JP2011000273A - Magnetic body access preventing device and magnetic resonance diagnostic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more securely prevent generation of magnetic attraction than before.SOLUTION: Loop coils 11, 12 and 13 are set on a floor surface or under the floor surface near a bed 4 for mounting a subject 200. An access detecting part 15 detects the access of a magnetic body to an MRI apparatus 100 based on the change of induced electromotive force generated in the respective loop coils 11, 12 and 13 caused by the change of the strength of the magnetic field leaking from a static magnetic field generated in a static magnetic field magnet 1. A preventive motion control part 16 and a preventive motion part 17 perform preventive motions for preventing the magnetic body from being attracted with the magnetic field to the MRI apparatus 100 in response to the detection of the access of the magnetic body to the MRI apparatus 100 by the access detecting part 15.

Description

  The present invention relates to a magnetic substance approach prevention device that issues an alarm regarding the approach of a magnetic substance to a magnetic resonance diagnostic apparatus, and a magnetic resonance diagnostic apparatus that has a function for issuing such an alarm.

  The magnetic field generated by the magnetic resonance diagnostic apparatus extends to the outside of the magnetic resonance diagnostic apparatus. For this reason, so-called magnetic field attraction, in which the magnetic substance is attracted to the magnetic resonance diagnostic apparatus by the magnetic field, can occur.

  In recent years, the intensity of a magnetic field generated by a magnetic resonance diagnostic apparatus has become very large. For this reason, a large object may be aspirated or the moving speed of the aspirated object may increase, and the aspirated object or the magnetic resonance diagnostic apparatus may be damaged by a collision between the aspirated object and the magnetic resonance diagnostic apparatus. There was a fear.

JP 2004-350888 A

For this reason, it is stipulated as a rule for using the magnetic resonance diagnostic apparatus that the magnetic substance is not allowed to approach the magnetic resonance diagnostic apparatus. However, human error is said to occur with a probability of 3 × 10 ⁻³ and cannot be completely eliminated. For this reason, it has been difficult to sufficiently prevent magnetic field attraction by relying only on human attention.

  Therefore, in order to ensure safety, a technician or nurse may use a handy type magnetic substance detector to inspect whether an object approaching the magnetic resonance diagnostic apparatus contains a magnetic substance. However, in such an inspection, the presence or absence of a magnetic substance by the subject is inspected relatively strictly, but the inspection is relatively sweet for an object that a technician or nurse carries in the vicinity of the magnetic resonance diagnostic apparatus. There is a tendency to tend. For this reason, for example, a medical device such as an infusion stand, a stretcher, a wheelchair, or an oxygen cylinder may be brought into the vicinity of the magnetic resonance diagnostic apparatus even if it contains a magnetic substance, and magnetic field attraction may occur. It was.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to more reliably prevent the occurrence of magnetic attraction than in the past.

  A magnetic substance approach prevention device according to a first aspect of the present invention includes a loop coil disposed on or under a floor near a bed provided in the magnetic resonance diagnostic apparatus for placing a subject. The approach of the magnetic substance to the magnetic resonance diagnostic apparatus is detected based on the change of the induced electromotive force generated in the loop coil due to the change of the intensity of the leakage magnetic field from the static magnetic field generated by the magnetic resonance diagnostic apparatus. An approach detection unit, and the approach detection unit for preventing the magnetic substance from being attracted to the magnetic resonance diagnostic apparatus when the approach of the magnetic substance to the magnetic resonance diagnostic apparatus is detected. And a prevention operation unit that performs the prevention operation.

