Vol 50, No 1-3 (2019)

Nuclear magnetic resonance (NMR) spectroscopy has been used to study the structure of the product and possible intermediates in the polymerization of 2-hydroxyethyl methacrylate catalyzed by the oxovanadium (IV) complex. The assumption of the coordination nature of the polymerization is confirmed by noncovalent interactions between monomer and the catalyst, which has been examined by NMR on ¹H, ¹³C, and ¹⁷O nuclei. The catalyst affects remarkably the stereospecificity of the reaction. The resulting polymer with high molecular weight Mn ≈ 200,000 has a predominantly syndiotactic structure; the chain growth is satisfactorily described by the first-order Markov model with the statistical parameters P_r/m = 0.156 and P_m/r = 0.857.

Prior to the advent of nuclear magnetic resonance (NMR) data inversion, a common approach for handling the large amount of raw echo data collected by NMR logging was data compression for improving the inversion speed. A fast compression method with a high compression ratio is required for processing NMR logging data. In this paper, we proposed a hybrid method to compress NMR data based on the window averaging (WA) and principal component analysis (PCA) methods. The proposed method was compared with the WA method and the PCA method in terms of the compression times of simulated one-, two-, and three-dimensional NMR data, the inversion times of compressed echo data, and the accuracy of NMR maps created with and without compression. We processed NMR log data and compared the inversion results with different compression methods. The results indicated that the proposed method with a high compression speed and a high compression ratio can be used for NMR data compression, and its accuracy depended on the precompressed echo number, and it is obvious that the method have practical applications for NMR data processing, especially for multi-dimensional NMR.

The multi-contrast magnetic resonance imaging can provide rich clinical and diagnostic information, but it requires long scanning time in data acquisition. In this paper, we propose a reference guided joint reconstruction method to address this problem. The proposed method both incorporates the location and orientation priors on edge regions from a high-resolution reference image into joint sparsity constraints, enabling to effectively reconstruct high-quality multi-contrast images from the under-sampled k-space data. The alternating direction method of multipliers is used to solve the joint sparsity-promoting optimization problem. In addition, a generalized frame with multiple reference images is developed to further improve the reconstruction performance, and the proposed method in combination with parallel imaging is also demonstrated to analyze the feasibility in the practical multi-channel acquisition of multi-contrast images. The experiments have demonstrated the superiority of our proposed method compared to those existing reconstruction technologies in multi-contrast imaging.

Measuring time constants in multi-exponential decay phenomena is crucial in many areas of knowledge. However, besides the inherent difficulties to the mathematical structure of the problem analysis, noisy experimental data can make the task considerably difficult. One important example is nuclear magnetic resonance (NMR) logging data obtained from measurements of water and hydrocarbons in porous rocks from oil fields. To minimize the uncertainties, it is important to design experiments under controlled conditions. In this paper, we report a systematic study of high (500 MHz) and low (15 MHz)-field NMR \(T_2\) relaxation times performed on artificial sintered sand-glass samples saturated with water. Porosity and permeability were controlled by selecting the range of grains, and then applying a specific sintering temperature protocol to produce samples with different porous sizes, constant porosity, but varying permeability. The structure of porous was verified by microtomography and scanning electron microscopy techniques. Porosity and permeability were measured, respectively, by the free-gas expansion and steady-state methods. We analyze the NMR data using three different approaches: (1) Laplace inversion with optimized regularization based on measured noise level, (2) bi-exponential, and (3) q-exponential nonlinear least-squares. Upon a careful measurement protocol, we report that all methods yield essentially similar \(T_{2}\) distributions.

Silicon rubber insulators (SRIs) are widely used in power transmission lines as line support and as insulation between the line and the tower. Given that the aging of SRIs threatens the safety and stability of power grids, the accurate assessment of the aging status of SRIs is crucial. In this study, a portable unilateral magnetic resonance (UMR) measuring system for the nondestructive testing of the aging status of SRIs was proposed. The proposed NMR measurement system includes a mini UMR sensor and a measurement circuit. Details of the mini UMR sensor structure and low-cost circuit design were discussed. The Carr–Purcell–Meiboom–Gill sequence was used to record the ¹H transverse relaxation curves of SRI sheds. Inverse Laplace transformation was employed to obtain the T₂ distribution, and two peaks in the T₂ distribution curve were observed. The long T₂ component was selected to quantify the aging degree because of its stability compared with the short T₂ component. To eliminate the inaccuracy of measurement introduced by the different chemical structures of SRIs produced by different companies, the aging status of the SRIs was represented by the changes in T₂ between the surface and internal materials of the SRI.

