SQUID-Detected Magnetic Resonance Imaging in Microtesla Magnetic Fields

We describe studies of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) of liquid samples at room temperature in microtesla magnetic fields. The nuclear spins are prepolarized in a strong transient field. The magnetic signals generated by the precessing spins, which range in frequency from tens of Hz to several kHz, are detected by a low-transition temperature dc SQUID (Superconducting QUantum Interference Device) coupled to an untuned, superconducting flux transformer configured as an axial gradiometer. The combination of prepolarization and frequency-independent detector sensitivity results in a high signal-to-noise ratio and high spectral resolution (～1 Hz) even in grossly inhomogeneous magnetic fields. In the NMR experiments, the high spectral resolution enables us to detect the 10-Hz splitting of the spectrum of protons due to their scalar coupling to a ³¹P nucleus. Furthermore, the broadband detection scheme combined with a non-resonant field-reversal spin echo allows the simultaneous observation of signals from protons and ³¹P nuclei, even though their NMR resonance frequencies differ by a factor of 2.5. We extend our methodology to MRI in microtesla fields, where the high spectral resolution translates into high spatial resolution. We demonstrate two-dimensional images of a mineral oil phantom and slices of peppers, with a spatial resolution of about 1 mm. We also image an intact pepper using slice selection, again with 1-mm resolution. In further experiments we demonstrate T₁-contrast imaging of a water phantom, some parts of which were doped with a paramagnetic salt to reduce the longitudinal relaxation time T₁. Possible applications of this MRI technique include screening for tumors and integration with existing multichannel SQUID systems for brain imaging.     

Tailored magnetic nanoparticles for direct and sensitive detection of biomolecules in biological samples

We developed nanoparticles with tailored magnetic properties for direct and sensitive detection of biomolecules in biological samples in a single step. Thermally blocked nanoparticles obtained by thermal hydrolysis, functionalized with specific ligands, are mixed with sample solutions, and the variation of the magnetic relaxation due to surface binding is used to detect the presence of biomolecules. The binding significantly increases the hydrodynamic volume of nanoparticles, thus changing their Brownian relaxation frequency which is measured by a specifically developed AC susceptometer. The system was tested for the presence of Brucella antibodies, a dangerous pathogen causing brucellosis with severe effects both on humans and animals, in serum samples from infected cows and the surface of the nanoparticles was functionalized with lipopolysaccharides (LPS) from Brucella abortus. The hydrodynamic volume of LPS-functionalized particles increased by 25-35% as a result of the binding of the antibodies, measured by changes in the susceptibility in an alternating magnetic field. The method has shown high sensitivity, with detection limit of 0.05 microg x mL(-1) of antibody in the biological samples without any pretreatment. This magnetic-based assay is very sensitive, cost-efficient, and versatile, giving a direct indication whether the animal is infected or not, making it suitable for point-of-care applications. The functionalization of tailored magnetic nanoparticles can be modified to suit numerous homogeneous assays for a wide range of applications.     

A Ferromagnetic Shimming Method for NMR/MRI Magnets Adopting Two Consecutive Optimization Techniques: Linear?Programming and Evolution Strategy

Shimming is very important for nuclear magnetic resonance (NMR) magnets because image resolution is highly dependent on the homogeneity of the magnetic field. There are two types of shimming: active and passive. Active shimming is done using coils with adjustable current. Passive shimming involves pieces of steel with good magnetic qualities. The steel pieces are placed near a superconducting magnet. They are magnetized and produce their own magnetic field. Additional magnetic fields (produced by coils or steel) add to the original magnetic field of the superconducting magnet in such a way that the total field becomes more homogeneous. In this paper, we developed a passive shimming method adopting consecutive optimization techniques, i.e., linear programming (LP) and evolution strategy (ES). The LP is relatively fast and mostly guarantees a global minimum for a linear problem, whereas the ES is easy to formulate and can digitize design variables. So we suggested an optimization method combining both the LP and the ES consecutively for passive shimming of NMR magnets.     

