JP2017015620A - Magnetic shield device, magnetic filed noise reduction method, and spinal cord induction magnetic field measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic shield device for a spinal cord induction magnetic field measuring system that can reduce a magnetic field noise.SOLUTION: The present magnetic shield device is a magnetic shield device used for a spinal cord induction magnetic field measuring system that applies an electric stimulation to a subject through electrodes attached to the subject and measures a magnetic field from the spinal cord of the subject induced by the electric stimulation with a magnetic sensor, and comprises: a magnetic shield cover that covers the electrodes; and a fixing member that can fix the magnetic shield cover so that the magnetic shield cover and the magnetic sensor have a certain relative positional relationship.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a magnetic shielding device, a magnetic field noise reduction method, and a spinal cord induced magnetic field measurement system.

  The spinal nerve activity diagnosis is a general diagnostic method used when there is a high possibility that the spinal cord has a lesion such as limb numbness or paralysis. At the time of diagnosing nerves, currently, image diagnosis by MRI (Magnetic Resonanse Imaging), CT (Computed Tomography), etc. is mainly used. It is possible to grasp the morphologically damaged part due to the pressure of the nerve or the lesion.

  However, it is often seen that the part that actually inhibits the nerve function is not all the deformed part of the spinal cord or nerve. Therefore, not only image diagnosis but also neurological findings such as listening to medical history are necessary for accurate spinal cord function diagnosis, and doctors are required to have experience and skill.

  Therefore, auxiliary diagnosis of nerve function by electrophysiological examination is indispensable. The methods currently used mainly are somatosensory evoked potentials, transcranial magnetic stimulation muscle evoked potentials, needle electromyograms, etc., but all are potential measurements from the body surface, so only rough diagnosis is possible. Not done.

  Among electrophysiological examination methods, there is spinal cord evoked potential measurement as a method capable of diagnosing spinal cord function in detail. Spinal cord evoked potential measurement can measure detailed electrical activity in nerves by placing an electrode near the nerve. However, since the catheter-like electrode is inserted to the vicinity of the nerve of the subject, the invasiveness to the subject is high, and a doctor needs a high technique for the insertion. In view of the above background, there is a need for a diagnostic method that can easily evaluate the detailed nerve function of the spinal cord in a non-invasive manner.

  When current is generated inside or outside the cell due to neural activity, a magnetic field due to the current is generated around the current. Unlike a current, a magnetic field is hardly affected by living tissue such as bone or soft tissue. It is theoretically known that magnetic field measurement has higher spatial resolution than potential measurement.

  Therefore, there is biomagnetic field measurement as a method for measuring a weak magnetic field generated by the activity of nerves and muscles of a living body outside the living body. For biomagnetic field measurement, a system using a SQUID (Superconducting quantum interference device) has been developed and actually measured as a magnetoencephalograph or magnetocardiograph. In general, since a biomagnetic field is very small with respect to an environmental magnetic field such as geomagnetism, the biomagnetic field measurement is usually performed in a magnetic shield room that shields the environmental magnetic field.

  In recent years, a spinal evoked magnetic field measurement system (spinal dynamometer) that measures the spinal evoked magnetic field generated by the nerve activity of the spinal cord using this biomagnetic field measurement has been developed, and it is now possible to evaluate the detailed nerve activity. . In order to measure the spinal magnetic field, which is weak compared to the magnetic field generated by brain and heart activity, a method of measuring the spinal evoked magnetic field when an electrical stimulus is intentionally applied to the nerve from the subject's skin is used. It has been.

  Electrical stimulation to the nerve is performed by applying an electric current to an electrode placed on the skin of the subject, but the current used for this electrical stimulation also generates a magnetic field, and magnetic field noise (noise) is measured against the measurement of weak spinal evoked magnetic fields. ) That is, in order to measure the spinal cord evoked magnetic field more accurately, it is necessary to reduce the magnetic field caused by the current during electrical stimulation to such an extent that the measurement is not affected. As a method of shielding and reducing the magnetic field noise derived from electrical stimulation, a method of covering an electrical stimulation application portion with a ferromagnetic material, a conductor, a superconductor, or the like, which is the same material as the shield room has been proposed.

