High Static Magnetic Field Research Articles

Cellular disorders induced by high magnetic fields

To evaluate whether static high magnetic fields (HMFs), in the range of 10-17 T, affect the cytoskeleton and cell organization in different types of mammalian cells, including fibroblasts, epithelial cells, and differentiating neurons. Cells were exposed to HMF for 30 or 60 minutes and subsequently assessed for viability. Cytoskeleton arrays and focal adhesions were visualized using immunofluorescence microscopy. Cell exposure to HMF over 10 T in the case of cycling cells, and over 15 T in the case of neurons, affected cell viability, apparently because of cell detachment from culture dishes. In the remaining adherent cells, the organization of actin assemblies was perturbed, and both cell adhesion and spreading were impaired. Moreover, in the case of neurons, exposure to HMF induced growth cone retraction and delayed cell differentiation. Cell exposure to HMF (over 10T and 15 T in the case of cycling cells and neurons, respectively) affects the cell cytoskeleton, with deleterious effects on cell viability, organization, and differentiation. Further studies are needed to determine whether such perturbations, as observed here in cultured cells, have consequences in whole animals.

Shining light on electrons under extreme conditions

Strongly-correlated two-dimensional (2D) electron fluids occur in artificial semiconductor heterostructures of high perfection that are subjected to quantizing magnetic fields. Under conditions of high magnetic fields, low temperatures in the millikelvin range and low electron density, the 2D quantum fluids display dispersive low-energy collective excitations that represent time- and space-dependent oscillations in the charge and/or the orientations of spin. These collective modes manifest fundamental interactions that are responsible for electron correlation. Studies of low-lying collective excitation modes play pivotal roles in the low-temperature phases of the electron liquids and offer venues of studying energetics, coherence, magnetization, instabilities and quantum phase transitions of the 2D system. In 1978 a proposal by Burstein, Pinczuk and Buchner suggested that resonant inelastic light scattering methods would have the sensitivity required to study elementary excitations of 2D electron systems in semiconductors. We review here recent light scattering results obtained from 2D electron fluids in semiconductor quantum structures under extreme conditions of low temperature and large magnetic field. In these experiments, resonant inelastic light scattering methods probe fundamental behaviors due to interactions with a sensitivity that will keep light scattering studies at the frontiers of research of quantum fluids in low dimensional electron systems.

High field magnetic transitions in the mixed holmium–yttrium iron garnetHo0.43Y2.57Fe5O12

High static magnetic field magnetization measurements have been performed up to 23 T onHo0.43Y2.57Fe5O12 single crystals athelium temperature (T = 4.2 K) with fields applied along the three main cubic axes: , and . The change from the spontaneous ferrimagnetic structure in zero magnetic field to the fullyferromagnetic one in high field takes place through several intermediate phases separatedby transitions with step-like magnetization behaviour, but without any observed hysteresis.Using the effective spin Hamiltonian approximation, we show that the general features ofthese transitions can be accounted for by a large magnetocristalline anisotropy of theHo3+ moments of the uniaxial type along the localz axis of each rare-earth site. The model is in better agreement with the experimentsthan its Ising limit, widely used before, but is still unsuccessful in predicting the‘umbrella’ magnetic structures found by previous neutron and NMR experiments.

Effects of high static magnetic field exposure on different DNAs.

The effects of magnetic fields produced by permanent magnets on different DNA sources were investigated in vivo and in vitro. Escherichia coli DNA, plasmid, and amplification products of different lengths were used as the magnetic field target. The in vivo assays did not reveal any DNA alterations following exposure, demonstrating the presence of cell dependent mechanisms, such as the repair system and the buffering action of the heat shock proteins DNA K/J (Hsp 70/40). The in vitro assays displayed interactions between the magnetic field and DNA, revealing principally that magnetic field exposure induces DNA alterations in terms of point mutations. We speculate that the magnetic field can perturb DNA stability interacting with DNA directly or potentiating the activity of oxidant radicals. This genotoxic effect of the magnetic field, however, is minimized in living organisms due to the presence of protective cellular responses.

Mass spectrometry as an emerging tool for systems biology.

Completion of the human genome project has created a blueprint of the genes and proteins necessary to construct and maintain a complex organism. Understanding how the molecular entities of human cells and tissues function will require sophisticated experiments to decipher how these molecules interact as a system. Beyond genes and proteins, metabolites encompass another important level of the system. To understand cellular systems, high-throughput strategies to investigate the functions of proteins and metabolites within the context of the system are necessary. Thus, understanding gene function (and ultimately biological systems) will require methods to broadly and quickly determine how the amounts and forms of various molecules are changing (Figure 1). Three considerations are relevant: (i) broad and unbiased measurement tools; (ii) comprehensive separation techniques; and (iii) informatics to analyze the data. This article will discuss mass spectrometry for the measurement of proteins and metabolites.

