JPH0370545A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PURPOSE:To reduce burden of an operator and improve safety by detecting an inroad of a magnetic body into a static magnetic field by means of an inroad detecting device and making the static magnetic field disappear based on this detecting signal by means of a putting out device. CONSTITUTION:An apparatus is furnished with a superconductive magnet stage 3 provided with a static magnetic field generating device, a device 4 placed on the stage and detecting an inroad of a magnetic body in a static magnetic field, a putting out device 5 as a temp. elevating device putting out the static magnetic field based on an electric current i as a detecting signal from the detecting device and a bed 8. when such a magnetic body that disturbs the static magnetic field inroads, as the static magnetic field is changed and an inroad detecting device detects a change in the static magnetic field and accordingly detects inroad of a magnetic body and transmits a detecting signal to the putting out device, which makes the static magnetic field disappear based on this detecting signal. Therefore, it is unnecessary for an operator to perform an examination if a patient has a magnetic body whenever the patient enters in a room and it results in reducing burden of the operator. In addition, there exists no possibility that a worker other than the operator brings accidentally a magnetic body in the room and it results in breakage of the apparatus.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention provides a method for obtaining a magnetic resonance image of a subject (usually a patient) with a safety device against the intrusion of magnetic substances into a static magnetic field. The present invention relates to a magnetic resonance imaging device (hereinafter referred to as an MHI device).

(Prior technology) A superconducting magnet is equipped with a superconducting magnet that generates a static magnetic field by passing a current through a superconducting coil in a superconducting state.A subject is placed in this static magnetic field, and a high-frequency magnetic field is applied in a direction perpendicular to this static magnetic field to perform magnetic resonance. A superconducting MR system is known in which a phenomenon is generated and a gradient magnetic field is applied so as to be superimposed on a static magnetic field, which is detected by an MR multiplied signal probe obtained from a subject and imaged.

This superconducting MRI apparatus normally generates a high magnetic field of 0.2 T (tesla) or more.

Therefore, when a magnetic body enters the static magnetic field, an attractive force is generated in the magnetic body in accordance with the magnitude of the magnetic permeability of the magnetic body, and the static magnetic field is disturbed. Magnetic materials include ferromagnetic materials with high magnetic permeability such as iron, which has a large attractive force even for small objects, and paramagnetic materials such as aluminum, which have a large attractive force even if they have low magnetic permeability and are relatively heavy. There are diamagnetic materials with low magnetic permeability such as copper that are magnetized in the direction opposite to the direction of the magnetic field and weaken the magnetic flux.

For example, if a patient's post-surgery hemostasis clip is small but made of ferromagnetic material, it will exert a large attraction force that will disturb the static magnetic field. There is a danger that it will be drawn into the magnet and come off.

As described above, it is difficult to judge from the outside whether an object is actually attracted to a superconducting magnet due to the relationship between the strength of the static magnetic field and the permeability of the magnetic material.

Therefore, in order to prevent accidents such as magnetic objects being drawn into the magnet, operators must use a magnetic material detector or similar device to test whether or not a patient is carrying any magnetic material before the patient enters the examination room. I was going.

(Problems to be Solved by the Invention) Since the operator has to conduct a magnetic substance possession test every time a patient enters the room, there is a problem in that the burden on the operator is large.

In addition, there was a problem in that a worker other than the operator accidentally brought in a magnetic material, which was attracted to the superconducting magnet and damaged the MR device.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a magnetic resonance imaging apparatus that reduces the burden on the operator and improves safety.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the device according to claim 1 of the present invention comprises static magnetic field generating means for generating a static magnetic field by passing a current through a coil; The apparatus includes an intrusion detecting means for detecting intrusion into the static magnetic field of a magnetic substance that disturbs the static magnetic field, and a dissipating means for dissipating the static magnetic field based on a detection signal from the detecting means.

Further, the device according to claim 2 of the present invention includes a static magnetic field generating means that generates a static magnetic field by passing a current through a superconducting coil in a superconducting state, and detects intrusion into the static magnetic field of a magnetic substance that disturbs the static magnetic field. and a vanishing means for vanishing the static magnetic field based on a detection signal from the detecting means.

Furthermore, the device according to claim 3 of the present invention is the device according to claim 1 or 2, wherein the dissipation means includes resistance means for converting electrical energy caused by a current flowing through the coil into thermal energy. .

