Magnetic NMR Research Articles

Spatial and Temporal Variations of a Screening Current Induced Magnetic Field in a Double-Pancake HTS Insert of an LTS/HTS NMR Magnet.

This paper presents experimental and simulation results of a screening current induced magnetic field (SCF) in a high temperature superconductor (HTS) insert that constitutes a low-/high-temperature superconductor (LTS/HTS) NMR magnet. In this experiment, the HTS insert, a stack of 50 double-pancake coils, each wound with Bi2223 tape, was operated at 77 K. A screening current was induced in the HTS insert by three magnetic field sources: 1) a self field from the HTS insert; 2) an external field from a 5-T background magnet; and 3) combinations of 1) and 2). For each field excitation, which induced an SCF, its axial field distribution and temporal variations were measured and compared with simulation results based on the critical state model. Agreement on field profile between experiment and simulation is satisfactory but more work is needed to make the simulation useful for designing shim coils that will cancel the SCF.

Stress Analysis of a High Temperature Superconductor Coil Wound With Bi-2223/Ag Tapes for High Field HTS/LTS NMR Magnet Application

The electromagnetic stress distribution inside a HTS insert is one of the key issues for construction of a high field high/low temperature superconductor (HTS/LTS) magnet. The rmiddotJmiddotB formulae is widely used for the stress calculation of the coil, due to its simplicity. However, the assumption of this calculation makes it impossible to consider the effects of the bobbin, an epoxy impregnated structure, on stress of the coil. In this work, stress analysis methods are reported. The governing equation defined from the force equilibrium state was adopted and used to analyze what the stress of the HTS coil wound with Bi2223/Ag conductor. The validness of the stress analysis method was confirmed by comparison with experimental results, especially in the coil with epoxy impregnation. The numerical and experimental procedures are described and both results are discussed.

Accelerated Hydrolysis of Aspirin Using Alternating Magnetic Fields

The major problem of current drug-based therapy is selectivity. As in other areas of science, a combined approach might improve the situation decisively. The idea is to use the pro-drug principle together with an alternating magnetic field as physical stimulus, which can be applied in a spatially and temporarily controlled manner. As a proof of principle, the neutral hydrolysis of aspirin in physiological phosphate buffer of pH 7.5 at 40 °C was chosen. The sensor and actuator system is a commercially available gold nanoparticle (NP) suspension which is approved for animal usage, stable in high concentrations and reproducibly available. Applying the alternating magnetic field of a conventional NMR magnet system accelerated the hydrolysis of aspirin in solution.

Mg2+ modulation of EMCV IRES key activity fragment equilibria and r(G·C) base-pair kinetics

NMR magnetization transfer from water and ammonia-catalyzed exchange of the imino proton have been used to probe enhanced thermostability and conformational rearrangements induced by Mg(2+) in two key activity fragments r(CACCUGGCGACAGGUG) and r(GGCCAAAAGCC) of the encephalomyocarditis virus (EMCV) picornavirus internal ribosome entry site (IRES). We have measured some of their r(G*C) base-pair lifetimes and dissociation constants under different MgCl(2) conditions, and we compare them with those of other short RNA duplexes. The RNA fragment r(CACCUGGCGACAGGUG) adopts two topologies, a palindromic duplex with two conformations and a hairpin, whose equilibrium can be monitored: the duplex form is destabilized by Mg(2+) and temperature, a delicate balance wherein the entropic contribution of the free energy helps populate the hairpin state. For both fragments, the opening rates of the r(G*C) pairs are lower in the presence of Mg(2+) and their dissociation constants are smaller or comparable. Analysis of the results suggests that Mg(2+) has a preferential and specific effect on the r(CACCUGGCGACAGGUG) hairpin in the region close to the r(G*C) closing pair of the GCGA tetraloop, and the ion moves diffusively around r(GGCCAAAAGCC), thereby differentiating the GNRA and RAAA hairpin motifs that are both involved in the biological regulation functions of the EMCV IRES.

