JP7636933B2 - MEASURING APPARATUS, MEASURING METHOD, AND PROGRAM - Google Patents

Description

The present invention relates to a measurement device, a measurement method, and a program.

Conventionally, there are methods for acquiring tomographic images and the like for the diagnosis of a living body (see Patent Documents 1 to 3). One such method is electrical impedance tomography (EIT), in which a plurality of electrodes are arranged around a living body, and a distribution of electrical conductivity within the living body is detected based on a potential difference between other electrodes measured by passing a current therethrough, and a cross-sectional image of the living body is obtained from the distribution.
Patent Document 1: U.S. Patent Application Publication No. 2017/0303991 Patent Document 2: International Publication No. 2011/086512 Patent Document 3: International Publication No. 2010/113067

In a first aspect of the present invention, a measurement device is provided. The measurement device may include an electrode unit having a plurality of electrodes in contact with a living body. The measurement device may include a magnetic sensor array having a plurality of magnetic sensor cells and capable of detecting an input magnetic field. The measurement device may include a current control unit that causes a current to flow through the living body by at least one electrode pair of the plurality of electrodes. The measurement device may include a magnetic field measurement data acquisition unit that acquires magnetic field measurement data based on an input magnetic field detected from the living body by the magnetic sensor array while a current is flowing through the living body. The measurement device may include a potential measurement data acquisition unit that acquires potential measurement data based on a potential difference detected by at least one electrode pair of the plurality of electrodes while a current is flowing through the living body. The measurement device may include an estimation unit that estimates a current flowing in the living body or a conductivity in the living body based on the magnetic field measurement data and the potential measurement data.

The estimation unit may weight the magnetic field measurement data and the electric potential measurement data to estimate the current flowing within the living body or the conductivity within the living body.

The estimation unit may perform weighting using a weighting factor based on the magnetic field measurement data and the electric potential measurement data.

The estimation unit may weight the magnetic field measurement data and the electric potential measurement data with a weighting coefficient based on at least one of the measurement quantities, the average value of the measurement quantity, or the maximum value of the measurement quantity.

The estimation unit may perform weighting using a weighting factor based on a magnetic field sensitivity matrix indicating the sensitivity of the magnetic field measurement data to current or conductivity in the living body and a potential sensitivity matrix indicating the sensitivity of the potential measurement data to current or conductivity in the living body.

The estimation unit may weight at least one of the elements of the magnetic field sensitivity matrix and the electric potential sensitivity matrix with a weighting coefficient based on the average value of the elements, or the maximum value of the elements.

The estimation unit may perform weighting using a weighting coefficient based on singular values obtained by singular value decomposition from the magnetic field sensitivity matrix and the electric potential sensitivity matrix.

The estimation unit may weight the singular values with a weighting factor based on at least one of the singular values, the average value of the singular values, or the maximum value of the singular values.

The current control unit may pass an alternating current through the living body via at least one electrode pair.

The measuring device may include a control unit that synchronizes the current flowing through the living body through at least one electrode pair with the acquisition of magnetic field measurement data by the magnetic field measurement data acquisition unit and the acquisition of electric potential measurement data by the electric potential measurement data acquisition unit.

The current control unit may apply a current to an electrode pair consisting of two adjacent electrodes among the plurality of electrodes, shifting the electrodes one by one, thereby passing a current through the living body.

The estimation unit may include a signal space separation unit that separates the spatial distribution of the magnetic field indicated by the magnetic field measurement data into a magnetic field to be measured from the living body and a disturbance magnetic field. The estimation unit may include a calculation unit that calculates the current or conductivity in the living body based on the separated magnetic field to be measured and potential measurement data.

Each of the multiple magnetic sensor cells may have multiple magnetic sensors each having a magnetic resistance element and magnetic concentrators arranged on both ends of the magnetic resistance element. The signal spatial separation unit may separate the spatial distribution of the magnetic field using, as basis vectors, signal vectors output by each of the magnetic sensors when a magnetic field having a spatial distribution of an orthonormal function is detected by the magnetic sensor array.

The estimation unit may remove magnetic field components arising from the leads connected to the multiple electrodes from the magnetic field measurement data.

In a second aspect of the present invention, a measurement method is provided. The measurement method may include a step of passing a current through a living organism by at least one electrode pair of a plurality of electrodes. The measurement method may include a step of acquiring magnetic field measurement data based on an input magnetic field detected from the living organism by a magnetic sensor array while a current is being passed through the living organism. The measurement method may include a step of acquiring electric potential measurement data based on an electric potential difference detected by at least one electrode pair of the plurality of electrodes while a current is being passed through the living organism. The measurement method may include a step of estimating a current flowing in the living organism or a conductivity in the living organism based on the magnetic field measurement data and the electric potential measurement data.

In a third aspect of the present invention, a program is provided. The program may cause a computer to function as a signal space separation unit that separates the spatial distribution of the magnetic field indicated by the magnetic field measurement data based on the input magnetic field detected from the living body by the magnetic sensor array while a current is being passed through the living body by at least one electrode pair of the multiple electrodes into a measurement target magnetic field from the living body and an external disturbance magnetic field. The program may cause a computer to function as a calculation unit that calculates a current or conductivity in the living body based on the separated measurement target magnetic field and potential measurement data based on a potential difference detected by at least one electrode pair of the multiple electrodes while a current is being passed through the living body.

Note that the above summary of the invention does not list all of the necessary features of the present invention. Also, subcombinations of these features may also be inventions.

1 shows the configuration of a measurement device 10 according to the present embodiment. 1 shows the configuration of a magnetic sensor unit 110 according to the present embodiment. 2 shows the configuration and arrangement of magnetic sensor cells 220 in a magnetic sensor array 210 according to the present embodiment. 4 shows an example of input/output characteristics of a magnetic sensor having a magnetoresistive element according to the present embodiment. 2 shows an example of the configuration of a sensor unit 300 according to the present embodiment. 4 shows an example of input/output characteristics of the sensor unit 300 according to the present embodiment. 5 shows an example of the configuration of a magnetic sensor 520 according to the present embodiment. 1 shows the configuration of a measurement device 10 according to the present embodiment. An example in which the measurement device 10 of this embodiment measures a magnetic field using the magnetic sensor array 210 will be described. 1 shows an example of the arrangement of a plurality of electrodes 800 of the measurement device 10 of this embodiment. 1 shows the distribution of current in a cross section of a living body 50 parallel to the XZ plane. 1 shows the distribution of magnetic fields and currents detected by the measurement device 10 of this embodiment in a cross section of a living body 50 parallel to the XZ plane. 10A and 10B are schematic diagrams showing divided regions in a living body 50 in a cross section parallel to an XZ plane when the conductivity is calculated by the measuring device 10 of the present embodiment. 2 shows a measurement flow of the measuring device 10 according to the present embodiment. 22 illustrates an example computer 2200 in which aspects of the present invention may be embodied, in whole or in part.

The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

Figure 1 shows the configuration of a measurement device according to this embodiment. The measurement device 10 measures the magnetic field generated by passing a current through a living body 50 such as a subject, and the electric potential of the living body 50, and estimates parameters related to the electric current in the living body 50 from these measurement results. The measurement device 10 may be used to obtain an internal image of the living body 50.

The measuring device 10 includes a main body 20 and an information processing unit 30. The main body 20 is a component for passing a current through a living body 50 to sense the electric potential and magnetic field, and includes a current control unit 100, a magnetic sensor unit 110, a head 120, a drive unit 125, a base unit 130, and a pole unit 140.

The current control unit 100 is placed in contact with the surface of the living body 50 during measurement, and flows a current through the living body 50 while measuring the potential of the surface of the living body 50. The magnetic sensor unit 110 is placed in a position facing the measurement target part of the living body 50 (for example, the lungs of the subject) during measurement, and senses the magnetic field from the living body 50. The head 120 supports the magnetic sensor unit 110 and makes the magnetic sensor unit 110 face the living body 50. The driving unit 125 is provided between the magnetic sensor unit 110 and the head 120, and changes the orientation of the magnetic sensor unit 110 relative to the head 120 when performing calibration. The driving unit 125 according to this embodiment includes a first actuator that can rotate the magnetic sensor unit 110 360 degrees around the Z axis in the figure, and a second actuator that rotates the magnetic sensor unit 110 around an axis perpendicular to the Z axis (the X axis in the state in the figure), and uses these to change the azimuth angle and zenith angle of the magnetic sensor unit 110. In addition, the magnetic sensor unit 110 may be capable of rotating around the measurement target around the Y axis in the figure.