  A magnetic substance approach prevention apparatus according to a second aspect of the present invention is generated by a loop coil arranged in the vicinity of a bed provided in the magnetic resonance diagnostic apparatus for placing a subject and the magnetic resonance diagnostic apparatus. An approach detection unit for detecting an approach of a magnetic body to the magnetic resonance diagnostic apparatus based on a change in an induced electromotive force generated in the loop coil due to a change in the strength of a leakage magnetic field from a static magnetic field, and the approach detection A preventive operation unit that performs a preventive operation to prevent the magnetic substance from being attracted to the magnetic field by the magnetic resonance diagnostic apparatus in response to the approach of the magnetic substance to the magnetic resonance diagnostic apparatus detected by the unit; A switch for turning on / off the electrical connection between the loop coil and the proximity detector, and a predetermined first timing prior to the start of transmission of an excitation pulse in the magnetic resonance diagnostic apparatus, A detection unit that detects a predetermined second timing after the transmission of the excitation pulse is stopped, and until the second timing is detected after the detection unit detects the first timing And a control means for controlling the switch so as to turn off the electrical connection between the loop coil and the approach detection unit.

  A magnetic resonance diagnostic apparatus according to a third aspect of the present invention includes a static magnetic field magnet that generates a static magnetic field, a bed on which the subject is placed, and a transmitter that transmits excitation pulses to be applied to the subject. And a loop coil disposed on or under the floor near the bed, and the induced electromotive force generated in the loop coil due to a change in the strength of the leakage magnetic field from the static magnetic field. An approach detection unit for detecting the approach of the magnetic body to the bed, and the magnetic body is attracted to the magnetic resonance diagnostic apparatus in response to the approach detection unit detecting the approach of the magnetic body to the bed. A preventive operation unit that performs a preventive operation to prevent the occurrence of a failure, a switch that turns on / off electrical connection between the loop coil and the proximity detection unit, and the excitation pulse according to a predetermined pulse sequence In addition to controlling the transmitter, from the first timing prior to the first transmission of the excitation pulse according to the pulse sequence to the second timing after the last transmission of the excitation pulse according to the pulse sequence And a control means for controlling the switch so as to turn off the electrical connection between the loop coil and the approach detection unit.

  According to the present invention, occurrence of magnetic attraction can be prevented more reliably than before.

The figure which shows the structure of the magnetic resonance imaging apparatus which concerns on one Embodiment of this invention. The perspective view which shows the installation condition of the loop coil in FIG. The figure which shows the detailed structure of the coil opening-and-closing part in FIG. The flowchart which shows the process sequence of the main control part for control of the coil opening / closing part in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a magnetic resonance imaging apparatus (MRI apparatus) 100 according to the present embodiment. The MRI apparatus 100 shown in FIG. 1 includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a gradient magnetic field power supply 3, a bed 4, a bed control unit 5, a transmission RF coil unit 6, a transmission unit 7, a reception RF coil unit 8, and a reception. Unit 9, computer system 10, loop coils 11, 12, 13, coil opening / closing unit 14, approach detection unit 15, prevention operation control unit 16, and prevention operation unit 17.

  The static magnetic field magnet 1 has a hollow cylindrical shape and generates a uniform static magnetic field in an internal space. As the static magnetic field magnet 1, for example, a permanent magnet, a superconducting magnet or the like is used.

  The gradient magnetic field coil 2 has a hollow cylindrical shape and is disposed inside the static magnetic field magnet 1. The gradient magnetic field coil 2 is a combination of three types of coils corresponding to the X, Y, and Z axes orthogonal to each other. The gradient magnetic field coil 2 generates a gradient magnetic field in which the above three coils are individually supplied with electric current from the gradient magnetic field power supply 3 and the magnetic field intensity changes along the X, Y, and Z axes. The Z-axis direction is, for example, the same direction as the static magnetic field. The gradient magnetic fields of the X, Y, and Z axes respectively correspond to, for example, the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr. The slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section. The phase encoding gradient magnetic field Ge is used to change the phase of the magnetic resonance signal in accordance with the spatial position. The readout gradient magnetic field Gr is used for changing the frequency of the magnetic resonance signal in accordance with the spatial position.