Spectral and temporal features of multiple spontaneous NMR-maser emissions

When a system composed of dissolved laser-polarized xenon with negative spin temperature is put inside a high field NMR magnet, a series of spontaneous maser emissions can be observed. We report here their spectral and temporal features using a processing model derived from the solution of the Bloch equations in the presence of radiation damping. We show, in particular, that by combining Fourier transformation and squared modulus, a parameter allowing the characterization of the burst of transverse magnetization can be determined. This parameter is shown to be correlated with the radiated energy. Moreover, this processing clearly reveals features which can probably be assigned to effects resulting from distant dipolar fields. Finally, the analysis of the experimental data reveals an unexpected behavior of the 129 Xe transverse self-relaxation.

Mobile NMR for geophysical analysis and materials testing

Initiated by well logging NMR, portable NMR instruments are being developed for a variety of novel applications in materials testing, process analysis and control, which provides new opportunities for geophysical investigations. Small-diameter cylindrical sensors can probe short distances into the walls of slim-line logging holes, and single-sided sensors enable non-destructive testing of large objects. Both sensors are characterized by small sensitive volumes. Barrel-shaped magnets that accommodate the sample in their center have higher sensitivity due to a larger sensitive volume but can accommodate only samples like drill cores, which fit in size to the diameter of the magnet bore. Both types of magnets can be scaled down to the size of a coffee mug to arrive at sub-compact NMR equipment. Portable NMR magnets are reviewed in the context of applications related to geophysics.

Water-filled Cavities in the Voltage-Sensing Domain of a Potassium Channel Embedded in Lipid Bilayers

S1-S4 voltage-sensing domains (VSD) are conserved structural modules found in a large variety of voltage-sensitive membrane proteins. We investigated the topology, hydration properties and protein-lipid interactions of the VSD from KvAP in lipid membranes using neutron diffraction and solid-state NMR techniques. Neutron diffraction experiments demonstrate that the VSD changes the water distribution and profiles of POPC:POPG bilayers. To explore the topology of the VSD in the membrane, we uniformly deuterated the protein and incorporated it into lipid bilayers. A significant fraction of the protein scattering length density is observed in the head-group region of the bilayer. The protein density and water distribution within the bilayer largely overlap, suggesting a high degree of protein hydration within the membrane. Solid-state NMR magnetization transfer data are consistent with deep penetration of water molecules into bilayer-embedded VSDs. We hypothesize that VSDs have water filled cavities, which may be essential for VSD function.

A Comparative 13C NMR Study of Local Ordering in a Homologous Series of Bent-core Liquid Crystals

A 13C NMR study is carried out in a number of banana-shaped molecules belonging to a homologous series. The derivatives contain chlorine or bromine substituent(s) in the center ring of 1,3-phenylene bis[4'-alkenyloxy biphenyl]-4-carboxylate (nPBBC), and different terminal chain lengths are systematically compared in terms of their local order parameters and their ability to form an aligned nematic phase in the NMR magnet. The chemical shift anisotropy tensors measured from nPBBC by fitting the 13C powder patterns are now extensively used on these molecules to interpret their observed 13C chemical shifts in the nematic phase. The bend angles are estimated as a function of temperature in two members of the nPBBC series. Conformation twists in the bent-core region inferred from the local molecular biaxial paramters are discussed.

Effects of Magnetic Nanoparticles on Magnetic Resonance and Spin Relaxation in Systems of Different Viscosity

AbstractNuclear Magnetic Resonance (NMR) technique is a convenient method to monitor magnetic nanoparticles in different biomedical applications and observe changes induced by the particles. To better understand the specifics of the magnetic resonance and spin relaxation in the systems with magnetic nanoparticles, the NMR spectra and magnetization dynamics of the host protons are studied in the model systems of different viscosity and some biological systems in the presence of magnetic nanoparticles. The results confirmed that nanoparticles affect the proton relaxation kinetics of liquid solutions, changing the relaxation time (T1) significantly, whereas in systems of high viscosity the relaxation times are unchanged. The kinetics in intermediate systems is multi-exponential. A complicated picture is observed in biological systems, demonstrating contributions of liquid-like and solid-like behavior.