A fourth aspect of the present invention provides a device according to the second aspect, in which the vanishing means includes temperature raising means for raising the temperature of the superconducting coil to a critical temperature or higher.

(Function) Claims 1 and 2 characterized by the following functions of the device having the above configuration:
In the described device, the static magnetic field changes when a magnetic substance enters to the extent that it disturbs the static magnetic field.

The intrusion detection means detects the intrusion of the magnetic material by detecting changes in the static magnetic field, and sends a detection signal to the erasure means. The vanishing means vanishes the static magnetic field based on this detection signal.

In the device according to claim 3, the resistance means of the dissipation means converts the current flowing through the coil from electrical energy to thermal energy to dissipate the static magnetic field.

In the apparatus according to claim 4, the temperature raising means of the vanishing means raises the temperature of the superconducting coil to a critical temperature or higher. The superconductivity of the superconducting coil is rapidly lost.

(Example) Examples of the present invention will be described in detail below.

FIG. 1 shows an external appearance of a superconducting MRI apparatus 1 according to a first embodiment of the present invention. FIG. 2 is a sectional view taken along the line AA shown in FIG.

This superconducting MRI apparatus 1 includes a superconducting magnet pedestal 3 equipped with a static magnetic field generating means 2 that generates a static magnetic field, and an intrusion detecting means 4 arranged on the pedestal 3 and detecting the intrusion of a magnetic material into the static magnetic field. , a dissipating means 5 as a temperature raising means for dissipating the static magnetic field based on the current i as a detection signal from the detecting means 4, and a bed 8 on which the patient is placed.

The static magnetic field generating means 2 includes a superconducting coil 2b disposed in liquid helium 2a, a vacuum section 2C disposed around the liquid helium 2a to keep the liquid helium 2a cool, and
A valve 2C is disposed on the top of the pedestal 3 and opens to allow outside air to enter the vacuum section 2C, and an explosion-proof valve 2C is provided to prevent internal pressure from increasing when the liquid helium 2a evaporates into helium gas. It has a valve 2d.

The intrusion detection means 4 detects the electromotive force caused by the movement of magnetic lines of force passing through the detection coil 4a in the X direction, as shown in FIG.

The vanishing means 5 has a controller 6 that receives the current i sent out from the intrusion detecting means 4, and a valve opening/closing section 7 that opens the valve 2C, and by opening the valve 2C, the vacuum Outside air is allowed to enter the portion 2C, and the superconducting coil 2b is heated to a critical temperature or higher to lose its superconductivity.

Next, the operation of the apparatus 1 of the first embodiment will be explained with reference to FIGS. 4 and 5.

FIG. 4 is a sectional view taken along the line BB shown in FIG. 1, and shows the state before the magnetic body 9 enters the static magnetic field region. The magnetic material 9 is made of a ferromagnetic material that is strong enough to disturb the static magnetic field.

Magnetic field lines M. As shown in the figure, is formed in a loop shape so as to pass through the opening 3a and protrude from both ends of the opening 3a in the axial direction of the opening 3a.

Here, as shown in FIG. 5, when the magnetic body 9 enters the static magnetic field region, the magnetic lines of force Ml are attracted toward the magnetic body 9, and the static magnetic field is disturbed. It will move in the X direction. Then, the detection coil 4
An electromotive force is generated at a, and a current i due to this electromotive force flows through the controller 6.

The controller 6 sends an open signal SO to the valve opening/closing section 7 based on this current i.

The valve opening/closing unit 7 opens the valve 2C based on the opening signal SO.

When the valve 2c is opened, outside air enters the vacuum section 2C, thereby causing the vacuum section 2C to lose its insulation effect and at the same time, the liquid helium 2a begins to boil and evaporate. This evaporated helium gas escapes to the outside through the explosion-proof valve 2d.

The superconducting coil 2b near the location where the liquid helium 2a has evaporated partially loses its superconductivity.

Next, the superconducting coil 2b at the part where the superconductivity is partially lost becomes a current resistance and generates heat, and this heat further warms other low temperature parts of the superconducting coil 2b, so the superconducting coil 2b The area where the superconductivity has been lost spreads at an accelerated pace, promoting the generation of heat. The generated heat further promotes evaporation of the liquid helium 2a. This phenomenon is called quenching, and the static magnetic field disappears within a short time.