The base unit 130 is a base that supports the other components. The subject, which is the living organism 50, may stand on the base unit 130 or sit in front of the base unit 130 during measurement. The pole unit 140 supports the head 120 at the height of the living organism 50 that is to be measured. The pole unit 140 may be extendable in the vertical direction to adjust the height of the head 120.

The information processing unit 30 is a component for processing the measurement data from the main body unit 20 and outputting it by display, printing, etc. The information processing unit 30 may be a computer such as a PC (personal computer), tablet computer, smartphone, workstation, server computer, or general-purpose computer, or may be a computer system in which multiple computers are connected. Alternatively, the information processing unit 30 may be a dedicated computer designed for specific information processing, or may be dedicated hardware realized by a dedicated circuit.

2 shows the configuration of the magnetic sensor unit 110 according to this embodiment. The magnetic sensor unit 110 has a magnetic sensor array 210 and a sensor data collection unit 230. The magnetic sensor array 210 is configured by arranging a plurality of magnetic sensor cells 220 capable of detecting a magnetic field in three axial directions in a three-dimensional manner. As an example, the plurality of magnetic sensor cells 220 each have a plurality of magnetic sensors each having a magnetic resistance element and a magnetic concentrator plate arranged at least on one end and the other end of the magnetic resistance element. Note that it is preferable that the magnetic concentrator plate is arranged at both ends of the magnetic resistance element in order to increase the sampling accuracy of the spatial distribution of the magnetic field described later. In this figure, the magnetic sensor array 210 has a plurality of magnetic sensor cells 220 (for example, 8 magnetic sensor cells 220 in the X direction, 8 magnetic sensor cells 220 in the Y direction, and 2 magnetic sensor cells 220 in the Z direction, totaling 128 magnetic sensor cells) arranged in a planar manner in each of the X direction, Y direction, and Z direction.

The sensor data collection unit 230 is electrically connected (not shown) to the multiple magnetic sensor cells 220 included in the magnetic sensor array 210, and collects and processes magnetic field measurement data (detection signals) from the multiple magnetic sensor cells 220 and supplies them to the information processing unit 30.

3 shows the configuration and arrangement of the magnetic sensor cells 220 in the magnetic sensor array 210 according to this embodiment. Each magnetic sensor cell 220 has a plurality of sensor units 300x-z (hereinafter collectively referred to as "sensor units 300") each having a magnetic resistance element. In this embodiment, the sensor unit 300x is arranged along the X-axis direction and can detect a magnetic field in the X-axis direction. The sensor unit 300y is arranged along the Y-axis direction and can detect a magnetic field in the Y-axis direction. The sensor unit 300z is arranged along the Z-axis direction and can detect a magnetic field in the Z-axis direction. As shown by the enlarged view indicated by the dashed and dotted lines in this figure, in this embodiment, each sensor unit 300 has a magnetic concentrator plate arranged on both ends of the magnetic resistance element. Therefore, each sensor unit 300 can clearly define the sampling point in space in each axis direction by sampling the spatial distribution of the magnetic field using a magnetic resistance element arranged in a narrow position between the magnetic concentrator plates. The configuration of each sensor unit 300 will be described in detail later.

The multiple magnetic sensor cells 220 are arranged at equal intervals of Δx along the X-axis direction, Δy along the Y-axis direction, and Δz along the Z-axis direction. The position of each magnetic sensor cell 220 in the magnetic sensor array 210 is represented by a set [i, j, k] of position i in the X-axis direction, position j in the Y-axis direction, and position k in the Z-axis direction. Here, i is an integer that satisfies 0≦i≦Nx-1 (Nx indicates the number of magnetic sensor cells 220 arranged in the X-axis direction), j is an integer that satisfies 0≦j≦Ny-1 (Ny indicates the number of magnetic sensor cells 220 arranged in the Y-axis direction), and k is an integer that satisfies 0≦k≦Nz-1 (Nz indicates the number of magnetic sensor cells 220 arranged in the Z-axis direction).

In this figure, the three-axis directions of the magnetic field detected by the sensor units 300x, 300y, and 300z are the same as the three-dimensional direction in which the magnetic sensor cells 220 are arranged. This makes it easy to grasp each component of the distribution of the measured magnetic field. In addition, it is preferable that the sensor units 300x, 300y, and 300z do not overlap each other when viewed from each of the three-dimensional directions in which the magnetic sensor cells 220 are arranged in each magnetic sensor cell 220, and that one end is provided on the gap side provided between the multiple sensor units 300, and the other end is extended in each of the three axial directions away from the gap. As an example, in this figure, a gap is provided in the lower left corner when viewed from the front of the magnetic sensor cell 220, and the sensor units 300x, 300y, and 300z are provided so that one end is in contact with the gap, and the other end is extended in each of the X-axis, Y-axis, and Z-axis directions away from the gap. In this figure, the sensor units 300x, 300y, and 300z are arranged along three mutually perpendicular sides from one corner of the cubic magnetic sensor cell 220, and a gap is provided at the one corner. In addition, it is preferable that the coils or magnetic bodies of the sensor units 300x, 300y, and 300z described later are arranged so as not to overlap each other. This makes it possible to clarify the measurement point, and to further facilitate grasping each component of the measured magnetic field. Furthermore, the other-axis sensitivities of the sensor units 300x, 300y, and 300z can be regarded as equivalent to each other, making it easier to perform the linear algebra calibration calculation described later. This other-axis sensitivity is generated by mutual interference caused by the coils or magnetic bodies of the sensor units 300x, 300y, and 300z. However, the three-axis directions of the magnetic field to be detected and the three-dimensional direction in which the magnetic sensor cells 220 are arranged may be different. When the two are different, there are no restrictions on the arrangement of the sensor unit 300 within the magnetic sensor cell 220 or the arrangement direction of the magnetic sensor cell 220, and the degree of freedom in designing the magnetic sensor array 210 can be increased.

Figure 4 shows an example of the input/output characteristics of a magnetic sensor having a magnetic resistance element according to this embodiment. In this figure, the horizontal axis indicates the magnitude B of the input magnetic field input to the magnetic sensor, and the vertical axis indicates the magnitude V_xMR0 of the detection signal of the magnetic sensor. The magnetic sensor has, for example, a giant magneto-resistance (GMR) element or a tunnel magneto-resistance (TMR) element, and detects the magnitude of the magnetic field in a predetermined uniaxial direction.

Such a magnetic sensor has high magnetic sensitivity, which is the slope of the detection signal V_xMR0 relative to the input magnetic field B, and can detect very small magnetic fields of about 10 pT. On the other hand, the detection signal V_xMR0 of the magnetic sensor saturates when the absolute value of the input magnetic field B is about 1 μT, for example, and the range in which the linearity of the input/output characteristics is good is narrow. Therefore, adding a closed loop that generates a feedback magnetic field to such a magnetic sensor can improve the linearity of the magnetic sensor. Such a magnetic sensor will be described next.

Figure 5 shows an example of the configuration of the sensor unit 300 according to this embodiment. The sensor unit 300 is provided inside each of the multiple magnetic sensor cells 220, and has a magnetic sensor 520, a magnetic field generation unit 530, and an output unit 540. Note that part of the sensor unit 300, for example the amplifier circuit 532 and the output unit 540, may be provided on the sensor data collection unit 230 side rather than on the magnetic sensor cell 220 side.

The magnetic sensor 520 has a magnetic resistance element such as a GMR element or a TMR element, similar to the magnetic sensor described in FIG. 4. The magnetic sensor 520 also has magnetic concentrators arranged at both ends of the magnetic resistance element. The magnetic resistance element of the magnetic sensor 520 may be formed so that, when the positive direction of the magnetic sensing axis is the +X direction, the resistance value increases when a magnetic field in the +X direction is input, and the resistance value decreases when a magnetic field in the -X direction is input. That is, by observing the change in the resistance value of the magnetic resistance element of the magnetic sensor 520, the magnitude of the magnetic field B input to the magnetic sensor 520 can be detected. For example, if the magnetic sensitivity of the magnetic sensor 520 is S, the detection result of the magnetic sensor 520 for the input magnetic field B can be calculated as S×B. Note that the magnetic sensor 520 is connected to a power source, for example, and outputs a voltage drop corresponding to the change in resistance value as the detection result of the input magnetic field. The configuration of the magnetic sensor 520 will be described in detail later.

