JPS63160315A - Gradient magnetic-field coil device for magnetic resonance imaging system - Google Patents

Abstract

PURPOSE:To reduce the vibration of a spool and the noise sharply by fixing a ring-shaped rib made of a non-magnetic metal to the central part of the spool in the axial direction. CONSTITUTION:A ring-shaped rib made of a non-magnetic metal material such as stainless steel is fixed to the central part of a spool 8 in the Z-axis direction. Because Young's modulus of the metal material is high as compared with that of a non-metal material such as a resin-laminated material, it is possible to enhance the rigidity of the spool 8 against the deformation in the diametric direction. Accordingly, it is possible to reduce the vibration of the spool due to the electromagnetic force of a gradient magneticfield coil.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gradient magnetic field coil device for a magnetic resonance image knob device, and more specifically, to a gradient coil device for a magnetic resonance image knob device. The present invention relates to a gradient magnetic field coil device for a magnetic resonance imaging apparatus, which includes a coil wound around a single winding frame to generate a gradient magnetic field.

[Conventional technology]

Figure ≠ shows the magnet part of a conventional magnetic resonance imaging device. In the same figure.

A gradient magnetic field coil (2) wound around a winding frame is arranged inside the opening of the static magnetic field generating magnet (1).

(3) indicates the bed device, and (3) indicates the subject. Figure 1 shows the configuration of a conventional gradient magnetic field coil (2). It is wound and held in a cylindrical winding frame (rIr) made of material.

For magnetic resonance imaging with the above configuration, a spatially uniform magnetic field K generated by the magnet h (1),
It is necessary to superimpose a gradient magnetic field that increases linearly with distance from the center.

Figure 6 shows the distribution of the magnetic field generated by the gradient magnetic field coils. Ru.

In Figure 6 (al), the biaxial gradient magnetic field coil (7
)teeth.

A circular coil is arranged symmetrically around the 0 point of the axis center.

Currents (Il) in opposite directions are applied to the coil pair.

A biaxial magnetic field (Hl is formed, but the strength of the magnetic field is uniform in the plane perpendicular to the two axes, and in the biaxial direction, it changes from reverse polarity to positive polarity in proportion to the distance from the center 0 point. In addition, in Figure 6 (bl), the X-axis gradient magnetic field coil (Y) has ≠ saddle-shaped coils arranged symmetrically around the 0 point of the axis center. A current (11) is passed through the coil in the direction of the arrow in the figure, generating a magnetic field in two axes, but the strength of the magnetic field is proportional to the X coordinate, and in the plane perpendicular to the X axis, The y-axis gradient magnetic field coil (6) is obtained by rotating the X-axis gradient magnetic field coil (jl) by σ around two axes.

In a magnetic resonance imaging apparatus, a current passed through a gradient magnetic field coil has a pulse-like waveform as shown in FIG. 7(a). For this reason, an electromagnetic mechanical force having a waveform similar to the current waveform is generated in the gradient magnetic field coil. The electromagnetic mechanical force generated in the coil is transmitted to one winding frame (f) K, and the winding frame (
r), vibrations and noise as shown in FIG. 7 (bl) are generated.

Since the gradient magnetic field coil is fixed to a cylindrical winding frame (1) K, in order to reduce the vibration and noise of the gradient magnetic field coil,
It is effective to increase the rigidity of the winding frame (J') and reduce the vibration of the first winding frame (rl).In order to increase the rigidity of the sixth winding frame Trl, it is effective to use a metal material with a high Young's modulus as the first winding frame material. However, because the gradient magnetic field coil is driven by a pulsed current as shown in Fig. 7 (al).

When a conductive material is used for the winding frame (J'), an eddy current is induced in the winding frame frl by the pulsed magnetic field generated by the gradient magnetic field coil, and the spatial distribution and temporal waveform of the gradient magnetic field are distorted. In addition, if a magnetic metal material such as a steel plate is used for the winding frame (rl), it will also distort the static magnetic field distribution generated by the magnet.For this reason, as a winding frame material for the gradient magnetic field coil,
As a result of investigating the vibration characteristics of such a single cylindrical winding frame (♂), in which a non-conductive material such as W fat laminate is used, the natural vibration mode of the first winding frame (J') is shown in Figure r ( alJb
Biaxial deformation as shown in (c) and (al,
It is a composite of radial deformation such as (bl, (cl).The vibration mode based on radial deformation is generated from several tens of 2 low frequencies, It has become clear that suppression of vibration based on radial deformation is effective in reducing vibration noise.

The following function is included in the natural frequency α based on radial deformation.

Here, (t, l is the thickness of the reel, (D) is the diameter, (E)
is the Young's modulus of the bobbin material, and (ρ) is the density.

Therefore, in order to increase the natural frequency based on radial deformation and reduce the generated vibration, it is sufficient to increase the plate thickness (tl) of one winding frame (lr), but the price and weight of one winding frame increases.

[Problem to be Solved by the Invention 3] In the conventional gradient magnetic field coil device for a magnetic resonance apparatus as described above, large vibrations are generated in the winding frame when the coil is excited, and noise is generated from the winding frame due to the vibration. However, there was a problem in that it caused pain to the subject located inside the reel. Also,
In order to reduce the vibration of the winding frame, it is possible to increase the thickness of the winding frame made of non-conductive material to reduce vibrations caused by radial deformation, but this would require an expensive and heavy winding frame. The problem was that it was necessary.

