Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2001-06-26
2002-12-03
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S315000, C324S321000
Reexamination Certificate
active
06489769
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nuclear magnetic resonance apparatus which uses a nuclear magnetic resonance (NMR) signal and which can be utilized in a medical field, and in analyzing a component and structure of an industrial material, agricultural produce, and the like. The present invention particularly relates to a nuclear magnetic resonance apparatus for generating a strong static magnetic field which is comparable to a conventional superconducting magnet in a homogeneity aria without using liquid helium.
2. Description of Related Art
A nuclear magnetic resonance is a phenomenon in a magnetic system including a magnetic moment and angular momentum, and is a resonance phenomenon in a frequency (Larmor frequency) inherent in the magnetic system. For example, as shown in
FIG. 1
, a static magnetic field H
0
made by a magnet is applied to a sample, and a radio frequency magnetic field H
1
is further applied to the sample from a direction vertical to the static magnetic field via a transmission coil. At present, a pulse nuclear magnetic resonance(NMR) apparatus is a mainstream, in which a very short (3 to 6 &mgr;s) and strong high-frequency pulse is applied to the sample, and all signals spreading in a chemical shift are simultaneously resonated and simultaneously observed.
Moreover, in order to obtain a image, a magnetic field whose strength differs with a position called a gradient magnetic field is superimposed onto the static magnetic field, and a position is identified by shifting a resonance frequency for each position. An image method of exciting (selectively exciting) a predetermined section only by a necessary thickness with a high frequency, subsequently applying the gradient magnetic field in two directions in the section, and obtaining the sectional image by a two-dimensional Fourier method is generally used.
The aforementioned nuclear magnetic resonance apparatus (hereinafter referred to as an NMR apparatus) utilizing the aforementioned nuclear magnetic resonance phenomenon is basically constituted of a magnet for forming the static magnetic field, a coil for generating another high-frequency pulse and detecting an NMR signal, a receiver for receiving the NMR signal, and the like. Data useful in analyzing a structure of an organic compound, such as a chemical shift amount of each atom and spin-spin coupling constant can be obtained by the NMR apparatus.
Moreover, a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) utilizing the nuclear magnetic resonance phenomenon is constituted of: at least a magnet as static magnetic field generation means; a gradient magnetic field for applying space information to the signal; a high-frequency irradiation system; an NMR signal detection system; a probe coil which surrounds a test object such as a human body and actually performs high-frequency irradiation and signal detection; and a controller for controlling these components and processing the obtained signal. A space distribution of a nuclide which generates the signal is visualized by the nuclear magnetic resonance (NMR) signal obtained by irradiating the test object disposed in the presence of the static magnetic field with the high frequency. Since the MRI apparatus does not use a X-ray, the apparatus is safe not only for the human body subjected to a measuring operation but also for an object to be measured including the human body, a sufficient resolution is obtained, and a practical value is remarkably high.
As the static magnetic field generating magnet constituting the nuclear magnetic resonance apparatus, a resistive magnet of 0.5 to 2.2 T, and a superconducting magnet of 0.5 to 18.8 T have heretofore been used, and a permanent magnet is also used in some case. The static magnetic field generating magnet of the nuclear magnetic resonance apparatus has an enhanced sensitivity for a ferromagnetic field, and enables analysis of a large amount of detailed information. Therefore, the superconducting magnet using a superconducting material is superior in the strength, stability and uniformity of the magnetic field.
Therefore, in the recent nuclear magnetic resonance apparatus, the superconducting magnet using a superconducting coil formed of a metal-based superconducting wire material such as niobium and titanium is used to form a main magnetic field (static magnetic field). However, when the superconducting coil is utilized, liquid helium is used to cool the coil at an extremely low temperature. This raises a problem that a large amount of expensive liquid helium is required and running cost is high.
Moreover, the metal-based superconducting wire material such as niobium and titanium is produced by a complicated manufacturing process and thermal treatment. Therefore, the superconducting coil is much more expensive than a usual electromagnet coil formed of a copper wire, and the apparatus main body becomes extremely expensive. Additionally, a refrigerant (liquid helium and liquid nitrogen) utility for operating the superconducting magnet requires a special technique, and is technically complicated and intricate. Therefore, it is difficult to say that the utilization is a simple technique. These big problems hinder a high-performance nuclear magnetic resonance apparatus from spreading.
Furthermore, since the superconducting magnet requires a large cooling structure, and a leak magnetic field is also huge, an exclusive room for installing the magnet is necessary. This remarkably limits an apparatus installation condition, and also limits an apparatus utilization field.
On the other hand, an example of a small and simple nuclear magnetic resonance apparatus is proposed in Japanese Patent Application Laid-Open No. 135823/1997, in which a direct cooling type superconducting magnet is used instead of the conventional helium cooling type superconducting magnet. This nuclear magnetic resonance apparatus is more convenient than the apparatus using the conventional helium cooling type superconducting magnet, but the superconducting coil formed of the superconducting wire material is used to form the main magnetic field. Since the superconducting wire material is extremely expensive, the whole apparatus becomes expensive. Moreover, since a refrigerator is used to cool the superconducting coil in a vacuum container, a coil portion becomes large-sized. In this case, the advantage that the apparatus is small-sized and convenient cannot sufficiently be utilized. Furthermore, since a heat capacity of the superconducting coil is large, a time necessary for cooling the coil at a predetermined temperature with the refrigerator is long. There is also a problem that a time from the start of cooling until the start of measurement is long.
To solve the aforementioned conventional problem, the present applicant of the present invention has developed and filed a prior application for the nuclear magnetic resonance apparatus in which a high-temperature superconductor is used (Japanese Patent Application Laid-Open No. 248810/1999). In this apparatus, a superconducting current flows through the high-temperature superconductor which is cooled in a vacuum insulating container and to which the magnetic field is applied. Then, the superconductor captures the magnetic field to constitute a magnetic field supply member, the magnetic field is used as the main magnetic field, and the NMR signal of a material to be measured disposed in the magnetic field is detected by a detection coil and spectrometer disposed adjacent to the material to be measured.
In the nuclear magnetic resonance apparatus, the superconducting current flows through the high-temperature superconductor, the magnetic field is captured, and the magnetic field supply member is constituted. Therefore, a strong static magnetic field comparable to the conventional superconducting magnet can be formed without using the expensive liquid helium.
However, as shown in
FIG. 2
, a magnetic field distribution generated in the conventional high-temperature su
Ito Yoshitaka
Mizutani Uichiro
Nakamura Takashi
Oka Tetsuo
Uzawa Jun
Griffin & Szipl, P.C.
Lefkowitz Edward
Riken
Shrivastav Brij B.
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