Preparation of diamond nanocrystals from catalysed carbon black in a high magneticfield

Under a static high magnetic field of 10 T, diamond-like carbon (DLC) nanocrystals andgraphite-coated n-diamond nanoparticles have been synthesized after a pyrogenation of carbonblack and a nanometre-sized iron catalyst at atmospheric pressure and a temperature of1100 °C.The product is analysed by x-ray diffraction, Raman spectroscopy, transmission electronmicroscopy and electron-probe microanalysis. The average size of the DLC nanopowders isabout 20 nm, and that of the graphite-coated n-diamond particles is about 100 nm. Theyield of diamond is as high as 30%.

Levitation of metallic melt by using the simultaneous imposition of the alternating and the static magnetic fields

This study developed a new levitation method, which used the simultaneous imposition of static and alternating magnetic fields. Dynamic behavior was measured for pure Cu and pure Ni melts levitated by the proposed method. The oscillation due to surface tension and convection in levitated Cu melts were hardly observed at static magnetic fields exceeding 1 T. Only the rotation of this axis parallel to the static magnetic field was observed under high static magnetic fields. The proposed method demonstrated that metallic melt could be statically levitated like a solid sphere. It was also found that stable levitation of paramagnetic Ni melt was rather difficult at static magnetic fields exceeding 5 T, because of the magnetization force.

Neurobehavioral effects among subjects exposed to high static and gradient magnetic fields from a 1.5 Tesla magnetic resonance imaging system--a case-crossover pilot study.

The interactive use of magnetic resonance imaging (MRI) techniques is increasing in operating theaters. A study was performed on 17 male company volunteers to assess the neurobehavioral effects of exposure to magnetic fields from a 1.5 Tesla MRI system. The subjects' neurobehavioral performances on a neurobehavioral test battery were compared in four 1-hr sessions with and without exposure to magnetic fields, and with and without additional movements. Adverse effects were found for hand coordination (-4%, P < 0.05; Pursuit Aiming II) and near visual contrast sensitivity (-16% and -15%, P < 0.10; Vistech 6000). The results from the remaining tests were inconclusive due to a strong learning effect. No additional effect from gradient fields was detected. The results indicate that working near a 1.5 Tesla MRI system may lead to neurobehavioral effects. Further research is recommended, especially in members of operating teams using interactive MRI systems.

Skin temperature changes induced by strong static magnetic field exposure.

High intensity static magnetic fields, when applied to the whole body of the anesthetized rat, have previously been reported to decrease skin temperature. The hypothesis of the present study was that in diamagnetic water, molecules in the air play significant roles in the mechanism of skin temperature decrease. We used a horizontal cylindrical superconducting magnet. The magnet produced 8 T at its center. A thermistor probe was inserted in a subcutaneous pocket of the anesthetized rats to measure skin temperature. Animals (n=10) were placed in an open plastic holder in which the ambient air was free to move in any direction (group I). Animals (n=10) were placed in a closed holder in which the air circulation toward the direction of weak magnetic field was restricted (group II). Each holder was connected to a hydrometer to measure humidity around the animal in the holder. The data acquisition phase consisted of a 5 min baseline interval, followed by inserting the animal together with the holder into the center of the magnet bore for a 5 min exposure and a 5 min postexposure period outside the bore. In group I, skin temperature and humidity around the animal significantly decreased during exposure, followed by recovery after exposure. In group II, skin temperature and humidity did not decrease during the measurement. The skin temperature decrease was closely related to the decrease in humidity around the body of the animal in the holder, and the changes were completely blocked by restricting the air circulation in the direction of the bore entrance. Possible mechanisms responsible for the decrease in skin temperature may be associated with magnetically induced movement of water vapor at the skin surface, leading to skin temperature decrease.

Protocol to determine the optimal intraoral passive shim for minimisation of susceptibility artifact in human inferior frontal cortex

At higher static magnetic field (B 0) strengths (≥3 T), the study of human inferior frontal cortex (IFC) when utilising a variety of MRI techniques is severely hampered by the presence of susceptibility artifacts. This is particularly the case for blood oxygenation level-dependent functional MRI, where large signal voids are generally encountered in the frontal lobes. A previous study described an approach to artifact correction involving a mouth insert consisting of a prototype diamagnetic passive shim [Magn. Reson. Med. 48 (2002), 906]. Here we extend that method by investigating the effect of five different intraoral passive shims on B 0 homogeneity and echoplanar imaging susceptibility artifacts within the brain, and particularly the IFC, of six subjects. The optimal passive shim is shown to be subject- and study-specific, providing an average reduction in mean absolute B 0 offset within the IFC of 57%, along with a concomitant reduction in echoplanar susceptibility artifact. All subjects were at ease while wearing the intraoral shims. A 4-min in vivo protocol to determine the optimal passive shim from the available set, utilising intrinsic structural and B 0 subject data, is described and shown to be accurate and reliable.