NMR-based biosensing with optimized delivery of polarized 129Xe to solutions

Laser-enhanced (LE) 129Xe nuclear magnetic resonance (NMR) is an exceptional tool for sensing extremely small physical and chemical changes; however, the difficult mechanics of bringing polarized xenon and samples of interest together have limited applications, particularly to biological molecules. Here we present a method for accomplishing solution 129Xe biosensing based on flow (bubbling) of LE 129Xe gas through a solution in situ in the NMR probe, with pauses for data acquisition. This overcomes fundamental limitations of conventional solution-state LE 129Xe NMR, e.g., the difficulty in transferring hydrophobic xenon into aqueous environments, and the need to handle the sample to refresh LE 129Xe after an observation pulse depletes polarization. With this new method, we gained a factor of >100 in sensitivity due to improved xenon transfer to the solution and the ability to signal average by renewing the polarized xenon. Polarized xenon in biosensors was detected at very low concentrations, 相似文献   

Three-dimensional multiexcitation magnetoacoustic tomography with magnetic induction

Magnetoacoustic tomography with magnetic induction (MAT-MI) is a hybrid imaging modality proposed to image electrical conductivity contrast of biological tissue with high spatial resolution. This modality combines magnetic excitations with ultrasound detection through the Lorentz force based coupling mechanism. However, previous studies have shown that MAT-MI method with single type of magnetic excitation can only reconstruct the conductivity boundaries of a sample. In order to achieve more complete conductivity contrast reconstruction, we proposed a multiexcitation MAT-MI approach. In this approach, multiple magnetic excitations using different coil configurations are applied to the object sequentially and ultrasonic signals corresponding to each excitation are collected for conductivity image reconstruction. In this study, we validate the new multiexcitation MAT-MI method for three-dimensional (3D) conductivity imaging through both computer simulations and phantom experiments. 3D volume data are obtained by utilizing acoustic focusing and cylindrical scanning under each magnetic excitation. It is shown in our simulation and experiment results that with a common ultrasound probe that has limited bandwidth we are able to correctly reconstruct the 3D relative conductivity contrast of the imaging object. As compared to those conductivity boundary images generated by previous single-excitation MAT-MI, the new multiexcitation MAT-MI method provides more complete conductivity contrast reconstruction, and therefore, more valuable information in possible clinical and research applications.     

Estimating intravoxel fiber architecture using constrained compressed sensing combined with multitensor adaptive smoothing

In diffusion magnetic resonance imaging (dMRI), the accuracy of fiber tracking and analysis depends directly on that of intravoxel fiber architecture reconstruction. Several methods have been proposed that estimate intravoxel fiber architecture using low angular resolution acquisitions owing to their shorter acquisition time and relatively low b‐values. But these methods are highly sensitive to noise. We propose an approach to estimating intravoxel fiber architecture in low angular resolution dMRI. The method consists in using a constrained compressed sensing (CCS) method, also known as crossing fiber angular resolution of intravoxel architecture (CFARI) technique, in combination with multitensor adaptive smoothing in which a diffusion‐weighted (DW) image smoothing scheme is constructed according to the properties of the multitensor field estimated using CFARI. The results on synthetic, physical phantom and real brain DW images show that the proposed method is able to better resolve fiber architectures while correctly preserving image edge information, which provides a new tool for investigating the microstructures of biological tissues and for fiber tractography. © 2015 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 25, 285–296, 2015     

"Add to subtract": a simple method to remove complex background signals from the 1H nuclear magnetic resonance spectra of mixtures

Because of its highly reproducible and quantitative nature and minimal requirements for sample preparation or separation, (1)H nuclear magnetic resonance (NMR) spectroscopy is widely used for profiling small-molecule metabolites in biofluids. However (1)H NMR spectra contain many overlapped peaks. In particular, blood serum/plasma and diabetic urine samples contain high concentrations of glucose, which produce strong peaks between 3.2 ppm and 4.0 ppm. Signals from most metabolites in this region are overwhelmed by the glucose background signals and become invisible. We propose a simple "Add to Subtract" background subtraction method and show that it can reduce the glucose signals by 98% to allow retrieval of the hidden information. This procedure includes adding a small drop of concentrated glucose solution to the sample in the NMR tube, mixing, waiting for an equilibration time, and acquisition of a second spectrum. The glucose-free spectra are then generated by spectral subtraction using Bruker Topspin software. Subsequent multivariate statistical analysis can then be used to identify biomarker candidate signals for distinguishing different types of biological samples. The principle of this approach is generally applicable for all quantitative spectral data and should find utility in a variety of NMR-based mixture analyses as well as in metabolite profiling.     

