JPH09135823A - Nuclear magnetic resonance device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive nuclear resonance device which is small-sized and lightweight and which can facilitate its maintenance and management, by using, as a main coil, a high temperature super-conductive coil which can be operated at a temperature below the temperature of liquefied nitrogen, and by providing a cooler such as a Joule Thomson refrigerator for cooling the main coil, and a power source and a lead part which are made of a high temperature super-conductive material. SOLUTION: An MRN device comprises a main coil 11 and a power lead which are made of a high temperature super-conductive material, and a Joule Thomson refrigerator 44 used as a cooling system, and a super-conductive magnetic system composed of a main coil 11 stored in a container 41, power leads 41, 42 for electrically connecting the main coil 11 to an external power source, and the closed loop type Joule Thomson refrigerator 44. Further, the diameter of a room temperature magnetic field space (bore) B is set to a value with which a human arm can be inserted therein or to a value less than the former value. As a material constituting power leads 42, 43, a high temperature super-conductive material which is operated at a temperature which is equal to or below the temperature of liquefied nitrogen and has an electric resistance which is zero, and accordingly, the height of a cryostat can be lowered, thereby it can be small-sized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact, lightweight and portable nuclear magnetic resonance apparatus, and more particularly to a nuclear magnetic resonance apparatus suitable for medical diagnosis.

[0002]

2. Description of the Related Art A nuclear magnetic resonance spectrometer is, for example, a chemical substance having a magnetic moment existing in a living body [proton (1H), carbon-13 (13C), phosphorus-31.
(31P) is a typical nuclide. ] Resonance (Nuclea
This is an analyzer that can non-destructively trace the chemical reaction occurring in cells, tissues, and organs as it is by using the phenomenon of r Magnetic Resonance (NMR).

There are numerous medical applications of NMR,
Among them, an MR imaging device (so-called MRI) capable of observing a brain perspective view and the like is a generally widely known application example.

As an example showing that the NMR apparatus typified by MRI can be used for diagnosing a disease, there is a diagnosis of a genetic disease called Max-Adr syndrome in which phosphorylase does not function.

Phosphorylase is an enzyme having a role of converting glycogen into glucose in muscle cells.
Patients with this illness become tired with the slightest amount of exercise.

[0006] Place the patient's arm in such symptoms in a magnetic field of the NMR apparatus, the change in pH due to it exercised ³¹
Phosphorylase, which should be involved in the synthesis of glucose, does not function in the muscle tissue of the patient as measured by P-NMR. In a normal person, glucose metabolism lowers the intracellular pH, whereas in a patient,
There is no change in intracellular pH.

[0007]

By the way, when the NMR spectrometer is viewed from the aspect of the apparatus, a static magnetic field coil for generating a first magnetic field, a radio frequency magnetic field pulse for generating a second magnetic field, and a reception for receiving an NMR signal. Device, an AD converter that enables analog signals to be processed by a computer, a system that controls operations for converting digitized time domain data into a frequency domain spectrum, pulse generation, timing control such as gate on / off, etc. It is composed of a controller, a display console, a storage disk device, and the like.

In such an NMR apparatus, the most important part that characterizes the performance of the apparatus is the part (magnet) that generates a static magnetic field.

It is no exaggeration to say that the performance of this magnet determines the performance of the device. No matter how good the other parts, such as the electronic circuit, are, the upper limit of the spectrometer performance determined by the magnitude of the magnetic field cannot be exceeded.

Here, the magnets used in the NMR spectrometer include permanent magnets (PM), electromagnetic magnets (EM), and superconducting magnets (Superco).
There are three types of nducting magnets (SCM), but a superconducting magnet that works at liquid helium (He) temperature can obtain a magnetic field strength (several tesla to ten and several tesla) that cannot be obtained by a permanent magnet or an electromagnetic magnet.

The fact that the magnetic field strength can be made high means that the group of nuclear magnetic moments in the actually observed resonance state, that is, the transverse magnetization component of the magnetization becomes large.
The S / N ratio can be improved. Further, the superconducting magnet has good magnetic field stability and uniformity.

The stability and homogeneity of the magnetic field are measured by NMR
It determines the reproducibility and resolution of the spectrum.

Under these circumstances, a superconducting magnet is mainly used as the magnet of the NMR apparatus, and its cooling mechanism is composed of a liquid He storage type cryostat.

However, the NMR apparatus using the liquid He storage type cryostat has the following problems.

First, for structural reasons, the size of the cryostat for accommodating the magnet part is roughly the size of one drum or a refrigerator for home use, and all NMR spectrometers that have been commercially available so far have this size. . Therefore, it is not portable and very heavy.

Further, since the liquid He has a problem of evaporative leakage and the like, a supply system (for example, about 0.5 liter per hour) is required, which is very troublesome when considering the filling time and frequency.

