WO2024075669A1 - 電磁気センサの配置提案方法および配置提案装置、ならびに電流源の位置推定方法 - Google Patents

電磁気センサの配置提案方法および配置提案装置、ならびに電流源の位置推定方法 Download PDF

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WO2024075669A1
WO2024075669A1 PCT/JP2023/035835 JP2023035835W WO2024075669A1 WO 2024075669 A1 WO2024075669 A1 WO 2024075669A1 JP 2023035835 W JP2023035835 W JP 2023035835W WO 2024075669 A1 WO2024075669 A1 WO 2024075669A1
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sensors
electromagnetic
sensor
arrangement
current source
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PCT/JP2023/035835
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French (fr)
Japanese (ja)
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朋寛 五味
定 冨田
立 梅林
宙人 山下
祐輔 武田
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株式会社島津製作所
国立研究開発法人理化学研究所
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
    • A61B5/242—Detecting biomagnetic fields, e.g. magnetic fields produced by bioelectric currents

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  • This disclosure relates to a method and device for proposing placement of electromagnetic sensors, and a method for estimating the position of a current source.
  • a technology uses multiple electromagnetic sensors placed on the surface of a subject's body to detect biological activity inside the body.
  • MEG magnetoencephalography
  • multiple sensors placed on the subject's head can detect brain magnetism that occurs with neural activity.
  • current source estimation it is desirable to accurately estimate the location of the brain's active area, which acts as a current source (hereinafter referred to as "current source estimation").
  • current source estimation One measure to improve the accuracy of current source estimation is to measure the brain magnetism with high sensitivity.
  • the positional relationship between the sensor and the head is important. Specifically, it is important to bring the sensor close to the brain's active area and to place the sensor in an appropriate position according to brain activity.
  • SQUID superconducting quantum interference device
  • the present disclosure has been made to solve the above problems, and one objective of the present disclosure is to propose an arrangement of multiple sensors suitable for current source estimation. Another objective of the present disclosure is to provide a method for optimally utilizing the outputs of multiple sensors.
  • the method for proposing the placement of electromagnetic sensors is a method for proposing the placement of multiple electromagnetic sensors to be placed on the biological surface surrounding a target area inside the subject, using a forward model for estimating an electromagnetic field generated at the positions of the multiple electromagnetic sensors due to biological activity inside the subject, and includes the steps of setting calculation conditions including the position of the target area and possible positions for placing the multiple electromagnetic sensors, calculating a proposed placement of all or a part of the multiple electromagnetic sensors to estimate the position of a current source inside the subject based on the set calculation conditions, and outputting the proposed placement.
  • the current source position estimation method disclosed herein is a method for estimating the position of a current source inside a subject using the detection results of multiple electromagnetic sensors that are placed on the biological surface of the subject and each detects an electromagnetic field generated by biological activity taking place in a target area inside the subject, and includes the steps of setting calculation conditions including the position of the target area and the arrangement of the multiple electromagnetic sensors, calculating priorities of all or a part of the multiple electromagnetic sensors based on the calculation conditions, and estimating the position of the current source using the detection results of the electromagnetic sensors selected based on the priorities.
  • the electromagnetic sensor placement suggestion device is a device that proposes the placement of multiple electromagnetic sensors to be placed on the biological surface surrounding a target area inside the subject, using a forward model for estimating the electromagnetic field generated at the positions of the multiple electromagnetic sensors due to biological activity inside the subject, and includes an input unit to which calculation conditions including the position of the target area and possible positions of the multiple electromagnetic sensors are input, a calculation device that calculates a proposed placement of all or a part of the multiple electromagnetic sensors to estimate the position of a current source inside the subject based on the calculation conditions, and an output unit that outputs the proposed placement.
  • the layout proposal method and layout proposal device disclosed herein can propose a layout of multiple sensors suitable for current source estimation.
  • the position estimation method disclosed herein allows the position of a current source to be accurately estimated using the detection results of a high-priority sensor selected from among multiple electromagnetic sensors.
