JPH0779953A - Mr imaging apparatus - Google Patents

Abstract

PURPOSE:To prevent the fluctuation of a magnetostatic field and restrain the vibration of a magnet main body due to a phase deviation from a self-shield (iron) even when a superconducting magnet main body (magnetostatic field) is vibrated by a vibration of a gradient magnetic field coil or a helium freezer at the time of measurement of a subject by an MR imaging apparatus. CONSTITUTION:A plurality of fixed bolts 11 are arranged at any places of a self-shield 4 to clamp and integratedly fix the self-shield 4 and a superconducting magnet main body 2 and each of the fixed bolts 11 is completely fixed by a locking nut 12 so that the superconducting magnet main body is directly and rigidly fixed to the self-shield 4 and is also locked and integratedly supported. Thus, a vibration of the superconducting magnet 2 is restrained and the superconducting magnet operates with the self-shield integratedly and synchronously so as to eliminate a phase deviation with the self-shield 4 due to such a vibration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a yoke magnet (self-shielding magnet) of an MR imaging apparatus, and particularly, to reduce vibration of a superconducting magnet body generated by a helium refrigerator or a gradient magnetic field coil added to the superconducting magnet. The present invention also relates to a structure for synchronizing the movement of the self-shielding material with the movement of the self-shielding material.

[0002]

2. Description of the Related Art Generally, an apparatus utilizing a nuclear magnetic resonance (NMR) phenomenon is used for structural analysis and research of physical properties of organic compounds, and is one of important analysis means for atomic arrangement and electronic structure of substances. Has become. In recent years, the application of this technology to the medical field has been advanced, and its use as a magnetic resonance (MR) imaging device for obtaining information such as hydrogen atom distribution in the human body and spin relaxation time as a tomographic image of an arbitrary cross section has been promoted. There is.

In such an MR imaging apparatus, it is necessary to apply a gradient magnetic field within a uniform static magnetic field in order to determine the irradiation observation surface of the subject. The static magnetic field and the gradient magnetic field are applied to the superconducting magnet 2 as shown in FIG.
It is provided by the self-shield 4 and the gradient coil 6.

A gradient magnetic field coil 6 is provided in the superconducting magnet 2 for generating a uniform static magnetic field (for example, 5000 gauss). Although not shown, the gradient magnetic field coil 6 is made of synthetic resin, and as an example, FRP core, X, Y,
It is configured by stacking and winding Z coil windings and molding them with resin. Then, the coil windings are excited in each by applying a pulse current, for example, at the time of measurement. Such a gradient magnetic field coil 6 is fastened and fixed to the superconducting magnet 2 by bolts 6a of support members at both ends thereof.

Since the gradient magnetic field coil 6 is placed in a very large static magnetic field (0.5T to 1.5T), a large electromagnetic force is exerted on the coil winding due to the static magnetic field and the pulse current during measurement. It acts to generate a large vibration, and the superconducting magnet 2 also vibrates accordingly. Further, the superconducting magnet 2 is filled with liquid helium in order to bring the internal superconducting coil into a superconducting state, and the helium refrigerator 3 is directly attached to the outer peripheral portion of the superconducting magnet in order to reduce evaporation and vaporization of the liquid helium as much as possible. It is assembled. Although it is necessary to operate this constantly, the superconducting magnet 2 was vibrated due to the vibration of the helium refrigerator 3.

However, since the superconducting magnet 2 is installed only on the base plate 4a of the self-shielding member 4 and is movable and adjustable for adjusting the magnetic field homogeneity, its vibration does not occur in the self-shielding member 4. Therefore, the self-shielding material 4 did not transmit the vibration, and did not exert the vibration suppressing effect on the vibration of the superconducting magnet 2.

For this reason, the uniform static magnetic field generated by the superconducting magnet is moved by the vibration of the magnet, but the self-shield material facing the vibration of the magnet itself is stationary and fixed.
It became equivalent to the self-shielding material moving in that vibration cycle, and it was subject to external magnetic field fluctuations, and in the end it was in the same state as the magnetic field was fluctuating. Therefore, when a subject is imaged in such a state, the image is caused to flow in the phase encoding direction due to fluctuations in the static magnetic field, which adversely affects the image and is a major cause of image deterioration.