21 Tesla Micro-MRI of Rat Skin

Abstract*Aim:* A rapid ultra high resolution ex vivo MRI imaging method was evaluated to visualize rat skin structure. The main objectives were:1.qualitative assessment of viable epidermis, hair, oil and fat-rich skin features by multi-contrast approach;2.achievement of spatial resolution up to 15 microns; 3.comparison of skin histology with MRI skin features obtained by 21 Tesla magnetic resonance imaging (MRI) imager. *Introduction:* The ultrawide bore 900 MHz magnet has high resolution NMR magnet has a central field of 21.1 T. The high resolution MRI technique has potential for both quantitative and non-invasive morphological evaluation at micrometer level. The MRI signal was sensitive to water protons and glycolipid distribution in the skin. At 21 Tesla, both contrast and resolution are enhanced utilizing thin slices up to 100 microns. Multiple contrast by magnetization transfer contrast (MTC), spin–lattice relaxation (T1-weighting), combination of T2 and magnetic field in-homogeneity (T2*-weighting) may provide resolution up to 15 microns with distinct proton-fat contrast. Materials and Methods: On histology and MRI co-registered images, skin features of epidermis, dermis, hair, sebaceous glands were compared. For spin echo(SE) and gradient echo(GE) imaging utilized the MSME_Bio and GEFC (Bruker Biospin, Billerika) methods at short TE=8 ms and TR=100,200,500,1000 ms(for T1 weighted) and TE= 8,16, 24 ms, TR=1000 ms(for T2 weighted), matrix of 256 x 256 and 0.1-0.3 mm slice thickness, NEX=4. The MSME_MTR was used for MT images. The MRI visible skin features regions were identified for epidermis, dermis, hair follicles and oil glands. Distinct epidermis and intact hair and root thickness served as good skin quality. *Results:* At high resolution 25 μm, SE T1-weighted images showed distinct epidermis, brighter brightest stratum corneum; brightgray papillary (collagen) and reticular dermis (glycolipids). The hair follicles and sebaceous glands appeared gray (Figure 1). Signal intensity was proportional to TR. At TE=8 ms, water and lipids appeared distinct in the dermis. The T2-weighted images highlighted the stratum corneum (dark thin band at top), viable epidermis (white band below the stratum corneum), hair follicles/sebaceous glands (light channels running vertically through the skin), and dermis (dark regions between hair follicles)(Figure 1 and Table 1). Water-fat phantom showed distinct intensity (Figure1E). In plane resolution was 100 micron and contrast enhancement was achieved by multicontrast approach. Histology-MRI comparison: Epidermis, hair root, follicles, sebaceous gland were comparable. *Conclusion:* High resolution SE short TE images demonstrate distinct contrast properties as preliminary data. High CNR and better morphology both require ultra high magnetic field using T2* weighted and magnetization transfer weighted MRI imaging to achieve high in-plane and spatial resolution.