  For example, by applying electrical stimulation after covering a part of a living body to which electrical stimulation is applied, wiring and surface electrodes with a magnetic shield cover, the pulsed magnetic field generated by pulsed electrical stimulation is blocked from the magnetometer, and the pulsed magnetic field A technique is disclosed that can measure an original weak magnetic field with a superconducting quantum interference device magnetometer in a state that is not affected by (see, for example, Patent Document 1).

  However, only shielding of the magnetic field caused by electrical stimulation with a magnetic shield material containing a ferromagnetic material so far does not provide an effective method for reducing magnetic field noise, particularly in the measurement of spinal cord-induced magnetic fields. This is because the magnetic field noise caused by the change in the position of the magnetic shield material made of a ferromagnetic material accompanying the movement of the arm cannot be reduced.

  That is, in order to efficiently generate the spinal cord-induced magnetic field, electrical stimulation is currently applied to the median nerve or ulnar nerve in the arm. Therefore, the electrode used for electrical stimulation is installed at the elbow joint of the subject. At this time, the activity of surrounding muscles is also induced in addition to nerves by electrical stimulation with electric current. In order to obtain the greatest possible spinal evoked magnetic field, the electrical stimulation applied to the nerve is relatively large. Therefore, electrical stimulation induces muscle activity as well as nerves, and the subject's arm moves greatly.

  Since a magnetic shield material made of a ferromagnetic material or a combination of a ferromagnetic material and a conductor contains at least a high magnetic permeability material, the magnetic shield material itself generates a magnetic field. When the generated magnetic field does not change with time, in the magnetic measurement, the generated magnetic field does not affect the measurement. However, in the measurement of the spinal cord evoked magnetic field, the subject's arm moves greatly by electrical stimulation. Therefore, only the conventional magnetic field shielding method that covers the vicinity of the electrode with the magnetic shield material causes the ferromagnetic material, which is the magnetic shield material, to move with the movement of the arm, resulting in a time change of the magnetic field and measuring the spinal cord-induced magnetic field. There was a problem that the environment of the low magnetic field noise required above could not be realized.

  This invention is made | formed in view of said point, and makes it a subject to provide the magnetic shielding apparatus for spinal cord induction magnetic field measurement systems which can reduce magnetic field noise.

  The magnetic shielding apparatus applies magnetic stimulation to the subject through an electrode attached to the subject, and uses a magnetic field in a spinal cord-induced magnetic field measurement system that measures a magnetic field from the spinal cord of the subject induced by the electrical stimulation with a magnetic sensor. A shielding apparatus, comprising: a magnetic shielding cover that covers the electrode; and a fixing member that can fix the magnetic shielding cover so that a relative positional relationship with the magnetic sensor is constant. .

  According to the disclosed technology, it is possible to provide a magnetic shielding device for a spinal cord evoked magnetic field measurement system capable of reducing magnetic field noise.

It is a figure explaining the spinal cord induction magnetic field measurement system which concerns on 1st Embodiment. It is a figure explaining the magnetic shielding apparatus which concerns on 1st Embodiment. It is a figure explaining the fixing method of a part of test subject's body in the magnetic shielding apparatus which concerns on 1st Embodiment. It is FIG. (1) explaining the magnetic shielding apparatus which concerns on 2nd Embodiment. It is FIG. (2) explaining the magnetic shielding apparatus which concerns on 2nd Embodiment. It is FIG. (3) explaining the magnetic shielding apparatus which concerns on 2nd Embodiment. It is a figure explaining the fixing method of a part of test subject's body in the magnetic shielding apparatus which concerns on 2nd Embodiment. It is a figure which shows the example of a measurement of the spinal cord induction magnetic field which concerns on the comparative example 1. FIG. It is a figure which shows the example of a measurement of the spinal cord induction magnetic field which concerns on the comparative example 2. FIG. It is a figure which shows the example of a measurement of the spinal cord induction magnetic field which concerns on a present Example.

  Hereinafter, embodiments will be described with reference to the drawings. In addition, in each drawing, the same code | symbol is attached | subjected to the same component and the overlapping description may be abbreviate | omitted.

<First Embodiment>
FIG. 1 is a diagram for explaining a spinal cord evoked magnetic field measurement system according to the first embodiment. FIG. 2 is a diagram for explaining the magnetic shielding apparatus according to the first embodiment. 1 and 2, the spinal cord evoked magnetic field measurement system 1 includes a spinal cord evoked magnetic field measuring device 10, a magnetic shielding device 20A, an electrical stimulation device 30, and an electrode 40 as main components. ing. A part of the spinal cord evoked magnetic field measurement system 1 is disposed in the magnetic shield room 100. In FIG. 1, the illustration of the magnetic shielding device 20 </ b> A and the electrode 40 is omitted, and is shown in detail in FIG. 2.