  • FIG. 1 is a diagram showing a schematic diagram of an overall configuration of a data processing system used in a method for proposing an arrangement of electromagnetic sensors
  • FIG. 13 is a diagram conceptually illustrating a method for proposing an arrangement of an OPM sensor.
  • 13 is a flowchart illustrating an example of a procedure for a placement proposal process.
  • FIG. 13 is a diagram showing an example of sensor arrangement and measurement results when magnetoencephalography is performed twice using 11 OPM sensors.
  • FIG. 5 is a diagram comparing the measurement accuracy of the first measurement (uniform arrangement) shown in FIG. 4 with the measurement accuracy of the second measurement (optimal arrangement).
  • System Configuration> 1 is a diagram showing a schematic diagram of an overall configuration of a data processing system 1 used in a method for proposing an arrangement of an electromagnetic sensor according to the present embodiment.
  • OPM sensor 2 which is a small magnetic sensor that operates at room temperature
  • the data processing system 1 includes a plurality of OPM sensors 2, an input device 3, an output device 4, and a processing device 10.
  • the data processing system 1 is configured to estimate the location of biological activity (current source) in the subject's brain using the detection results from the plurality of OPM sensors 2.
  • Each of the multiple OPM sensors 2 is placed on the surface of the subject's head by a user (medical personnel, etc.) and detects the magnetic field generated at each placement position by biological activity taking place in the subject's brain.
  • the multiple OPM sensors 2 may be in direct contact with the surface of the subject's head, or may not be in direct contact with the surface of the subject's head.
  • a cover member that holds the sensor 2 may be attached to the subject's head. Note that FIG. 1 shows an example in which four OPM sensors 2 are placed on the surface of the subject's head.
  • each OPM sensor 2 Since each OPM sensor 2 operates at room temperature, it does not need to be placed inside a Dewar like the SQUID described above. Therefore, the placement of multiple OPM sensors 2 can be easily changed depending on brain activity.
  • the input device 3 is, for example, a pointing device such as a keyboard or a mouse, and accepts input information (such as calculation conditions described below) from the user.
  • the information input to the input device 3 is sent to the processing device 10.
  • the output device 4 is, for example, a liquid crystal display (LCD) panel, and is a display that shows information to the user.
  • LCD liquid crystal display
  • the processing device 10 has, as its main hardware elements, a sensor interface 11, an input interface 12, an output interface 13, a storage device 14, and an arithmetic unit 15.
  • the processing device 10 may be realized, for example, by a general-purpose computer, or may be realized by a computer (such as a server) dedicated to the data processing system 1.
  • the sensor interface 11 is an interface for connecting the processing device 10 to the multiple OPM sensors 2, and realizes the input and output of signals between the processing device 10 and the multiple OPM sensors 2.
  • the input interface 12 is an interface for connecting the processing device 10 to the input device 3, and realizes the input and output of signals between the processing device 10 and the input device 3.
  • the output interface 13 is an interface for connecting the processing device 10 to the output device 4, and realizes the input and output of data between the processing device 10 and the output device 4.
  • the storage device 14 stores information (programs, etc.) used for processing by the arithmetic device 15. Note that input information (such as calculation conditions described below) input by the user to the input device 3 is stored in the storage device 14.
  • the calculation device 15 has a CPU (Central Processing Unit) and performs "current source estimation” to estimate the position of the current source (place of biological activity) in the subject's brain using the information stored in the storage device 14 and the measurement results of multiple OPM sensors 2.
  • CPU Central Processing Unit
  • the computing device 15 causes the output device 4 to display the position of the current source obtained by current source estimation as the location of biological activity. By looking at the content displayed on the output device 4, the user can grasp the location of the location of biological activity in the subject's brain.