FIG. 6 shows an external appearance of an MHI device 10 according to a second embodiment of the present invention.

This MRI apparatus 10 includes a pedestal 13 equipped with a coil 12b as a static magnetic field generating means for generating a static magnetic field, and a pedestal 13 disposed on the pedestal 13 to prevent a magnetic material 9 (see FIG. 5) from entering the static magnetic field. An intrusion detection means 14 for detecting an intrusion, a vanishing means 15 for vanishing the static magnetic field based on a current i as a detection signal from the detection means 14, and a bed 8 on which a patient is placed.
It has

The intrusion detection means 4 detects the electromotive force caused by the movement of magnetic lines of force passing inside the detection coil 4a in the X direction, as shown in FIG. 3 described above.

The vanishing means 15 has a controller 16 that receives the current i sent out from the intrusion detecting means 4, and a resistance means 17 that converts electrical energy caused by the current flowing through the superconducting coil 12b into thermal energy.

This resistance means 17 includes an electromagnetic switch 17a and a resistor 1.
7b, and in response to the switching signal Sc from the controller 16, the electromagnetic switch 17a is set to the normal contact point Pn.
The current flowing through the superconducting coil 12b is switched to the emergency contact Pe, and the current flowing through the superconducting coil 12b is passed through the resistor 17b, converting this electrical energy into thermal energy, rapidly attenuating the current flowing through the superconducting coil 12b, and rapidly reducing the static magnetic field. It is something that makes it disappear.

The operation of this MRI apparatus 10 will be explained with reference to FIGS. 4 and 5 mentioned above.

From the normal state where the magnetic body 9 does not enter the static magnetic field region as shown in FIG. 4, the magnetic body 9 changes as shown in FIG.
enters the static magnetic field region, the magnetic field line M4
, and the static magnetic field causes lines of magnetic force passing inside the disturbance detection coil 4a to move in the X direction. The detection coil 4a sends the electromotive force caused by the movement of the magnetic lines of force in the X direction to the controller 16 as a current.

The controller 16 sends a switching signal Sc to the resistance means 17.

The resistance means 17 switches the electromagnetic switch 17a from the normal contact Pn to the emergency contact Pe based on this switching signal Sc.

When the electromagnetic switch 17a is switched, the superconducting coil 12
The current flowing through the superconducting coil 12b flows through the resistor 17b, and this current is converted into thermal energy, and the current flowing through the superconducting coil 12b rapidly attenuates, and the static magnetic field rapidly disappears.

FIG. 7 shows an external appearance of a superconducting MHI device 20 according to a third embodiment of the present invention. FIG. 8 is a sectional view taken along the line CC shown in FIG. 7.

This superconducting MRI apparatus 20 includes a superconducting magnet pedestal 23 equipped with a static magnetic field generating means 22 that generates a static magnetic field, and a superconducting magnet pedestal 23 that is disposed on this pedestal 23 and prevents a magnetic material 9 (see FIG. 5) from entering the static magnetic field. The apparatus includes an intrusion detection means 4 for detecting an intrusion detection means 4, a dissipation means 25 for dissipating the static magnetic field based on a current i as a detection signal from the detection means 4, and a bed 8 on which a patient is placed.

The static magnetic field generating means 22 has a superconducting coil 22b disposed within liquid helium 22a, and a vacuum section 22c disposed around the liquid helium 22a to keep the liquid helium 22a cold.

The intrusion detection means 4 detects the electromotive force caused by the movement of magnetic lines of force passing inside the detection coil 4a in the X direction, as shown in FIG. 3 described above.

The vanishing means 25 is arranged near the controller 26 that receives the current i sent out from the intrusion detecting means 4 and the static magnetic field generating means 22, and is used as a heater as a temperature raising means for raising the temperature of the superconducting coil 22b to a critical temperature or higher. coil 27
and a heating power source 28 which also serves as temperature raising means and supplies heating power to the heater coil 27. When the controller 26 of the vanishing means 25 receives the current i sent out from the intrusion detection means 4, it sends out a heating signal sh for causing the heating power source 28 to supply heating power to the coil 27, and The coil 27 is heated.

The operation of the superconducting MRI apparatus 20 of the third embodiment will be explained with reference to FIGS. 4 and 5 described above.