Behavioral effects of static high magnetic fields on unrestrained and restrained mice

High-strength static magnetic fields are common tools in clinical imaging, but the behavioral effects are not well characterized. Previous studies on rats showed that fields of 7 T or above produced locomotor circling, conditioned taste aversion (CTA) and c-Fos in vestibular nuclei. To determine the generality of the behavioral effects on a smaller species, we subjected restrained or unrestrained mice to 30-min exposures in a 14.1-T field. Mice were given saccharin immediately prior to magnet or sham exposure on 3 consecutive days. All mice exposed to the magnet developed a CTA, and a significant number displayed tight circling and suppression of rearing. Unrestrained mice exhibited larger effects than restrained mice. These effects, similar to the effects in rats, may be the result of a vestibular disturbance caused by the magnetic field.

NMR-microscopy with TrueFISP at 11.75 T

The purpose of this paper is to demonstrate that a fully balanced gradient echo technique (TrueFISP) can be used for microscopic experiments at high static magnetic field strengths. TrueFISP experiments were successfully performed on homogeneous and inhomogeneous objects at 11.75 T. High-resolution TrueFISP images were obtained from phantoms, plants, formalin-fixed samples, and from an isolated beating rat heart with an in-plane resolution of 78 μm and a slice thickness of 500 μm. The signal-to-noise ratio (SNR) gain of TrueFISP compared to conventional gradient echo or spin echo sequences will allow faster acquisition times or an improvement in spatial resolution for microscopic experiments.

The National High Magnetic Field Laboratory at Los Alamos National Laboratory

Los Alamos National Laboratory (LANL) is the home institution of the Pulsed Field Facility of the National High Magnetic Field Laboratory (NHMFL). The NHMFL laboratories are the only facilities in the US (among a few world-wide) to host qualified users while running strong in-house science programs related to high magnetic field research. At Los Alamos, the NHMFL advances the frontiers of condensed matter physics at extreme conditions of high magnetic field, low temperature and pressure, utilizing start-of-the-art pulsed magnets and unique experimental capabilities. This paper will describe the current and future plans of pulsed magnet technology and science at the NHMFL Pulsed Field Facility at LANL.

Common mode signal rejection methods for MRI: Reduction of cable shield currents for high static magnetic field systems

AbstractThis experiment was conducted to identify common mode currents that flow on the shield of a coaxial cable and to investigate techniques that reduce their effects at high fields of ≥3 Tesla. It will be shown that there are two different methods of common mode interference for two different coil types. First, is the transceive case, where common mode cable shield currents flow as a result of unbalanced loop voltages that couple to the cable shield. In the second case, unwanted common mode signals are induced from the field of the transmission coil onto the cable shield of the receive‐only coil. Two important factors relating to the investigation of common mode signals are danger to the patient from an RF burn and the reduction of the signal‐to‐noise ratio (SNR) because of extra noise being introduced into the MRI environment. It will be shown that through the use of cable shield traps and balun matching circuits, common mode signals can be reduced significantly, increasing patient safety and SNR. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 19B: 1–8, 2003.

Fast, Fully Automated Global and Local Magnetic Field Optimization for fMRI of the Human Brain

The aim of this novel technique is to allow researchers, particularly those operating at high static magnetic field strengths on fMRI applications, to tailor the static magnetic field within the brain. The optimum solution for their experimental needs is reached, utilizing the full potential of the active shims at their disposal. The method for shimming human brain, which incorporates automatic brain segmentation to remove nonbrain tissue from the optimization routine, is presented and validated. The technique is fast, robust, and accurate, achieving the global minimum to a static field homogeneity function of the in vivo brain. Both global and specified local regions of the brain can be selected on which to optimize the shims without requiring skilled intervention. The effectiveness of the automated local shim is demonstrated in an olfactory fMRI study where significant activations in the orbitofrontal cortex were very clear when the above method was employed.

Magnet and wire technology at the K.U.Leuven Pulsed Field laboratory

The K.U.Leuven Pulsed Field Facility is well equipped to accommodate a large variety of experiments in solid-state physics under extreme conditions of high magnetic fields (>50 T) and low temperatures (down to 50 mK). This is supported by an extensive research program focused on the development of advanced concepts and materials for increasing the attainable magnetic fields as well as the reliability and service life of pulsed field coils. Pulsed field magnets with optimized reinforcement as well as multi-composite (MC) wire are under development. The combination of Zylon/spl reg/ for internal reinforcement and strong axial compression has resulted in the development of 75 T class pulsed magnets using soft copper as the conductor material. The MC wire is a new concept; it consists of a glass fiber sleeve braided around a core containing thin conductor wires and reinforcement fibers. The core composition and geometry can be varied to obtain the required properties of strength and electrical conductivity. For a proof of principle, an MC wire was developed with an ultimate tensile strength of 1 GPa and a conductivity of 38% IACS at 300 K.