  The static magnetic field magnet 1 and the gradient magnetic field coil 2 are accommodated in a gantry. In the gantry, a cavity (imaging space) is formed along the inner periphery of the gradient coil 2.

  The subject 200 is inserted into the imaging space of the gantry while being placed on the top 4a of the bed 4. The couchtop 4a of the couch 4 is driven by the couch controller 5 and moves in the longitudinal direction and the vertical direction. Usually, the bed 4 is installed such that the longitudinal direction thereof is parallel to the central axis of the static magnetic field magnet 1.

  The transmission RF coil unit 6 includes at least one coil and is disposed inside the gradient coil 2. The transmission RF coil unit 6 receives a high frequency pulse from the transmission unit 7 and generates a high frequency magnetic field.

  In FIG. 1, the static magnetic field magnet 1, the gradient magnetic field coil 2, and the transmission RF coil unit 6 are shown broken on a vertical plane passing through their central axes.

  The transmission unit 7 transmits a high-frequency pulse corresponding to the Larmor frequency to the transmission RF coil unit 6. As a result, an excitation pulse is transmitted from the transmission RF coil unit 6.

  The reception RF coil unit 8 includes at least one coil and is disposed inside the gradient coil 2. The reception RF coil unit 8 receives a magnetic resonance signal emitted from the subject under the influence of the excitation pulse. An output signal from the reception RF coil unit 8 is input to the reception unit 9.

  The receiving unit 9 generates magnetic resonance signal data based on the output signal from the reception RF coil unit 8.

  The computer system 10 includes an interface unit 10a, a data collection unit 10b, a reconstruction unit 10c, a storage unit 10d, a display unit 10e, an input unit 10f, and a main control unit 10g.

  The interface unit 10a is connected to the gradient magnetic field power source 3, the bed control unit 5, the transmission unit 7, the reception unit 9, and the like. The interface unit 10a inputs and outputs signals exchanged between these connected units and the computer system 10.

  The data collection unit 10b collects digital signals output from the reception unit 9 via the interface unit 10a. The data collection unit 10b stores the collected digital signal, that is, magnetic resonance signal data, in the storage unit 10d.

  The reconstruction unit 10c performs post-processing, that is, reconstruction such as Fourier transform, on the magnetic resonance signal data stored in the storage unit 10d, and obtains spectrum data or image data of the desired nuclear spin in the subject 200. Ask.

  The storage unit 10d stores magnetic resonance signal data and spectrum data or image data for each patient.

  The display unit 10e displays various information such as spectrum data or image data under the control of the main control unit 10g. As the display unit 10e, a display device such as a liquid crystal display can be used.

  The input unit 10f receives various commands and information input from the operator. As the input unit 10f, a pointing device such as a mouse or a trackball, a selection device such as a mode switch, or an input device such as a keyboard can be used as appropriate.

  The main control unit 10g has a CPU, a memory, and the like (not shown), and controls the MRI apparatus as a whole. The main control unit 10g controls the gradient magnetic field power source 3, the transmission unit 7, and the reception unit 9 so that a scanning operation for imaging the subject 200 is performed according to a pulse sequence to be applied for the imaging. It has a function. The main control unit 10g has a function of controlling the operation of the coil opening / closing unit 14 in synchronization with the execution of the control for the scanning operation according to the pulse sequence.

  FIG. 2 is a perspective view showing an installation state of the loop coils 11, 12 and 13.

  As shown in FIG. 2, the loop coils 11, 12, and 13 are embedded under the floor surface of the imaging room 300 in which the MRI apparatus 100 is installed. Alternatively, the loop coils 11, 12, and 13 may be disposed on the floor surface of the imaging room 300. If the loop coils 11, 12, and 13 are located in the vicinity of the MRI apparatus 100, the arrangement of the coils may be arbitrary, but they are arranged so as to surround the bed 4 as shown in FIG. 2. It is desirable.