  • ⁇ Proposal of sensor arrangement suitable for current source estimation> In order to accurately estimate the position of a current source in the brain, it is desirable to measure the brain magnetism with high sensitivity using multiple OPM sensors 2. In order to measure the brain magnetism with high sensitivity, the positional relationship between the multiple OPM sensors 2 and the current source in the brain is important. Specifically, it is important to place the multiple OPM sensors 2 in appropriate positions according to the position of the current source in the brain.
  • the calculation device 15 is configured to perform a process for proposing an arrangement of the OPM sensor 2 suitable for current source estimation (hereinafter also referred to as the "arrangement proposal process").
  • arrangement proposal process a process for proposing an arrangement of the OPM sensor 2 suitable for current source estimation
  • the arrangement proposal process is also simply referred to as the "proposed arrangement.”
  • FIG. 2 is a diagram conceptually showing a method for proposing the placement of the OPM sensor 2 by the placement proposal process.
  • the steps of setting calculation conditions, calculating the proposed placement, and outputting the proposed placement are carried out in this order.
  • calculation conditions used for calculating the proposed arrangement are set based on the input information input to the input device 3 and the information stored in the storage device 14.
  • the calculation conditions include "possible sensor arrangement positions,”"number of sensors s,””sensor SNR (Signal-to-Noise Ratio),”"brainmodel,””targetregion,””objective function f,” and the like.
  • Sensor placement positions is data indicating positions where OPM sensors 2 can be placed on the surface of the subject's head.
  • sensor placement positions includes the maximum number of OPM sensors 2 that can be placed (hereinafter also referred to as the "maximum number m") and the coordinates of the positions where the sensors can be placed.
  • the coordinates of the sensor placement positions can be determined, for example, based on image data obtained by MRI or a three-dimensional scanner of the subject's head.
  • FIG. 2 shows an example in which the coordinates of the possible sensor placement positions are discrete values
  • the coordinates of the possible sensor placement positions may be virtual positions where the OPM sensor 2 cannot actually be placed.
  • the “number of sensors s" is the number of OPM sensors 2 actually placed on the subject's head surface.
  • the number of sensors s is a value equal to or less than the maximum number of sensors m. In the example shown in FIG. 2, the number of sensors s is "4.”
  • the “sensor SNR” is the SNR of the OPM sensor 2.
  • the “sensor SNR” is used to determine the "constant ⁇ " used in the placement calculation described below.
  • the "brain model” is a model of the subject's brain structure using a triangular mesh or the like.
  • the brain model may be one that is generated based on the results of measuring the subject's brain by MRI, or it may be one that assumes the subject's brain is a standard brain and substitutes it with an existing standard brain model.
  • the "target region” is a location within the brain model where biological activity is expected to occur.
  • the vertices within the target region within the brain model will be treated as the positions of the current source (current dipole).
  • the number of vertices included in the target region may be one or multiple.
  • the "objective function f" is a function used in the calculation of the proposed placement, which will be described later. As will be described later, the “objective function f" is determined according to the "target area.”
  • the "objective function f" is set to a function that maximizes the diagonal sum (sum of diagonal components) of the vertices in the target region, but this is not limited to this. Any of the functions listed in Table 1 of Olaf Hauk et. al., "Towards an objective evaluation of EEGMEG source estimation methods - The linear approach (Olaf Hauk)" may be used as the objective function.
  • FIG. 3 is a flowchart showing an example of the procedure of the above-mentioned placement proposal process.
  • the calculation device 15 sets calculation conditions based on the input information input to the input device 3 and the information stored in the storage device 14 (step S10).
  • the calculation conditions include possible sensor placement positions (maximum number of placements m, coordinates of each placement), number of sensors s, sensor SNR, brain model, target region, objective function f, etc.
  • step S11 the calculation device 15 sets the priority p to the initial value "1" (step S11). After that, the calculation device 15 moves the process to step S30.
  • the computing device 15 arbitrarily selects one sensor position whose priority has not yet been determined from among the multiple possible sensor placement positions (step S30).
  • the forward model matrix G is a matrix that indicates a forward model solution that expresses the correspondence between the current dipole moment of a current source when a current dipole moment is applied to the vertices of the brain model to make them current sources, and the magnetic field generated at the position of the OPM sensor 2 (the magnetic field measured by the OPM sensor 2).