21 Tesla Micro-MRI of Rat Skin

*Aim:* A rapid ultra high resolution ex vivo MRI imaging method was evaluated to visualize rat skin structure. The main objectives were:1.qualitative assessment of viable epidermis, hair, oil and fat-rich skin features by multi-contrast approach;2.achievement of spatial resolution up to 15 microns; 3.comparison of skin histology with MRI skin features obtained by 21 Tesla magnetic resonance imaging (MRI) imager. *Introduction:* The ultrawide bore 900 MHz magnet has high resolution NMR magnet has a central field of 21.1 T. The high resolution MRI technique has potential for both quantitative and non-invasive morphological evaluation at micrometer level. The MRI signal was sensitive to water protons and glycolipid distribution in the skin. At 21 Tesla, both contrast and resolution are enhanced utilizing thin slices up to 100 microns. Multiple contrast by magnetization transfer contrast (MTC), spin–lattice relaxation (T1-weighting), combination of T2 and magnetic field in-homogeneity (T2*-weighting) may provide resolution up to 15 microns with distinct proton-fat contrast. On histology and MRI co-registered images, skin features of epidermis, dermis, hair, sebaceous glands were compared. For spin echo(SE) and gradient echo(GE) imaging utilized the MSME_Bio and GEFC (Bruker Biospin, Billerika) methods at short TE=8 ms and TR=100,200,500,1000 ms(for T1 weighted) and TE= 8,16, 24 ms, TR=1000 ms(for T2 weighted), matrix of 256 x 256 and 0.1-0.3 mm slice thickness, NEX=4. The MSME_MTR was used for MT images. The MRI visible skin features regions were identified for epidermis, dermis, hair follicles and oil glands. Distinct epidermis and intact hair and root thickness served as good skin quality. At high resolution 25 μm, SE T1-weighted images showed distinct epidermis, brighter brightest stratum corneum; brightgray papillary (collagen) and reticular dermis (glycolipids). The hair follicles and sebaceous glands appeared gray (Figure 1). Signal intensity was proportional to TR. At TE=8 ms, water and lipids appeared distinct in the dermis. The T2-weighted images highlighted the stratum corneum (dark thin band at top), viable epidermis (white band below the stratum corneum), hair follicles/sebaceous glands (light channels running vertically through the skin), and dermis (dark regions between hair follicles)(Figure 1 and Table 1). Water-fat phantom showed distinct intensity (Figure1E). In plane resolution was 100 micron and contrast enhancement was achieved by multicontrast approach. Histology-MRI comparison: Epidermis, hair root, follicles, sebaceous gland were comparable. *Conclusion:* High resolution SE short TE images demonstrate distinct contrast properties as preliminary data. High CNR and better morphology both require ultra high magnetic field using T2* weighted and magnetization transfer weighted MRI imaging to achieve high in-plane and spatial resolution.

Abstract 5382: Accelerated Triacylglyceride Dynamics Induced by Cardiac PPARα Overexpression are Potentiated by Adrenergic Stress to Reveal Increased Reliance on Endogenous Lipid Stores

Peroxisome proliferator-activated receptor alpha (PPARα) is a nuclear receptor involved in regulating fatty acid utilization and is implicated in the pathogenesis of diabetic cardiomyopathy. However, the involvement of PPARα in the specific utilization of endogenous lipid stores and the consequences for triacylglyceride (TAG) formation in the cardiomyocyte remain unknown. Thus, we examined TAG dynamics in isolated perfused hearts of transgenic mice exhibiting cardiac-specific over-expression of PPARα under normal and stressed conditions. Hearts from MHC-PPARα overexpressing mice (PPAR) and non-transgenic (NTG) littermates were isolated and retrogradely perfused in a 14.1 T NMR magnet with buffer containing 0.4 mM [2,4,6,8,10,12,14,16]-13C palmitate, as a source of long chain fatty acids (LCFA) + 10 mM glucose. Dynamic 13C NMR observations of the beating heart and endpoint mass spectrometry provided TAG turnover at baseline work (PPAR, n=12; NTG, n=7) and adrenergic stress (10–7 M isoproterenol, ISO) (PPAR ISO, n=5; NTG ISO, n=6). ISO elevated rate pressure product by 27% and 25% in NTG and PPAR, respectively (P<0.05). At baseline workloads, PPAR contained 45% more TAG than NTG (P <0.05) and TAG turnover was elevated in PPARα mice by 191% over NTG. ISO did not affect TAG content in either NTG or PPAR. However, ISO induced large increases in TAG turnover in PPAR from 1454 ± 232 to 2532 ±334 nanomoles/mg prot/min (P<0.05), without affecting TAG turnover in NTG. The near doubling of TAG turnover with elevated content in MHC-PPARα hearts indicates upregulated baseline lipid metabolism via both utilization and storage pathways. Surprisingly, the adrenergic stress response potentiates the already elevated TAG dynamics in MHC-PPARα hearts, indicating persistence in matching LCFA storage rates to maintain this elevated endogenous lipid pool. Elevated TAG content in PPAR was maintained during ISO, despite increased reliance on endogenous TAG to meet the increased energy demand as compared to NTG. Therefore, activation of LCFA oxidation enzymes by PPARα is coupled in complementary fashion to the activation of LCFA storage kinetics, suggesting an expanded role for PPARα in the induction of TAG turnover.

