JPH01303140A - Nuclear magnetic resonance diagnosing device - Google Patents

Abstract

PURPOSE:To reduce a noise due to an inclination magnetic field coil by adhering a buffer to the whole outside surface of a structure with adhesives by a supporting body and fitting the inclination magnetic field coil group to the outer surface of the buffer so that the inside can be equally contacted. CONSTITUTION:On the outer circumference of a supporting body 1, four coil groups of saddle-shaped coils 2a-2d to generate an inclination magnetic field in a Y axis direction are arranged, and the supporting body 1 is composed of a buffer layer 1a, a shell and an inside damping layer 1c to lie between coils. Coil groups 3a-3d arranged in an X axis direction to form 90 deg. in the Y axis direction are overlapped and fitted and an interlayer material 4 is provided at the clearance of respective coils. Though the interlayer material 4 absorbs the oscillation in the same way as the shell 1b, selection is performed from the material having the characteristic of that the intensity in which the deformation due to the electromagnetic force of the coil does not damage the stability of a magnetic field. Coil groups 2a-2d and 3a-3d are tightened and fixed with a tightening belt 5 from these outer-most circumferential part. Thus, the oscillation generated at the coil group of the inclination magnetic field coil is equally transferred to the supporting body, absorbed by the buffer, and thus, attenuation can be executed and the noise at the time of measuring a person to be tested is suppressed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gradient magnetic field coil for a nuclear magnetic resonance diagnostic apparatus,
The present invention relates to a sound reduction structure suitable for reducing impact noise generated by gradient magnetic field coils.

[Conventional technology]

Conventional gradient coils are made of high-strength materials, such as “F
Using RP etc. as a support, placing a coil on its outer periphery, and interposing a cushioning material only between the support and the coil,
The coil had a structure that was identified using identification metal fittings at multiple points. As a result, the vibration of the coil is transmitted to the support body even if a cushioning material is inserted, causing the support body to vibrate and generate noise.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not give sufficient consideration to effectively damping the transmission of the pulse load applied from the coil to the support body due to the electromagnetic force caused by the pulse current flowing through the coil, and as a result, the support body vibrates and produces a loud impact sound. It was occurring. In addition, a structure that rapidly attenuates the vibrations of the support body and a means to prevent the resonance phenomenon caused by the vibration body when the support body is cylindrical are not adopted, and the noise caused by the continuous impact sound that occurs during measurement of the subject is not adopted. It was large, reaching 60-8C) dB (A scale). This noise eventually deteriorates the sound environment in the test subject's space, and may even cause the test subject to move during measurement. The aim is to further reduce the amount of stress and provide a comfortable testing environment for the test subject.

[Means to solve the problem]

The above-mentioned problems include a magnet that generates a static magnetic field, a group of gradient magnetic field coils that are installed in the static magnetic field and that generate independent gradient magnetic fields in three axial directions perpendicular to each other, and a support that supports the group of gradient magnetic field coils. In the nuclear magnetic resonance diagnostic apparatus, the support has a buffer material bonded to the entire outer surface of the structure with an adhesive having an adhesive strength equal to or higher than the tensile strength of the constituent materials, and This problem is solved by a nuclear magnetic resonance diagnostic apparatus in which the gradient magnetic field coil group is attached to the surface so that the inner sides thereof are evenly in contact with each other.

Further, the vibration damping body may be bonded to the inner surface of the structure with an adhesive having an adhesive strength equal to or higher than the tensile strength of the constituent material of the outer vibration damping body, and the support body may be cylindrical. The outer peripheral side of the gradient magnetic field coil group may be identified by a band-shaped tightening material.

[Effect]

The coil is necessarily identified on the support, but if the identified points are concentrated, vibrations are easily transmitted from that point to the support. As shown in FIG. 6, the electromagnetic force of the coil acts as a uniformly distributed load F on the support 1, so that the electromagnetic force is applied evenly and dispersed, thereby reducing vibration. On the other hand, the support is centered around the structure, with a cushioning material attached to the outer surface of the structure and a vibration damping material bonded to the inner surface with a strength equal to or higher than the tensile strength of each material. Although the structure is designed to work as one, the buffer material provided between the gradient magnetic field coil and the structure converts the vibrations of the gradient magnetic field coil into heat, absorbs energy, and reduces transmission to the structure. . In addition, the vibration energy transmitted to the structure is further converted into heat by a vibration damper lined with adhesive on the inner layer, which serves to rapidly damp the vibrations of the structure. Furthermore, sound reduction can be achieved by using a material for the inner layer vibration damping body that also has sound absorbing properties that suppress vibrations into the air.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

As shown in FIG. 8, the magnetic field generating section, which is the subject measurement part of this device, includes a magnet 6 that generates a static magnetic field, a gradient magnetic field coil 12 placed inside the magnet 6, and further inside the gradient magnetic field coil 12, A probe 7 is provided for irradiating a high frequency magnetic field onto a subject 9 and for detecting nuclear magnetic resonance signals. The subject 9 and the probe 7 are mounted on a bed 8. The gradient magnetic field coil 12 is moved by the gradient magnetic field power supply 10 according to a measurement sequence. The probe 7 uses an RF transmitter/receiver 11 to irradiate a high frequency magnetic field RF and receive and amplify the signal.

