JP2007215635A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the occurrence of an emergency situation such as a quench phenomenon beforehand, to notify it and to safely evacuate a subject. <P>SOLUTION: The MRI apparatus comprises an emergency information input means for inputting the information of emergency situation occurrence, and a notifying means for notifying the subject arranged in a static magnetic field space of the emergency situation information; and an emergency situation control means for stopping the operation of a gradient magnetic field power source, a high frequency magnetic field power source and a reception coil and evacuating the subject arranged in the static magnetic field space to the outside of the apparatus on the basis of the emergency situation information. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention measures nuclear magnetic resonance (hereinafter referred to as `` NMR '') signals from hydrogen, phosphorus, etc. in a subject and images nuclear density distribution, relaxation time distribution, etc. , "MRI"), and in particular, related to notification in the event of an emergency and evacuation of the subject.

  MRI equipment measures NMR signals generated by nuclear spins that make up the tissues of the subject, especially human body, and visualizes the shape and function of the head, abdomen, limbs, etc. in two or three dimensions It is a device to do. In imaging, the NMR signal is given different phase encoding depending on the gradient magnetic field, frequency-encoded, and measured as time series data. The measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.

  In the MRI apparatus, a superconducting coil is used to generate a uniform magnetic field space. In order to obtain a superconducting state, the superconducting coil is stored in a pressure vessel filled with liquid helium, and a uniform superconducting current flows through the coil to generate a uniform magnetic field. However, when the superconducting state breaks down due to some cause, for example, vibration of the coil, external noise, etc., and transitions to the normal conducting state, resistance is generated in the coil, and the current value in the coil is rapidly reduced. Furthermore, a large amount of liquid helium is vaporized by the heat generated from the resistance. This phenomenon is called a quench phenomenon.

When the quench phenomenon occurs, a large amount of helium gas is generated. Therefore, in order to protect the subject or the like, it is necessary to detect the occurrence of the quench phenomenon and discharge the helium gas. Patent Document 1 has a vaporization detection means for detecting helium gas and an opening / closing means for shutting off the inside and outside of the examination room, and the opening / closing means is activated when the vaporization detection means detects the vaporization of helium gas. Therefore, a configuration is disclosed in which the indoor and outdoor blocked states that are normally blocked can be released.
JP 2003-287250 A

However, the configuration disclosed in Patent Document 1 still has problems to be improved from the viewpoint of subject protection. That is, the subject remains in the MRI apparatus without being notified of the quench phenomenon, and the gradient magnetic field and the high-frequency magnetic field are continuously applied during imaging. In particular, the noise of the gradient magnetic field is large in the MRI apparatus, making it difficult to notify by voice the occurrence of an emergency such as a quench phenomenon during imaging.
Therefore, an object of the present invention is to detect the occurrence of an emergency such as a quench phenomenon in advance and notify the occurrence of the emergency and to evacuate the subject safely.

In order to achieve the above object, the MRI apparatus of the present invention is configured as follows. That is, a static magnetic field generating means for generating a uniform magnetic field space and three sets of gradient magnetic field generating coils for generating a gradient magnetic field whose magnetic field intensity changes linearly along the three axial directions of x, y, and z A high-frequency magnetic field generating coil for inducing magnetic resonance of the subject, a receiving coil for detecting a magnetic resonance signal of the subject, a gradient magnetic field power source, a high-frequency magnetic field power source, and superconducting the subject A bed transported in the coil, a control means for controlling the operation of the gradient magnetic field generating coil, the high frequency magnetic field generating coil, and the receiving coil, and a console for performing control commands, image reconstruction, and image display, and Emergency information input means for inputting information on occurrence of an emergency, notification means for notifying a subject placed in the static magnetic field space of the emergency information, and the inclination based on the emergency information Magnetic field power supply and the above It stops the operation of the receiver coil and frequency magnetic field power supply, and a emergency control means for retracting out of the apparatus a subject disposed in the static magnetic field space.
Thus, the quench phenomenon is predicted to the operator or the subject, and the safety of the apparatus is improved by giving a time delay until the quench phenomenon occurs.

  According to the MRI apparatus of the present invention, it is possible to detect the occurrence of an emergency in advance, notify the occurrence thereof, and safely evacuate the subject.

  Hereinafter, preferred embodiments of the MRI apparatus of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments of the invention, and the repetitive description thereof is omitted.