The magnetic field generating unit 530 applies a feedback magnetic field to the magnetic sensor 520 that reduces the input magnetic field detected by the magnetic sensor 520. For example, the magnetic field generating unit 530 generates a feedback magnetic field B_FB that is in the opposite direction to the magnetic field B input to the magnetic sensor 520 and has an absolute value that is approximately the same as the input magnetic field, and operates to cancel out the input magnetic field. The magnetic field generating unit 530 includes an amplifier circuit 532 and a coil 534.

The amplifier circuit 532 outputs a current according to the detection result of the input magnetic field of the magnetic sensor 520 as a feedback current I_FB. When the magnetic resistance element of the magnetic sensor 520 is configured as a bridge circuit including at least one magnetic resistance element, the output of the bridge circuit is connected to the input terminal pair of the amplifier circuit 532. The amplifier circuit 532 outputs a current according to the output of the bridge circuit as a feedback current I_FB. The amplifier circuit 532 includes, for example, a transconductance amplifier, and outputs a feedback current I_FB according to the output voltage of the magnetic sensor 520. For example, if the voltage-current conversion coefficient of the amplifier circuit 532 is G, the feedback current I_FB can be calculated as G x S x B.

The coil 534 generates a feedback magnetic field B_FB according to the feedback current I_FB. The coil 534 is wound so as to surround the magnetoresistance element of the magnetic sensor 520 and the magnetic concentrator plates arranged on both ends of the magnetoresistance element. It is desirable that the coil 534 generates a uniform feedback magnetic field B_FB throughout the magnetic sensor 520. For example, if the coil coefficient of the coil 534 is β, the feedback magnetic field B_FB can be calculated as β×I_FB. Here, the feedback magnetic field B_FB is generated in a direction that cancels the input magnetic field B, so that the magnetic field input to the magnetic sensor 520 is reduced to B−B_FB. Therefore, the feedback current I_FB is expressed as follows:

By solving equation (1) for the feedback current I_FB, it is possible to calculate the value of the feedback current I_FB in the steady state of the sensor unit 300. If it is assumed that the magnetic sensitivity S of the magnetic sensor 520 and the voltage-current conversion coefficient G of the amplifier circuit 532 are sufficiently large, the following equation can be calculated from equation (1).

The output unit 540 outputs an output signal V_xMR according to the feedback current I_FB that the magnetic field generating unit 530 flows to generate the feedback magnetic field B_FB. The output unit 540 has, for example, a resistive element with a resistance value R, and outputs a voltage drop caused by the feedback current I_FB flowing through the resistive element as the output signal V_xMR. In this case, the output signal V_xMR is calculated from equation (2) as follows:

As described above, the sensor unit 300 generates a feedback magnetic field that reduces the magnetic field input from the outside, thereby effectively reducing the magnetic field input to the magnetic sensor 520. As a result, the sensor unit 300 can prevent the detection signal V_xMR from becoming saturated even if the absolute value of the input magnetic field B exceeds 1 μT by using, for example, a magnetoresistance element having the characteristics shown in FIG. 4 as the magnetic sensor 520. The input/output characteristics of such a sensor unit 300 are described below.

Figure 6 shows an example of the input/output characteristics of the sensor unit 300 according to this embodiment. In this figure, the horizontal axis indicates the magnitude B of the input magnetic field input to the sensor unit 300, and the vertical axis indicates the magnitude V_xMR of the detection signal of the sensor unit 300. The sensor unit 300 has high magnetic sensitivity and can detect a minute magnetic field of about 10 pT. Furthermore, the sensor unit 300 can maintain good linearity of the detection signal V_xMR even if the absolute value of the input magnetic field B exceeds 100 μT, for example.

That is, the sensor unit 300 according to this embodiment is configured so that the detection result for the input magnetic field B has linearity within a predetermined range of the input magnetic field B, for example, the absolute value of the input magnetic field B being several hundred μT or less. By using such a sensor unit 300, for example, a weak magnetic signal from the living body 50 can be easily detected.

Figure 7 shows an example of the configuration of the magnetic sensor 520 according to this embodiment. As an example, the magnetic sensor 520 according to this embodiment has a magnetic resistance element 702 and magnetic concentrators 704 and 706 arranged at one end and the other end of the magnetic resistance element 702. The magnetic concentrators 704 and 706 are arranged so as to sandwich the magnetic resistance element 702 between them. That is, the magnetic concentrators are arranged at both ends of the magnetic resistance element 702. In Figure 7, the magnetic concentrator 704 arranged at the right end of the magnetic resistance element 702 along the magnetic sensing axis in a front view is a magnetic concentrator provided on the positive side of the magnetic sensing axis, and the magnetic concentrator 706 arranged at the left end of the magnetic resistance element 702 is a magnetic concentrator provided on the negative side of the magnetic sensing axis. When a magnetic field is input to the magnetic concentrators 704 and 706 from the negative side to the positive side of the magnetic sensing axis, the resistance of the magnetic resistance element 702 may increase or decrease. The magnetic sensing axis may be along the direction of magnetization fixed by the magnetization fixed layer that forms the magnetoresistance element 702. The magnetic concentrators 704 and 706 are made of a soft magnetic material such as iron. By arranging the magnetic concentrators 704 and 706 made of a soft magnetic material at one end and the other end of the magnetoresistance element 702, the magnetic lines of force passing through the magnetoresistance element 702 can be increased, thereby increasing the sensitivity of the magnetic sensor 520.

In this figure, an example in which the magnetic concentrator is disposed at both one end and the other end of the magnetoresistance element 702 is shown, but the magnetic concentrator may be disposed at only one end or the other end of the magnetoresistance element 702. However, in order to further increase the sensitivity of the magnetic sensor 520, it is preferable to provide a magnetic concentrator at both one end and the other end of the magnetoresistance element 702. In addition, when a magnetic concentrator is provided at both one end and the other end of the magnetoresistance element 702, the position of the magnetoresistance element 702, which is located in a narrow position between the two magnetic concentrators 704 and 706, becomes the magnetic sensing portion, i.e., the spatial sampling point, so that the magnetic sensing portion becomes clear and the compatibility with the signal spatial separation technology described later can be further improved. In this way, by using a magnetic sensor 520 in each sensor unit 300 in which magnetic concentrators 704 and 706 are arranged on both ends of a magnetic resistance element 702, the measuring device 10 according to this embodiment can sample the spatial distribution of the magnetic field at an extremely narrow position (for example, 100 μm or less) in each axial direction, sandwiched between the magnetic concentrators on both ends, as shown in FIG. 3, and therefore the sampling accuracy (positional accuracy) is higher than when the spatial distribution of the magnetic field is sampled using a SQUID coil (up to 2 cm) that measures biomagnetic fields.

Figure 8 shows the configuration of the measurement device 10 according to this embodiment. As an example, the current control unit 100 of the main body 20 shown in Figure 1 has multiple electrodes 800, lead wires 805, a current control unit 810, and a potential measurement data acquisition unit 815, the magnetic sensor unit 110 has a magnetic sensor array 210 and a sensor data collection unit 230, and the information processing unit 30 has an estimation unit 870. Note that the electrode unit of the present application may be anything that includes at least multiple electrodes 800, and may be, for example, the current control unit 100.

The multiple electrodes 800 are each electrically connected to a current control unit 810 via a lead wire 805, and are arranged in a line at the same height in the Y-axis direction corresponding to the measurement target part of the living body 50, in contact with the surface of the living body 50. Of the multiple electrodes 800, electrodes 800 (1) to (5) are shown in FIG. 8. The number of electrodes 800 is not particularly limited as long as it is two or more, but 8 to 16 electrodes are preferable from the viewpoint of measurement accuracy.

The current control unit 810 is connected to the magnetic sensor unit 110 and the potential measurement data acquisition unit 815, and passes a current through the living body 50 through at least one electrode pair of the multiple electrodes 800, and measures the potential of at least one electrode pair of the multiple electrodes 800. The current control unit 810 may pass an AC current through the living body 50 through at least one electrode pair. The current control unit 810 may have an AC power source for supplying an AC current to the electrode pair, or may be connected to an external AC power source. The current control unit 810 may pass a current through the electrode pair of the multiple electrodes 800 in response to a synchronization signal from the control unit 820 of the magnetic sensor unit 110. The current control unit 810 may, as an example, pass an AC current of 1 mA or less through the living body 50 in synchronization with the synchronization signal.