  • the forward model matrix G satisfies the following formula (1).
  • Equation (1) "B” is the magnetic field vector generated at the position of the OPM sensor 2
  • "J” is the density vector of the true current of the current source in the brain
  • “G” is the forward model matrix (a matrix that indicates the forward model solution).
  • the forward model matrix G is a matrix that converts the current of the current source into a magnetic field generated at the position of the OPM sensor 2, and is also called the “lead field matrix” in the field of magnetoencephalography. This forward model matrix G corresponds to an example of the "forward model” of this disclosure.
  • the calculation unit 15 calculates the forward model matrix G p of the priority level p by using the following formula (2).
  • the calculation device 15 calculates a forward model matrix G p of the priority level p by adding a forward model matrix g corresponding to one sensor whose priority level is undetermined and selected in step S30 to the forward model matrix G p- 1 of the previous priority level p -1 .
  • the size of the forward model matrix Gp is (priority p) ⁇ (number of vertices v). Therefore, when the priority p reaches the number of sensors s, the forward model matrix Gs becomes (number of sensors s) ⁇ (number of vertices v).
  • the number of vertices v is the number of vertices of the brain model (the number of points where current dipoles simulating neural activity are placed).
  • the calculation device 15 uses the forward model matrix G calculated in step S31 to calculate the estimated model matrix R (step S32).
  • the estimated model matrix R is a matrix corresponding to an estimated model for estimating the position of a current source in the brain from the detection results of the OPM sensor 2 placed on the head surface.
  • the estimated model matrix R satisfies the following equation (3).
  • Equation (3) "J" is the density vector of the true current of the current source in the brain, "J'” is the density vector of the estimated current of the current source in the brain, and “R” is the estimated model matrix (a matrix that indicates the estimated model solution).
  • the estimated model matrix R is a matrix that converts the true current (true value) of the current source into a magnetic field generated at the sensor position, and further converts the converted magnetic field back into an estimated current (estimated solution) of the current source.
  • the estimated model matrix R is also called a "resolution matrix” in the field of magnetoencephalography. This estimated model matrix R corresponds to an example of an "estimated model” in this disclosure.
  • the calculation unit 15 calculates the estimation model matrix R p of the priority level p by using the following formula (4).
  • G p ′ is a transposed matrix of the forward model matrix G p
  • ⁇ is a constant determined according to the sensor SNR
  • I is a unit matrix. Note that the matrix size of the estimated model matrix R p is (number of vertices v) ⁇ (number of vertices v).
  • the calculation device 15 calculates the difference matrix ⁇ R p by using the following equation (5) (step S33).
  • R p is the estimated model matrix R of the priority order p
  • R p-1 is the estimated model matrix R of the priority order p-1.
  • the calculation device 15 determines whether or not the difference matrix ⁇ R p has been calculated for all sensor positions whose priorities have not yet been determined (step S34).
  • step S34 If the difference matrix ⁇ R p has not been calculated for all sensor positions whose priorities are undetermined (NO in step S34), the calculation device 15 returns the process to step S30 and repeats the processes of steps S30 to S34 until the difference matrix ⁇ R p has been calculated for all sensor positions whose priorities are undetermined.
  • the calculation device 15 identifies the sensor position whose priority is not yet determined and whose objective function f( ⁇ R p ) based on the difference matrix ⁇ R p is optimal, and sets the identified sensor position as the position whose priority is p (step S40).
  • the objective function f is determined according to the position of the target region, as described later.
  • the calculation device 15 determines whether the priority p has reached the number of sensors s (step S41). If the priority p has not reached the number of sensors s (NO in step S41), the calculation device 15 moves the process to step S20 and increments the priority p by 1, and then repeats the processes of steps S30 to S34. The processes of steps S30 to S34 are repeated until the priority p reaches the number of sensors s.
