Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Utility Patent
1999-02-25
2001-01-02
Arana, Louis (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S321000
Utility Patent
active
06169402
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a nuclear magnetic resonance (NMR) system or spectrometer for use in the field of medical treatment and also for component and structure analysis of industrial materials, farm products and others.
An NMR system gives various data useful for the structure analysis of most organic compounds, for example, the degree of chemical shift of each atom, spin—spin coupling constants relaxation time, etc. The NMR system is basically composed of a magnet for generating a static magnetic field, a coil for generating a different radio-frequency magnetic field pulse to detect NMR signals, a receiver for receiving the NMR signals, a system controller, etc. In a stronger magnetic field, the NMR system gives a greater amount of information data for more detailed analysis of samples. The magnet, used in NMR systems is therefore preferably a superconducting magnet in view of the intensity, the stability and the homogeneity of the magnetic field produced by a magnet of this type.
A magnetic resonance imaging (MRI) system is one typical application of NMR to medical treatment, in which the magnetic resonance occurring in the human body is utilized so as to directly trace the chemical reaction having occurred in tissues or organs to give, for example, encephalophotoscopic laminagraphy images.
The MRI system comprises at least a magnet for generating a static magnetic field, magnetic field gradients for giving positional information to NMR signals, a radio-frequency oscillator unit, an NMR signal detector unit, a probe coil that surrounds the subject to be examined, for example, a human body or the like, for radiating radio-frequency electromagnetic waves and detecting signals, and a controller for controlling those units and processing the signals obtained. In operation of the MRI system high-frequency electromagnetic waves are used to irradiate the subject placed in the static magnetic field to produce NMR signals and the space distribution of the nuclides having generated the signals is imaged. The MRI system is safe as no harmful radiation is used, and, in addition, its resolving power is high. The practical value of the system is therefore extremely high.
In many conventional instruments for analysis based on NMR and MRI systems a superconducting magnet is used that comprises a superconducting coil of a metallic superconducting wire material of, for example, niobium, titanium or the like, for producing the main magnetic field. Such coils are cooled with liquid helium to be at an ultra-low temperature. Therefore, they require a large amount of expensive liquid helium, and are problematic in that their running cost is high. The metallic superconducting wire material of niobium, titanium or the like is produced in a complicated process that comprises specific heat treatment. Therefore, the superconducting coil is much more expensive than copper coils used in ordinary electromagnets, and the utilizing systems are extremely expensive. In addition, driving the superconducting magnet requires cryogen gases (liquid helium and liquid nitrogen), for which a specific operation technique is necessary. From the above it is clear that the technique of using a superconducting magnet is complicated, expensive and highly problematic. These problems are serious and present a barrier to the popularization of high-performance NMR and MRI systems.
One example of a small-sized and simple NMR system has been proposed in Japanese Patent Laid-Open Publication No. Hei 9-135823, in which a direct-cooling type superconducting magnet by using refrigerators is used in place of the conventional helium-cooling type superconducting magnet as the main magnetic field generating source, and forms a simple NMR system for medical treatment, as compared with conventional large-sized NMR systems.
The NMR system proposed is operated in a more simplified manner than the NMR systems having a conventional helium-cooling type superconducting magnet. However, a superconducting coil of a superconducting wire material is still used for producing the main magnetic field. The superconducting wire material is extremely expensive, and therefore the system which comprises a superconducting coil of the wire material is also expensive. In addition, since the superconducting coil housed in a vacuum container is cooled with a refrigerator, the coil unit is large and therefore reduces the advantages and simplicity of the system. Moreover, the superconducting coil in the system has a large heat capacity and therefore takes a long time until it is cooled with a refrigerator to a predetermined temperature when actual measurement can be made. Thus, the system still has various problems.
SUMMARY OF THE INVENTION
The present invention provides a nuclear magnetic resonance apparatus comprising:
a high-temperature superconducting bulk;
a cooling means for cooling the high-temperature superconducting bulk;
a vacuum insulated container surrounding the high temperature superconducting bulk and the cooling means;
a magnetizing coil positioned such that the high-temperature superconducting bulk is within a magnetic field produced by the magnetizing coil;
a space for placing a subject to be examined, positioned such that the subject is within a magnetic field produced by the high-temperature superconducting bulk; and
a detector coil for detecting any nuclear magnetic resonance signals produced by the subject.
The high-temperature superconductor bulk that acts as the superconducting magnet comprises, as the essential component, superconductor oxide chemically represented by RE—Ba—Cu—O whereby RE indicates at least one or more of yttrium (elemental symbol, Y), samarium (Sm), lanthanum (La), neodymium (Nd), europium (Eu), gadolinium (Gd), erbium (Er) and ytterbium (Yb).
When yttrium-based, neodymium-based, samarium-based and other high-temperature superconductors having a superconducting transition temperature Tc of not lower than 90 K (Kelvin) are produced in a so-called melt process method where the starting material is once fused by overheating it at a temperature higher than its melting point and then again solidified, shaped bodies are obtained in which large crystals have grown. These are referred to as superconducting bulks. Fine grains of an insulating phase are dispersed throughout the bulk to form a texture of the matrix having superconductivity. The pinning points that result from the existence of the dispersed insulating phase trap magnetic flux. In this manner, the superconducting bulk acts as a pseudo-permanent magnet.
The superconducting bulk as produced in the melt process have a superconducting transition temperature falling between 90 K and 96 K and are characterized in that their texture comprises large crystals of a superconducting phase having a size of from 1 mm to 100 mm and fine grains of an insulating phase dispersed inside the large crystals and having a grain size of not larger than 50 &mgr;m (preferably, not larger than 10 &mgr;m).
The molar ratio of RE:Ba:Cu in the superconducting phase chemically represented by RE—Ba—Cu—O is 1:2:3 or so, while that in the insulating phase is 2:1:1 or so, though the elements may be mutually substituted with each other in some degree. In the superconducting bulks, the molar ratio of the superconducting phase to the insulating phase preferably falls between 10:1 and 1:1. If the insulating phase is smaller than 9% (i.e. if the molar ratio noted above oversteps 10:1), the sample will be greatly deformed when it is fused so that it could not retain the original shape which it had before heat treatment, or in other words the shapability of the sample is poor. On the other hand, if the insulating phase is larger than 50% (i.e. if the molar ratio noted above oversteps 1:1), the insulating phase will be the major phase and lower the superconducting characteristics of the bulks.
In producing the superconducting bulks, platinum (Pt) may be added thereto in an amount of from 0.1% to 10% for promoting fine dispersion of insulating phase grains in the texture
Ito Yoshitaka
Oka Tetsuo
Uzawa Jun
Yabuno Ryohei
Yanagi Yousuke
Aisin Seiki Kabushiki Kaisha
Arana Louis
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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