JPH041926Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention is used in the field of medical diagnostic equipment or magnetic resonance imaging (MRI) equipment.

The present invention relates to an automatic impedance matching adjustment device for an MRI apparatus that automatically adjusts the impedance matching of an MRI apparatus.

(b) Prior art Figure 4 shows the circuit configuration of a high-frequency coil of an MRI apparatus. 1 is a high frequency transmitting coil, 2 is a variable capacitor, and 3 is a fixed capacitor.

There are two types of high-frequency coils: one for transmitting and one for receiving. In the case of receiving (not shown), the voltage applied to the capacitor is small, so it is possible to match the impedance by changing the capacitance of the capacitor depending on the voltage using a variable cap, etc. .

(c) Problems to be solved by the invention However, in the case of transmission, the withstand voltage of the capacitor becomes a problem, and the capacitance of the vacuum capacitors 2a and 2b is manually changed to match and adjust the impedance. . This is because, due to the nature of MRI, the capacitance of the capacitor cannot be changed by the power of a motor or the like that disturbs the static magnetic field.

The purpose of the present invention is to provide an automatic impedance adjustment device for an MRI apparatus that includes an actuator with a simple mechanism that changes the capacitance of a capacitor without disturbing the static magnetic field.

(d) Means for solving the problem The above object is to provide two containers that seal a fluid and include a movable member that reciprocates due to the fluid pressure, a fluid conduit interposed between these containers, This is achieved by providing a variable capacitor that is connected to one movable member and whose capacity changes as the movable member moves, and a drive means that reciprocates the other movable member.

(E) Function A variable capacitor is a capacitor whose capacitance changes by linear movement, and its capacitance is changed by a movable member that reciprocates with fluid.In this case, the movable member is made of an insulator, and the movable member is made of an insulator. The drive source of the system is placed in isolation. With this configuration of main parts, the capacitance of the capacitor can be changed without disturbing the static magnetic field.

(F) Embodiment A preferred embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 is a schematic vertical sectional view showing one embodiment.

The variable capacitor 2a or 2b is a vacuum container 2d
The capacitance changes depending on the positional relationship with the capacitor elements 2e and 2e' in the capacitor elements 2e and 2e'.

2f is a bellows, and a force is always acting in the direction of the arrow (←), and the expansion and contraction of the bellows 2f causes the electrode 2 to
The capacitance of the capacitor between c and 2c' changes.

4 and 4' are containers connected by a thin conduit 6. 5, 5' are movable members composed of bellows, and containers 4, 4' and movable members 5,
5' and conduit 6, fluid 7 is sealed off.

8 is an insulator that insulates the container 4 and the capacitor 2a or 2b, and 9 is an insulator that connects the movable member 5 and the capacitor 2a.

A compression spring 10 provides a force (→) that overcomes the force of the bellows 2f in the direction of the arrow, and always applies a compressive force to the fluid 7. A screw shaft 12 drives the movable member 5' and is connected to the motor 11.

Further, the encoder 13 is for controlling the drive system.

As shown in the figure, the rotation of the motor 11 is controlled by the movable member 5'.
Move or reciprocate in the direction of the arrow.

In this illustrated example, the movable member 5' is extended (← direction), pressure is applied to the fluid 7, and the movable member 5 is moved in the ← direction, so that the bellows 2f is moved in the ← direction.
The capacitance of the capacitor 2a changes automatically.

Here, the electrodes 2c and 2c' are the high frequency transmitting coil 1
, it is better to insulate with members 8 and 9.

Of course, this does not apply to cases where the configuration of the capacitors 2a and 2b is not as shown in the figure and the container 4 or the like may be connected.

The length of the connecting tube 6 is the strength of the static magnetic field of the MRI device,
It also depends on whether there is a magnetic shield or not, but approximately 3 to 4 meters are required.

The condenser 2a shown in FIG. 4 requires quite delicate adjustment, so if the fluid 7 thermally expands due to changes in ambient temperature, the capacitance of the condenser 2a will also change slightly, which is not preferable. Therefore, it is preferable to design the total volume of the fluid 7 to be as small as possible. However, if the containers 4, 4' themselves are made smaller, the effective area of the bellows 5, 5' becomes smaller, which is not preferable in terms of accuracy.

The fluid 7 is preferably water or oil with low kinematic viscosity, but water is better in terms of thermal expansion coefficient.

Further, the bellows 5, 5' are preferably welded bellows rather than formed bellows because the free length can be shortened even at the same displacement position.

FIG. 2 is a longitudinal sectional view of a main part of an embodiment in which a connecting pipe 6' made of an insulator is used instead of the conduit 6; in this case, the insulator shown in the embodiment of FIG. 8 becomes unnecessary, and the connecting rod 9 does not need to be an insulator.

FIG. 3 is a sectional view of a main part showing still another embodiment, in which the movable members 5, 5' are used under internal pressure.

In general, it is believed that using bellows under external pressure rather than internal pressure is more useful in terms of service life.

In the embodiment shown in FIG. 1, the compression spring 10 is not necessary if the direction of the force of the bellows 2f against the capacitors 2a and 2b is always in the opposite direction.

Further, if the connecting conduit 6 is made of a flexible member, a motor etc. can be easily arranged.

(G) Effects According to the present invention, the capacitance of the capacitor can be automatically changed without disturbing the static magnetic field using a simple and highly accurate actuator, and there is no need for human intervention.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical sectional view showing one embodiment of the present invention, FIG. 2 is a partial vertical sectional view showing another embodiment,
FIG. 3 is a schematic sectional view showing still another embodiment,
FIG. 4 is a circuit diagram of the main part of the high-frequency coil of the MRI apparatus. 2 is a variable capacitor, 4 is a container, 5 is a movable part, 6 is a connecting pipe, 7 is a fluid, 8 is an insulator, 9 is a connecting insulator, 10 is a compression spring, 11 is a motor, 1
2 is a drive screw, and 13 is an encoder.

Claims (1)

[Scope of utility model registration request] Two containers that seal fluid and include a movable member that reciprocates due to the fluid pressure, a fluid conduit interposed between these containers, and a fluid conduit that is connected to one movable member and whose volume is increased by the movement of the movable member. 1. An automatic impedance adjustment device for an MRI apparatus, comprising a variable capacitor that changes the impedance, and a drive means that reciprocates the other movable member.