[0008]

As described above, the conventional M
In the R imaging apparatus, since the gradient magnetic field coil in the static magnetic field is directly supported by the main body (vacuum container) with respect to the superconducting magnet, the vibration of the coil winding at the time of measurement directly vibrates the superconducting magnet. It was On the other hand, a helium refrigerator for preventing the evaporation of liquid helium is directly attached to the magnet body and is always in operation, so that the superconducting magnet is constantly vibrated. However, since the vibration of this superconducting magnet is not transmitted to the self-shield and is not subject to vibration suppression, the self-shielding material is fixed (does not move in synchronization) against the vibration of the superconducting magnet (vibration of the static magnetic field). However, the external magnetic field is changed, and the static magnetic field of the superconducting magnet is eventually changed due to the effect of the external magnetic field, and the measured image has an adverse effect such as causing an image deletion phenomenon.

The present invention has been made in view of the above problems, and the static magnetic field is not changed even when the superconducting magnet body vibrates due to the vibration of the gradient magnetic field coil or the helium refrigerator during measurement. An object of the present invention is to provide an MR imaging apparatus capable of suppressing vibration of a magnet.

[0010]

To achieve the above object, the present invention magnetically shields a leakage magnetic field of a superconducting magnet which generates a uniform static magnetic field, and therefore, an iron self-installed device is provided around the outside of the superconducting magnet. The shield member and the main body (vacuum container) of the superconducting magnet are constrained and integrally supported by a rigid member.

[0011]

According to the present invention, since the gradient magnetic field coil during measurement and the superconducting magnet that is vibrated by the helium refrigerator are restrained and integrally supported by the rigid member directly on the self-shielding material having a large mass, the superconducting magnet main body is provided. The vibration is synchronized with the self-shielding material without vibration, and the self-shielding material serves as a damping weight to suppress the vibration.

As a result, even if the coil winding of the gradient magnetic field coil vibrates at the time of measurement or vibrates by operating the helium refrigerator, the vibration of the superconducting magnet due to this vibration moves in synchronization with the self-shielding material. , The influence of the external magnetic field fluctuation due to the deviation of the self-shielding material from the magnet is eliminated. In addition, the vibration of the superconducting magnet body is also considerably suppressed by the self-shielding material serving as a damping weight, and the vibration that had a bad effect on the superconducting magnet can be reduced.
It is possible to obtain an MR imaging device with a simple structure and high stability and high measurement accuracy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an external view of an MR imaging apparatus according to the present invention, and FIG. 2 is a partial sectional view showing the main structure of FIG.

As shown in FIG. 3, the MR imaging apparatus 1 includes a superconducting magnet 2, a helium refrigerator 3, a self-shielding material 4, a shim tube 5, a gradient magnetic field coil 6, a transmission / reception coil 7, a control means 8 and a display means 9. It is mainly composed of.

The superconducting magnet 2 generates a uniform static magnetic field in a space having a predetermined size, and the helium refrigerator 3 suppresses evaporation of liquid helium as a refrigerant for cooling the superconducting coil in the superconducting magnet 2. The self-shielding material 4 magnetically shields the magnetic field leaking from the superconducting magnet 2, and the gradient magnetic field coil 6 superimposes the gradient magnetic field on the uniform static magnetic field to act.
Further, the subject 20 is arranged at a position where the gradient magnetic field acts within the static magnetic field, and the transmission / reception coil 7 is arranged near the outer periphery of the subject 20. The transmission / reception coil 7 may be provided separately for transmission and reception. The gradient magnetic field coil 6 and the transmission / reception coil 7 are connected to a control device 8, and the control device 8 is connected to an operation console 10 having a display means 9 such as a CRT. In such an MR imaging apparatus 1, first, the examination site of the subject 20 is positioned within a uniform static magnetic field generated by the superconducting magnet 2, and a gradient current, for example, is applied to the gradient magnetic field coil 6, whereby By generating a gradient magnetic field for slice selection and applying an irradiation signal (RF pulse) to the transmission / reception coil 7, a magnetic resonance action is caused in the subject 20. Then, the output signal based on the magnetic resonance action encoded in two directions is detected by the transmission / reception coil 7, this output signal is processed by the control device 9 to obtain an image of a specific portion of the subject 20, and this image is displayed. It is designed to be displayed on the means 9. .

The superconducting magnet 2 is a vacuum heat insulating container, and is formed by forming a through hole 2b in the axial direction of a hollow columnar body 2a. On the other hand, the shim tube 5 and the gradient magnetic field coil 6 have a cylindrical shape and are provided in the through hole 2b of the superconducting magnet 2.