  First, an overall outline of an example of the MRI apparatus of the present invention will be described with reference to FIG. The MRI apparatus shown in FIG. 1 is used to generate a static magnetic field generator 1 for generating a uniform magnetic field space and a gradient magnetic field in which the magnetic field strength changes linearly along the three axial directions of x, y, and z. Three sets of gradient magnetic field generating coils 2, a high frequency magnetic field generating coil 3 for inducing the NMR phenomenon of the subject 10, a receiving coil 4 for detecting the NMR signal of the subject, and a gradient magnetic field power source 5 A high-frequency magnetic field power source 6, a bed 7 for transporting the subject into the static magnetic field generator 1, a control unit 8 for controlling the operations of the gradient magnetic field generating coil 2, the high-frequency magnetic field generating coil 3, and the receiving coil 4. A control unit, a calculation unit, a storage unit, and a display unit, and an operation console 9 for issuing a control command, reconstructing an image, and displaying an image.

  Further, the MRI apparatus of the present invention includes an emergency control unit 11 to which emergency occurrence information is input, and a notification unit 12 for notifying the subject 10 of emergency information. When emergency information is input to the emergency control unit 11 from inside or outside the device, the emergency control unit 11 discriminates the content of the emergency information and determines the content of the emergency information from the control unit in the console 9 (not shown; (Abbreviated as “part”). The control unit searches the storage unit in the console (not shown; hereinafter abbreviated as storage unit), and acquires information content and treatment content to be notified to the subject 10 corresponding to the input emergency information. To do. In the storage unit, information contents and treatment contents to be notified to the subject for each emergency are registered in advance. Then, the control unit outputs the acquired information content to be notified to the subject 10 to the notification unit 12, and controls the MRI apparatus to execute the treatment content. The notification unit 12 outputs information content to be notified to the subject 10 toward the subject 10.

Hereinafter, each embodiment of the MRI apparatus of the present invention according to the contents of an emergency will be described in detail.
(First embodiment)
A first embodiment of the MRI apparatus of the present invention will be described. In the present embodiment, the static magnetic field generator 1 is a superconducting magnet that includes a superconducting coil, and performs an emergency response when a quench phenomenon occurs in the superconducting coil as an emergency.

  An example of this embodiment is shown in FIG. FIG. 2 shows a quench phenomenon detection unit 14 for detecting a quench phenomenon of the superconducting coil 13 in the static magnetic field generator 1 and its precursor, and quench phenomenon information detected by the quench phenomenon detection unit 14 is input to the emergency control unit 11. It is shown that. Further, FIG. 2 shows that the quench phenomenon detection unit 14 detects the induced voltage indicating the change in the superconducting current generated in the search coil 15 and the search coil 15, and the induced voltage detected by the detection unit 16 is A. A / D conversion unit 17 that performs / D conversion, and the A / D converted induced voltage data is output to the emergency control unit 11.

The search coil 15 is disposed in the vicinity of the superconducting coil 13 and measures a change in the current of the superconducting coil 13. That is, when a current flows through the superconducting coil 13, a magnetic field as shown in FIG. The search coil 15 measures a magnetic field based on this superconducting current at regular time intervals, for example. When the current of the superconducting coil 13 does not vary with time and is a constant value, the magnetic flux Φ passing through the search coil 15 does not change, so that no induced voltage is induced in the search coil 15. On the other hand, when the current value of the superconducting coil 13 changes, the magnetic flux Φ passing through the search coil 15 changes. Therefore, the induced voltage V generated in the search coil 15 is N as the number of turns of the search coil.
V = N (dΦ / dt) (1)
It can be expressed as. If the equation (1) is used, the current change in the superconducting coil can be converted into an induced voltage induced in the search coil 15 as shown in FIG. The induced voltage induced in this way is detected by the detection circuit 16, and the detected induced voltage is digitized by the A / D converter 17 and then output to the emergency control unit 11.

That is, from the above equation (1), the fluctuation of the current flowing through the superconducting coil 13 is converted into the induced voltage induced in the search coil 15 through the fluctuation of the magnetic flux passing through the search coil 15, and this induced voltage is detected. As a result, the fluctuation of the superconducting current is indirectly detected.
The method of measuring the current of the superconducting coil is not limited to the search coil 15, and any method may be used as long as the current of the superconducting coil can be measured.

  The emergency control unit 11 monitors the time variation of the current value of the current flowing through the superconducting coil 13 by monitoring the induced voltage data from the quench phenomenon detecting unit 14 or its integrated value. FIG. 3 shows an example of the current fluctuation in the superconducting coil when the quench phenomenon occurs and the corresponding fluctuation in the induced voltage from the quench phenomenon detector 14.