Calix[4]arene sulfonic acid complexes with acetic acid CH₃COOH and its derivatives CCl₃COOH, CF₃COOH were studied by nuclear magnetic resonance (NMR). The formation of guest–host type complexes was shown by magic angle spinning (MAS) NMR and high-resolution NMR techniques. Increase in calixarene molecule conformational flexibility with moisture content rising was observed by ¹³C MAS NMR. Consequently, CCl₃COOH, CF₃COOH molecules vacate calixarene cavity at relative humidity RH > 33%. While the complex with CH₃COOH remains stable up to RH = 64%. The self-diffusion processes were investigated by ¹H pulsed field gradient technique. Spin-echo attenuation curves show non-exponential shape indicating the occurrence of several phases with a different translational mobility. The existence CCl₃COOH, CF₃COOH acid molecules inside the calixarene cavity leads to average self-diffusion coefficient D_s^aver reduction compared with pure calix[4]arene sulfonic acid. The values of D_s^aver for the CH₃COOH complex are close to average self-diffusion coefficient of calix[4]arene sulfonic acid. From D_s^aver proton conductivities σ_calc on the basis of the Nernst–Einstein equation were calculated. Calculated σ_calc and experimental σ_exp conductivities are agreed well in the RH range from 33% to 75%. At low water content (RH = 10%) σ_exp is about one order of magnitude less compare with σ_calc in calixarene and its complexes with CH₃COOH and CCl₃COOH. It may be explained by low conductivity boundary formation at these conditions between grains in process of target sample preparation for conductivity measurement.

In this paper, the distributions of the ¹H nuclear magnetic resonance (NMR) spin–lattice and spin–spin relaxation times are used to characterize the mobility of different sections of macromolecules of aliphatic polyurethanes and the cross-linking density of polymer chains. The NMR relaxometry method with inversion of integral transformation is applied to study the effect of poly (ethylene glycol) and glycerol phosphate calcium on the polymer dynamics.

In this work, a low-field microfluidic nuclear magnetic resonance (NMR) detection device was developed by fabricating a multi-layer microfluidic NMR probe. In combination with biological sensor technology based on immunomagnetic nanoparticles (IMNPs), the microfluidic NMR detection device was used to rapidly distinguish the concentration of target tumor markers. The experimental results show that the concentration of the target tumor markers can be differentiated with high sensitivity and specificity by the rate of the transverse relaxation time change ΔT₂ even with interference from other biomarkers. A good linear relationship between ΔT₂ and the concentration of the target tumor markers was also found, indicating that the microfluidic NMR device could be used for quantitative detection of tumor markers. Finally, the validity of the microfluidic NMR device for detecting target tumor markers was proved by comparison with a commercial cell counter, and the results detected by the two devices have a good consistency with a correlation coefficient of 0.996. In conclusion, the presented low-field microfluidic NMR device is a potential tool for the rapid and accurate quantitative detection of tumor markers.

A 25 mm diameter 250 MHz crossed-loop resonator was designed for rapid scan electron paramagnetic resonance imaging. It has a saddle coil for the driven resonator and a fine wire, loop gap resonator for the sample resonator. There is good separation of E and B fields and high isolation between the two resonators, permitting a wide range of sample types to be measured. Applications to imaging of nitroxide, trityl, and LiPc samples illustrate the utility of the resonator. Using this resonator and a trityl sample the signal-to-noise of a rapid scan absorption spectrum is about 20 times higher than for a first-derivative CW spectrum.