  The reason why the magnetic shield room 100 is used is to measure a spinal evoked magnetic field, which is a weak magnetic field generated from a living body. The magnetic shield room 100 can be configured by, for example, a laminate of a plate material made of permalloy or the like, which is a high magnetic permeability material, and a plate material made of a conductor such as copper or aluminum.

  The magnetic shield room 100 has an internal space with a size of, for example, about 2.5 m × 3.0 m × 2.5 m, and includes a door 110 that can transport apparatus tools and allow people to go in and out. The door 110 can be configured by stacking a plate material made of permalloy or the like, which is a high magnetic permeability material, and a plate material made of a conductor such as copper or aluminum, like the other portions of the magnetic shield room 100.

  In the present specification, the high magnetic permeability material refers to a material having a relative magnetic permeability greater than 1000. Examples of such materials include iron, nickel, cobalt alone, alloys thereof (including amorphous alloys, powders, and nanoparticles), ferrite, and the like in addition to permalloy.

  Hereinafter, the spinal cord evoked magnetic field measurement system 1 will be described in more detail. A bed 150 is installed in the magnetic shield room 100. In addition, a spinal cord evoked magnetic field measuring apparatus 10 is installed in the magnetic shield room 100, and a signal line 51 used for measurement, control, and the like is attached to the spinal cord evoked magnetic field measuring apparatus 10. The signal line 51 is composed of a twisted cable or the like to reduce magnetic field noise, and is drawn out of the magnetic shield room 100 through a hole 121 opened in the magnetic shield room 100.

  In the spinal cord evoked magnetic field measurement system 1, the subject 300 lies on his / her back on the bed 150 placed in the magnetic shield room 100, and the spinal cord evoked magnetic field is measured in a resting state. By performing the measurement in a resting state, not only the burden on the subject 300 is small, but also the positional deviation from the measuring device due to unnecessary movement of the subject 300, magnetic field noise from the muscle caused by muscle tension, etc. Can be reduced.

  The spinal cord inducing magnetic field measuring apparatus 10 includes a dewar 11 and a SQUID magnetometer 12 as main components. The dewar 11 holds liquid helium necessary for the cryogenic operation of the SQUID magnetometer 12. For example, the dewar 11 includes a protrusion 11x so as to be suitable for the measurement of the spinal cord-induced magnetic field, and the SQUID magnetometer 12 is installed in the protrusion 11x in a direction in which the spinal cord-induced magnetic field can be measured.

  The protuberance 11x in which the SQUID magnetometer 12 is installed is brought close to the cervical vertebra from the lower side of the subject 300 lying on the bed 150. Measurements can be made.

  When measuring spinal evoked magnetic fields, it is necessary to intentionally cause neural activity by electrical stimulation. Therefore, the electrode 40 is attached on the skin of the elbow joint of the subject 300, and electrical stimulation is applied. The electrode 40 includes an anode and a cathode, and is attached on the skin where a signal can be efficiently applied to the median nerve or the like of the elbow joint of the subject 300.

  A signal line 52 is attached to the electrode 40 to send a stimulus. The signal line 52 is composed of a twisted cable or the like in order to reduce magnetic field noise. The signal line 52 is drawn out of the magnetic shield room 100 through a hole 122 opened in the magnetic shield room 100 and is connected to the electrical stimulation device 30 installed outside the magnetic shield room 100.

  In order to cause neural activity of the subject 300, the electrical stimulation device 30 can pass a pulsed current between the anode and the cathode of the electrode 40. For electrical stimulation at the time of measuring spinal evoked magnetic fields, for example, a pulse current having a magnitude of about 4.0 to 6.0 mA is applied at 5 Hz. The magnetic field induced from the spinal cord induced by this electrical stimulation is measured by the SQUID magnetometer 12.

  In the spinal cord evoked magnetic field measurement system 1, the current itself used for the electrical stimulation when the electrical stimulation is applied becomes magnetic field noise. Specifically, the magnetic field created by the pulse current flowing between the signal line 52 from the electrical stimulator 30 to the electrode 40 and the anode-cathode of the electrode 40 enters the SQUID magnetometer 12 and becomes magnetic field noise.