The current control unit 810 may measure the potential difference between the electrode pairs of the multiple electrodes 800 while passing a current through the living body 50. The current control unit 810 may measure the potential difference between the electrode pairs in response to a synchronization signal from the control unit 820 of the magnetic sensor unit 110, and output the potential measurement data to the potential measurement data acquisition unit 815.

The potential measurement data acquisition unit 815 is connected to the control unit 820 and the estimation unit 870, and acquires potential measurement data from the current control unit 810 based on a potential difference detected at at least one of the multiple electrode pairs while a current is being passed through the living body 50. The potential measurement data acquisition unit 815 may acquire potential measurement data indicating the potential difference measured by the current control unit 810 in response to a synchronization signal from the control unit 820. The potential measurement data acquisition unit 815 may perform processing such as AD conversion on the potential measurement data, and output the processed potential measurement data to the estimation unit 870.

The magnetic sensor array 210 has multiple magnetic sensor cells 220 and can detect input magnetic fields in three-axis directions at multiple locations in three-dimensional space. Each of the multiple magnetic sensor cells 220 has multiple sensor units 300x-z as described above. In this figure, of the multiple magnetic sensor cells 220 that the magnetic sensor array 210 has in each dimensional direction, the parts related to positions [i, j, k], [i+1, j, k], [i, j+1, k], and [i, j, k+1] are shown.

The sensor data collection unit 230 has a control unit 820, multiple magnetic field measurement data acquisition units 830, multiple AD converters 840, a clock generator 842, a calibration calculation unit 850, and a memory unit 860.

The control unit 820 is connected to the current control unit 810, the potential measurement data acquisition unit 815, and the multiple magnetic field measurement data acquisition units 830, respectively, and controls synchronous detection between the current control unit 810, the potential measurement data acquisition unit 815, and the magnetic field measurement data acquisition unit 830. The control unit 820 synchronizes the current flowing through the living body 50 by at least one electrode pair with the acquisition of magnetic field measurement data by the magnetic field measurement data acquisition unit 830 and the acquisition of potential measurement data by the potential measurement data acquisition unit 815. The control unit 820 outputs a common synchronization signal to the current control unit 810, the potential measurement data acquisition unit 815, and each magnetic field measurement data acquisition unit 830. The control unit 820 may use the common synchronization signal to match the timing at which the current control unit 810 flows with the timing at which the multiple magnetic field measurement data acquisition units 830 acquire magnetic field measurement data from each sensor cell, and the timing at which the potential measurement data acquisition unit 815 acquires potential measurement data. As an example, the control unit 820 outputs a synchronization signal with a frequency of 10 to 100 KHz.

The magnetic field measurement data acquisition units 830 are each connected to the multiple sensor units 300x-z of the corresponding magnetic sensor cells 220 and the corresponding AD converters 840. The magnetic field measurement data acquisition unit 830 acquires magnetic field measurement data based on the input magnetic field detected from the living body 50 by the magnetic sensor cells 220 of the magnetic sensor array 210 while a current is flowing through the living body 50. The magnetic field measurement data acquisition unit 830 may acquire the magnetic field measurement data in response to a synchronization signal from the control unit 820. The magnetic field measurement data acquisition unit 830 may multiply the magnetic field measurement data by the synchronization signal and output the data. The magnetic field measurement data acquisition unit 830 may acquire only frequency components equal to the reference signal from the magnetic field measurement data output by the multiple sensor units 300x-z of the corresponding magnetic sensor cells 220, using the current signal applied by the current control unit 810 as a reference signal. The magnetic field measurement data acquisition unit 830 may perform processing such as low-pass filtering on the magnetic field measurement data.

Each of the AD converters 840 is connected to a clock generator 842 and a corresponding calibration calculation unit 850, and converts the analog signal (magnetic field measurement data V_xMR in FIG. 6) acquired by the corresponding magnetic field measurement data acquisition unit 830 into digital magnetic field measurement data (Vx, Vy, Vz). Here, Vx, Vy, and Vz are measurement values (e.g., digital voltage values) obtained by converting the magnetic field measurement data from the sensor units 300x, 300y, and 300z into digital form.

The clock generator 842 generates a sampling clock and supplies a common sampling clock to each of the multiple AD converters 840. Each of the multiple AD converters 840 then performs analog-to-digital conversion according to the common sampling clock supplied from the clock generator 842. Therefore, all of the multiple AD converters 840 that perform analog-to-digital conversion of the outputs of the three-axis sensor units 300x-z provided at different positions operate synchronously. This allows the multiple AD converters 840 to simultaneously sample the detection results of the three-axis sensor units 300x-z provided in different spaces.

Each of the calibration calculation units 850 is connected to a corresponding storage unit 860, calibrates the magnetic field measurement data from the AD converter 840 using the calibration parameters, and outputs the calibrated data to the storage unit 860. The calibration of the magnetic field measurement data by the calibration calculation unit 850 is outlined below. The magnetic field input to the magnetic sensor cell 220 at the position [i, j, k] is B (Bx, By, Bz), and the detection result of the three-axis magnetic sensor by the sensor units 300x, 300y, and 300z is V (Vx, Vy, Vz). In this case, if the magnetic sensor characteristic of the three-axis magnetic sensor is a matrix S, the detection result V of the three-axis magnetic sensor can be expressed as follows:

Here, Sxx, Syy, and Szz represent the sensitivity in the main axis direction of sensor units 300x, 300y, and 300z, respectively, and Sxy, Sxz, Syx, Syz, Szx, and Szy represent the sensitivity in the other axis directions. Also, Vos,x, Vos,y, and Vos,z represent the offset in the main axis direction of sensor units 300x, 300y, and 300z, respectively. Note that since V (Vx, Vy, Vz), which is the detection result of the three-axis magnetic sensor, is detected in synchronization with the AC current applied to the living body 50, it is possible to ignore these offsets.

Since each sensor unit 300 has linearity in the detection result for the input magnetic field within the range of the input magnetic field to be detected, each element of the matrix S has an approximately constant coefficient that is unrelated to the magnitude of the input magnetic field B. Even if the sensor unit 300 has other-axis sensitivity, if the detection result of the sensor unit 300 has linearity, each element of the matrix S has an approximately constant coefficient that is unrelated to the magnitude of the input magnetic field B.

Therefore, the calibration calculation unit 850 can convert the magnetic field measurement data V (Vx, Vy, Vz) into the magnetic field measurement data B (Bx, By, Bz) indicating the ^original input magnetic field, as shown in the following equation, by using the inverse matrix S -1 of the matrix S and the offset (Vos, x, Vos, y, Vos, z). This conversion also holds when the sensor units 300x to z are equipped with the above-mentioned magnetic concentrator. This is because the magnetic sensor cell 220 is configured as a three-axis magnetic sensor using the sensor units 300x to z, and conversion using linear algebra is possible.

The calibration calculation unit 850 calculates the inverse matrix S ^-1 and offset (Vos, x, Vos, y, Vos, z) of the matrix S using the environmental magnetic field measurement data, and converts the magnetic field measurement data acquired by the magnetic field measurement data acquisition unit 830 into magnetic field measurement data B using these calibration parameters and supplies it to the memory unit 860.

As described above, since each sensor unit 300 has linearity, the calibration calculation unit 850 can convert the magnetic field measurement data into magnetic field measurement data B using approximately constant coefficients. In other words, the approximately constant coefficients used by the calibration calculation unit 850 can be determined as a set of calibration parameters using the environmental magnetic field data.

The memory unit 860 is connected to the estimation unit 870, stores the magnetic field measurement data B calibrated by the calibration calculation unit 850, and supplies it to the estimation unit 870.