  Each of the loop coils 11, 12 and 13 is induced by a change in magnetic flux density passing through the inside thereof, and generates a voltage. The loop coils 11, 12, and 13 are desirably configured so as to obtain appropriate sensitivity by appropriately adjusting the winding method, the number of windings, the interval between coil windings, and the like.

  The coil opening / closing part 14 includes three switches 14a, 14b and 14c as shown in FIG. The switches 14a, 14b, and 14c are provided between the loop coils 11, 12, and 13 and the approach detection unit 15 as shown in FIG. The switches 14a, 14b, and 14c turn on / off the electrical connection between each of the loop coils 11, 12, and 13 and the approach detection unit 15 under the control of the main control unit 10g.

  The approach detection unit 15 monitors the change in voltage generated in each of the loop coils 11, 12, and 13 and detects the approach of the magnetic body to the MRI apparatus 100 based on this change.

  The prevention operation control unit 16 operates the prevention operation unit 17 in response to the proximity detection unit 15 detecting that the magnetic body is approaching the MRI apparatus 100.

  The prevention operation unit 17 performs a prevention operation for preventing the magnetic material from being attracted to the MRI apparatus 100 by a magnetic field. For example, a sound reproducing device, a light emitting device, a display device, an airbag device, or a magnetic field disappearance means can be applied as the prevention operation unit 17.

  Next, the operation of the MRI apparatus 100 configured as described above will be described.

The static magnetic field magnet 1 generates a magnetic field for diagnosis in the imaging space inside. This magnetic field also leaks outside the imaging space of the static magnetic field magnet 1. The magnetic field generated by the static magnetic field magnet 1 is a static magnetic field that does not change with time, and the leaking magnetic field is also a static magnetic field. However, when a magnetic material approaches the MRI apparatus 100, the magnetic field strength (magnetic flux density) changes under the influence. The amount that the magnetic flux density passing through the loop coils 11, 12, and 13 changes at a certain time dt is dΦ, the amount that the magnetic flux density around the loop coils 11, 12, and 13 changes at the time dt is dB, If the area inside 13 is represented by S, the voltage V generated at both ends of the loop coils 11, 12, 13 is
V = − (dΦ / dt) = − (dB / dt) × S
It becomes. Since the area S does not change, the voltage V has a magnitude corresponding to dB / dt. That is, the voltage V has a magnitude corresponding to the amount of change in magnetic flux density per unit time. Therefore, the approach detection unit 15 determines that the magnetic body is approaching when any one of the voltages V generated by the loop coils 11, 12, and 13 exceeds the threshold value. Note that the threshold value is set to be larger than a voltage generated in accordance with a change in a normal static magnetic field in consideration of the performance of the static magnetic field magnet 1 and the like. That is, it is difficult to make the intensity of the magnetic field generated by the static magnetic field magnet 1 completely constant, and it actually fluctuates. Therefore, a threshold value is set so that the change in the voltage V corresponding to the change in the magnetic field is not erroneously detected as the approach of the magnetic body.

  The prevention operation control unit 16 waits for the approach detection unit 15 to determine that the magnetic body is approaching. Then, the prevention operation control unit 16 controls the prevention operation unit 17 to execute the prevention operation in response to the determination that the magnetic body is approaching. Under this control, the prevention operation unit 17 performs the prevention operation. When the prevention operation unit 17 is an audio playback device, the prevention operation is an output of a voice message. When the prevention operation unit 17 is a light emitting device, the prevention operation is light emission. When the prevention operation unit 17 is a display device, the prevention operation is a display of a text message, an icon, or the like. The contents of the voice message and the text message are, for example, “A magnetic substance is approaching the MRI apparatus”. When the prevention operation unit 17 is an airbag device, the prevention operation is the deployment of the airbag. When the prevention operation unit 17 is a magnetic field disappearance unit, the prevention operation is the disappearance of the static magnetic field generated by the static magnetic field magnet 1.

