JP2004329963A - Biomagnetism measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a function to prevent improper adjustment or failure of measurement because of shortage of cooling a sensor from occurring, in a method to monitor remaining quantity of refrigerant for cooling a SQUID sensor in a biomagnetism measuring apparatus. <P>SOLUTION: The biomagnetism measuring apparatus prohibits starting enforced measuring and has a method to warn a remaining quantity of refrigerant is not more than a remaining value enabling magnetism measurement, when the remaining quantity of refrigerant in a cryostat including the SQUID sensor in the biomagnetism measuring apparatus is not more than the preset remaining value enabling magnetism measurement. The failure of measurement because of shortage of cooling the SQUID sensor is surely prevented from occurring by not only warning but also controlling biomagnetism measuring software to prohibit measurement enforcedly when the monitored remaining quantity of refrigerant is not more than the preset value, in the method to monitor the remaining quantity of refrigerant for cooling the SQUID sensor in the biomagnetism measuring apparatus. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a biomagnetic measurement apparatus including a SQUID (Superconducting Quantum Interference Device) magnetometer that measures a weak magnetic signal generated from the heart, brain, or the like of an adult, child, or fetus. In particular, the present invention relates to a biomagnetism measurement device including a mechanism for measuring a remaining amount of a refrigerant for cooling a SQUID sensor to an operation temperature.

  A weak biomagnetic signal generated from the heart or brain of an adult, a child, a fetus, etc. is detected using a SQUID (Superconducting Quantum Interference Device) magnetometer, which is a highly sensitive magnetic detection element, and the heart is detected. A biomagnetic measuring device for detecting abnormalities of the brain and brain has been developed.

  Since the SQUID is formed using a superconductor, it is necessary to perform measurement in a state where the SQUID is cooled by a low-temperature refrigerant such as liquid helium. In that case, it is important to monitor the remaining amount of the refrigerant.

  Patent Literature 1 discloses a biomagnetism measurement device having a function of periodically monitoring the remaining amount of refrigerant for cooling a SQUID sensor and issuing an alarm when the remaining amount of refrigerant is equal to or less than a specified value. ing.

JP-A-11-281723

  The technology disclosed in Patent Literature 1 automatically measures the remaining amount of refrigerant at preset time units, and issues an alarm when the remaining amount of refrigerant is equal to or less than a lower limit. However, one measurement takes a long time, and it takes about 20 to 30 minutes to 1 hour. Since there was no alarm for the remaining refrigerant before the start of the measurement, the measurement was started, but a shortage of the remaining refrigerant occurred during the measurement. Measurement may fail.

  An object of the present invention is to avoid wasting of time due to a shortage of the refrigerant remaining during measurement and failure of measurement, thereby avoiding wasting time or putting unnecessary burden on the subject. An object of the present invention is to provide a biomagnetic measurement device.

  It is also an object of the present invention to provide an apparatus for automatically displaying a replenishment schedule so that the replenishment timing can be known so that the measurement does not fail halfway due to a shortage of the remaining amount of refrigerant.

  The configuration of the present invention for solving the above-mentioned problem is as follows.

  A magnetic sensor including a superconducting quantum interference device (SQUID) for detecting a magnetic field generated from a subject, a cryostat for maintaining the superconducting quantum interference device at a low temperature, and a magnetic flux including a driving circuit for the superconducting quantum interference device A biomagnetic measuring apparatus comprising: a measuring circuit; a control means for controlling the magnetometer circuit; a storage means for storing measurement data; and a data processing device for analyzing the measurement data stored in the storage means. Further, the cryostat further includes a refrigerant remaining amount measuring unit that measures the remaining amount of the refrigerant for maintaining the superconducting quantum interference device at a low temperature, and the refrigerant remaining amount measuring unit before the measurement starts. When the remaining amount of the refrigerant is measured and the remaining amount of the refrigerant in the cryostat is expected to be equal to or less than a preset magnetically measurable remaining value by the end of the measurement. Is biomagnetic measurement apparatus having a control mechanism for controlling such measurement can not be started.

  Although any means may be used as the refrigerant remaining amount measuring means, it is general to supply a current to a rod-shaped member made of a superconductor and measure the residual amount based on the resistance value. This is based on the fact that the portion of the rod-shaped superconductor that is in contact with the refrigerant has an electrical resistance of 0, whereas the portion of the rod-shaped superconductor where the electrical resistance is generated due to the lack of the refrigerant generates resistance. The liquid level of the refrigerant is detected based on the value.