Further, since liquid He is expensive, there is a problem in terms of maintenance cost.

Therefore, the conventional NMR spectrometers are large and very expensive, and the maintenance is difficult, and their introduction is limited to some large hospitals and research institutions, which hinders their spread. Has become.

These problems are common to all devices using the nuclear magnetic resonance phenomenon.

It is therefore an object of the present invention to provide a nuclear magnetic resonance apparatus that is small in size, lightweight, easy to maintain and inexpensive.

[0021]

The NMR apparatus of the present invention comprises:
In order to achieve this purpose, the main coil is a high temperature superconducting coil that operates at a temperature below the liquid nitrogen temperature, and a refrigerator such as a Joule Thomson refrigerator that cools this main coil, a power source consisting of a high temperature superconductor, and the above main It is characterized in that it is provided with a lead portion for electrically connecting to the coil.

In the NMR apparatus of the present invention, the main coil is downsized by using the high temperature superconducting coil, and the cryostat is downsized by using the high temperature superconductor.
For example, the miniaturization of the cooling mechanism by using a Joule Thomson refrigerator greatly improves portability, and a portable NMR apparatus is constructed. In addition, since it is not necessary to supplement the working gas, the operability is remarkably improved.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION A specific NMR apparatus to which the present invention is applied will be described below.

This NMR apparatus is a portable or desktop type apparatus, and as shown in FIG. 1, a superconducting magnet system containing a main coil 11 which is a high temperature superconducting coil operating at a temperature of liquid nitrogen or lower. 1, a pump unit 2 including a pump of a refrigerator and a pump for vacuum exhaust for cooling the main coil 11 to a temperature of liquid nitrogen or lower, and a data processing device 3 with a display for displaying measurement results. Become.

Each pump of the pump unit 2 is connected to the superconducting magnet system 1 by a connecting pipe 4, while the data processing device 3 is connected to the superconducting magnet system 1 by a signal line 5. Alternatively, the signal line 5 may be replaced by a wireless data communication mechanism using infrared rays or the like.

Specifically, as shown in FIG. 2, the pump section 2 includes a small compressor 21 for supplying a working gas to a Joule-Thomson refrigerator, which is a cooling means of the superconducting magnet system 1, and a superconducting magnet system 1. Is connected to the gas connector of the Joule-Thomson refrigerator or the vacuum exhaust port of the superconducting magnet system 1 by the connecting pipe 4.

On the other hand, as the other system configuration, a configuration similar to that of a conventional NMR apparatus is adopted. For example, an RF-related unit necessary for acquiring an NMR signal and an ultra-compact for analyzing the obtained data. Processor (MP
U), and software for deriving a diagnosis result or evaluation of treatment effect based on the analysis result, a simple display function, and the like.

FIG. 2 shows an outline of these. In this system, N from the superconducting magnet system 1
The MR signal is amplified by an amplifier (preamplifier / power amplifier) 31, and further converted into a digital signal by an A / D converter 32 so that the analog signal can be processed by a computer, and then is taken into a microminiaturized arithmetic processing unit 33.

The captured data is displayed on the display 34.
Is displayed on the screen and is output from the printer as needed. Further, this data is stored in the main storage device 35 having a hard disk, a magneto-optical disk, or the like as a storage medium, and is analyzed based on a database for medical diagnosis,
It is used as a judgment material for diagnosis or evaluation of therapeutic effect.

Further, the microminiaturized arithmetic processing unit 33 also has a role of controlling the application of the second magnetic field (radio frequency magnetic field) in the superconducting magnet system 1, and the pulse programmer 36, the RF gate unit and the pulse generator 37. The RF amplifier 38 applies a radio-frequency magnetic field that rotates at the resonance frequency of the target nucleus on a plane perpendicular to the static magnetic field in a short-time pulse form.

The above is the schematic configuration of the NMR apparatus. In the NMR apparatus of this embodiment, the main coil 11 and the power lead are made of a high temperature superconducting material, and the cooling method is a Joule-Thomson refrigerator. Characterize. Therefore, next, the structure of the superconducting magnet system 1 will be described in detail.

As shown in FIG. 3, the superconducting magnet system 1 includes a main coil 11 in a container 41, and the main coil 1.
Power lead 4 for electrically connecting the
2, 43, and a closed-loop Joule-Thomson refrigerator 44.

Here, the container 41 includes a radiation shield 45,
It has a three-layer structure of a cryostat 46 and a magnetic shield 47, and is structured so as to be reliably thermally and magnetically isolated from the outside. The inside of the container 41 is evacuated by the turbo pump 22 connected to the vacuum exhaust port 48 to maintain a high vacuum.

The main coil 11 is composed of a high temperature superconducting coil, and the central space thereof is a room temperature magnetic field space (bore) B. The present NMR device is extremely small, and the room temperature magnetic field space B is large enough to accommodate a finger or arm.