The magnetic properties of nanocrystalline CoLa0.1Fe1.9O4 ferrite under an external AC magnetic field

CoLa_0.1Fe_1.9O₄ ferrite nanocrystal was synthesized under an induced AC magnetic field by the emulsion method. From XRD pattern, it is shown that all the samples are cubic structure of the spinel ferrite. The morphology of samples synthesized under an induced AC magnetic field was flake-like in shape from TEM image. Both the strength and acting time of external magnetic field influence the crystallite sizes of samples. Magnetic properties of samples were measured by vibrating samples magnetometer (VSM). The changing morphology of sample when an external magnetic field was applied, which might be responsible for the low magnetic properties.     

NMR of room temperature samples with a flux-locked dc SQUID

Superconducting quantum interference devices (SQUIDs) are the most sensitive detectors of magnetic fields. Since SQUIDs detect the magnetic flux rather than its rate of change, they can be used to great advantage to measure nuclear magnetic resonance (NMR) signals at low fields and frequencies. We have used a dc (direct-current) SQUID operated in flux-locked mode to significantly improve upon our previous low-field NMR results performed using an RF (radio-frequency) SQUID. The increase in sensitivity gained by using the dc SQUID has helped in reducing the signal acquisition time by a factor of more than 100 compared with our earlier measurements using an RP SQUID. We have also obtained a simple one-dimensional T₁-contrasted NMR image of a two-component sample consisting of mineral oil and tap water at room temperature. Our results highlight the sensitivity of the SQUID as an NMR detector and the promise of using SQUIDs in NMR imaging at low fields for both medical applications and for materials' nondestructive evaluation     

Observation of a Possible Metallic State Induced by a Parallel Magnetic Field in Superconducting Au0.7In0.3 Samples With Very Low Normal-state Sheet Resistance

We report the observation of an apparent metallic state induced by a parallel magnetic field in Au_0.7In_0.3 samples with very low normal-state sheet resistance. These samples can be modeled as a random array of superconductor-normal metal-superconductor (SNS) junctions. For both the thin planar and cylindrical films, the magnetic field was applied parallel to the substrate of the sample and measurement currents. For the mesoscopic rings, however, a perpendicular field was used. Our electrical transport and tunneling measurements suggest that the samples consist of superconducting In-rich islands not linked by Josephson coupling in the metallic state. The physical origin of the metallic state is discussed.      

A Method for Improving CNN-Based Image Recognition Using DCGAN

Image recognition has always been a hot research topic in the scientific community and industry. The emergence of convolutional neural networks(CNN) has made this technology turned into research focus on the field of computer vision, especially in image recognition. But it makes the recognition result largely dependent on the number and quality of training samples. Recently, DCGAN has become a frontier method for generating images, sounds, and videos. In this paper, DCGAN is used to generate sample that is difficult to collect and proposed an efficient design method of generating model. We combine DCGAN with CNN for the second time. Use DCGAN to generate samples and training in image recognition model, which based by CNN. This method can enhance the classification model and effectively improve the accuracy of image recognition. In the experiment, we used the radar profile as dataset for 4 categories and achieved satisfactory classification performance. This paper applies image recognition technology to the meteorological field.     