FIG. 3 (a) is a schematic diagram of a current change from the stable superconducting state to the normal conducting state due to the occurrence of the quench phenomenon. The vertical axis represents current and the horizontal axis represents time.
FIG. 3 (b) is a schematic diagram showing changes in the induced voltage generated in the search coil 15, where the vertical axis represents voltage and the horizontal axis represents the same time as in FIG. 3 (a).
During the period from time t0 to time t1, the superconducting coil 13 is in a stable superconducting state, and a stable state in which the current value of the superconducting current is constant over time continues. In this stable period, since the current value is substantially constant, the induced voltage from the quench detection unit 14 remains substantially 0 (zero). Note that in the superconducting state, a minute fluctuation in current occurs even in the steady state, and this phenomenon is reflected in the schematic diagram in FIG.

Next, assuming that the superconducting state starts to break down at time t1, as shown in FIG. 3 (a), a momentary slight current fluctuation, which is a precursor of the quenching phenomenon, occurs in the superconducting coil 13 at time t1. . At the same time, the quench detection unit 14 detects the slight current fluctuation and outputs a slight induced voltage to the emergency control unit 11 as shown in FIG.
From this time t1 to the start time t2 of the next quench state is a transition state in which the transition to the quench state occurs, and the current flowing through the superconducting coil 13 gradually decreases as shown in FIG. 3 (a). In synchronization with the decrease in current, the quench detection unit 14 outputs an induced voltage that gradually increases, as shown in FIG. 3 (b). The period from time t0 to time t1 is several seconds to ten and several seconds.

  Next, when a transition is made from time t2 to the quenching state, the value of the current flowing through the superconducting coil 13 decreases rapidly as shown in FIG. 3 (a) in the period after time t2. In synchronization therewith, the quench detection unit 14 outputs an induced voltage having a large amplitude as shown in FIG. 3 (b).

  As described above, by detecting the precursor phenomenon of the quench phenomenon and the subsequent transition state, it is possible to predict the quench phenomenon that continues to occur. For this purpose, the threshold voltage Vth of the induced voltage is defined, and when the induced voltage V output from the quench detection unit 14 exceeds the threshold voltage Vth, it is determined that the precursor phenomenon of the quench phenomenon has occurred. In other words, when the induced voltage output by the quench detection unit 14 exceeds the threshold voltage Vth, it can be seen that the superconducting coil has a precursor phenomenon of the quench phenomenon and is in a transition state, and the quench phenomenon that continues to occur can be predicted in advance. It becomes possible.

This threshold voltage Vth needs to be a value at which a statistically significant difference is recognized as compared with the fluctuation of the induced voltage in the steady state. For example, the threshold voltage Vth can be set by statistical processing from the actual value of the change in the induced voltage. Specifically, when the frequency distribution of the induced voltage representing the precursor of the quenching phenomenon obtained by measuring the quenching phenomenon many times is represented, a Gaussian distribution is obtained as shown in FIG. Here, the vertical axis represents the frequency of the induced voltage, and the horizontal axis represents the induced voltage output from the quench detection unit 14. If the mean value of the induced voltage is Vav and the standard deviation is σ, due to the nature of the Gaussian distribution,
Vth = Vav + σ <V → Predicts the quench phenomenon with a probability of 83.4%
Vth = Vav + 2σ <V → Predicts the quench phenomenon with a probability of 97.5%
Vth = Vav + 3σ <V → It becomes possible to detect the precursor of the quenching phenomenon with a probability of 99.9%. Accordingly, the threshold voltage Vth can be set by setting a desired probability and obtaining the threshold voltage Vth corresponding to the probability. Then, when the induced voltage V output from the quench detection unit 14 exceeds the threshold voltage Vth set in this way, the quench phenomenon can be predicted in advance with a set probability or more. Accumulation of the induced voltage that represents the precursor of the quenching phenomenon obtained by measuring the above quenching phenomenon is performed by the storage unit of the console 9, and the calculation of the threshold voltage Vth is performed by the calculation unit of the console 9. The induced voltage Vth is stored in the storage unit and notified to the emergency control unit 11.

  The emergency control unit 11 determines the occurrence of the quench phenomenon using the threshold voltage Vth obtained as described above. That is, the emergency control unit 11 compares the threshold voltage Vth notified from the console 9 with the induced voltage data V input from the quench detection unit 14. If V <Vth, the emergency control unit 11 determines that the superconducting coil is in a stable superconducting state, and continues to monitor the current value of the superconducting coil via the quench detection unit 14. When V ≧ Vth, the emergency control unit 11 determines that a quench phenomenon has occurred in the superconducting coil and has shifted to the transition state, and notifies the control unit of the console 9 of the occurrence of the quench phenomenon. Upon receiving this notification, the control unit controls the treatment when a quench phenomenon occurs, which will be described in detail below.