The interaction of sulfadiazine (SDZ) and its main metabolite N-acetyl-SDZ (N-ac-SDZ) with model humic acid was investigated with stable paramagnetic nitroxide spin probes. Leonardite humic acid (LHA) was mixed with laccase to enhance the amount of reactive quinone groups of LHA and then incubated with nitroxide spin-labelled analogs of SDZ and N-ac-SDZ. The labeling at the pyrimidine moiety of SDZ leaves the aniline moiety susceptible to covalent binding to LHA, which is blocked by the N-acetylation. A broadened electron spin resonance (ESR) signal was observed for SDZ, which increased immediately after incubation and indicates strong restriction of the re-orientational motion of the spin probe, i.e., immobilization due covalent binding of the aniline moiety of SDZ to reactive quinone sites of LHA. A fast first-order reaction with a time constant of 17.6 ± 3.4 h of covalent binding was determined. The broadened ESR signal of N-ac-SDZ declined immediately after incubation with LHA and is caused by unspecific sorption to LHA, not by covalent binding. Short time constants of the bound and free SDZ were found for the reduction by the antioxidant sodium ascorbate demonstrating that SDZ and N-ac-SDZ are not physically entrapped by LHA.

The ^63,65Cu nuclear magnetic resonance (NMR) spectra have been obtained in the external magnetic field H₀ = 11.7 T at the temperature range from 20 to 350 K and the static magnetic susceptibility, χ(T), has been measured in single-crystalline CuFeO₂. The temperature dependences of the ^63,65Cu NMR line shifts, K(T), and the magnetic susceptibility, χ(T), can be satisfactorily described by Curie–Weiss law at T > 60 K. It is worth noting that the behavior of K(T) and χ(T) is different below T = 60 K. The deviation of K(T) from the Curie–Weiss law indicates the short-range order at T < 60 K in CuFeO₂.

The state of interfaces in Co/Cu superlattices with various thicknesses of non-magnetic Cu layers (t_cu) has been studied by the methods of nuclear magnetic resonance (NMR) and X-ray reflectometry. The samples glass/Fe(5 nm)/[Co(1.5 nm)/Cu(t_cu)]₁₀/Cr(3 nm) were fabricated by the method of magnetron sputtering on glass substrates under constant current in the ULVAC MPS-4000-C6 device. The ⁵⁹Co NMR spectra were taken in a local magnetic field in the frequency range of 90–240 MHz at 4.2 K in the pulsed NMR spectrometer. The spin echo signal was formed by a sequence of two coherent radio-frequency pulses (τ_p)_x − t_del − (τ_p)_y − t_del – echo forming an alternate magnetic field with the round component amplitude H₁ of about 10 Oe in a resonance coil. It has been shown both by NMR and X-ray reflectometry that the structure of interfaces deteriorates with an increase of the Cu layers thickness, and similar dependences of the parameters characterizing structural imperfection of interfaces were obtained by these two methods.

Determination of the transient water content distribution in porous materials with both swiftness and accuracy during the unsaturated permeability tests seems somewhat difficult. The traditional water content measurement methods using relatively large probes generally, which exhibit inconvenience and inefficiency to some extent, do unavoidably some destructive exercises on the specimens. In this paper, the saturation (water content) distribution in a white Portland cement specimen that had a dry density of 1.35 g/cm³ was measured swiftly and non-destructively by employing the nuclear magnetic resonance (NMR) technology. Unsaturated hydraulic conductivities of the white Portland cement specimen corresponding to different suctions were obtained using the instantaneous profile (IP) method. It appears from the obtained results that under a dry density of 1.35 g/cm³, the unsaturated hydraulic conductivity of the white Portland cement varies between 10⁻¹¹ and 10⁻⁷ m/s; with the decreasing suction, the hydraulic conductivity increases mildly and sharply, respectively, in the high and modest suction ranges, and stalls in the low suction range; and it enjoys both efficiency and preciousness to measure the water content distribution in the specimen with the NMR technology.

Multicoil (MC) B₀ shimming, a new shimming technology developed in the recent years, exhibits unique advantages. Irregularly shaped coils can further improve the shimming effect of the MC, but they increase the difficulty and complexity of MC design. In this paper, the shimming characteristics of MC in C-type permanent magnets are studied. Aiming at improving the efficiency of finding the optimal shape for irregular MC, this paper presents a method that uses genetic algorithm and simulated annealing (GASA) to optimize irregular MC shapes for shimming. By simulating the shimming of the irregular MC of the flat-plate model and shoulder-joint model in C-type permanent magnets, the effects of parameters such as complexity, size, and number of groups of coils are analyzed. The shimming of MC in superconducting magnets and permanent magnets is compared and the optimization efficiencies of the genetic algorithms and genetic–annealing algorithms are compared. The results show that an irregular MC can achieve a better shimming effect for a locally nonuniform B₀ field in a sample boundary region of a C-type permanent magnet. GASA is found to be a more stable and highly efficient optimization method.