Method for determining molar concentrations of metabolites in complex solutions from two-dimensional 1H-13C NMR spectra

One-dimensional (1D) (1)H nuclear magnetic resonance (NMR) spectroscopy is used extensively for high-throughput analysis of metabolites in biological fluids and tissue extracts. Typically, such spectra are treated as multivariate statistical objects rather than as collections of quantifiable metabolites. We report here a two-dimensional (2D) (1)H-(13)C NMR strategy (fast metabolite quantification, FMQ, by NMR) for identifying and quantifying the approximately 40 most abundant metabolites in biological samples. To validate this technique, we prepared mixtures of synthetic compounds and extracts from Arabidopsis thaliana, Saccharomyces cerevisiae, and Medicago sativa. We show that accurate (technical error 2.7%) molar concentrations can be determined in 12 min using our quantitative 2D (1)H-(13)C NMR strategy. In contrast, traditional 1D (1)H NMR analysis resulted in 16.2% technical error under nearly ideal conditions. We propose FMQ by NMR as a practical alternative to 1D (1)H NMR for metabolomics studies in which 50-mg (extract dry weight) samples can be obtained.     

Demagnetization effect of rectangular and ring-shaped samples madeof electrical sheets placed in a stationary magnetic field

The method of summation used for calculating magnetic-field strength is applied to determine the demagnetization coefficient of rectangular and ring-shaped samples made of an anisotropic electrical sheet and of isotropic silicon and silicon-free sheets. The calculations refer to a standard strip used in an Epstein test (of its shortening and contraction) and to the sample which is usually placed in an anisometer, i.e. in a homogeneous external magnetic field. Changes in the demagnetization coefficient are determined for different crystallographic orientation in the above-mentioned sheets. The relation between the magnetization direction of the ring-shaped sample and its demagnetization is affected. In the case of electrical steel strips, the results allow the determination of the real magnetization characteristics for the sample     

Magnetic field measurement near a superconducting film using a 2-dimensional field-dependence of Josephson current through a Nb tunnel junctions sensor

Two-dimensional (2-D) magnetic field dependences of Niobium/niobium tunnel junction current Ic were first used in order to measure the magnetic field near the superconducting film. The 2-D magnetic field dependences of superconducting Josephson current Ic through the niobium/niobium tunnel junction can be changed by the external magnetic field. So, we measured the magnetic field using this superconducting tunnel junction fabricated by DC-magnetron apparatus as a magnetic sensor. The 2-D magnetic field dependences of Ic through the junction without and with the Nb thin-film sample were compared. With the Nb thin-film sample, extension of the characteristics in the perpendicular direction Hz to the sample was observed because of the Meissner effect of the superconducting thin-film sample. Moreover, the magnetic field Hz perpendicular to the Nb thin-film sample has been added in the triangle shape as a following sequence: (0)-(1000)-(0)-(2000)-(0)-(3000)-(0)-(4000)-(0)-(5000 A/m)-(0). Significant changes in the measured Ic-H (Hy,Hz) characteristics were observed above the certain value of Hz > 3000 A/m. We consider the shift of the measured Ic-H dependence in the Hz minus direction occurred because of the flux quanta were trapped in the sample superconducting niobium film after the Hz value had been added greater than 3000 A/m.     

Towards Single Biomolecule Imaging via Optical Nanoscale Magnetic Resonance Imaging

Nuclear magnetic resonance (NMR) spectroscopy is a physical marvel in which electromagnetic radiation is charged and discharged by nuclei in a magnetic field. In conventional NMR, the specific nuclei resonance frequency depends on the strength of the magnetic field and the magnetic properties of the isotope of the atoms. NMR is routinely utilized in clinical tests by converting nuclear spectroscopy in magnetic resonance imaging (MRI) and providing 3D, noninvasive biological imaging. While this technique has revolutionized biomedical science, measuring the magnetic resonance spectrum of single biomolecules is still an intangible aspiration, due to MRI resolution being limited to tens of micrometers. MRI and NMR have, however, recently greatly advanced, with many breakthroughs in nano‐NMR and nano‐MRI spurred by using spin sensors based on an atomic impurities in diamond. These techniques rely on magnetic dipole–dipole interactions rather than inductive detection. Here, novel nano‐MRI methods based on nitrogen vacancy centers in diamond are highlighted, that provide a solution to the imaging of single biomolecules with nanoscale resolution in‐vivo and in ambient conditions.     