  • the processing device 10 can provide the user with a proposed placement of the s OPM sensors 2 (a sensor placement suitable for estimating the position of the current source in the subject's brain).
  • the user can accurately estimate the position of the current source by placing the s OPM sensors 2 according to the proposed placement displayed on the output device 4. If the proposed placement includes a virtual position where the OPM sensor 2 cannot actually be placed, the OPM sensor 2 can be placed in a position closest to the virtual position and where the OPM sensor 2 can actually be placed.
  • the forward model matrix G is a matrix that converts the current density vector "J" of a current source in the brain into a magnetic field vector "B" generated at the position of the OPM sensor 2.
  • Equation (6) "B” is the magnetic field vector generated at the position of the OPM sensor 2, "r” is the position (coordinate) of the OPM sensor 2, “J” is the current density vector of the current source in the brain, and “r'” is the position (coordinate) of the current source in the brain.
  • the components of the forward model matrix G can be found by calculating equation (6) above.
  • "J" is a current density vector, and if its direction is not specified, a huge number of equations will have to be calculated; however, in the field of current source estimation, it is considered reasonable to assume that the current flows in a direction perpendicular to the brain model, so “J” can be uniquely determined.
  • the position "r" of the OPM sensor 2 can be determined by the possible sensor placement positions set in the calculation conditions.
  • the position "r'" of the current source can be determined by the vertex position of the brain model set in the calculation conditions. For this reason, by calculating the Biot-Savart equation for one current source (vertex) for the maximum number of sensor placements m, the components of the forward model matrix G for that one current source can be calculated.
  • Biot-Savart's law can be written as the maximum number m of sensors per current source, as shown in equation (7) below.
  • the calculation device 15 can calculate the components of the forward model matrix G using the above-mentioned method.
  • the "target region” set in the calculation conditions is used to set the "objective function f".
  • the relationship between the target region and the objective function f will be described in detail below.
  • the objective function f is a function based on the difference matrix ⁇ R.
  • the difference matrix ⁇ R is obtained by taking the difference of the estimated model matrix R
  • the objective function f will be described here as being based on the estimated model matrix R for ease of understanding.
  • the first to fourth rows and first to fourth columns of the estimated model matrix R are the matrix elements related to the target region, as shown in equation (10) below.
  • estimation model matrix R in detail, it is possible to see the influence that the true current of vertex 1 has on the estimated current of vertices 1 to v, and the influence that the true current of vertices 1 to v has on the estimated current of vertex 1.
  • the estimation model matrix R is a matrix that has values only in the diagonal components where true values exist.
  • the objective function f can be set to a function that maximizes the diagonal sum (the sum of the diagonal components) of the vertices in the target region.
  • the calculation device 15 determines the objective function f according to the position of the target region (more specifically, the vertices in the target region).
  • the objective function f can be set to a function that maximizes the diagonal sum of elements r11 to r44 of the estimated model matrix R, as shown in equation (11) below. In situations where the region where brain activity occurs can be predicted but the exact location cannot be narrowed down, it is conceivable to take a broad target region like this.
  • the objective function f can be set to a function that maximizes the diagonal component r11 of the estimated model matrix R. In situations where the region in which brain activity will occur can be predicted with pinpoint precision, it is expected that the target region will be narrowed in this way.
  • the objective function f may also be set to a function that maximizes the ratio between the diagonal sum (sum of diagonal components) and the off-diagonal sum (sum of off-diagonal components) of the target region, as shown in the following formula (12).
  • the objective function f may be set to a function that maximizes the ratio between the diagonal sum of the target region and other elements.
  • the calculation device 15 calculates the forward model matrix G and the estimated model matrix R based on calculation conditions including the target area and possible sensor placement positions.
  • the calculation device 15 sets and outputs a proposed placement (priority order p) of the OPM sensors 2 using as an index the optimum objective function f set based on the estimated model matrix R.