Magnetic field generated by shielding current in highTc superconducting coils for NMR magnets

Numerical electromagnetic field analyses of highTc superconducting tape in coils were carried out to calculate the magnetic field generated bythe shielding (magnetization) current in superconducting tape. The numericalmodel employs the power law electric field–current density characteristic andthe thin strip approximation, in which the current component normal to thewide face of the tape is neglected. The shielding (magnetization) currents lead tonon-uniform current distributions in the superconducting tape in the coils. Themagnetic field generated by the shielding (magnetization) current can deteriorate thefield quality and could be a concern in insert coils for NMR magnets using highTc superconducting tape.

Preparation and properties of Eu–Ba–Cu–O superconducting bulk magnets for NMR application

We have investigated the fabrication and the superconducting and field trapping properties of large melt-textured Eu–Ba–Cu–O bulk superconductors for the purpose of application as a compact NMR magnet. We successfully fabricated c-axis oriented single-grain bulk samples up to 65 mm in diameter by melt-processing under a low oxygen partial pressure. The samples of 33 and 47 mm diameters could trap magnetic fields of 1.4 and 1.7 T at 77 K, respectively. The position dependence of T c in the sample of 33mm diameter is very small throughout the sample. In 65 mm-sized sample, however, T c and J c lowered in inner region of the sample, leading to lowering of maximum trapped field. Trapped magnetic field was improved with keeping for long time at maximum temperature in melt-processing.

Field Mapping, NMR Lineshape, and Screening Currents Induced Field Analyses for Homogeneity Improvement in LTS/HTS NMR Magnets.

This paper describes two general methods: field map processing and NMR lineshape analysis, that we are currently using for the on-going research of field improvement techniques specifically applied to our 700 MHz LTS/HTS NMR magnet. The validity of the methods is verified with comparison between calculations and experiments. Also, a simple but effective analysis has been used to identify the principal source of a remanent magnetic field measured in the bore of the 700 MHz LTS/HTS NMR magnet: the Screening Current induced Field (SCF) from the 100-MHz HTS insert, comprised of 48 double pancake coils, each wound with Bi2223 tape.

Field Stability of a 600 MHz NMR Magnet in the Driven-Mode Operation

Although high-temperature superconductors (HTS) are very promising for high-field generation over 25 T, it is difficult to apply them to an NMR magnet because of their low index values and the difficulty caused by superconducting joints. The properties of HTS appear to cause poor magnetic field stability in the persistent-mode operation. Therefore, in this study, a high-field NMR magnet including HTS coils will be operated in the driven-mode. In order to evaluate the magnetic field stability in the driven-mode, we modified a 14 Tesla (600 MHz) vertical NMR magnet. With regard to the magnet, persistent switches for axial shim coils (z <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> , Z <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1,</sup> Z <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) as well as the main coil were removed for constant operation with a power supply. In addition, a 1 W Gifford-McMahon (GM) cryocooler at 4 K and HTS current leads were installed in the cryostat to re-condense boiled helium gas. As a result, there was a long-term change of about 6 ppm in the magnetic field stability, but, in the short-term (a few hours), a change of about 2 ppm was observed. By the z <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> shim control, in combination with the NMR field measurement, an averaged magnetic field drift of less than 0.0001 ppm/h was achieved.

