scholarly journals About Magnets and Superconductors of Mr Scanners

2021 ◽  
Author(s):  
Željko Đ. Vujović
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Liquid Helium ◽  
Liquid Nitrogen ◽  
Magnesium Diboride ◽  
Variable Magnetic Field ◽  
Gradient Field ◽  
Main Magnetic Field ◽  
Superconducting Material ◽  
Main Magnet

Abstract The topic of this paper are parts of modern MR devices, in which the magnet windings are located. MR scanner magnets are made of four types of electromagnetic windings: 1) The main magnet, made of superconducting material, creates a variable magnetic field; 2) X coil, made of a resistive material, creates a variable magnetic field, horizontally, from left to right, across scanning tube; 3) Y coil creates varaing magnetic field, vertically, from botom to top; 4) Z coil creates varaing magnetic field, longitudinally, from head to toe, within scanning tube.Superconductors, which create the main magnetic field, should be cooled by liquid helium and liquid nitrogen. Main magnets made of superconductors should use cryostat, with cooling vessels with liquid helium and liquid nitrogen, thermal insulation and other protective elements of magnet system. The types of magnets that exist in the basic configurations of MR scanners are analyzed. Scanners in the form of a closed cylindrical cavity create their own, magnetic, fields by passing current through the solenoid, which is held at the temperature of the superconductor. The superconductors used exclusively are: niobium-titanium (NbTi), niobium-tin (Nb3Sn), vanadium-gallium (V3Ga) and magnesium-diboride (MgB2). Only magnesium diboride is a high temperature superconductor, with a critical temperature Tc = 390K. The three remaining superconductors are low temperature. New high-temperature superconductors have been discovered, as well as room-temperature superconductors. Newly discovered superconducting materials are not used in MR scanners. The magnet structure of the MR scanner is complex. The resonant frequency changes at each point of the field in a controlled manner. The windings of the main magnet made of superconducting material in the form of microsial fibers are built into the copper core. The nonlinear gradient field is created by windings of conductive material. It is added to the main magnetic field. Thus, the resulting magnetic field is obtained.

Simulation and Optimization of a Permanent Magnet for Small-Sized MRI by Genetic Algorithm

2013 ◽  
Vol 341-342 ◽  
pp. 577-580
Author(s):  
Yi Yuan Cheng ◽  
Ling Xia ◽  
Wei He
Keyword(s):  
Magnetic Field ◽  
Permanent Magnet ◽  
Homogeneous Magnetic Field ◽  
Main Magnetic Field ◽  
Resonance Imaging ◽  
Simulation And Optimization ◽  
Field Uniformity ◽  
Main Magnet ◽  
Magnetic Resonance Imaging Mri ◽  
The Magnetic Field

The main magnet produces the main magnetic field in the imaging area as one of the important parts of the magnetic resonance imaging (MRI) system. In a permanent MRI magnet, the widespread end effect causes a non-uniform magnetic field distribution and affects the imaging quality. In this paper, an H-type permanent magnet for small-sized MRI applications was designed; in particular, we added an optimized shimming ring outside the pole piece to improve the magnetic field uniformity. Genetic algorithms are used to solve the complex and nonlinear calculation of the magnetic field. The simulation results show that the magnet optimized by the proposed method generates a homogeneous magnetic field that can be easily implemented in practice.

scholarly journals Peculiarities of simulation of magnetic field in electromechanical nodes of magnetic-levitation transport system by the method of secondary sources

2015 ◽  
Vol 1 (2) ◽  
pp. 49-61 ◽  
Author(s):  
Dmitry Maksimovic Filippov
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Liquid Nitrogen ◽  
Permanent Magnets ◽  
Magnetic Levitation ◽  
High Temperature Superconductors ◽  
Liquid Nitrogen Temperature ◽  
Magnetic Systems ◽  
Secondary Sources ◽  
Working Model

In recent years increasingly discusses the prospects of application of high-temperature superconductors (HTS) as the winding current-carrying elements of magnetic systems for various purposes. It seems particularly attractive possibility of such systems at liquid nitrogen temperature. The article describes the prototype of module of the magnetic system which is made on the basis of high-temperature superconducting tapes, designed for the installation and testing on a working model of a static levitation. In the working model levitation of the platform carried by the interaction of the magnetic field of the assembly of permanent magnets mounted on the platform with a field similar to assemblies located in the track structure. Compact HTS module replaces the two assemblies of permanent magnets mounted on the platform. Each block of the module represents HTS racetrack coil with current inputs, power structure, positioning system and bracing which is placed in a cryostat, providing at minimum wall thickness of the required mechanical strength and thermal insulation at liquid nitrogen temperature. The prototype of unified superconducting module successfully passed preliminary tests.