  • the layout proposal method according to this embodiment can propose a layout of multiple OPM sensors 2 suitable for current source estimation. This makes it possible to efficiently optimize the sensor layout, which was difficult with conventional SQUIDs. Furthermore, it enables highly sensitive (highly accurate) magnetoencephalography. It also makes it possible to reduce the number of sensors required for current source estimation, thereby reducing the hardware costs of the magnetoencephalography system.
  • Figure 4 shows an example of sensor arrangement and measurement results when performing two magnetoencephalographic measurements using 11 OPM sensors 2.
  • the entire brain is treated as the test area and 11 OPM sensors 2 are evenly placed on the surface of the head.
  • the position of the current source is then tentatively determined from the measurement results of the 11 evenly placed OPM sensors 2.
  • the left brain is tentatively determined as the tentative position of the current source. Note that the part of the left brain where intensity above a predetermined value is concentrated may also be determined as the tentative position of the current source.
  • the provisional position of the current source tentatively measured in the first measurement (left brain) is set as the "target area" and the above-mentioned placement proposal process is performed, and the 11 OPM sensors 2 are repositioned according to the proposed placement obtained in the placement proposal process.
  • the position of the current source is then officially measured from the measurement results of the 11 repositioned OPM sensors 2.
  • the measurement result of maximum intensity is seen in a position closer to the true value (true abnormal area). In other words, the estimation accuracy of the current source has improved in the second measurement.
  • Fig. 5 is a diagram comparing the measurement accuracy of the first measurement (uniform arrangement) and the second measurement (optimal arrangement) shown in Fig. 4. It can be said that the estimation accuracy of the current source is higher when the position error between the true value and the estimated value (i.e., the shortest distance between the coordinate j1 of the maximum intensity in the true value and the coordinate j2 of the maximum intensity in the estimated current) is smaller and when the spatial spread of the estimated current (the maximum length of the area where the estimated current is measured) is smaller.
  • the position error between the true value and the estimated value i.e., the shortest distance between the coordinate j1 of the maximum intensity in the true value and the coordinate j2 of the maximum intensity in the estimated current
  • the spatial spread of the estimated current the maximum length of the area where the estimated current is measured
  • the position error between the true value and the estimated value was 33.16 mm, and the spatial spread of the estimated current was 48.28 mm
  • the position error between the true value and the estimated value was 5.18 mm
  • the spatial spread of the estimated current was 34.38 mm, which is an improvement.
  • the position error between the true value and the estimated value has improved significantly (by about 28 mm), and with optimal placement, the maximum intensity of the estimated current is only about 5 mm away from the true value (the abnormal region that is the true source of activity).
  • multiple OPM sensors 2 are evenly arranged on the head surface to tentatively measure the position of the current source, the tentatively measured position of the current source is set as the target region and a placement proposal process is performed, and the multiple OPM sensors 2 are re-arranged according to the proposed placement obtained in the placement proposal process to determine the position of the current source for the second measurement.
  • the provisional position of the current source it is sufficient to measure the provisional position of the current source, and it is not necessarily limited to using the OPM sensor 2.
  • the provisional position of the current source may be measured using fMRI (functional Magnetic Resonance Imaging) or the like.
  • fMRI functional Magnetic Resonance Imaging
  • a doctor's opinion may be involved in determining the provisional position of the current source.
  • step S50 of FIG. 3 described above in addition to displaying the proposed layouts of each priority level on the output device 4, the position error between the target area and the result of current source estimation (the position error between the true current and the estimated current) for each proposed layout may be displayed on the output device 4.
  • the user can look at the output device 4 and check whether the position error in the proposed layout for each priority order is within an acceptable range, and then decide the number of sensors s to be used for current source estimation. Therefore, it is also possible to reduce the number of sensors s to be used for current source estimation as necessary, making it possible to reduce the hardware costs of the magnetoencephalography system.
  • the sensor to which the layout proposal method according to the present disclosure can be applied is not limited to the OPM sensor 2.