When the magnetic material 9 enters the static magnetic field region as shown in FIG. 5 from the normal state in which the magnetic material 9 does not enter the static magnetic field region as shown in FIG. 9, and the static magnetic field causes lines of magnetic force passing through the disturbance detection coil 4a to move in the X direction. Detection coil 4
a sends the electromotive force caused by the movement of the magnetic lines of force in the X direction to the controller 26 as a current.

The controller 26 sends a heating signal sh to the heating power source 28.

The heating power source 28 operates the coil 27 based on this heating signal sh.
supplies heating power to the

When heating power is supplied and the heater coil 27 is heated, the temperature of the superconducting coil 22b becomes equal to or higher than the critical temperature, and the superconductivity of the superconducting coil 22b is rapidly lost. Therefore, the static magnetic field is rapidly lost.

In the superconducting MHI device of the first embodiment described above, the cooling function due to evaporation of the liquid helium 22a as a cooling medium is lost, so the static magnetic field is lost in a very short time.

In the MHI device of the second embodiment, normal conduction type MRI
It can be applied to both a superconducting MRI device and a superconducting MRI device.

In the devices of the first to third embodiments, it is determined whether or not the magnetic material is drawn into the magnet by determining whether the magnetic material changes the static magnetic field. It is possible to avoid the dangerous situation where the body is suddenly drawn into the magnet.

Although one embodiment has been described above, the present invention is not limited to this, and various modifications can be made without changing the gist thereof.

For example, although the intrusion detection means detects the movement of magnetic lines of force, it may be configured to measure the magnetic field strength and output changes in the magnetic field strength as a current. Further, the intrusion detection means may be one that sends out a signal only when an electromotive force greater than or equal to -window is generated. As a means for increasing the temperature, in addition to those shown in the apparatuses of the first and third embodiments, a liquid helium valve is opened to discharge liquid helium, and the temperature of the superconducting coil is raised to a critical temperature or higher. Good too.

[Effects of the Invention] According to the present invention detailed above, the intrusion detection means detects the intrusion of a magnetic substance into the static magnetic field, and the static magnetic field is extinguished by the extinguishing means based on this detection signal. Therefore, it is possible to provide a magnetic resonance imaging apparatus that reduces the burden on the operator and improves safety.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a first implementation device of the present invention, Fig. 2 is a sectional view of this device, Fig. 3 is an explanatory diagram of electromotive force generation of a detection coil, and Fig. 4 is a B shown in Fig. 1. An explanatory diagram showing the state before the magnetic material in the -B cross section enters the static magnetic field region, FIG. 5 is an explanatory diagram showing the change in magnetic field lines when the magnetic material enters the static magnetic field region, and FIG. 6 is an explanatory diagram of the present invention. 7 is a schematic configuration diagram of the second implementation device of the present invention, and FIG. 8 is a schematic configuration diagram of the third implementation device of the present invention.
The figure is a cross-sectional view of this device. 1.10.20. ...MRI apparatus, 2.Static magnetic field generation means, 2b, 22b..Superconducting coils, 4.Intrusion detection means, 5.Disappearance means (temperature raising means), 8.Magnetic material , 12b...Coil, 15...Disappearance means (resistance means), 25...Disappearance means, 27...
Heater coil (temperature increasing means), 28... Heating power source (temperature increasing means), i... Current, So, Sc, S
h...Signal. 30 Figure Figure

Claims (4)

[Claims] (1) A static magnetic field generating means that generates a static magnetic field by passing a current through a coil, an intrusion detecting means that detects the intrusion into the static magnetic field of a magnetic substance that disturbs the static magnetic field, and based on a detection signal from this detecting means. and a vanishing means for vanishing the static magnetic field. (2) static magnetic field generating means that generates a static magnetic field by passing a current through a superconducting coil in a superconducting state; an intrusion detecting means that detects the intrusion into the static magnetic field of a magnetic substance that disturbs the static magnetic field; A magnetic resonance imaging apparatus comprising: a vanishing means for vanishing the static magnetic field based on a detection signal. (3) The magnetic resonance imaging apparatus according to claim 1 or 2, wherein the vanishing means includes a resistance means for converting electrical energy caused by a current flowing through the coil into thermal energy. (4) The magnetic resonance imaging apparatus according to claim 2, wherein the vanishing means includes temperature raising means for raising the temperature of the superconducting coil to a critical temperature or higher.