Availability of NMR microscopic observation of mouse embryo disorder: examination in malformations induced by maternal administration of retinoic acid.

Nuclear magnetic resonance (NMR) microscopy is a magnetic resonance imaging method with enhanced spatial resolution due to the use of a high static magnetic field and high magnetic field gradients. It is considered to be a useful tool for non-invasive and continuous investigation of tissue and organs at the histological level. In this study, we applied NMR microscopy to assessment of morphology in mouse embryos using a developmental disorder model induced by retinoic acid administration. Pregnant mice were given 50 mg/kg all-trans retinoic acid at 8.5 dpc. Embryos were collected at several time points after treatment and examined by NMR microscopy after fixation. Two-dimensional and three-dimensional spin echo sequences were used. Tissue contrast on two-dimensional images changed according to length of repetition time and echo time, and also to developmental stage of embryos. Two-dimensional and three-dimensional images nondestructively demonstrated defects in development of the skeleton and soft tissue, e.g. hypoplasia of vertebrae in the lumbar and tail regions and dysplasia of the spinal cord, in embryos exposed to retinoic acid. These morphological abnormalities were confirmed by conventional assessment after imaging. Although further improvements are required, NMR microscopy will provide a new approach for multi-parameter assessment of embryonic development under physiological and pathological conditions.

Large-scale microwave cavity search for dark-matter axions

We have built and operated a large-scale axion detector, based on a method originally proposed by Sikivie, to search for halo axions. The apparatus consists of a cylindrical tunable high-Q microwave cavity threaded axially by a static high magnetic field. This field stimulates axions that enter the cavity to convert into single microwave photons. The conversion is resonantly enhanced when the cavity resonant frequency is near the axion rest mass energy. The experiment is cooled to 1.5 K and the electromagnetic power spectrum emitted by the cavity is measured by an ultra-low-noise microwave receiver. The axion would be detected as excess power in a narrow line within the cavity resonance. The apparatus has achieved a power sensitivity better than ${10}^{\ensuremath{-}23} \mathrm{W}$ in the mass range $2.9--3.3 \ensuremath{\mu}\mathrm{eV}.$ For the first time the rf cavity technique has explored plausible axion models, assuming axions make up a significant fraction of the local halo density. The experiment continues to operate and will explore a large part of the mass in the range of $1--10 \ensuremath{\mu}\mathrm{eV}$ in the near future. An upgrade of the experiment is planned with dc superconducting quantum interference device microwave amplifiers operating at a lower physical temperature. This next generation detector would be sensitive to even more weakly coupled axions contributing only fractionally to the local halo density.

The EPSILON experimental pseudo-symmetric trap

Within the framework of the Adaptive Plasma Experiment (APEX) conceptual project, a trap with closed magnetic field lines, the Experimental Pseudo-Symmetric Closed Trap (EPSILON), is examined. The APEX project is aimed at theoretical and experimental development of the physical foundations for a steady state thermonuclear reactor designed on the basis of an alternative magnetic trap with tokamak-like large β plasma confinement. A discussion is given of thefundamental principle of pseudo-symmetry, which a magnetic configuration with tokamak-like plasma confinement should satisfy. Examples are given of calculations in the paraxial approximation of pseudo-symmetric curvilinear elements with a poloidal modulus B isoline. The EPSILON trap, consisting of two direct axisymmetric mirrors linked by two curvilinear pseudo-symmetric elements, is considered. To increase the equilibrium β, the plasma currents are short-circuited within curvilinear equilibrium elements. An untraditional scheme of MHD stabilization for a trap with closed field lines by use of axisymmetric mirrors with a divertor is analysed. The experimental installation EPSILON-One Mirror Element (OME), which is under construction for experimental investigation of stabilization by divertor, is discussed. The opportunity for applying the ECR method of plasma production in EPSILON-OME in conditions of high density and low magnetic field is examined.

Magnetization of UPd 2Al 3 in ultra-low temperature and high magnetic fields

Magnetization processes of a uranium heavy-fermion superconductor UPd 2Al 3 is studied at temperatures down to 0.4 K in a static high magnetic field. The sweep ratio of a magnetic field is very low, 0.0015 T/min and measurements are done in completely isothermal processes. A sharp isothermal metamagnetic transition and a hysteresis have been first observed at B =17.9 T and at ultra-low temperatures when an external field is applied perpendicular to the c-axis. The hysteresis Δ B is about 0.02 T at 0.4 K. This hysteresis and sharp jump of the magnetization suggest that this transition is a first-order transition.