  The magnetic field noise generated by the signal line 52 is reduced by twisting cable transmission or transmission by light, etc. However, with respect to the magnetic field noise generated by the pulse current flowing between the anode and the cathode of the electrode 40, these structures are used. I cannot solve it. Therefore, in the present embodiment, the fixed magnetic shielding device 20A is used in order to reduce magnetic field noise generated by the pulse current used for electrical stimulation and to measure the spinal cord-induced magnetic field more accurately.

  The magnetic shielding device 20 </ b> A includes a magnetic shielding cover 21 and a fixing member 22. The magnetic shielding cover 21 can be made of, for example, a high magnetic permeability material such as permalloy having a high magnetic permeability. As the magnetic shielding cover 21 is made of a material having a high magnetic permeability, the magnetic shielding effect can be enhanced. The magnetic shielding cover 21 is provided with a space 25 that holds a part 310 of the body of the subject 300.

  The fixing member 22 is a fixing member that can fix the magnetic shielding cover 21 so that the relative positional relationship with the SQUID magnetometer 12 is constant.

  Here, the “fixing member that can be fixed so that the relative positional relationship with the SQUID magnetometer is constant” refers to the relative to the SQUID magnetometer when the magnetic shielding device is incorporated into the spinal cord evoked magnetic field measurement system. It means a fixing member configured to fix the magnetic shielding cover to a predetermined member so that the positional relationship is constant.

  The fixing member 22 can be configured to fix the magnetic shielding cover 21 to the bed 150, for example. Alternatively, the fixing member 22 can fix the magnetic shield cover 21 to a heavy object such as the floor of the magnetic shield room 100, the dewar 11 of the spinal cord induction magnetic field measuring apparatus 10, or any member that can be fixed to the heavy object. You may comprise.

  In the present embodiment, the magnetic shielding device 20A can fix the magnetic shielding cover 21 and the magnetic shielding cover 21 to the bed 150 so that the relative positional relationship between the SQUID magnetometer 12 is constant. The example which has is shown. And the example which the magnetic shielding cover 21 was fixed to the bed 150 with the fixing member 22 when the magnetic shielding apparatus 20A was integrated in the spinal cord induction magnetic field measurement system 1 is shown.

  The magnetic shielding cover 21 is grounded by a ground wire. When the fixing member 22 is made of a nonmagnetic metal such as copper or aluminum, the magnetic shielding cover 21 may be grounded via the fixing member 22. The shape of the magnetic shielding cover 21 is preferably cylindrical in order to reduce magnetic field noise generated by a pulse current flowing between the anode and the cathode of the electrode 40.

  In measurement of the spinal cord evoked magnetic field, the subject 300 lies on the bed 150 with a light burden such as lying on his back, and electrical stimulation is applied by the electrode 40 attached to the surface of the subject 300. The position where the electrode 40 is attached is a place where stimulation is easily applied to the nerve, for example, an elbow joint part or a knee joint part.

  In order to reduce magnetic field noise generated by the pulse current flowing between the anode and cathode of the electrode 40, the magnetic shielding cover 21, the electrode 40, the body part 310 of the subject 300 to which the electrode 40 is attached, and the body What is necessary is just to install so that the peripheral part of the part 310 may be covered. Here, the body part 310 is, for example, an elbow joint part or a knee joint part.

  However, the body part 310 of the subject 300 to which electrical stimulation is applied induces muscle activity simultaneously with neural activity, so that the body part 310 of the subject 300 moves in response to the applied electrical stimulation. .

  Therefore, if the magnetic shielding cover 21 moves accompanying the movement of the body part 310 of the subject 300, the movement of the magnetic shielding cover 21 generates a spatial change in the magnetic field, resulting in a large magnetic field noise.

  That is, the SQUID magnetometer 12 used for the measurement of the biomagnetic field is a magnetic sensor that outputs a temporal change in magnetic flux as a voltage. Moreover, the high magnetic permeability material which is the material of the magnetic shielding cover 21 creates a spatially nonuniform magnetic field around it. Therefore, when the relative positional relationship between the SQUID magnetometer 12 and the magnetic shielding cover 21 changes, a time change occurs in the magnetic flux measured by the SQUID magnetometer 12, and the time change of the output becomes magnetic field noise.