HTS Magnetic Field Damper for Short-Term Fluctuations in the Driven-Mode

Although high-temperature superconductors (HTS) are very promising for high-field generation over 25 Tesla, it is difficult to apply them to an NMR magnet because of their low index values and the difficulty caused by superconducting joints. The properties of HTS appear to cause poor magnetic field stability in the persistent-mode operation. Therefore, in this study, a high-field NMR magnet including HTS coils will be operated in the driven-mode. We evaluated the magnetic field drift of a 14 Tesla (600 MHz) NMR magnet in the driven-mode. The magnetic field stability in several hours was about 2 ppm. However, in a shorter-term, magnetic field fluctuations with a main period of approximately 0.01 Hz remained. These fluctuations are unfavorable for a precise NMR measurement. In order to reduce the field fluctuation, we tested the damper coil by making a closed-loop circuit using Bi-2223 tapes. The damper coil was cooled by a single-stage GM cryocooler in the magnetic field. The inside magnetic field of the damper coil was measured with an NMR Teslameter. The shielding current in the damper coil canceled out the field fluctuation, which indicates that the damper coil worked effectively.

High-Field Magnet Design Under Constant Hoop Stress

NMR magnets using high-temperature superconductors (HTS) to generate high magnetic field exceeding 25 Tesla are currently being designed by some research organizations. To design a magnet, the critical current density, J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , of superconductors in the high-field region is an important factor. In addition, electromagnetic force in superconductors should be considered for magnet quench and degradation of superconductors. Hoop stress is a very important factor in the design of multi-solenoid magnets. A modeling magnet consisting of multi-coils has been assumed for the calculation of several properties under the condition that the maximum hoop stress of every coil has the same value. The calculations show that there are certain relationships among the central magnetic field Bo, the magnet volume, and the stored energy. The results showed that these values correlate with the exponential of B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> squared.

A New Configuration of High-Resolution NMR Spectrometer With Superconducting Split-Magnet

New NMR magnets have successfully been developed and tested. The new NMR magnets consist of superconducting split-pair magnets with a room temperature cross-bore. Probes with solenoidal antenna are inserted from the horizontal branch of the cross-bore. The most benefit of the split-pair magnet is a significant improvement of the signal to noise ratio (SNR). With room temperature probes, the SNR of the standard 0.1% ethylbenzene in CDCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> reached 416 and 1487 for 300 MHz and 600 MHz system, respectively. With a cryogenic probe under development, the SNR improved to 4500 in 600 MHz. A new 300 MHz NMR system has also been fabricated and is under test for a new physicochemical application.

NMR Upgrading Project Towards 1.05 GHz

An NMR spectrometer over 1 GHz requires the contribution of high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconductors(HTS). However, a persistent-mode operation with HTS cannot satisfy the field stability of 0.01 ppm/h at present. This is a great barrier for applying HTS to an NMR magnet. To overcome this problem, a new project was undertaken in Japan in October 2006. In the course of the project, we will develop a highly stabilized power supply, field-compensation methods, and measurement techniques that allow a certain field fluctuation. By integrating them, the feasibility of HTS to NMR will be demonstrated. We performed a long-term operation of a 600 MHz NMR magnet in the driven-mode. Allowable field fluctuation of the existing internal lock system for solution NMR was evaluated by a model experiment. As the next step, the innermost Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coil of the 600 MHz NMR magnet will be replaced with a Bi-2223 coil, and the field homogeneity, as well as the field stability, will be evaluated. In the final step of the project, the replacement of the innermost coil of the existing 920 MHz NMR magnet will be planned. The targeting field is 24.7 T (1.05 GHz for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H NMR resonance frequency). The solid-state NMR on <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> O nuclei in a labeled peptide will be demonstrated using a magic angle spinning probe; the probe has a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H decoupling frequency of 1.05 GHz.