  Thus, when outputting a voice message, emitting light, displaying a character message or an icon, etc., it is possible to call attention to a person who is trying to bring the magnetic body close to the MRI apparatus 100, and the magnetic body is MRI. It is possible to prevent the device 100 from being approached. Further, when the automatic door is closed or the airbag is deployed, it is possible to physically prevent the magnetic material from being brought closer to the MRI apparatus 100 any more. When the disappearance of the static magnetic field is executed, even if the magnetic body is brought close to the MRI apparatus 100, it is possible to prevent the magnetic field from being attracted. As a result, it is possible to prevent magnetic attraction from occurring more reliably than before.

  Even if the magnetic body is not close to the loop coils 11, 12, and 13 and there is a certain distance between the magnetic body and the loop coils 11, 12, and 13, the periphery of the loop coils 11, 12, and 13 The leakage magnetic field is disturbed by the influence of the magnetic substance, and the magnetic flux density passing through the loop coils 11, 12, and 13 changes. In particular, since the loop coils 11, 12, and 13 are disposed in the vicinity of the MRI apparatus 100, the leakage magnetic field around the loop coils 11, 12, and 13 is stable. For this reason, the threshold value can be set relatively small, and a relatively small disturbance of the leakage magnetic field can be detected as the approach of the magnetic body. Furthermore, since the drip stand, stretcher, wheelchair, or oxygen cylinder is large in size, the leakage magnetic field around the loop coils 11, 12, 13 is likely to be disturbed. For this reason, it is possible to detect the approach of a drip stand, stretcher, wheelchair, oxygen cylinder, or the like before the magnetic field attraction occurs, and take preventive action.

  Furthermore, the magnetic substance contained in an infusion stand, a stretcher, a wheelchair, or an oxygen cylinder is often present at a low position (position close to the floor). For this reason, when an infusion stand, a stretcher, a wheelchair, or an oxygen cylinder approaches the MRI apparatus 100, the leakage magnetic field at a low position tends to be more disturbed. Since the loop coils 11, 12, and 13 are disposed in the vicinity of the floor surface, the loop coils 11, 12, and 13 can generate a large voltage V corresponding to the large disturbance of the leakage magnetic field as described above. Particularly high detection sensitivity can be obtained for the approach of an infusion stand, stretcher, wheelchair, or oxygen cylinder.

  Now, in order for the approach detection unit 15 to detect the approach of the magnetic material as described above, each of the loop coils 11, 12, and 13 needs to be electrically connected to the approach detection unit 15. However, when performing a scanning operation, an excitation pulse is transmitted from the transmission RF coil unit 6. This excitation pulse also changes the magnetic flux density through the loop coils 11, 12, 13, so that a voltage is generated in each of the loop coils 11, 12, 13. In addition, since the excitation pulse has a very large energy compared to the fluctuation of the leakage magnetic field, the voltage generated in each of the loop coils 11, 12 and 13 becomes large. And when such a big voltage is input into the approach detection part 15 as it is, there exists a possibility that the electric circuit which comprises the approach detection part 15 may be damaged.

  Therefore, the main control unit 10g executes a process as shown in FIG.

  First, the main control unit 10g normally turns on all the switches 14a, 14b, and 14c to connect the loop coils 11, 12, and 13 to the approach detection unit 15, respectively. In this state, in step Sa1, the main control unit 10g waits for an instruction to start scanning by the user. In this state, if the start of scanning is instructed by the user, for example, by pressing a start button provided in the input unit 10f, the main control unit 10g advances from step Sa1 to step Sa2.

  In step Sa2, the main control unit 10g instructs the coil opening / closing unit 14 to open the coil. Then, in the coil opening / closing part 14, the switches 14a, 14b, 14c are turned off, and the loop coils 11, 12, 13 are opened. After that, the main control unit 10g executes control for realizing a scanning operation according to a predetermined pulse sequence as a process of another routine.