The estimation unit 870 estimates the current flowing in the living body 50 or the conductivity in the living body 50 based on the magnetic field measurement data from the memory unit 860 and the potential measurement data from the potential measurement data acquisition unit 815. The estimation unit 870 may estimate the current value or conductivity for multiple areas in the living body 50 based on the magnetic field measurement data and the potential measurement data acquired at the same timing. The estimation unit 870 may estimate the current value or conductivity by weighting the magnetic field measurement data and the potential measurement data. The estimation unit 870 may weight with a weighting coefficient based on the magnetic field measurement data and the potential measurement data. In addition, the estimation unit 870 may weight with a weighting coefficient based on a magnetic field sensitivity matrix (also called a lead field matrix) indicating the sensitivity of the magnetic field measurement data to the current or conductivity in the living body 50 and a potential sensitivity matrix (also called a lead field matrix) indicating the sensitivity of the potential measurement data to the current or conductivity in the living body 50. Here, the estimation unit 870 may calculate the values of the matrix elements of the magnetic field sensitivity matrix and the electric potential sensitivity matrix by the finite element method (FEM) that models the living body 50. The estimation unit 870 may also store weighting coefficients that have been optimized in advance and perform weighting with the weighting coefficients.

The estimation unit 870 includes a basis vector storage unit 880, a signal space separation unit 890, and a calculation unit 895. The estimation unit 870 uses the basis vector storage unit 880 and the signal space separation unit 890 to reduce disturbance magnetic fields in the magnetic field measurement data.

The basis vector storage unit 880 is connected to the signal space separation unit 890, and stores in advance the basis vectors required for the signal space separation unit 890 to perform signal separation of the magnetic field measurement data B, and supplies these to the signal space separation unit 890.

The signal space separation unit 890 is connected to the storage unit 860 and the calculation unit 895, and separates the spatial distribution of the magnetic field indicated by the magnetic field measurement data output by the storage unit 860 into a magnetic field to be measured from the living body 50 and a disturbance magnetic field. For example, the signal space separation unit 890 performs signal separation on the spatial distribution of the magnetic field indicated by the magnetic field measurement data B, using the signal vectors output by each of the multiple magnetic sensors 520 when the magnetic sensor array 210 detects a magnetic field having a spatial distribution of a normal orthogonal function as basis vectors. The signal space separation unit 890 acquires the basis vectors necessary for signal separation from the basis vector storage unit 880. Then, the signal space separation unit 890 uses the basis vectors acquired from the basis vector storage unit 880 to perform signal separation on the spatial distribution of the magnetic field indicated by the magnetic field measurement data B into a magnetic field to be measured and a disturbance magnetic field, and calculates the magnetic field to be measured while suppressing the disturbance magnetic field. The signal space separation unit 890 may calculate and output the magnetic fields to be measured at multiple magnetic field positions on the surface of the living body 50 where the magnetic sensor array 210 is not positioned.

The calculation unit 895 receives magnetic field measurement data indicating the magnetic field to be measured from the signal space separation unit 890, and calculates the current value or conductivity in the living body 50 based on the magnetic field measurement data and the potential measurement data. The calculation unit 895 may calculate the distribution of the current value or the distribution of the conductivity in the living body 50 through which a current is passed by the electrode pair.

The calculation unit 895 may remove the magnetic field components generated from the lead wire 805 connected to the electrode 800 from the current control unit 810 from the magnetic field measurement data before calculating the current value or conductivity. The calculation unit 895 may store in advance the magnetic field components caused by the different lead wires 805 for each of the multiple electrode pairs through which a current flows during measurement. The calculation unit 895 may store the magnetic field generated by the lead wire 805 and cancel the stored magnetic field components from the magnetic field measurement data. For example, the magnetic field generated by the lead wire 805 may be calculated from the path of the lead wire connected to each electrode (for example, at least one of the length and position of the lead wire 805 placed on the living body 50, particularly in the area on the living body 50 facing the magnetic sensor array 210 during measurement). In addition, the magnetic field generated by the lead wire 805 may be obtained by measuring in advance the magnetic field generated by the lead wire 805 when a current flows for each electrode pair. Furthermore, the magnetic field generated by the lead wire 805 may be estimated by performing a simulation based on the path of the lead wire 805.

Figure 9 shows an example in which the measurement device 10 of this embodiment measures a magnetic field using a magnetic sensor array 210 arranged on a curved surface. The magnetic sensor array 210 may be arranged facing the electrode 800 of the current control unit 100, for example, at a position 20 to 50 mm away from the living body 50, without contacting the electrode 800 of the current control unit 100.

In the magnetic sensor array 210, a plurality of magnetic sensor cells 220 (for example, 12 magnetic sensor cells 220 in the X direction, 8 magnetic sensor cells 220 in the Y direction, and 2 magnetic sensor cells 220 in the Z direction, totaling 192 magnetic sensor cells) are arranged in a curved shape in each of the X direction, Y direction, and Z direction. Each magnetic sensor cell 220 is arranged at a lattice point included in the curved shape in a three-dimensional lattice space. Note that here, the lattice points are lattice-like points that are equally spaced at predetermined intervals (for example, intervals of 5 to 15 mm) in the X direction, Y direction, and Z direction, respectively. As an example, each magnetic sensor cell 220 is arranged so as to follow a curved surface that has a convex in a direction perpendicular to the X direction, Y direction, or Z direction when viewed from one of the X direction, Y direction, and Z direction. In this figure, an example is shown in which each magnetic sensor cell 220 is arranged so as to follow a curved surface that has a convex in the positive direction of the Z axis when viewed from the Y direction. In this case, the magnetic sensor array 210 may form a curved shape having a convex in the positive direction of the Z axis by arranging each magnetic sensor cell 220 at a lattice point in a three-dimensional lattice space so that each vertex of each magnetic sensor cell 220 is arranged as far in the negative direction of the Z axis as possible without exceeding a range that does not exceed a predetermined curved surface having a convex in the positive direction of the Z axis.

The measurement device 10 measures the magnetic field by positioning the magnetic sensor array 210 so that the center position in the Y-axis direction coincides with the center position of the multiple electrodes 800 and/or the measurement target part, and the center position in the X-axis direction of the measurement target part of the living body 50 is located at the center of the curved surface. This allows the measurement device 10 to perform signal spatial separation using measurement data B measured at a position close to the living body 50, which is the source of the magnetic field to be measured, and to separate the magnetic field to be measured and the disturbance magnetic field with high accuracy. Note that in this case, it is preferable for the magnetic sensor array 210 to have a curvature of the curved surface that is approximately equal to the curvature around the subject's chest, since this allows the magnetic field to be measured at a position closer to the living body 50, which is the source of the magnetic field to be measured.

Figure 10 shows an example of the arrangement of multiple electrodes 800 of the measurement device 10 of this embodiment. Note that Figure 10 shows an example of passing a current through an electrode pair consisting of electrodes (2) and (3). The multiple electrodes 800 may be arranged on a surface facing the measurement target part of the living body 50. The multiple electrodes 800 are arranged side by side at equal intervals around the living body 50. For example, 8 to 16 electrodes 800 may be arranged side by side at equal intervals in contact with the surface of the living body 50 on the side where the magnetic sensor array 210 is arranged, surrounding the measurement target on the cross section (XZ plane) of the living body 50.

The multiple electrodes 800 may be, for example, independent electrodes attached to the surface of the living body 50 by a sticker or the like. The multiple electrodes 800 may also be fixed to a belt around the abdomen with the contact surface exposed, or may be placed in contact with the living body 50 by wrapping the belt around the living body 50 and fixing it. The multiple electrodes 800 may have the same shape. Each of the multiple electrodes 800 may be circular, elliptical, polygonal, or the like.

Figure 11 shows a cross section parallel to the XZ plane of a portion of the measuring device 10 of this embodiment. In Figure 11, the dotted arrows in the living body 50 roughly indicate the flow of secondary current in the living body 50. When the measuring device 10 passes current through the multiple electrodes 800 in contact with the living body 50, the electrodes 800 measure the potential difference, and the magnetic sensor array 210 detects the input magnetic field on one side of the living body 50. The measuring device 10 passes AC current through an electrode pair consisting of, for example, two electrodes 800 (2) and (3), which causes a secondary current to flow in the living body 50. The measuring device 10 detects the magnetic field generated while the electrode pair is passing AC current with the magnetic sensor array 210, detects the potential with the multiple electrodes 800, and can calculate the distribution of current or conductivity in the living body 50 from the detected magnetic field and potential.