  In the above description, the induced voltage V was compared with the reference voltage Vth at a certain time, but the history of the induced voltage V at a plurality of times was recorded, the fluctuation pattern of the induced voltage V, and the above-mentioned many times of quenching. It may be determined whether or not the state is in the transition state by comparing with the fluctuation pattern of the induced voltage V obtained by measuring the phenomenon.

  In addition, when the frequency distribution of the transition state start time t1 and the quench phenomenon start time t2 is obtained using the measurement data obtained by measuring the quench phenomenon many times, the quench phenomenon starts from the transition state start time. Can be estimated. This estimated value is used in the treatment at the time of occurrence of the quench phenomenon, which will be specifically described below. The calculation for estimating the margin time and the storage of the estimated value of the margin time are performed by the calculation unit and the storage unit of the console 9, respectively.

Next, a specific example of treatment when the quench phenomenon occurs will be described.
When the emergency controller 11 recognizes the occurrence of the quench phenomenon based on the induced voltage data input from the quench detector 14, the emergency controller 11 notifies the controller of the occurrence of the quench phenomenon. Upon receiving this notification, the control unit searches the storage unit and acquires information content and treatment content to be notified to the subject 10 when the quench phenomenon occurs. Then, the control unit outputs the acquired information content to be notified to the subject 10 to the notification unit 12, and controls the MRI apparatus to execute the treatment content.

  The information content to be notified to the detected subject 10 can be an alarm (siren) or voice information that tells the content of an emergency. For example, “Quench has occurred. Please calm down and evacuate according to the instructions of the engineer” as the voice information to notify the emergency situation. Alternatively, it can be light information such as a warning light. Alternatively, the notification unit 12 may include a display unit in the vicinity of the subject 10 to display information contents to be notified to the subject 10. In this case, the margin time until the above-described quench phenomenon occurs may be indicated and the sound may be counted down. Alternatively, a vibration part that contacts the subject may be provided, and the occurrence of an emergency may be transmitted to the subject 10 by vibration. Alternatively, a plurality of types of notification described above may be combined. FIG. 2 shows an example of a rotating warning light.

  On the other hand, an example of the treatment content is to stop the imaging sequence being executed. That is, the control unit of the console 9 controls the control unit 8 to stop the application of the gradient magnetic field and the high frequency magnetic field and the measurement of the NMR signal. Preferably, the control unit drives the bed 7 so that the subject 10 arranged in the MRI apparatus is sent out of the apparatus. Further, the control unit may control each driving unit (not shown) so as to brighten the illumination in the examination room and open the partition, windows, and doors that separate the examination room and the outside of the examination room.

  As described above, according to the present embodiment, it is possible to predict the occurrence of the quench phenomenon, notify the occurrence of the quench phenomenon, and safely and reliably evacuate the subject.

(Second Embodiment)
Next, a second embodiment of the MRI apparatus of the present invention will be described. The present embodiment is a form for performing an emergency response when an earthquake occurs in a remote place as an emergency and the seismic wave is transmitted toward the MRI apparatus of the present invention.

  An example of this embodiment is shown in FIG. When an earthquake occurs in a remote location, it takes time until the seismic wave is transmitted to the location of the MRI apparatus. The time is proportional to the distance between the remote location and the location of the MRI apparatus, and is about several seconds to several tens of seconds. On the other hand, there is an earthquake detection device 21 at a remote location, and the earthquake information (observation point, seismic intensity, etc.) detected by this earthquake detection device 21 is immediately input to the emergency control unit 11 of the MRI device via the Internet or telephone line 22. Is done. Alternatively, after the earthquake information is accumulated and analyzed in the earthquake analysis server 23 in another location, the analysis information (the location of the earthquake, the seismic intensity, etc.) is input to the emergency control unit 11 via the Internet or telephone line 22. May be. In any case, the MRI apparatus can detect the occurrence of an earthquake several seconds to several tens of seconds before the arrival of the seismic wave.

  The emergency control unit 11 to which the earthquake information is input predicts the seismic intensity at the location of the MRI apparatus based on the earthquake information. If the predicted value is less than the threshold, nothing is done. On the other hand, if the predicted value is equal to or greater than the threshold value, the time required for the seismic wave to reach the location of the MRI apparatus is predicted, and the earthquake information such as the predicted seismic intensity and the predicted time is reported to the control unit of the console 9. . This threshold value is a value set in the emergency control unit 11 via the console 9 in advance. In addition, since the seismic intensity and the surplus time are well-known techniques already performed by the Japan Meteorological Agency and the like, they may be calculated based on earthquake information input from the outside using the known techniques.