A magnetometer circuit including a drive circuit for the superconducting quantum interference device, a control unit for controlling the magnetometer circuit, a storage unit for storing measurement data, and a data processing device for analyzing the measurement data stored in the storage unit are physical They do not need to be separately provided, and may be processed as software in one computer. The control to prevent the measurement from starting means, for example, performing software processing so that the screen does not shift to the measurement start screen. Further, the cryostat has a refrigerant remaining amount measuring means for measuring the remaining amount of the refrigerant for keeping the superconducting quantum interference device at a low temperature, and the remaining amount is equal to or less than the remaining amount lower limit value that can be magnetically measured. However, if it is near the lower limit, the bias current of the SQUID may be adjusted to make the state of the magnetic sensor measurable. , Check the remaining amount, and if the remaining amount is below the preset magnetic
There is provided a biomagnetism measuring apparatus having a function of adding as a determination condition whether or not the state of a magnetic sensor is capable of magnetic measurement after adjusting a bias current of a SQUID.

  According to the present invention, in the method of monitoring the remaining amount of the refrigerant for cooling the SQUID sensor in the biomagnetic measurement device, the remaining amount of the refrigerant is monitored and, when the remaining amount is equal to or less than a set value, a warning is issued. It is an object of the present invention to provide a method for reliably preventing a failure in measurement due to insufficient cooling of the SQUID sensor by forcibly controlling the magnetic measurement software to disable measurement.

  An embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a biomagnetism measuring apparatus according to an embodiment of the present invention. As shown in FIG. 1, in a magnetically shielded room 1, a bed 4 on which a subject 9 lays down, a plurality of (multiple channels) SQUID magnetic sensors, and a refrigerant (liquid helium) for maintaining the SQUID magnetic sensors in a superconducting state. Alternatively, a cryostat 2 in which liquid nitrogen is stored and a gantry 3 for mechanically holding the cryostat 2 are arranged. The bed 4 is movable in the X, Y, and Z directions. Outside the magnetic shield room 1, a drive circuit 5 of the SQUID magnetometer, an amplifier circuit and a filter circuit unit 6, a computer 7 for data acquisition and data analysis, and a circuit 8 for taking an external reference signal such as an electrocardiograph And are arranged.

  The biomagnetic signal detected by the SQUID magnetic sensor is amplified by the amplifier circuit and the filter circuit unit 6, and a low-pass filter that passes a frequency signal lower than the set frequency, a high-pass filter that passes a frequency signal higher than the set frequency, a commercial power supply After undergoing signal processing such as a notch filter that cuts only the frequency, the data is taken into the personal computer 7 as raw data. A signal waveform from a circuit 8 for obtaining an external reference signal such as an electrocardiograph is taken into a personal computer 7 as raw data. Further, the personal computer 7 can store the acquired raw data in a raw data file and display the waveform on a screen, or perform signal processing of the waveform, isomagnetic field map processing, and the like to display the waveform.

  In addition, as means for monitoring the remaining amount of the refrigerant in the cryostat 2, a liquid level gauge 10 is provided. The sensor unit of the liquid level gauge 10 is installed in the cryostat 2. Refrigerant remaining amount data measured by the liquid level meter 10 is taken into the personal computer 7, and the remaining amount display and data management are performed by the refrigerant remaining amount monitoring software of the personal computer 7.

  FIG. 2 shows a configuration of a sensor unit and a refrigerant of a liquid level gauge in a cryostat according to an embodiment of the present invention. In FIG. 2, a cryostat 12 is provided with a sensor 11 of a liquid level meter for measuring the remaining amount of the refrigerant 13 for keeping the superconducting quantum interference device at a low temperature.

  FIG. 3 is a diagram showing a processing flow of liquid level measurement software and biomagnetism measurement software according to an embodiment of the present invention.

In the processing flow of FIG. 3, after the software is started, the operator selects various processing screens using icons or menus 21. The various processing screens include at least a biomagnetic measurement screen 26, a biomagnetic system adjustment screen 23, and a biomagnetic data analysis screen 24. When the measurement screen 26 is selected, first, before the measurement screen 26 is displayed, the refrigerant remaining amount confirmation 22 is performed. Next, when the remaining refrigerant value obtained by the remaining refrigerant check 22 in the decision branch 25 is equal to or less than the set remaining magnetic value that can be measured by the magnetism, the measurement screen 26 is not displayed, and the shortage of the remaining refrigerant is determined. A warning 27 is given and the process returns to the icon or menu selection 21. If the measured value is equal to or larger than the remaining amount that can be measured by the magnetic field set in the decision branch 25, a measurement screen 26 is displayed. In the measurement screen 26, when the measurement time of the biomagnetic measurement is input 28, the refrigerant remaining value at the end of the measurement is calculated 29. When the remaining amount is equal to or larger than the possible remaining amount, the standby state 34 in which measurement can be started is set.