  Therefore, in the processing shown in FIG. 4, the main control unit 10g waits for the completion of the scanning operation. If the scanning operation is completed, the main control unit 10g proceeds from step Sa3 to step Sa4.

  In step Sa4, the main control unit 10g instructs the coil opening / closing unit 14 to connect the coil. Then, in the coil opening / closing unit 14, the switches 14a, 14b, 14c are turned on, and the loop coils 11, 12, 13 are connected to the approach detection unit 15, respectively.

  By such processing, when the excitation pulse is transmitted, the loop coils 11, 12, and 13 are opened and are not electrically connected to the approach detection unit 15. Therefore, the approach detection unit 15 is prevented from being damaged due to the excitation pulse. Since each of the loop coils 11, 12, and 13 is connected to the approach detection unit 15 except when scanning is performed, the approach of the magnetic body can be reliably detected.

  This embodiment can be variously modified as follows.

  One or two of the loop coils 11, 12, 13 may be omitted. In particular, when the MRI apparatus 100 is arranged close to the side wall of the radiographing room 300 and there is a low possibility that a magnetic material exists between the side wall and the MRI apparatus 100, the loop coil to be arranged at that position. May be omitted. Alternatively, an arbitrary number of loop coils may be additionally provided in addition to the loop coils 11, 12, and 13.

  When the transmission level of the excitation pulse is not so high as to cause the loop coils 11, 12, and 13 to generate a voltage that can damage the approach detection unit 15, the coil switching unit 14 and the coil switching unit in the main control unit 10 g It is also possible to omit 14 control functions.

  If any processing is performed between the time when the scan start instruction is given and the time when the excitation pulse is transmitted for the first time, the loop coils 11, 12, and 13 may be opened after the processing is completed. Similarly, if any processing is performed between the time when the excitation pulse is last transmitted and the time when the scanning operation is completed, prior to the start of the processing, each of the loop coils 11, 12, 13 is connected to the approach detection unit 15. You may connect to.

  An infusion stand, a stretcher, a wheelchair, or an oxygen cylinder is generally brought into the imaging room when the subject 200 is carried into the imaging room. The subject 200 is placed on the top plate 4a in a state where the top plate 4a is pulled out to the maximum from the imaging space, that is, in a state where the top plate 4a is positioned at a so-called out limit. The top 4a is sent to the imaging space after the necessity to start scanning, and is pulled out to the out limit after the scanning is completed. For this reason, each of the loop coils 11, 12, and 13 may be connected to the approach detection unit 15 only when the top plate 4 a is positioned at the out limit. The bed of the MRI apparatus generally has a function of detecting whether or not the top plate is positioned at the out limit. Therefore, if the coil opening / closing part 14 is controlled in accordance with the detection signal, the above operation can be realized. In this case, the control of the coil opening / closing unit 14 can be performed by the main control unit 10g, or can be performed by providing a control unit different from the main control unit 10g. In this case, each of the loop coils 11, 12, and 13 is connected to the approach detection unit 15 not only when the top plate 4 a is positioned at the out limit but also when it is positioned in a predetermined region near the out limit. You may do it.

  It is configured as a magnetic substance approach prevention device having the loop coils 11, 12, 13, the coil opening / closing unit 14, the approach detection unit 15, the prevention operation control unit 16 and the prevention operation unit 17, and the function of controlling the coil opening / closing unit 14. Alternatively, it may be implemented to be used with a separate MRI apparatus.

  The coil opening / closing part 14 and its control in the above embodiment are also effective when detecting the approach of a magnetic body using a loop coil arranged at a location different from the vicinity of the floor surface.