The present invention was made in order to solve the above-mentioned problems, and an object of the present invention is to obtain a gradient magnetic field coil device for a magnetic resonance imaging apparatus that can reduce vibration noise.

[Means for solving problems]

In the gradient magnetic field coil device for a magnetic resonance imaging apparatus according to the present invention, an annular rib made of a non-magnetic metal material is fixed to the axial center of one winding frame.

[For production]

In this invention, since the axial center of the winding frame is fixed to the annular rib made of non-magnetic metal material, the rigidity against radial deformation of the first winding frame is high, and the vibration caused by the radial deformation is high.
Noise is significantly reduced.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and in FIG. 1, (ri) is an annular rib made of a non-magnetic metal material such as stainless steel fixed to the center of the winding frame (Ir) in the biaxial direction. be.

In addition, the same reference numerals as in FIG. 5 indicate the same parts.

According to the above structure, since the Young's modulus of metal materials is generally higher than that of non-metallic materials such as resin laminates, by fixing one annular rib, the winding frame (fl
The rigidity against radial deformation can be increased. Therefore, the annular rib (5F) forms a short-circuit ring that can reduce the vibration of the reel due to the electromagnetic force of the gradient magnetic field coil, but as shown in Fig. 1, the axis of the reel (I) When installed at the center of the direction.

Since it is located at the center of the gradient magnetic field coil, which is called a symmetrical arrangement, it is shown in Fig. 6 fa1. (As you can see from bl.

The gradient magnetic field does not interlink with the annular rib. Therefore, there is no fear that the gradient magnetic field will be distorted due to the induction of eddy currents.

As described above, the annular rib made of a metal material with a higher Young's modulus than non-metallic materials such as resin laminates is fixed to the center of the first reel frame (1). r) The rigidity against radial deformation can be increased, and vibration noise when the coil is energized can be significantly reduced.

FIG. 2 shows another embodiment, in which the annular rib fixed to the axial center of the winding frame (J') is an annular rib made of a non-magnetic metal material divided into co-parts in the circumferential direction. Rib member (ria)
The circular annular rib members (ria) and (rib) made up of (rib) are fastened to each other with bolts (10).

The gradient magnetic field coil winding frame with the above configuration (II is a rib member (ria) in which one annular rib (ri) is divided in the circumferential direction) (
Since the rib (b) is fastened with the bolt (10), the one-ring rib (ri) can be easily attached from the outer periphery of the winding frame <Ir), and can be firmly fixed to the winding frame (lr). can.

Further, FIG. 3 shows another embodiment, in which the winding frame (r) is.

It consists of a winding frame member (ra) (J'b) divided in the axial direction, and an annular rib (ri) in the middle of the frame member (ra) (J'b).
/) is fixed.

The winding frame (lr) with this configuration has a winding frame member (fa) (r, b) divided into two parts in the axial direction, which is connected by an annular rib (ri) and a bolt (ll) provided at the center in the axial direction. Because they are fastened together, they have high rigidity against radial deformation, and at the same time, the required length of each reel member (ra) (rb,)
Since it is shortened to about 1/2 of the total length, it has the advantage that it can be manufactured at low cost.

〔Effect of the invention〕

The invention will be apparent from one or more of the descriptions.

An annular rib made of a non-magnetic metal material is fixed to the axial center of the winding frame of the gradient magnetic field coil, increasing the rigidity of the winding frame against radial deformation. Vibration and noise can be significantly reduced.

In addition, since the annular rib is placed at the axial center of the winding frame, the gradient magnetic field does not interlink with the annular rib, and even if a highly rigid metal material is used for the annular rib, eddy currents will not occur. There is no risk of induced magnetic gradient distortion.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of one embodiment of the present invention, Fig. 2 is another embodiment (al is a front view, (bl is a side view, Fig. 3 is a front sectional view of another embodiment, Figure ≠ is a partially cutaway perspective view of the magnet section of a conventional magnetic resonance imaging device, Figure 5 is a perspective view of a conventional gradient magnetic field coil device, and Figure 6 shows the generation distribution of the one in Figure 3. Schematic diagram: Figure 7 is a waveform diagram of drive current and vibration in the one shown in Figure 5; Figure R is a schematic diagram showing the axial vibration mode of the winding frame in the one shown in Figure 1; It is a schematic diagram showing the radial vibration mode of the winding frame in the figure. (/1 - magnet, (2)... gradient S field coil, (
g)... Winding frame, (ra), (tb)... Winding frame member, (ri) φ, annular rib, (ri a), (ri b)... annular rib member. In each figure, the same reference numerals indicate the same or corresponding parts. Folder 2 (a) (b) 9at9b: Day yF'Y"-rib protector 8a, 8b winding frame section Fig. 9X.

Claims (4)

[Claims] (1) A cylindrical winding frame attached to the opening of a magnet for generating a static magnetic field, a gradient magnetic field coil wound and held on this winding frame, and a non-magnetic metal fixed to the axial center of the winding frame. A gradient magnetic field coil device for a magnetic resonance imaging device, comprising an annular rib made of a material. (2) The gradient magnetic field coil device for a magnetic resonance imaging apparatus according to claim 1, wherein the nonmagnetic metal material is stainless steel. (3) A gradient magnetic field coil device for a magnetic resonance imaging apparatus according to claim 1, wherein the annular rib is formed by fastening annular rib members divided in the circumferential direction with bolts. (4) A gradient magnetic field coil device for a magnetic resonance imaging apparatus according to claim 1, wherein the winding frame comprises two winding frame members arranged in the axial direction with an annular rib sandwiched therebetween.