The helium refrigerator 3 is a helium compressor 3b.
And the cold head 3a are a set,
Among them, the cold head 3a is directly attached to the hollow cylindrical body 2a of the superconducting magnet 2, and the helium refrigerator 3 is constantly cooled to suppress evaporation of the refrigerant (liquid helium) contained in the superconducting magnet 2. The vibration of the helium refrigerator 3 is directly transmitted to the superconducting magnet 2 during operation.

The self-shield 4 is arranged in a non-contact manner with the superconducting magnet 2 so as to surround the superconducting magnet 2 at a constant interval with an iron material having a constant thickness.

The gradient magnetic field coils 6 are arranged in the directions of three axes orthogonal to each other and generate X and X, respectively.
The Y and Z coil windings are superposed, wound, and fixed by resin molding. The through hole 2b of the superconducting magnet 2 is formed.
It is supported and fixed inside. The gradient magnetic field is excited by passing a pulse current through the coil 6 at the time of measurement, but oscillation occurs when the current is passed. This vibration is transmitted to the superconducting magnet 2 and also vibrates the superconducting magnet 2.

Therefore, an embodiment of the present invention for solving the problem that the superconducting magnet 2 vibrates is shown in FIG.
This will be described with reference to FIG. First, as shown in FIG. 1, a plurality of fixing bolts 11 and a lock nut 12 for fixing the fixing bolts 11 are attached to arbitrary positions of the self-shield 4, and the superconducting magnet 2 and the self-shield 4 are respectively arranged at arbitrary positions. It is configured to be supported integrally with restraint and rigidly supported.

FIG. 2 is a partial sectional view of the fixing bolt portion. The plurality of fixing bolts 11 are adapted to tighten and fix the outer surface of the superconducting magnet 2 from the outer surface of the self-shield 4 at an arbitrary position, and further, the fixing bolts 11
Is fixed by a lock nut 12 so as to be completely rigid. As a result, the superconducting magnet 2 is rigidly fixed at an arbitrary position with respect to the self-shield 4 and restrained and integrally supported, and the vibration of the superconducting magnet 2 due to the operation of the helium refrigerator 3a is also reduced and the gradient magnetic field coil 6 is provided. Vibration of the superconducting magnet 2 at the time of energizing the pulse current at the time of measurement is also reduced. Moreover, self-shield 4
Moves in synchronism with the superconducting magnet 2, eliminating the influence of fluctuations in the external magnetic field due to the deviation between the self-shielding material (iron) and the magnet (static magnetic field), and eliminating the adverse effects of static magnetic field vibration (fluctuation). .

[0022]

According to the present invention, a superconducting magnet (static magnetic field)
Is integrally constrained and supported by the self-shielding material directly by the rigid member, the phase shift is eliminated and the degree of freedom of displacement is also reduced. As a result, even when the coil winding vibrates when the helium refrigerator is operating and when the gradient magnetic field coil is energized,
Vibration of the superconducting magnet (static magnetic field) is suppressed, and since the self-shielding material (iron) and the magnet (static magnetic field) are integrally synchronized, mutual deviation due to vibration is eliminated, and as a result, external magnetic field fluctuation effects Since the influence of the static magnetic field vibration (fluctuation) is eliminated, the uniformity and stability of the magnetic field are not lowered, and the measurement accuracy is improved.

[Brief description of drawings]

FIG. 1 is an external view of an MR imaging apparatus according to the present invention.

FIG. 2 is a partial cross-sectional view showing the main structure of FIG.

FIG. 3 is a schematic overall configuration diagram of an example of a conventional MR imaging apparatus.

[Explanation of Codes] 1 MR imaging device 2 Superconducting magnet 3 Helium refrigerator 4 Self-shield 5 Shim tube 6 Gradient field coil 7 Transmitting / receiving coil 8 Control means 9 Display means 10 Console 11 Fixing bolt 12 Lock nut 20 Subject

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location 8105-2J G01N 24/06 530 Z

Claims (1)

[Claims] 1. A superconducting magnet that generates a uniform static magnetic field, an iron self-shielding material that magnetically shields a leakage magnetic field generated by the superconducting magnet, and a gradient magnetic field coil that generates a gradient magnetic field in the static magnetic field. MR imaging including a transmission / reception coil for detecting an output signal based on the magnetic resonance action of the subject in the static magnetic field and the gradient magnetic field, and processing the output signal to obtain image information at a specific portion of the subject In the apparatus, the superconducting magnet is restrained and integrally supported by the self-shielding material.
Imaging equipment.