  If the remaining refrigerant value at the end of the measurement is equal to or less than the set magnetically measurable residual value by the decision branch 30, the bias current of the SQUID is adjusted 31 next, and the state of the magnetic sensor is determined by the decision branch 31. Is determined to be in a state where measurement of magnetism is possible, a standby state 34 in which measurement can be started even if the remaining amount is equal to or less than the set value of remaining amount for which magnetism can be measured. If the state of the magnetic sensor is determined not to be a state where magnetic measurement can be performed by the determination branch 31, the state 33 is forcibly set to the state 33 in which measurement cannot be started.

  FIG. 4 is a diagram showing an example of a refrigerant remaining amount display screen of the liquid level measurement software according to the embodiment of the present invention.

  The remaining amount of the refrigerant 13 (FIG. 2) of the cryostat 12 (FIG. 2) measured by the liquid level meter 10 (FIG. 1) is displayed on a screen of the computer 7 (FIG. 1) and on a refrigerant remaining amount screen 40 of FIG. Is done. On the refrigerant remaining amount screen 40, the refrigerant remaining amount is displayed by a remaining amount indicator 41 and a remaining amount numerical value. Further, based on the remaining refrigerant amount stored in the remaining refrigerant amount storage means, a refrigerant remaining amount reduction rate is calculated, and a refrigerant replenishment timing is calculated from the calculated reduction ratio and the current refrigerant remaining amount. You. Further, by clicking the setting button 43, the setting screen 50 of FIG. 5 is opened, and the setting of the refrigerant remaining amount display can be performed. The automatic measurement ON / OFF check button 51 is used to set whether or not to perform automatic measurement of the liquid level gauge. When the automatic measurement is ON, the number of hours at which the automatic measurement is performed is input to the automatic measurement cycle time setting input box 52. In addition, the SQUID sensor does not operate due to the shortage of the remaining amount of the refrigerant (magnetic measurement is impossible), and the value [%] is input to the measurement impossible remaining amount lower limit value setting input box 53. When the remaining amount of the refrigerant is equal to or less than the value input to the unmeasurable remaining amount lower limit setting input box 53, a warning indicating that the magnetic measurement is impossible is displayed on the screen of the computer 7 (FIG. 1).

FIG. 6 is a diagram illustrating an example of a measurement screen of the biomagnetism measurement software according to the embodiment of the present invention. In the processing flow of FIG. 3, one screen example of the measurement screen display 26 is the measurement screen 60 in FIG. A magnetic signal waveform 61 measured by the magnetic sensor of each channel is displayed. When measurement conditions such as a measurement time 64 are input and a measurement button 62 is clicked, the acquisition of magnetic signal waveform data is started. The progress from the start of data capture to the end of data capture is displayed on the indicator 63. When the automatic adjustment button 65 is clicked, the bias currents and offset voltages of the magnetic sensors of all channels are set to optimal values by the automatic adjustment processing. Even if the measurement cannot be started due to the shortage of the remaining refrigerant, if the measurement is near the lower limit, the bias current of the SQUID may be adjusted to make the state of the magnetic sensor measurable. If the automatic adjustment is performed by 65 and it is determined that the state of the magnetic sensor is capable of measuring the magnetic field, the measurement button 62 can be clicked to start capturing the magnetic signal waveform data.

  FIG. 7 is a diagram illustrating an example of an adjustment screen of the biomagnetism measurement software according to the embodiment of the present invention. In the processing flow of FIG. 3, one example of the adjustment screen display 23 is the measurement screen 70 in FIG. When the V-φ characteristic curve 71 of the magnetic sensor of each channel is displayed and the automatic adjustment button 72 is clicked, the bias current and the offset voltage of the magnetic sensors of all channels are set to optimal values by the automatic adjustment processing. When the manual adjustment button 73 is clicked, a screen for arbitrarily inputting and setting the bias current and offset voltage of the magnetic sensor of each channel opens. When the heat flash button 74 is clicked, the function of temporarily heating the magnetic sensor of the channel in which the magnetic flux has been trapped to return the superconducting state to the normal conducting state is executed.

  FIG. 8 is a diagram illustrating an example of an analysis screen of the biomagnetic measurement software according to the embodiment of the present invention. In the processing flow of FIG. 3, one screen example of the analysis screen display 24 is the analysis screen 80 in FIG. The biomagnetic signal data waveform 81 measured by the magnetic sensor of each channel is displayed, and the time axis and the scale of the magnetic field strength can be set by the display setting input box 82. FIG. 9 shows an iso-magnetic field map analysis as an analysis example different from the analysis example of FIG. 8, in which a contour map is displayed based on a biomagnetic signal detected by a magnetic sensor of each channel at a designated time. FIG. 5 is a diagram showing a screen 90. The scale and time setting of the isomagnetic field map 91 can be set in the reconstruction parameter setting input box 92.

