis is assumed parallel to the long molecular axis. Stochastic-Liouville simulations of slow-motion 9.4-GHz spectra for molecular ordering with a Maier–Saupe orientation potential reveal a linear dependence of the splittings, \(2A_{\hbox{max} }\) and \(2A_{\hbox{min} }\) , of the outer and inner peaks on order parameter \(S_{zz}\) that depends on the diffusion coefficient \(D_{{{\text{R}} \bot }}\) which characterizes fluctuations of the long molecular axis. This results in empirical expressions for order parameter and isotropic hyperfine coupling: \(S_{zz} = s_{1} \times \left( {A_{\hbox{max} } - A_{\hbox{min} } } \right) - s_{o}\) and \(a_{o}^{{}} = \tfrac{1}{3}\left( {f_{\hbox{max} } A_{\hbox{max} } + f_{\hbox{min} } A_{\hbox{min} } } \right) + \delta a_{o}\) , respectively. Values of the calibration constants \(s_{1}\) , \(s_{\text{o}}\) , \(f_{\hbox{max} }\) , \(f_{\hbox{min} }\) and \(\delta a_{o}\) are given for different values of \(D_{{{\text{R}} \bot }}\) in fast and slow motional regimes. The calibrations are relatively insensitive to anisotropy of rotational diffusion \((D_{{{\text{R}}//}} \ge D_{{{\text{R}} \bot }} )\) , and corrections are less significant for the isotropic hyperfine coupling than for the order parameter. PubDate: 2017-09-09 DOI: 10.1007/s00723-017-0940-7
Abstract: Abstract A basic model of magnetic resonance is considered. The model takes into account external static and orthogonal to it rotating magnetic fields together with fluctuating (local) field directed along the static field. The local field is considered as smooth normal stochastic process. New solutions for longitudinal relaxation are obtained in the region of adiabatic slow fluctuations and nonadiabatic losses are estimated. PubDate: 2017-09-08 DOI: 10.1007/s00723-017-0939-0
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