The main coil 11 is made of a high temperature superconducting wire [eg, silver-coated bismuth-based copper oxide (Bi, Pb) ₂ S, which operates at liquid nitrogen temperature (77K) or lower.
r ₂ Ca ₂ Cu ₃ O ₁₀ superconductor] and its concentric solenoid coil. The performance of this main coil 11 is as follows.

In the main coil 11 which is a superconducting coil, the magnetic field strength and the critical current density Jc (unit: A / mm)
Is determined within a range that satisfies the following empirical rule [Equation (1)].

EmJc ² = 10 ¹¹ (1) Here, Em is magnetic energy (= 1 / 2LI ² , L:
Inductance, I: current, unit: Joule),
It is a parameter determined by the size of the main coil 11 and the strength of the magnetic field. The magnetic energy Em has a larger value as the coil is larger and the magnetic field is higher.

Generally, the magnetic energy Em of the coil and the current density J of the superconducting coil, which are determined by the size of the coil and the magnetic field strength, satisfy the above empirical rule. Therefore, it can be seen from this equation (1) that the larger the high-field superconducting coil, the lower the current density J is selected.

On the other hand, in the case of a small and high magnetic field superconducting coil, the magnetic energy Em can be smaller than the magnetic energy Em (about 1 megajoule) of an ordinary large high magnetic field NMR apparatus because of its small size. According to the equation, the current density J of the small-sized high magnetic field superconducting coil can be selected higher accordingly. Conversely, the higher the current density of the superconducting coil, the smaller and lighter the coil can be made. Further, under the condition that the magnetic energy Em is constant, the smaller the coil is, the stronger the magnetic field generated can be, so that there is an important advantage that the S / N ratio of the NMR signal can be improved.

From this point of view, in the present apparatus, as described above, the diameter of the room temperature magnetic field space B is set to a size at which a human arm can be inserted or less.

Next, regarding the power leads 42 and 43,
These power leads 42 and 43 are current lead wires connecting between a power supply at room temperature and a superconducting coil (main coil 11) at extremely low temperature. In this example, these power leads 42 and 43 are also made of a superconductor.

In the case of a conventional lead wire made of copper, heat penetrates into the cryogenic portion by heat conduction therethrough and evaporates the refrigerant (eg, liquid nitrogen) in the coil. In order to reduce this heat conduction, it suffices to make the lead wire thin, but then the electrical resistance of the lead wire increases, and the heat penetration into the coil due to Joule heating increases.

On the other hand, as a constituent material of the power leads 42 and 43, a high-temperature superconductor that operates at a temperature of liquid nitrogen or lower [eg, silver-coated bismuth-based copper oxide (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ superconductor], Joule heat generation is suppressed because the electric resistance is zero, and thermal conductivity can be lowered because it is an oxide. That is, even if the cross-sectional area of the lead wire is increased and the length thereof is greatly reduced, the same amount of current can flow. The height of the cryostat can be reduced accordingly, so that the superconducting magnet system 1 can be miniaturized.

Further, in this NMR apparatus, as a cooling system, a Joule-Thomson refrigerator 44 of a type in which the working gas can be supplied by a small compressor is used. In the Joule-Thomson refrigerator 44, the working gas is, for example, only a small amount of nitrogen gas, the nitrogen gas compressed by the compressor 21 is introduced from the high-pressure gas port 49, and a part of the liquid is cooled by the Joule-Thomson effect. The gas that has become nitrogen LN and has not become liquid passes through the low pressure circuit LP and returns while cooling the high pressure side HP with a heat exchanger (Countercurrent Heat Exchanger), and then enters the compressor 21 again from the low pressure gas port 50.

FIG. 4 shows the basic principle of the Joule-Thomson refrigerator 44. The high-pressure nitrogen gas becomes part of the liquid nitrogen LN at the Joule-Thomson valve JT, and the gas that has not become liquid is compressed as low-pressure nitrogen gas into the compressor 2
Return to 1.

The Joule-Thomson refrigerator 44 described above is a refrigerator whose cooling stage is compatible with the size of an IC chip. The main coil 11 and the power leads 42 and 43 are
Since it suffices to cool with a cooling stage designed to suit each size, the use of this Joule-Thomson refrigerator 44 has a great merit that the miniaturization of the cryostat is not restricted.

Furthermore, this Jul Thomson refrigerator 44
Has the following advantages: First, since it is not necessary to replenish the working gas, the operability of the device can be significantly improved while the economic effect is obtained.
Further, since there is no operating part in the cooling part other than the compressor 21, mechanical vibrations cause the main coil 11 and the power lead 42,
It is possible to make the entire superconducting magnet system 1 resistant to quenching without adversely affecting 43. Further, the miniaturization of the cryostat makes it possible to reduce heat entering the main coil 11 and the power leads 42, 43 due to radiant heat transfer. It is known from the well-known Stefan-Boltzmann equation that the amount of radiant heat transfer from the hot wall surface to the cold wall surface is proportional to the surface area of the cold portion (that is, the main coil 11 and the power leads 42 and 43). The smaller the cryostat, the smaller the surface area of the low temperature portion, so that the amount of radiant heat transfer can be reduced. This exerts a force as a countermeasure against quenching due to heat intrusion into the superconductor, and contributes to improvement in reliability of the device.