Study of two-dimensional nuclear magnetic resonance (NMR) longitudinal and transverse relaxation time (T₁–T₂) responses of tight reservoirs and optimization of T₁–T₂ acquisition parameter are of significance for exploration and development of tight oil and gas reservoirs. In this paper, a tight sandstone digital model was generated using a micro-CT scanning technique, and the random-walk method was modified to simulate the T₁–T₂ measurements in a two-phase fluid-bearing tight sandstone. The echo data of the saturation-recovery Carr–Purcell–Meiboom–Gill pulse sequence were acquired and processed to obtain a T₁–T₂ map. We compared oil–water-bearing tight sandstone T₁–T₂ maps with gas–water-bearing tight sandstone T₁–T₂ maps, and analyzed how fluid types, various degrees of fluid saturation, acquisition parameters, and signal-to-noise ratio (SNR) of NMR data affected T₁–T₂ maps. The research indicated that NMR T₁–T₂ logging is more suitable for identifying gas-bearing reservoirs, rather than oil-bearing reservoirs. NMR-logging acquisition parameters have different influences on various fluid-bearing tight sandstone T₁–T₂ maps. Increasing either the magnetic field gradient or echo spacing leads to a leftward shift of the gas signal, but does not affect the water signal and the oil signal in a T₁–T₂ map; the T₁–T₂ map with a mixed group of wait time is better than that with a long or short group of wait time in providing fluid relaxation information. The NMR data with lower SNR result in stronger divergence of fluid signal in T₁–T₂ map, rendering it more difficult to identify the fluid according to the map, and a data SNR more than 21 is recommended.

The ultra-short TE (UTE) technique has been recently used to investigate lumbar cartilaginous endplates (CEPs). However, parameters of UTE have not been investigated, especially optimal second TE is unclear. The aim of this study was to investigate the use of an optimal second TE with UTE for visualizing CEPs. The subjects included 20 volunteers without LBP who did not undergo lumbar spine surgery. A UTE sequence with fat suppression was used, and TEs were set at 0.16 ms as first TE, and 4.6, 9.2, 13.8, 18.2 ms as second TE. Analyzed images subtracted each second TE image from first TE image. Two researchers measured contrast ratio (CR) between CEPs and vertebral bodies (VBs), intervertebral discs (IVDs). ICCs between two researchers were calculated for CRs (r = 0.924, 0.939). CR between CEP and VB of 13.8 and 18.4 ms was significantly higher than that of other TEs (p < 0.01). CR between CEP and IVD of 9.2 and 13.8 ms was significantly higher than that of other TEs (p < 0.01, 0.05). CEPs were evaluated using subtraction images obtained with UTE. The first TE was 0.16 ms, the optimal second TE was suggested to be 13.8 ms for evaluating human CEPs.

Red Blood Cells (RBCs) are ideally suited as a model system for study of water diffusion in biological tissue. We used a pulsed-field-gradient nuclear magnetic resonance technique to measure the time-dependent self-diffusion coefficient D(t) in water-mouse RBC suspension at different diffusion times. A new method of interpretation of the experimental time dependence of the self-diffusion coefficient D(t) for fluid in heterogeneous media is proposed, and this study presents a new approximation describing water diffusion in such system. Three types of water were determined, which differs according to the self-diffusion coefficients: bulk water, extracellular and intracellular water. The water molecular exchange process among these three water states was investigated. The residence time for mice RBCs was obtained. Intracellular and extracellular water self-diffusion was restricted, and the sizes of restriction regions were 1.95 μm and 6.73 μm with S/V ratio 1.534 μm⁻¹ and 0.44 μm⁻¹, respectively. The cell wall permeability determined from the resident time as 4.7·10⁻⁵ m/s agreed with the permeability 5.4·10⁻⁵ m/s obtained from time dependence of intracellular water self-diffusion coefficient.

In the original publication, the acknowledgment section was not published and it is given below now.