Figure 12 shows the distribution of magnetic fields and currents detected by the measurement device 10 of this embodiment in a cross section parallel to the XZ plane. The signal space separation unit 890 of the measurement device 10 of this embodiment can calculate the measurement target magnetic fields of M (M ≧ 1) detection positions 1200 on the surface of the living body 50 based on the magnetic field detected by the magnetic sensor array 210. The detection positions 1200 may be set to the same positions as the positions where the electrodes 800 are placed. This allows the calculation unit 895 to calculate the currents J1 to JN of N (N ≧ 1) positions (voxels) in the living body 50 using the magnetic fields and potentials of the M detection positions 1200. Note that the detection positions 1200 may be approximately the same as the center position of the measurement target part in the Y-axis direction, and may also be approximately the same as the center position or within the length range of the electrode 800.

13 is a schematic diagram showing regions divided in a living body 50 in a cross section parallel to the XZ plane when the measurement device 10 of this embodiment calculates the conductivity. In FIG. 13, detection positions i1 to i4 are shown as an example. The detection position i indicates the position of the electrode 800 for measuring the electric potential measurement data, and also indicates the detection position of the magnetic field to be measured for the magnetic field measurement data (for example, the detection position 1200 in FIG. 12). The living body 50 is divided into k (k=1 to 9 in FIG. 13) regions Ω _k=1 to Ω _k=9 in a mesh shape, and the measurement device 10 can calculate the conductivity distribution in the living body 50 by calculating the conductivity in each region Ω.

Figure 14 shows the measurement flow of the measurement device 10 according to this embodiment.

In step 1300, the basis vector storage unit 880 stores the basis vectors. As an example, the basis vector storage unit 880 stores, as basis vectors, signal vectors output by each of the multiple magnetic sensors 520 when the magnetic sensor array 210 detects a magnetic field having a spatial distribution of a spherical harmonic function before measuring the magnetic field to be measured. That is, the basis vector storage unit 880 stores, as basis vectors, magnetic field signal vectors obtained by spatially sampling the spherical harmonic function when a predetermined point in space is designated as the coordinate origin. Here, the spherical harmonic function is a function obtained by restricting a homogeneous polynomial that is a solution to the n-dimensional Laplace equation to a unit sphere, and has orthonormality on the sphere. Note that the basis vector storage unit 880 may store the basis vectors before the signal space separation by the measurement device 10 (step 1330). The basis vector storage unit 880 may also store, as basis vectors, signal vectors that are predetermined based on simulation results or the like.

Next, in step 1310, the measuring device 10 acquires potential measurement data along with magnetic field measurement data based on the input magnetic field detected while current is being passed through the living body 50. The control unit 820 may output a synchronization signal for synchronous detection to the current control unit 810, the magnetic field measurement data acquisition unit 830, and the potential measurement data acquisition unit 815. The control unit 820 may output a synchronization signal at a frequency set by the user or a predetermined frequency.

The current control unit 810 may pass an alternating current having the same frequency as the synchronization signal through the living body 50 via the electrode pair during the period when the synchronization signal is received, while the magnetic field measurement data acquisition unit 830 and the potential measurement data acquisition unit 815 may acquire measurement data during the period when the synchronization signal is received. The current control unit 810 may apply a current to an electrode pair consisting of two adjacent electrodes out of the multiple electrodes 800 to pass a current through the living body 50. For example, the current control unit 810 may apply a current to an electrode pair consisting of two adjacent electrodes 800 in sequence while shifting the electrodes 800 one by one to pass a current through the living body 50.

Specifically, the current control unit 810 may pass current from all combinations of electrode pairs to the living body 50 by switching the electrode pairs with a relay or the like every one or more periods of the synchronization signal in the order of the electrode pairs of electrodes 800 (1) and (2), electrodes 800 (2) and (3), electrodes 800 (3) and (4), electrodes 800 (4) and (5), and electrodes 800 (5) and (1) in FIG. 11. The current control unit 810 may output the potential difference of all electrodes 800 or electrodes 800 other than the electrode pair to which the current is being applied to the potential measurement data acquisition unit 815 every time the electrode pairs are switched. The current control unit 810 may output the potential difference of each electrode 800 (2) to 800 (5) with the electrode 800 (1) as the reference potential. The current control unit 810 may also output the potential difference of the other electrode 800 with the electrode 800 of one of the electrode pairs to which the current is being applied as the reference potential. The current control unit 810 may also detect the potential difference between a specific electrode 800 and multiple other electrodes 800, and output the difference between the detected potential differences as the potential difference of the electrode pair consisting of the multiple other electrodes 800. For example, when obtaining the potential difference between electrodes 800(4) and (5), the current control unit 810 may calculate the difference between the potential difference between electrodes 800(4) and (1) and the potential difference between electrodes 800(5) and (1) as the potential difference between electrodes 800(4) and (5).

The potential measurement data acquisition unit 815 may multiply one or more potential measurement data measured for each electrode pair to which the signal is applied by a synchronization signal to acquire the data. The potential measurement data acquisition unit 815 may use the current signal applied by the current control unit 810 as a reference signal to acquire only frequency components of the potential measurement data equal to the reference signal. The potential measurement data acquisition unit 815 may filter the potential measurement data multiplied by the synchronization signal using an analog low-pass filter, perform AD conversion, etc., and output digital potential measurement data to the estimation unit 870.

The magnetic field measurement data acquisition unit 830 may acquire the magnetic field measurement data measured for each electrode pair by multiplying the data by a synchronization signal. The magnetic field measurement data acquisition unit 830 may filter the magnetic field measurement data multiplied by the synchronization signal using an analog low-pass filter and output the data.

Each of the multiple AD converters 840 performs analog-to-digital conversion on the acquired magnetic field measurement data and outputs it. The calibration calculation unit 850 may calibrate the acquired magnetic field measurement data and output it to the storage unit 860. The calibration calculation unit 850 may filter the magnetic field measurement data using a digital low-pass filter before calibration. The signal space separation unit 890 acquires the calibrated magnetic field measurement data B from the storage unit 860.

In step 1320, the signal space separation unit 890 obtains from the basis vector storage unit 880 the signal vectors that were stored as basis vectors by the basis vector storage unit 880 in step 1300. Note that in this flow, either step 1310 or step 1320 may be performed first.

In step 1330, the signal space separation unit 890 performs series expansion of the spatial distribution of the magnetic field indicated by the magnetic field measurement data B acquired in step 1310, using the signal vector acquired in step 1320 as a basis vector. Then, the signal space separation unit 890 performs signal separation of the spatial distribution of the magnetic field into the magnetic field to be measured and the disturbance magnetic field, from the vector obtained by the series expansion. Note that the orthonormal function may be a spherical harmonic function. Furthermore, when performing signal separation, the signal space separation unit 890 calculates the coefficients of the basis vectors by the least squares method.

Then, in step 1340, the signal space separation unit 890 suppresses the disturbance magnetic field based on the result of the signal separation in step 1330, calculates only the magnetic field to be measured, and outputs it to the calculation unit 895. This will be described in detail below.

The static magnetic field B(r) can be calculated as the spatial gradient of the potential V(r) using the potential V(r) that satisfies the Laplace equation ΔV(r)=0, as shown in the following equation: Here, r is a position vector that represents the position from the origin of the coordinate system, Δ is the Laplacian, μ is magnetic permeability, and ∇ is an operator that represents a vector differential operation.

The solution of the Laplace equation generally has a solution in the form of a series expansion using spherical harmonic functions Yl,m(θ,φ) which are orthonormal functions, so the potential V(r) can be expressed by the following equation. Here, |r| is the absolute value of the position vector r (distance from the coordinate origin), θ and φ are two argument angles in spherical coordinates, l is the azimuthal quantum number, m is the magnetic quantum number, α and β are multipole moments, and Lin and Lout are the series numbers for the space in front of the magnetic sensor array 210 and the space behind it as seen from the living body 50, respectively. The azimuthal quantum number l is a positive integer, and the magnetic quantum number m is an integer from -l to +l. That is, for example, when l is 1, m is -1, 0, and 1, and when l is 2, m is -2, -1, 0, 1, and 2. Since there is no single magnetic pole in the magnetic field, the azimuthal quantum number l in (Equation 7) starts from 1, not 0. The first term in (Equation 7) is a term inversely proportional to the distance from the coordinate origin, and indicates the potential existing in the space in front of the magnetic sensor array 210 as viewed from the living body 50. The second term in (Equation 7) is a term proportional to the distance from the coordinate origin, and indicates the potential existing in the space behind the magnetic sensor array 210 as viewed from the living body 50.