In the NMR apparatus having the above structure, the NMR
In order to measure the above, two kinds of magnetic fields are applied to a sample such as cells. The first is a strong static magnetic field. Under the influence of a large static magnetic field, the magnetic moment of the target nucleus in the sample is oriented either parallel or antiparallel to the magnetic field. Here, the energy of the magnetic moment parallel to the magnetic field is lower than the energy of the magnetic moment antiparallel to the magnetic field, and because the number of nuclei of this type is slightly higher, the population of nuclear magnetic moments, that is, the magnetization is the same as the static magnetic field. Turn to the direction.

Next, as a second magnetic field, when a radiofrequency magnetic field rotating on the plane perpendicular to the static magnetic field at the resonance frequency of the target nucleus is pulsed for a short time, the magnetization is determined by the magnitude of the radiofrequency magnetic field. Precession stops at that time interval at the frequency. Since an NMR device (NMR spectrometer) observes an in-plane component (transverse magnetization component) perpendicular to the static magnetic field direction of magnetization, which is the vector sum of nuclear magnetic moments in a resonance state, the larger the transverse magnetization, the greater the signal. The detection sensitivity of. When the pulse is cut in the state of being in a resonance phenomenon in this way, the target nucleus returns to its original orientation state while emitting electromagnetic waves (a process called relaxation).

Therefore, the transverse magnetization decays with time. If an NMR signal that disappears with this time (an analog signal in the time domain called FID) is converted into a spectrum in the frequency domain and data such as the relaxation time associated with the attenuation is used together, it is possible to analyze the biological tissue and the composition distribution.

Therefore, by using such an NMR apparatus, the metabolic function of the living body can be elucidated nondestructively. For example, in Japan, 40 in the early 1990s
The incidence of diabetes in adults over the age of 1 has already exceeded 1 in 10, which is a scale that can be regarded as one of the epidemics. The situation is similar in the world. Insulin-dependent diabetic patients control their insulin intake etc. by measuring the blood glucose level (glucose level in blood vessels) by cutting a part of their finger with a sword every day three times a day. It is a daily routine.

By using the NMR apparatus of the present invention, the same thing can be done non-invasively and not restricted to a specific place simply by inserting a finger into the bore. In addition, it can be applied to the metastatic ability of cancer only by blood and early prediction of recurrence, medical diagnosis by measuring in vivo pH, medical check in sports (for example, energy storage and exercise capacity of muscle, evaluation of fatigue), etc. .

[0053]

As is apparent from the above description, the NMR apparatus of the present invention allows the apparatus to be carried, which has been impossible in the past. Thus, for example, when a diabetic patient travels or the like, the device can be carried, illness management becomes extremely easy, and the patient can be released from place and time constraints.

Further, in the NMR apparatus of the present invention, the size of the room temperature magnetic field space (bore) is set to such a size that a finger or arm can be inserted, and the main coil is miniaturized, so that the strength of the generated magnetic field is easily guaranteed. Have advantages.

Further, the NMR apparatus of the present invention can be made much cheaper than the conventional one due to the downsizing of the apparatus, and since it is easy to maintain and manage, it can be used in general hospitals and homes. It can be widely spread.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an example of an NMR apparatus to which the present invention is applied.

FIG. 2 is a schematic diagram showing an example of a system configuration of an NMR apparatus to which the present invention is applied.

FIG. 3 is a schematic cross-sectional view showing a structural example of a superconducting magnet system.

FIG. 4 is a schematic diagram illustrating the principle of a Joule Thomson refrigerator.

[Explanation of symbols]

 1 superconducting magnet system 11 main coil 42, 43 power lead 44 Joule Thomson refrigerator B normal temperature magnetic field space (bore)

Claims (4)

[Claims] 1. A main coil is a high-temperature superconducting coil that operates at a temperature of liquid nitrogen or lower, and a refrigerator that cools the main coil and a lead that electrically connects a power source composed of a high-temperature superconductor to the main coil. And a magnetic resonance apparatus. 2. The nuclear magnetic resonance apparatus according to claim 1, wherein the refrigerator is a Joule-Thomson refrigerator. 3. The nuclear magnetic resonance apparatus according to claim 1, wherein the nuclear magnetic resonance apparatus is a portable type. 4. The nuclear magnetic resonance apparatus according to claim 1, which is used for medical diagnosis.