  However, in the magnetic shielding device 20A according to the present embodiment, the magnetic shielding cover 21 is fixed to a heavy object such as the bed 150 by the fixing member 22, so that the magnetic shielding cover 21 moves the body part 310 of the subject 300. There is no movement accompanying it.

  That is, since the relative positional relationship between the SQUID magnetometer 12 and the magnetic shielding cover 21 is always constant, the time change of the magnetic flux measured by the SQUID magnetometer 12 is reduced, and the time change of the output, that is, the magnetic field noise can be reduced. it can. That is, magnetic field noise generated by the pulse current used for electrical stimulation can be reduced.

  FIG. 3 is a diagram for explaining a method of fixing a part of the body of the subject with the magnetic shielding device, and shows a specific example of an apparatus for fixing the part 310 of the body of the subject 300.

  The body part 310 of the subject 300 inserted into the space 25 of the magnetic shielding cover 21 is fixed by, for example, filling a gap between the magnetic shielding cover 21 and the body part 310 of the subject 300 with the buffer material 60. The As the buffer material 60, for example, a small granular resin material such as microbeads, a fluid, or the like can be used.

  The cushioning material 60 surrounds the body part 310 of the subject 300 in a state where the cushioning material 60 is placed in a flexible container such as a cloth bag. The bag filled with the buffer material 60 is surrounded by, for example, a pressure applying member 70 that is inflated by pressurized air. The pressure application member 70 includes a space 70 </ b> S inflated with pressurized air, a high-pressure air supply / exhaust valve 70 </ b> E, and an air supply / exhaust device.

  As described above, the spinal cord evoked magnetic field measurement system 1 according to the first embodiment is induced by the electrode 40 attached to the subject 300, the electrical stimulation device 30 that applies electrical stimulation to the subject via the electrode 40, and electrical stimulation. The spinal cord-induced magnetic field measuring device 10 provided with the SQUID magnetometer 12 for measuring the magnetic field from the spinal cord of the subject 300 and the magnetic shielding device 20A. The magnetic shielding device 20 </ b> A includes a magnetic shielding cover 21 that covers the electrode 40 and a fixing member 22 that fixes the magnetic shielding cover 21, and the relative positional relationship between the magnetic shielding cover 21 and the SQUID magnetometer 12 is constant. It is being fixed with the fixing member 22 so that it may become.

  As a result, it is possible to prevent the magnetic shielding cover 21 from moving along with the movement of the body part 310 of the subject 300, the time change of the magnetic flux measured by the SQUID magnetometer 12 is reduced, and the time change of the output, that is, the magnetic field noise Can be reduced. That is, magnetic field noise generated by the pulse current used for electrical stimulation can be reduced. As a result, it is possible to measure the spinal cord evoked magnetic field with higher accuracy and to diagnose the spinal nerve function.

<Second Embodiment>
In 2nd Embodiment, the example of the magnetic shielding apparatus provided with the electromagnetic cover in addition to the magnetic shielding cover is shown. In the second embodiment, description of the same components as those of the already described embodiments may be omitted.

  4-6 is a figure explaining the magnetic shielding apparatus based on 2nd Embodiment. 5 and 6 are views of the magnetic shielding device viewed from the opening side of the magnetic shielding cover.

  4 and 5, the magnetic shielding device 20B according to the second embodiment is provided with an electromagnetic cover 23 that covers the electrode 40 inside the magnetic shielding cover 21. This is different from the magnetic shielding device 20A according to the embodiment (see FIG. 2 and the like).

  In FIG. 4, a part of the electromagnetic cover 23 is covered with the magnetic shielding cover 21, but the whole electromagnetic cover 23 may be covered with the magnetic shielding cover 21. The electromagnetic cover 23 can be comprised from conductors, such as copper and aluminum, for example. The electromagnetic cover 23 is provided with a space 26 that holds a part 310 of the body of the subject 300. That is, the electromagnetic cover 23 and the magnetic shielding cover 21 have a structure that covers the electrode 40 used for applying electrical stimulation, a part of the signal line 52, and a part 310 of the body of the subject 300.

  The electromagnetic cover 23 is fixed to the bed 150 by a fixing member 24. However, the electromagnetic cover 23 may be fixed to a heavy object such as a floor of the magnetic shield room 100, a dewar of the spinal cord induction magnetic field measuring apparatus 10, or any member that can be fixed to the heavy object by the fixing member 24. Good.