  • the layout proposal method according to the present disclosure can also be applied to, for example, a fluxgate sensor, a magneto resistance (MR) sensor, a magneto impedance (MI) sensor, a coil type sensor, or a nitrogen-vacancy center in diamond (NVC) sensor instead of or in addition to the OPM sensor 2.
  • MR magneto resistance
  • MI magneto impedance
  • NVC nitrogen-vacancy center in diamond
  • the field to which the placement proposal method according to the present disclosure can be applied is not limited to the field of magnetoencephalography.
  • the placement proposal method according to the present disclosure can also be applied to fields in which biomagnetic fields other than those of the brain (such as magnetic fields generated by biological activity in the heart, spinal cord, peripheral nerves, or muscles) are measured.
  • the sensors to which the layout proposal method according to the present disclosure can be applied are not limited to magnetic sensors. That is, the layout proposal method according to the present disclosure can also be applied to potential sensors that detect potentials generated by electrical activity of a living body, such as an electroencephalogram (EEG) sensor or an electromyogram (EMG) sensor.
  • EEG electroencephalogram
  • EMG electromyogram
  • the placement proposal method according to the present disclosure can also be applied to SQUIDs whose positions are difficult to change.
  • the SQUIDs are placed in a dewar filled with liquid helium, and it is difficult to easily change their positions.
  • the placement proposal method described above can be applied to a process of proposing the positions of SQUIDs useful for current source estimation among the large number of SQUIDs placed in advance on the subject's head.
  • multiple SQUIDs may be placed on the subject's head in advance, calculation conditions may be set including the position of the target area and the placement of the multiple SQUIDs, priorities of all or some of the multiple SQUIDs may be calculated based on the calculation conditions, and the position of the current source in the subject's brain may be estimated using the detection results of the electromagnetic sensor selected based on the priorities.
  • a high-priority SQUID can be selected from among the many SQUIDs pre-positioned on the subject's head, and the current source can be estimated using the measurement results of the selected SQUID. Therefore, even when using a SQUID whose position is difficult to change, it is possible to perform accurate current source estimation by pre-positioning a large number of electromagnetic sensors on the subject's head.
  • a method for proposing the placement of electromagnetic sensors is a method for proposing the placement of multiple electromagnetic sensors to be placed on a biological surface surrounding a target area inside a subject, using a forward model for estimating an electromagnetic field generated at the positions of the multiple electromagnetic sensors due to biological activity inside the subject, and includes the steps of setting calculation conditions including the position of the target area and possible positions for placing the multiple electromagnetic sensors, calculating a proposed placement of all or a part of the multiple electromagnetic sensors to estimate the position of a current source inside the subject based on the set calculation conditions, and outputting the proposed placement.
  • a proposed placement of sensors is calculated and output based on the calculation conditions. This makes it possible to provide the user with a proposed placement of sensors suitable for current source estimation. The user can accurately estimate the position of the current source by placing multiple electromagnetic sensors according to the proposed placement.
  • the step of calculating the proposed placement includes a step of calculating the priority of all or a part of the possible placement positions.
  • the placement suggestion method described in paragraph 2 can provide the user with the priorities of all or part of the possible placement locations.
  • the method for proposing an arrangement of an electromagnetic sensor described in 1 or 2 further includes a step of tentatively measuring the position of a current source.
  • the step of setting the calculation conditions includes a step of setting the tentatively measured position of the current source as the position of the target region.
  • the positions of the current sources are tentatively measured before the proposed placement is calculated, and the proposed placement is calculated based on the tentatively measured positions of the current sources. This allows the proposed placement to be calculated efficiently with high accuracy.
  • the step of setting the calculation conditions includes a step of setting the parameters of the forward model as the calculation conditions.
  • the proposed placement can be calculated by setting the parameters of the forward model as the calculation conditions.
  • the step of calculating the proposed arrangement includes a step of calculating the proposed arrangement using an estimation model for estimating the position of a current source from the detection results of all or a part of the multiple electromagnetic sensors.