Development of a Thin Film Magnetic Moment Reference Material

In this paper we present the development of a magnetic moment reference material for low moment magnetic samples. We first conducted an inter-laboratory comparison to determine the most useful sample dimensions and magnetic properties for common instruments such as vibrating sample magnetometers (VSM), SQUIDs, and alternating gradient field magnetometers. The samples were fabricated and then measured using a vibrating sample magnetometer. Their magnetic moments were calibrated by tracing back to the NIST YIG sphere, SRM 2853.     

Application of magnetic resonance imaging to non-destructive void detection in watermelon

A novel application of magnetic resonance imaging (MRI) is described. The possibility of utilizing MRI for non-destructive quality evaluation of watermelons was studied. In this study, we applied MRI to the detection of internal voids in watermelons. In order to increase the measurement rate, we employed a one-dimensional projection profile method instead of observing a two-dimensional cross-sectional image. The void detection was carried out with this technique over 30 samples and 28 samples were correctly evaluated. The measurement rate was 900 ms per sample, which is an acceptable speed for a sorting machine in the agricultural field.     

Measurement of Specific Absorption Rate and Thermal Simulation for Arterial Embolization Hyperthermia in the Maghemite-Gelled Model

Theoretical models are designed to be applied in hyperthermia treatment planning and to help optimize the surgical treatment procedures. However, it is difficult to obtain every physical parameter of the magnetic field in the living tissue in detail, which is necessary for the calculation. We therefore investigated the simulation of thermal distribution in arterial embolization hyperthermia (AEH) stimulated by the external ferrite-core applicator, and measured specific absorption rate (SAR) of magnetic nanoparticles in the maghemtite-gelled composite model. We used fiber optic temperature sensors (FOTS) to measure the values of SAR, which depend on the microstructure and sizes of particles and the intensity and frequency of external ac magnetic field. Detailed tests indicated that the attenuation of magnetic field was mainly focused on the vertical distance in the aperture of the apparatus. We built a simplified cylindrical phantom containing maghemite particles of 20 nm for thermal field simulation on the basis of SAR measurement. The results of simulation indicated that temperature elevation, induced by nanoparticles inside tumors under ac magnetic field, was dose-dependent. The temperature data acquired from the experiment were compatible with the theoretical results, which demonstrated that the current model considering the inhomogenous heat generation could provide accurate and reliable simulation results and a theoretical and technical basis for controlling temperature during AEH therapy     

Validation of a Time-Harmonic Numerical Model for Solving Magnetic Field in End Region of a Radial-Flux Machine

We present an analysis of the magnetic field in the end region of a radial-flux rotating machine. In numerical simulations, we used three familiar boundary conditions to replace the modeling of the end shields and frame. We made measurements for comparison, and the simulation results were quite consistent with the measurements. Our analysis shows that the eddy current in the end shields and frame influences the magnetic field in the end region slightly and that the use of a homogeneous Neumann boundary condition or a standard impedance boundary condition (SIBC) to replace the end shields and frame can solve the magnetic field in the end region more accurately than a homogeneous Dirichlet boundary condition. Validation by the measurements demonstrates that 3-D current-driven time-harmonic model with suitable boundary conditions can be used to solve the magnetic field in the end region quite accurately.      

Screening current induced magnetic field in REBCO superconducting coil wound by using split wire having intermittent inner split

REBCO-coated conductor having a high critical current is promising for applications in next generation apparatuses such as ultra-high field NMR, high-resolution MRI, and high-precision accelerator. However, it has an important challenge for application in NMR and MRI, due to the single core in REBCO superconducting layer. The single core induces a large screening current-induced magnetic field (screening current field), and it influences the controlling of center field in NMR/MRI magnet. To reduce the screening current field, we have recently developed a split wire having multi-core structure by inner split method (electrical separation by bending stress, ESBS). In experiment, short samples with linear inner split by a large bending stress of 80 N were prepared and tested. However, to fabricate a long length wire with good quality, it is better to use a smaller bending stress. In this study, a low-bending-stress inner split method is used to fabricate superconducting tapes with longitudinal split in their superconducting layer. The fabrication and experimental assessments for the wire and coil are carried out.