  The electromagnetic cover 23 is grounded by a ground wire. When the fixing member 24 is made of a nonmagnetic metal such as copper or aluminum, the electromagnetic cover 23 may be grounded via the fixing member 24. The shape of the electromagnetic cover 23 can be a shape that hardly interferes with the magnetic shielding cover 21 and does not give discomfort when the subject 300 is fixed, for example, a cylindrical shape. In this case, the electromagnetic cover 23 can be disposed substantially concentrically inside the magnetic shielding cover 21. For example, an annular gap 28 is provided between the electromagnetic cover 23 and the magnetic shielding cover 21.

  Thus, it is preferable that the electromagnetic cover 23 is provided inside the magnetic shielding cover 21 and the electromagnetic cover 23 and the magnetic shielding cover 21 are spatially separated by the gap 28 so that they do not contact each other. In other words, it is preferable that the mechanism for reducing the influence of the movement of the living body is divided into the magnetic shielding cover 21 and the electromagnetic cover 23, and that the movement of the electromagnetic cover 23 is not easily transmitted to the magnetic shielding cover 21.

  Thereby, since it is possible to prevent the movement of the body part 310 of the subject 300 from being directly transmitted to the magnetic shielding cover 21, magnetic field noise can be further reduced.

  In addition, like the magnetic shielding apparatus 20C shown in FIG. 6, the electromagnetic cover 23 and the magnetic shielding cover 21 are connected by a member 29 that absorbs vibration such as a spring, and the movement of the body part 310 of the subject 300 is directly magnetically shielded. A structure that does not reach the cover 21 may be used. In this case, the fixing member 24 that fixes the electromagnetic cover 23 is not necessary. In this case, the same effect as described above can be obtained.

  FIG. 7 is a diagram for explaining a method of fixing a part of the body of the subject with the magnetic shielding device, and shows a specific example of an apparatus for fixing the part 310 of the body of the subject 300.

  When the electromagnetic cover 23 is provided inside the magnetic shielding cover 21, the body part 310 of the subject 300 inserted into the space 26 of the electromagnetic cover 23 uses the buffer material 60 and the pressure application member 70 as in FIG. 3. Can be fixed. The same applies to both the magnetic shielding devices 20B and 20C.

<Measurement example>
FIG. 8 is a diagram illustrating a measurement example of the spinal cord evoked magnetic field according to Comparative Example 1, and the spinal cord evoked magnetic field when a 4.0 mA pulse is applied as electrical stimulation is measured by the SQUID magnetometer 12. The horizontal axis represents measurement time [ms], and the vertical axis represents measurement magnetic field [fT].

  FIG. 8 shows the SQUID magnetometer 12 of the spinal cord-induced magnetic field when the magnetic field noise generated by the pulse current flowing between the anode and the cathode of the electrode 40 for electrical stimulation is not shielded, that is, when the magnetic shielding cover 21 is not attached. It is a measurement result by. In FIG. 8, magnetic field noise due to a pulse current is observed between 0 ms and several ms, and the peak height is approximately 2500 fT.

  FIG. 9 is a diagram showing a measurement example of the spinal cord evoked magnetic field according to Comparative Example 2, and the spinal evoked magnetic field when a pulse of 4.0 mA is applied as electrical stimulation is measured by the SQUID magnetometer 12. The horizontal axis represents measurement time [ms], and the vertical axis represents measurement magnetic field [fT].

  FIG. 9 is a measurement result of the spinal cord induced magnetic field by the SQUID magnetometer 12 when the arm of the subject 300 is covered with the magnetic shielding cover 21. However, in this measurement, the magnetic shielding cover 21 is disposed so as to cover the arm of the subject 300 and the electrode 40, but the magnetic shielding cover 21 is not fixed using the fixing member 22. That is, the magnetic shielding cover 21 is not fixed so that the relative positional relationship with the SQUID magnetometer 12 is constant. The magnetic shielding cover 21 was made of permalloy and aluminum.

  In FIG. 9, compared to FIG. 8, although the large pulsed magnetic field noise due to the pulse current seen from the start of measurement is reduced, the magnetic shielding cover 21 itself is caused by the movement of the arm. A relatively moderate magnetic field noise is observed at about 1000 fT.