FIG. 1 is a diagram showing a configuration of a biomagnetism measuring device according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of a liquid level sensor and a refrigerant in a cryostat according to an embodiment of the present invention. FIG. 3 is a processing flowchart of liquid level measurement software and biomagnetism measurement software according to an embodiment of the present invention. The figure of the example of a refrigerant | coolant remaining amount display screen of the liquid level measurement software which is the Example of this invention. The figure of the example of a refrigerant | coolant residual amount display setting screen of the liquid level measurement software which is the Example of this invention FIG. 4 is a diagram illustrating an example of a measurement screen of biomagnetism measurement software according to an embodiment of the present invention. FIG. 5 is a diagram illustrating an example of an adjustment screen of the biomagnetism measurement software according to the embodiment of the present invention. FIG. 4 is a diagram illustrating an example of an analysis measurement screen of biomagnetism measurement software according to an embodiment of the present invention. FIG. 4 is a diagram illustrating an example of an analysis measurement screen of biomagnetism measurement software according to an embodiment of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Magnetic shield room, 2 ... SQUID magnetic sensor and cryostat, 3 ... Gantry, 4 ... Bed, 5 ... Drive circuit of SQUID magnetometer, 6 ... Amplifier circuit and filter circuit unit, 7 ... Computer, 8 ... Electrocardiograph etc. 9: Subject, 10: Level gauge, 11: Sensor unit of level gauge, 12: Cryostat, 13: Refrigerant, 21: Selection processing by icon or menu, 22: Refrigerant remaining Amount confirmation process, 23: Adjustment screen display, 24: Analysis screen display, 25: Determination branch based on refrigerant remaining value that can be measured magnetically, 26: Measurement screen display, 27: Remaining refrigerant amount shortage warning, 28: Measurement time input, 29: calculation processing of the remaining amount of refrigerant at the end of the measurement, 30: determination branch based on the remaining amount of refrigerant that can be measured magnetically at the end of the measurement, 31: SQUID via Current adjustment processing, 32: determination branch depending on whether the state of the magnetic sensor is in a state where magnetic measurement can be performed, 33: standby state in which measurement can be started, 34: forcedly incapable state, 40: refrigerant remaining amount display screen, 41 ... Refrigerant residual amount indicator, 42 ... Refrigerant residual value display, 43 ... Refrigerant residual amount display setting button, 44 ... Predictive replenishment time notification display, 50 ... Refrigerant residual amount display setting screen, 51 ... Refrigerant residual amount automatic measurement ON / OFF Setting check button, 52: Refrigerant remaining amount automatic measurement cycle time setting input box, 53: Refrigerant remaining amount lower limit setting input box that disables biomagnetic measurement, 60: Biomagnetic measurement screen, 61: Biomagnetic signal waveform, 62 ... Biomagnetic measurement start button, 63: progress indicator of measurement data acquisition, 64: measurement time setting input box, 65: bias current and off of magnetic sensor Automatic adjustment button of cut voltage, 70: Biomagnetic measurement system adjustment screen, 71: V-φ characteristic curve of magnetic sensor, 72: Automatic adjustment button of bias current and offset voltage of magnetic sensor, 73: Bias current of magnetic sensor And manual adjustment button of offset voltage, 74: heat flash button, 80: biomagnetic measurement data analysis screen (grid map waveform analysis), 81: biomagnetic measurement signal data waveform, 82: waveform display setting box, 90: biomagnetic measurement Data analysis screen (isomagnetic field map analysis), 91 ... isomagnetic field map, 92 ... isomagnetic field map display setting box.

Claims (2)

A magnetic sensor including a superconducting quantum interference device (SQUID) for detecting a magnetic field generated from a subject;
A cryostat for keeping the superconducting quantum interference device at a low temperature,
A magnetometer circuit including a drive circuit of the superconducting quantum interference device,
Control means for controlling the magnetometer circuit;
Storage means for storing measurement data;
A data processing device for analyzing the measurement data stored in the storage means,
A biomagnetic measurement device comprising:
Further, in the cryostat, refrigerant remaining amount measuring means for measuring the remaining amount of refrigerant for keeping the superconducting quantum interference device at a low temperature, and the remaining amount of refrigerant measured by the refrigerant remaining amount measuring means are stored. Comprising a refrigerant remaining amount storage means,
The refrigerant remaining amount in the cryostat is measured by the refrigerant remaining amount measuring means at least before the start of measurement, and the measurement result is stored in the refrigerant remaining amount storing means. A biomagnetism measuring apparatus comprising: a display unit that calculates a rate of decrease in the remaining amount of refrigerant based on the calculated rate of decrease and displays a timing of replenishing the refrigerant based on the calculated rate of decrease. The biomagnetic measurement device according to claim 1,
The display on the display means is in a calendar format.

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