The gradient magnetic field coil 12 is equipped with a coil that generates a gradient magnetic field in a direction orthogonal to three axes, and a coil 2a around the -axis.
~2d is shown schematically.

FIG. 7 shows an example of a typical sequence for measuring the magnetic resonance signals. This is a pulse train that simultaneously images N cross sections in a spin echo sequence. A high frequency magnetic field RF is applied as a 90'', 180° pulse with respect to the time axis T.

Depending on the time timing, the slice gradient magnetic field GS,
A phase encoding gradient magnetic field Gp and a nuclear magnetic resonance signal readout gradient magnetic field Gr are respectively applied, and sections 1 to N are continuously repeated according to the number N of multislices. The application time of each gradient magnetic field in this case varies depending on the imaging conditions, but is approximately in the range of several milliseconds to several tens of milliseconds,
The throughput of the rise and fall of the magnetic field is around 1 mS or less.

An embodiment of the present invention in which a uniaxial coil group of gradient magnetic field coils 12 is installed will be described with reference to FIGS. 1 and 2. Four saddle-shaped coil groups 2a, 2b, 2c, and 2d are arranged on the outer periphery of the support 1 to generate a gradient magnetic field in the Y-axis direction.
The support body 1 is provided with a buffer J? interposed between the support body 1 and the coil. ! 2
1a, a tube body 1b, and an inner damping layer 1c. FIG. 3 is a projection of FIG. 1 from the axial direction. Coil groups 3a, 3b, 3c, and 3d arranged in the X-axis direction, which forms 90 degrees with the Y-axis direction, are attached one on top of the other, and each coil An interlayer material 4 is provided in the gap. Similar to the tubular body 1b, the interlayer material 4 is also selected from materials having a strength that absorbs vibrations but does not impair the stability of the magnetic field when deformed by the electromagnetic force of the coil.

The belt 5 tightens the coils from the outermost periphery of the coil group 2.
Tightening identifies a to 2d and 3a to 3d. According to this identification method, since the coil group is tightened in a dispersive manner, the vibrations of the coils are only transmitted to the support body 1 in a dispersion-average manner.
It has the effect of lowering the order of vibration frequency. FIG. 3 is a three-dimensional view of the coils shown in FIGS. 1 and 2. ■ indicates the current direction correlation between coils. As a result, as shown in Fig. 4, the electromagnetic force of F is applied to the support 1 by the coil circumferential line segments 2a, 2 &2...2'I T 2 d2, and the electromagnetic force is as shown in Fig. 7. It is pulse-like as shown in the pulse sequence diagram. That vibration is the fifth
It has a main component in the n=2 vibration mode shown in Figure (a), and the vibration frequency is expressed by equation (1).

However, E: Young's modulus: moment of inertia of area ρ: density A: cross-sectional area a: radius n=2 The reason why n=2 can be determined from the state of application of electromagnetic force in FIG.

〔Effect of the invention〕

As described above, according to the present invention, vibrations generated in the coil group of the gradient magnetic field coils are evenly transmitted to the support body.

It can be attenuated by absorbing it with a cushioning material, and further reduced with a vibration damper, so it suppresses the noise during measurement of the examinee, and the noise environment in the examinee space is compared to the conventional noise level. It has the effect of being improved by 1/2 to 1/4.

[Brief explanation of the drawing]

Fig. 1 is an axial sectional view of a gradient magnetic field coil showing an embodiment of the present invention, Fig. 2 is a right side view of Fig. 1, Fig. 3 is a three-dimensional schematic diagram of Fig. 1, and Fig. 4 is an electromagnetic field generated by the coil. Figure 5 is a diagram showing the relationship between deformation order and vibration frequency, Figure 6 is a diagram showing the state of the load acting on the tube, Figure 7 is an example of the operation sequence of the device, and Figure 8 is a force action diagram. FIG. 1 is a configuration diagram of a nuclear magnetic resonance diagnostic apparatus centering on a measurement section. 1... Support body, 2a to 2d... Coil a" d,
1a... Buffer layer, 1b... Tube body, IC... Damping layer, 5... Tightening band, 12... Gradient magnetic field coil.

Claims (1)

[Claims] 1. A magnet that generates a static magnetic field, a group of gradient magnetic field coils that are provided within the static magnetic field and that generate independent gradient magnetic fields in three axial directions orthogonal to each other, and a group of gradient magnetic field coils. In the nuclear magnetic resonance diagnostic apparatus, the support has a cushioning material bonded to the entire outer surface of the structure with an adhesive having an adhesive strength equal to or higher than the tensile strength of its constituent materials, and A nuclear magnetic resonance diagnostic apparatus characterized in that the gradient magnetic field coil group is attached to the outer surface of a buffer material so that the inner sides thereof are evenly in contact with each other. 2. The nuclear magnetic resonance diagnosis according to claim 1, characterized in that a vibration damping member is bonded to the inner surface of the structure with an adhesive having an adhesive strength equal to or higher than the tensile strength of the constituent material of the vibration damping member. Device. 3. The nuclear magnetic resonance diagnostic apparatus according to claim 1 or 2, wherein the support body is cylindrical, and the outer peripheral side of the gradient magnetic field coil group is identified by a band-shaped tightening material.