  FIG. 10 is a diagram illustrating a measurement example of the spinal cord evoked magnetic field according to the present embodiment. The spinal cord evoked magnetic field when a pulse of 4.0 mA is applied as an electrical stimulus is expressed by using a fixed magnetic shielding device 20A and a SQUID. It is measured with a magnetometer 12. The horizontal axis represents measurement time [ms], and the vertical axis represents measurement magnetic field [fT].

  FIG. 10 shows a measurement result by the SQUID magnetometer 12 when the arm of the subject 300 is covered with the magnetic shielding cover 21 and the magnetic shielding cover 21 is fixed to the bed 150 by the fixing member 22 as shown in FIG.

  10, compared with FIG. 9, magnetic field noise due to a pulse current immediately after the start of measurement, or magnetic field noise having a relatively gentle peak due to movement of the magnetic shielding cover 21 accompanying movement of the arm due to electrical stimulation. The spinal cord-induced magnetic field of about 300 fT can be clearly measured.

  Thus, the magnetic shielding cover 21 is fixed to a heavy object such as the bed 150 by the fixing member 22 so that the relative positional relationship with the SQUID magnetometer 12 is constant, so that the magnetic shielding cover 21 is attached to the body of the subject 300. It has been confirmed that the magnetic field noise can be reduced because it does not move accompanying the movement of the portion 310.

  The preferred embodiments and examples have been described in detail above, but the present invention is not limited to the above-described embodiments and examples, and the above-described embodiments are not deviated from the scope described in the claims. Various modifications and substitutions can be made to the embodiments.

DESCRIPTION OF SYMBOLS 1 Spinal cord induction magnetic field measurement system 10 Spinal cord induction magnetic field measurement apparatus 11 Dewar 11x Protrusion part 12 SQUID magnetometer 20A, 20B, 20C Magnetic shielding device 21 Magnetic shielding cover 22, 24 Fixing member 23 Electromagnetic cover 25, 26, 70S Space 28 Clearance 29 Member 30 Electrical stimulation device 40 Electrode 51, 52 Signal line 60 Buffer material 70 Pressure applying member 70E Air supply / exhaust valve 100 Magnetic shield room 110 Door 121, 122 Hole 150 Bed 300 Subject 310 Part of subject's body

JP-A-7-67847

Claims (7)

A magnetic shielding device used in a spinal cord-induced magnetic field measurement system that applies an electrical stimulus to the subject via an electrode attached to the subject, and measures a magnetic field from the spinal cord of the subject induced by the electrical stimulus with a magnetic sensor,
A magnetic shielding cover covering the electrodes;
A magnetic shielding device comprising: a fixing member capable of fixing the magnetic shielding cover so that a relative positional relationship with the magnetic sensor is constant.   The magnetic shielding apparatus according to claim 1, wherein the magnetic shielding cover is made of a high permeability material.   The magnetic shielding apparatus according to claim 1, further comprising a member that fixes a part of the body of the subject within the magnetic shielding cover. An electromagnetic cover that covers the electrode is provided inside the magnetic shielding cover,
The magnetic shielding apparatus according to claim 1, wherein a gap is provided between the electromagnetic cover and the magnetic shielding cover.   The magnetic shielding apparatus according to claim 4, further comprising a member that fixes a part of the body of the subject within the electromagnetic cover. A magnetic field noise reduction method for use in a spinal cord-induced magnetic field measurement system in which an electrical stimulus is given to the subject via an electrode attached to the subject, and a magnetic field from the spinal cord of the subject induced by the electrical stimulus is measured by a magnetic sensor. ,
A magnetic field noise reduction method comprising: covering the electrode with a magnetic shielding cover, and fixing the magnetic shielding cover so that a relative positional relationship with the magnetic sensor is constant. An electrode attached to the subject;
An electrical stimulation device for applying electrical stimulation to the subject through the electrodes;
A spinal cord evoked magnetic field measuring device comprising a magnetic sensor for measuring a magnetic field from the spinal cord of the subject induced by the electrical stimulation;
A spinal evoked magnetic field measuring system comprising a magnetic shielding device,
The magnetic shielding device includes:
A magnetic shielding cover covering the electrodes;
A fixing member for fixing the magnetic shielding cover,
The spinal cord-induced magnetic field measurement system, wherein the magnetic shielding cover is fixed by the fixing member so that a relative positional relationship with the magnetic sensor is constant.

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