  • the step of calculating the proposed arrangement includes a step of calculating the proposed arrangement so that the difference between the estimation result of the estimation model obtained by setting the parameters of the estimation model as the calculation conditions and the position of the target area is small.
  • the proposed layout can be calculated so that the difference between the estimation result of the estimation model (position of the estimated current) and the position of the target area (position of the true current) is small.
  • the step of outputting the proposed arrangement includes a step of presenting to a user the difference between the estimation result of the estimation model and the position of the target area in the proposed arrangement.
  • the user can confirm the difference between the estimation result of the estimation model and the position of the target region as the accuracy of the current source estimation in the proposed placement.
  • the calculation conditions include at least one of the number of multiple electromagnetic sensors and the SNR (signal-noise ratio) of the multiple electromagnetic sensors in addition to the position of the target area and the possible placement positions.
  • the proposed placement can be calculated taking into account at least one of the number of electromagnetic sensors and the SNR.
  • the electromagnetic sensor is an OPM (Optically Pumped Magnetometer) sensor, a fluxgate sensor, an MR (Magneto Resistance) sensor, an MI (Magneto Impedance) sensor, a coil-type sensor, or an NVC (Nitrogen-Vacancy Center in Diamond) sensor.
  • OPM Optically Pumped Magnetometer
  • MR Magnetic Resistance
  • MI Magnetic Impedance
  • coil-type sensor a coil-type sensor
  • NVC Nonrogen-Vacancy Center in Diamond
  • a suggested placement of an OPM sensor, fluxgate sensor, MR sensor, MI sensor, coil-type sensor, or NVC sensor can be provided to a user.
  • the electromagnetic sensor is a magnetic sensor or an electric potential sensor that detects a magnetic field generated by electrical activity in the brain, heart, spinal cord, peripheral nerves, or muscles.
  • the placement suggestion method described in paragraph 9 can provide a user with suggested placements for magnetic sensors or electric potential sensors that detect magnetic fields generated by electrical activity in the brain, heart, spinal cord, peripheral nerves, or muscles.
  • the step of outputting the proposed arrangement includes a step of presenting the proposed arrangement to a user.
  • a method for estimating the position of a current source is a method for estimating the position of a current source inside a subject using detection results of a plurality of electromagnetic sensors arranged on a biological surface of the subject, each of which detects an electromagnetic field generated by biological activity taking place in a target area inside the subject, and includes the steps of setting calculation conditions including the position of the target area and the arrangement of the plurality of electromagnetic sensors, calculating priorities of all or a part of the plurality of electromagnetic sensors based on the calculation conditions, and estimating the position of the current source using the detection results of the electromagnetic sensors selected based on the priorities.
  • current source estimation is performed using the detection results of high-priority electromagnetic sensors among a large number of electromagnetic sensors. Therefore, even when using electromagnetic sensors (such as SQUIDs) whose positions are difficult to change, by placing a large number of electromagnetic sensors on the biological surface of the subject in advance, current source estimation can be performed with high accuracy using the detection results of high-priority sensors selected from a large number of electromagnetic sensors.
  • electromagnetic sensors such as SQUIDs
  • An electromagnetic sensor placement suggestion device is a device that uses a forward model for estimating an electromagnetic field generated at the positions of the electromagnetic sensors due to biological activity inside the subject to suggest a placement of multiple electromagnetic sensors to be placed on a biological surface surrounding a target area inside the subject, and includes an input unit to which calculation conditions including the position of the target area and possible positions of the multiple electromagnetic sensors are input, a calculation device that calculates a proposed placement of all or a part of the multiple electromagnetic sensors to estimate the position of a current source inside the subject based on the calculation conditions, and an output unit that outputs the proposed placement.
  • the layout proposal method described in paragraph 12 can achieve the same effect as the layout proposal method described in paragraph 1.
  • 1 Data processing system 2 OPM sensor, 3 Input device, 4 Output device, 10 Processing device, 11 Sensor interface, 12 Input interface, 13 Output interface, 14 Storage device, 15 Arithmetic unit.

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