  The present invention can also be applied to a magnetic resonance diagnostic apparatus that does not perform imaging.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Static magnetic field magnet, 2 ... Gradient magnetic field coil, 3 ... Gradient magnetic field power supply, 4 ... Bed, 4a ... Top plate, 5 ... Bed control part, 6 ... Transmission RF coil unit, 7 ... Transmission part, 8 ... Reception RF coil Unit: 9 receiving unit 10 computer system 10a interface unit 10b data collecting unit 10c reconstruction unit 10d storage unit 10e display unit 10f input unit 10g main control unit DESCRIPTION OF SYMBOLS 11, 12, 13 ... Loop coil, 14 ... Coil opening / closing part, 14a, 14b, 14c ... Switch, 15 ... Approach detection part, 16 ... Prevention operation control part, 17 ... Prevention operation part, 100 ... Magnetic resonance imaging apparatus (MRI) Apparatus), 200 ... subject.

Claims (5)

A loop coil disposed on or under the floor in the vicinity of the bed provided in the magnetic resonance diagnostic apparatus for placing the subject;
Based on the change of the induced electromotive force generated in the loop coil due to the change of the strength of the leakage magnetic field from the static magnetic field generated by the magnetic resonance diagnostic apparatus, the magnetic substance is approached to the magnetic resonance diagnostic apparatus or the bed. An approach detection unit to detect;
Preventing the magnetic resonance diagnostic apparatus from performing a prevention operation to prevent the magnetic substance from being attracted to the magnetic field in response to the approach detection unit detecting the approach of the magnetic substance to the magnetic resonance diagnostic apparatus. A magnetic substance approach prevention device comprising an operating part. A loop coil disposed in the vicinity of a bed provided in the magnetic resonance diagnostic apparatus for placing a subject;
An approach for detecting the approach of a magnetic body to the magnetic resonance diagnostic apparatus based on a change in an induced electromotive force generated in the loop coil due to a change in intensity of a leakage magnetic field from a static magnetic field generated by the magnetic resonance diagnostic apparatus A detection unit;
Preventing the magnetic resonance diagnostic apparatus from performing a prevention operation to prevent the magnetic substance from being attracted to the magnetic field in response to the approach detection unit detecting the approach of the magnetic substance to the magnetic resonance diagnostic apparatus. A moving part;
A switch for turning on / off electrical connection between the loop coil and the approach detection unit;
A detection unit for detecting a predetermined first timing prior to the start of transmission of the excitation pulse in the magnetic resonance diagnostic apparatus and a predetermined second timing after the transmission of the excitation pulse is stopped; ,
The switch is set to turn off the electrical connection between the loop coil and the approach detection unit during a period from when the first timing is detected by the detection unit to when the second timing is detected. A magnetic substance approach prevention device comprising a control means for controlling.   The magnetic body access preventing apparatus according to claim 2, wherein the loop coil is disposed on or below a floor near the bed.   4. The magnetic body approach according to claim 1, comprising a plurality of the loop coils, wherein the plurality of loop coils are installed at different positions around the bed. 5. Prevention device. A static magnetic field magnet that generates a static magnetic field;
A bed for placing the subject;
A transmitter for transmitting an excitation pulse for application to the subject;
A loop coil disposed on or under the floor near the bed;
An approach detection unit for detecting the approach of the magnetic body to the bed based on a change in the induced electromotive force generated in the loop coil due to a change in the intensity of the leakage magnetic field from the static magnetic field;
A preventive operation unit for performing a preventive operation to prevent the magnetic substance from being attracted to the magnetic field in the magnetic resonance diagnostic apparatus in response to the approach of the magnetic substance to the bed detected by the approach detection unit; ,
A switch for turning on / off electrical connection between the loop coil and the approach detection unit;
The transmitter is controlled to transmit the excitation pulse according to a predetermined pulse sequence, and the excitation pulse according to the pulse sequence from a first timing prior to first transmitting the excitation pulse according to the pulse sequence And a control means for controlling the switch so as to turn off the electrical connection between the loop coil and the proximity detector during a period from the last transmission to the second timing. Magnetic resonance diagnostic device.

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