Therefore, according to (Equation 6) and (Equation 7), the static magnetic field B(r) can be expressed by the following equation: Here, the first term in (Equation 8) represents the magnetic field source (magnetic field to be measured) existing in the space in front of the magnetic sensor array 210 as seen from the subject. Also, the second term in (Equation 8) represents the disturbance magnetic field created by the magnetic field source existing in the space behind the magnetic sensor array 210 as seen from the living body 50.

When the solution to the Laplace equation is expressed in the form of a series expansion using spherical harmonic functions, the general solution is an infinite series, but it is sufficient to obtain a sufficient SNR (signal-to-noise ratio, i.e., the ratio of the magnetic field signal to be measured to the disturbance magnetic field and sensor noise) to measure the magnetic field from the living body 50, and it is said that it is sufficient to express it as a series of about 10 terms. Also, for example, it is said that the series for signal space separation in a magnetoencephalograph is sufficient for Lin = 8 and Lout = 3. Therefore, in this embodiment, the case of Lin = 8 and Lout = 3 will be described as an example. However, the values of Lin and Lout are not limited to this, and may be any numerical value that is sufficient to sufficiently suppress the disturbance magnetic field and calculate only the magnetic field to be measured.

Here, the vectors representing the magnetic sensing axis directions and magnetic sensitivity of the sensor units 300x, y, and z in each magnetic sensor cell 220 are defined as nx, ny, and nz, respectively, and the subscript t is a transposed matrix, and al, m and bl, m are defined as follows. That is, al, m and bl, m are defined as vectors having components of the inner product of the vectors nx, ny, and nz representing the magnetic sensing axis directions and magnetic sensitivity of the sensor units 300x, y, and z and a spherical harmonic function, which is a three-dimensional vector signal. This means that in each magnetic sensor cell 220, the spherical harmonic function is sampled in an orthogonal coordinate system. Note that these al, m and bl, m are vectors having dimensions three times the number of magnetic sensor cells 220. In addition, each vector nx, ny, and nz representing the magnetic sensing axis directions and magnetic sensitivity of each sensor unit 300 may be a vector corresponding to the sensitivity in the main axis direction and the sensitivity in the other axis direction described above. nx may correspond to Sxx, Sxy, Sxz. ny may correspond to Syx, Syy, Syz. nz may correspond to Szx, Szy, Szz. In this way, the values of al, m and bl, m calculated including the sensitivity in the main axis direction of the sensor unit 300x, y, and z and the sensitivity correction in the other axis direction are stored in the basis vector storage unit 880. The magnetic measurement device 10 according to this embodiment, in which the basis vector storage unit 880 stores the values of al, m and bl, m calculated including the correction of the magnetic sensitivity (main axis sensitivity, other axis sensitivity), can correct the magnetic sensitivity (main axis sensitivity, other axis sensitivity) of each magnetic sensor cell 220 by performing correction in the calibration calculation unit 850 on the acquired magnetic field measurement data during operation.

Then, the sensor output vector Φ outputted from the magnetic sensor array 210 at a certain time can be expressed by the following equation.

Furthermore, Sin, Sout, Xin, and Xout are defined as follows. That is, Sin is defined as a vector with a total of Lin·(Lin+2) columns, in which each vector a is arranged in a column when m=-l to l is an integer from l=1 to l=Lin. Also, Sout is defined as a vector with a total of Lout·(Lout+2) columns, in which each vector b is arranged in a column when m=-l to l is an integer from l=1 to L=Lout. Also, Xin is defined as a vector with a total of Lin·(Lin+2) rows, in which each multipole moment α is arranged in a column when m=-l to l is an integer from l=1 to l=Lin. Also, Xout is defined as a vector with a total of Lout·(Lout+2) rows, obtained by transposing the vector in which each multipole moment β is arranged in a column in order from l=1 to l=Lin, where m=-1 to l is an integer.

Then, the sensor output vector Φ can be expressed as an inner product of a matrix S and a column vector X as shown in the following equation. Here, the matrix S indicates a basis vector, and is obtained, for example, by the signal space separation unit 890 from the basis vector storage unit 880 in step 1320. Furthermore, the column vector X indicates a coefficient related to the basis vector.

Based on the model formula of the sensor output vector Φ obtained by (Equation 12), the following formula is used to determine a vertical vector X that satisfies Φ=S·X by least squares approximation. This allows the signal space separation unit 890 to solve the spatial distribution of the magnetic field.

In this embodiment, as shown in FIG. 12, when calculating the magnetic field at multiple detection positions 1200 on the surface of the living body 50, the magnetic field at vector r of the multiple detection positions 1200 can be calculated based on the sensor output vector Φ by (Equation 14) using X obtained by (Equation 13). In (Equation 14), the first term indicates the magnetic field to be measured at the detection position 1200 on the surface of the living body 50, and the second term indicates the disturbance magnetic field.

The signal space separation unit 890 according to this embodiment can calculate the magnetic field for each of the multiple detection positions 1200 using (Equation 14). The signal space separation unit 890 outputs the result in which the disturbance magnetic field component (i.e., the component of the second term in (Equation 14)) has been suppressed. The signal space separation unit 890 may output only the magnetic field to be measured in the vector r of the detection position 1200, i.e., the component of the first term in (Equation 14).

The measuring device 10 may acquire the difference ΔB of the magnetic flux density at the time of measurement from the magnetic flux density in a predetermined reference state as magnetic field measurement data. The magnetic flux density in the reference state may be a magnetic flux density acquired by simulating the inside of the living body 50 as being uniform, or a magnetic flux density measured in a previous measurement. The measuring method and the calculating method of the magnetic flux density in the reference state and the magnetic flux density at the time of measurement may be the same as described above.

Next, in step 1350, the calculation unit 895 may obtain k conductivities Δσ as shown in FIG. 13 based on the magnetic field measurement data ΔB of the measurement target magnetic field component from the signal space separation unit 890 and the potential measurement data ΔV from the potential measurement data acquisition unit 815. First, (Equation 15) shows a formula for calculating the elements of the potential sensitivity matrix ^JE , and the forward problem showing the relationship between the conductivity Δσ and the potential ΔV can be expressed as (Equation 16) using the potential sensitivity matrix ^JE . In (Equation 15), Φ ^d shows the potential of the electrode pair to which the current is applied, and Φ ^m shows the potential of the electrode pair for measuring the potential measurement data. As shown in FIG. 13, i shows the detection position of the potential, and k shows the area in the living body 50. The calculation unit 895 may similarly calculate the conductivity Δσ using the detection magnetic field B of the magnetic sensor array 210 instead of the measurement target magnetic field B at the detection position 1200.

Next, (Equation 17) shows a formula for calculating the elements of the magnetic field sensitivity matrix ^JM , and the forward problem showing the relationship between the conductivity Δσ and the magnetic field ΔB can be expressed as (Equation 18) using the magnetic field sensitivity matrix ^JM . In (Equation 17), R is the position (vector quantity) from the coordinate origin of the magnetic sensor 520 (the center of the XZ plane of the living body 50 at the position of the electrode 800), and r' is the position from the coordinate origin to the region _Ωk in the living body 50. As shown in FIG. 13, i indicates the detection position, k indicates the region in the living body 50, the rows of the magnetic field sensitivity matrix ^JM indicate the values corresponding to each detection position i, and the columns of the magnetic field sensitivity matrix ^JM indicate the values corresponding to each region _Ωk .

The calculation unit 895 may generate a combined sensitivity matrix JEM by combining the calculated potential sensitivity matrix ^JE and magnetic field sensitivity ^{matrix JM} as shown in (Equation 19), and may use ^JEM to calculate the conductivity Δσ in a forward problem such as (Equation 20) that expresses the relationship between Δy indicating the magnetic field measurement data and the potential measurement data and the conductivity Δσ. Here, the magnetic field measurement data ΔB, the potential measurement data ΔV, and the conductivity Δσ are each a three-dimensional vector.