  The control unit of the console 9 receives a notification of the occurrence of an earthquake from the emergency control unit 11, searches the storage unit, and acquires information contents and treatment contents to be notified to the subject 10 when the earthquake occurs. Then, the control unit outputs the acquired information content to be notified to the subject 10 to the notification unit 12, and controls the MRI apparatus to execute the treatment content. Since the configuration of other MRI apparatuses is the same as that shown in FIG. 1, detailed description thereof is omitted. However, in the present embodiment, the static magnetic field generator 1 does not need to be a superconducting magnet using a superconducting coil, and may be a static magnetic field generator using a normal conducting magnet or a permanent magnet.

  The information content to be notified to the detected subject 10 is provided with sound information such as a siren and an emergency situation, light information such as a warning light, and a display section, as in the first embodiment. Display one or more information contents to be notified to the subject 10. Or you may carry out combining several.

  The voice information can be, for example, “An earthquake occurred in a remote place. Please calm down and evacuate according to the instructions of the engineer”. In addition, the time until the seismic wave reaches the display unit may be indicated and the sound may be counted down.

  On the other hand, as an example of treatment content, the control unit stops the imaging sequence being executed, as in the first embodiment described above. Further, similarly to the example of the first embodiment described above, the subject 10 arranged in the MRI apparatus is sent out of the apparatus, the illumination in the examination room is brightened, and the examination room and the outside of the examination room are separated. Opening the partition walls, windows and doors may be performed.

  As described above, according to the present embodiment, even when an earthquake occurs in a remote place, it is possible to notify the occurrence of the earthquake before the arrival of the seismic wave and to evacuate the subject safely and reliably. .

The figure explaining the structure of an example of the MRI apparatus of this invention. FIG. 4 is an example of the first embodiment of the present invention and is a diagram for explaining a quench detection unit. (a) is a figure explaining the current change of the superconducting coil when the quench phenomenon occurs, and (b) is a figure explaining the voltage change of the search coil when the quench phenomenon occurs. The figure explaining the statistical distribution of the voltage change of a search coil. The figure explaining the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Static magnetic field generator 2, Gradient magnetic field generating coil 2, 3 High frequency magnetic field generating coil, 4 Receiving coil 4, 5 Gradient magnetic field power supply, 6 High frequency magnetic field power supply, 7 Bed, 8 Control unit, 9 Console, 10 Subject, 11 Emergency Control Department

Claims (3)

A static magnetic field generating means for generating a uniform magnetic field space, and three sets of gradient magnetic field generating coils for generating a gradient magnetic field whose magnetic field intensity changes linearly along the three axial directions of x, y, and z; A high frequency magnetic field generating coil for inducing magnetic resonance of a subject, a receiving coil for detecting a magnetic resonance signal of the subject, a gradient magnetic field power source, a high frequency magnetic field power source, and a subject in a superconducting coil Magnetic resonance imaging, comprising: a bed to be transported to the table; control means for controlling the operation of the gradient magnetic field generating coil, the high frequency magnetic field generating coil, and the receiving coil; and a console for performing control commands, image reconstruction, and image display In the device
Emergency information input means for inputting information on occurrence of an emergency,
Notification means for notifying the subject placed in the static magnetic field space the emergency information;
Based on the emergency information, emergency control means for stopping the operation of the gradient magnetic field power source, the high-frequency magnetic field power source, and the receiving coil, and evacuating the subject arranged in the static magnetic field space from the apparatus When,
A magnetic resonance imaging apparatus comprising: The magnetic resonance imaging apparatus according to claim 1.
The static magnetic field generating means comprises a superconducting magnet that contains a superconducting coil,
A quench detection means for detecting a quench phenomenon of the superconducting state of the superconducting coil and its precursor,
The emergency information input means receives the quench phenomenon and its precursor information from the quench detection means,
The notifying means notifies the subject arranged in the static magnetic field space of the occurrence of the quench phenomenon and a margin time until the occurrence of the quench phenomenon based on the information on the quench phenomenon and its precursor. A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 1.
Earthquake information is input to the emergency information input means,
The said notification means notifies the subject arrange | positioned in the said static magnetic field space about the occurrence of an earthquake and the time until an earthquake wave arrives, The magnetic resonance imaging apparatus characterized by the above-mentioned.

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