Water accumulation as a function of temperature on specimens in an electron microscope cold stage

1986 ◽  
Vol 44 ◽  
pp. 114-115 ◽  
Author(s):  
M.K. Lamvik ◽  
D.A. Kopf ◽  
S.D. Davilla ◽  
J.D. Robertson
Keyword(s):  
Electron Microscope ◽  
Mass Loss ◽  
Liquid Helium ◽  
Liquid Nitrogen ◽  
Liquid Nitrogen Temperature ◽  
Liquid Helium Temperature ◽  
Helium Temperature ◽  
Cold Stage ◽  
Water Accumulation ◽  
Better Than

Last year we reported1 that there is a striking reduction in the rate of mass loss when a specimen is observed at liquid helium temperature. It is important to determine whether liquid helium temperature is significantly better than liquid nitrogen temperature. This requires a good understanding of mass loss effects in cold stages around 100K.

A new magnetic resonance head coil and head immobilization device for gamma knife radiosurgery: an analysis of geometric distortion and signal/noise characteristics

2002 ◽  
Vol 97 ◽  
pp. 563-568 ◽  
Author(s):  
Paul Jursinic ◽  
Robert Prost ◽  
Christopher Schultz
Keyword(s):  
Magnetic Resonance ◽  
Gamma Knife Radiosurgery ◽  
Geometric Distortion ◽  
Gradient Field ◽  
Main Magnetic Field ◽  
Content Type ◽  
Signal Noise ◽  
Noise Characteristics ◽  
Head Coil ◽  
Fine Print

Object. The authors report on a new head coil into which the Leksell aluminum localization frame can be easily and securely mounted. Mechanically, the head coil interferes little with the patient. Methods. The head coil, which is for magnetic resonance (MR) imaging, is a 12-element quadrature transmitand-receive high-pass birdcage coil with a nominal operation frequency (63.86 MHz). The coil was built into a plastic housing. This new head coil minimizes patient motion and provides a 20% increase in signal/noise ratios compared with standard head coils. An MR image test phantom was mounted in the coil and this allowed quantification of image distortion due to inhomogeneities in the main magnetic field, nonlinearity in the gradient field, and paramagnetism of the aluminum headframe. There were no significant differences in geometric distortion between the new head coil and the standard coil. Conclusions. The new head coil has advantages for reducing patient movement artifacts and has a better signal/noise ratio with no reduction in geometric accuracy.

Technology of creation of digital charts of the Earth's main magnetic field

2009 ◽  
Vol 11 (2) ◽  
pp. 1-6
Author(s):  
E. A. Zhalkovsky ◽  
V. I. Nikiforov ◽  
A. M. Merzly ◽  
A. E. Beriozko ◽  
A. A. Soloviev ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Main Magnetic Field

scholarly journals Predictions of the geomagnetic secular variation based on the ensemble sequential assimilation of geomagnetic field models by dynamo simulations

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Sabrina Sanchez ◽  
Johannes Wicht ◽  
Julien Bärenzung
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Wave Number ◽  
Main Magnetic Field ◽  
Candidate Model ◽  
Uncertainty Estimates ◽  
Geomagnetic Field Models ◽  
Dipole Configuration

Abstract The IGRF offers an important incentive for testing algorithms predicting the Earth’s magnetic field changes, known as secular variation (SV), in a 5-year range. Here, we present a SV candidate model for the 13th IGRF that stems from a sequential ensemble data assimilation approach (EnKF). The ensemble consists of a number of parallel-running 3D-dynamo simulations. The assimilated data are geomagnetic field snapshots covering the years 1840 to 2000 from the COV-OBS.x1 model and for 2001 to 2020 from the Kalmag model. A spectral covariance localization method, considering the couplings between spherical harmonics of the same equatorial symmetry and same azimuthal wave number, allows decreasing the ensemble size to about a 100 while maintaining the stability of the assimilation. The quality of 5-year predictions is tested for the past two decades. These tests show that the assimilation scheme is able to reconstruct the overall SV evolution. They also suggest that a better 5-year forecast is obtained keeping the SV constant compared to the dynamically evolving SV. However, the quality of the dynamical forecast steadily improves over the full assimilation window (180 years). We therefore propose the instantaneous SV estimate for 2020 from our assimilation as a candidate model for the IGRF-13. The ensemble approach provides uncertainty estimates, which closely match the residual differences with respect to the IGRF-13. Longer term predictions for the evolution of the main magnetic field features over a 50-year range are also presented. We observe the further decrease of the axial dipole at a mean rate of 8 nT/year as well as a deepening and broadening of the South Atlantic Anomaly. The magnetic dip poles are seen to approach an eccentric dipole configuration.

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