The calculation unit 895 may calculate the conductivity Δσ by multiplying the magnetic field measurement data and the electric potential measurement data, or the electric potential sensitivity matrix ^JE and the magnetic field sensitivity matrix ^JM by a weighting factor W, as shown in (Equation 21). The calculation unit 895 may use a diagonal matrix (W=diag( _wE , ... wE, _wM , ... _wM )) having a weighting factor _wE for the electric potential measurement data and a weighting factor _wM for the magnetic field measurement data as the weighting factor W. The calculation unit ₈₉₅ may optimize the weighting factor W so that changes in the magnetic field measurement data and changes in the electric potential measurement data have the same degree of influence on the conductivity Δσ. The calculation unit 895 may set the weighting factor W based on the measurement data or the sensitivity matrix.

The calculation unit 895 may weight the data with a weighting factor based on at least one of the magnetic field measurement data and the electric potential measurement data, the average of all the measurement amounts, or the maximum of all the measurement amounts. As an example, the calculation unit 895 may set the reciprocal of the average of all the magnetic field measurement data (magnetic field measurement data at all detection positions) as the weighting factor _wM , and the reciprocal of the average of all the electric potential measurement data (electric potential measurement data at all electric potential detection positions) as the weighting factor _wE .

The calculation unit 895 may weight the matrices with a weighting factor based on at least one element of the magnetic field sensitivity matrix and the electric potential sensitivity matrix, the average value of all elements, or the maximum value of all elements. For example, the calculation unit 895 may set the reciprocal of the average value of all elements (values) of the magnetic field sensitivity matrix ^JM as the weighting factor _wM , and the reciprocal of the average value of all elements (values) of the electric potential sensitivity matrix ^JE as the weighting factor _wE .

The calculation unit 895 may perform weighting with a weighting coefficient based on the singular values obtained by singular value decomposition from the magnetic field sensitivity matrix ^JM and the electric potential sensitivity matrix ^JE , and may set a weighting coefficient based on at least one of the singular values, the average value of all the singular values, or the maximum value of all the singular values. For example, the calculation unit 895 may set the reciprocal of the average value of all the singular values obtained by singular value decomposition of the magnetic field sensitivity matrix ^JM as the weighting coefficient _wM , and the reciprocal of the average value of all the singular values obtained by singular value decomposition of the electric potential sensitivity matrix ^JE as the weighting coefficient _wE .

In step 1350, the calculation unit 895 may calculate the current value flowing in the living body 50 based on the magnetic field measurement data B and the potential measurement data ΔV of the magnetic field component to be measured from the signal space separation unit 890. The calculation unit 895 may obtain N currents J1 to JN as shown in FIG. 12 from the magnetic field measurement data B1 to BM and the potential measurement data ΔV from the signal space separation unit 890. Here, the magnetic field measurement data B, the potential measurement data ΔV, and the currents J1 to JN are each three-dimensional vectors. First, the forward problem of converting the current J to the magnetic field B can be expressed as (Equation 22) using the magnetic field sensitivity matrix L. The values of the matrix elements of the magnetic field sensitivity matrix L may be calculated by the finite element method (FEM) that models the living body 50. The calculation unit 895 may calculate the current value in the same way using the detected magnetic field B of the magnetic sensor array 210 instead of the measured magnetic field B at the detection position 1200.

The calculation section 895 may similarly calculate the potential sensitivity matrix ^JE for the current value by the forward problem ΔV= ^JE ·J which shows the relationship between the potential ΔV and the current value J using the potential sensitivity matrix ^JE .

The calculation section 895 may use the magnetic field sensitivity matrix L and the electric potential sensitivity matrix ^JE calculated above to calculate the current values J1 to JN by weighting in the same manner as above.

Here, before calculating the current or conductivity, the calculation unit 895 may remove the magnetic field components caused by the lead wire 805 from the magnetic field measurement data measured for each electrode pair. The calculation unit 895 may determine the path of the lead wire 805, and obtain the magnetic field components caused by the lead wire 805 from the determined path by inverse calculation of the above-mentioned current calculation. The calculation unit 895 may calculate the magnetic field components caused by the lead wire 805, for example, from the determined path of the lead wire 805 and the current value using the Biot-Savart equation.

As described above, the calculation unit 895 can calculate the current or conductivity at multiple positions in the living body 50 and output the current density distribution or conductivity distribution in the living body 50. Step 1310 may be repeatedly executed, and even after obtaining the potential measurement data and magnetic field measurement data in the current application of all electrode pairs, the acquisition of measurement data for each current pair may be repeated. Steps 1330 to 1350 may be performed in parallel with step 1310, and the calculation results can be output in real time while measuring the potential and magnetic field along with the current application. In addition, the measurement device 10 of this embodiment can generate an image showing the impedance distribution in the living body 50 according to the current distribution of the calculation results and display it in multi-value form, for example, by using a part of the EIT technology on the display of the information processing unit 30.

The measurement device 10 of this embodiment can suppress disturbance magnetic fields using the signal space separation unit 890, and can accurately detect the magnetic field on the outer surface of the living body 50. The measurement device 10 of this embodiment can estimate the current or conductivity in the living body 50 using the magnetic field detection results and electric potential detection results of the magnetic sensor array 210, so that it can achieve higher accuracy than when only one of the results is used.

The magnetic sensor array 210 (or magnetic sensor cell 220) is not limited to being capable of detecting an input magnetic field in three axial directions, but may be capable of detecting an input magnetic field in one axial direction or two axial directions. The electrodes 800 may be arranged in multiple rows on the living body 50, or may be arranged in a row only on one side of the living body 50. All of the electrodes 800 do not need to have the function of both applying a current and measuring a potential, and the electrodes 800 for applying a current and the electrodes 800 for measuring a potential may be separate.

Various embodiments of the present invention may be described with reference to flow charts and block diagrams, where a block may represent (1) a stage of a process in which an operation is performed or (2) a section of an apparatus responsible for performing an operation. Particular stages and sections may be implemented by dedicated circuitry, programmable circuitry provided with computer readable instructions stored on a computer readable medium, and/or a processor provided with computer readable instructions stored on a computer readable medium. Dedicated circuitry may include digital and/or analog hardware circuitry and may include integrated circuits (ICs) and/or discrete circuits. Programmable circuitry may include reconfigurable hardware circuitry including logical AND, logical OR, logical XOR, logical NAND, logical NOR, and other logical operations, memory elements such as flip-flops, registers, field programmable gate arrays (FPGAs), programmable logic arrays (PLAs), and the like.

A computer-readable medium may include any tangible device capable of storing instructions that are executed by a suitable device, such that the computer-readable medium having instructions stored thereon comprises an article of manufacture that includes instructions that can be executed to create means for performing the operations specified in the flowchart or block diagram. Examples of computer-readable media may include electronic storage media, magnetic storage media, optical storage media, electromagnetic storage media, semiconductor storage media, and the like. More specific examples of computer-readable media may include floppy disks, diskettes, hard disks, random access memories (RAMs), read-only memories (ROMs), erasable programmable read-only memories (EPROMs or flash memories), electrically erasable programmable read-only memories (EEPROMs), static random access memories (SRAMs), compact disk read-only memories (CD-ROMs), digital versatile disks (DVDs), Blu-ray (RTM) disks, memory sticks, integrated circuit cards, and the like.

The computer readable instructions may include either assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source or object code written in any combination of one or more programming languages, including object-oriented programming languages such as Smalltalk®, JAVA®, C++, etc., and conventional procedural programming languages such as the "C" programming language or similar programming languages.

The computer-readable instructions may be provided to a processor or programmable circuit of a general-purpose computer, special-purpose computer, or other programmable data processing apparatus, either locally or over a wide area network (WAN) such as a local area network (LAN), the Internet, etc., to execute the computer-readable instructions to create means for performing the operations specified in the flowcharts or block diagrams. Examples of processors include computer processors, processing units, microprocessors, digital signal processors, controllers, microcontrollers, etc.

15 shows an example of a computer 2200 in which aspects of the present invention may be embodied in whole or in part. A program installed on the computer 2200 may cause the computer 2200 to function as or perform operations associated with an apparatus or one or more sections of the apparatus according to an embodiment of the present invention, and/or to perform a process or steps of the process according to an embodiment of the present invention. Such a program may be executed by the CPU 2212 to cause the computer 2200 to perform certain operations associated with some or all of the blocks of the flowcharts and block diagrams described herein.

The computer 2200 according to this embodiment includes a CPU 2212, a RAM 2214, a graphics controller 2216, and a display device 2218, which are interconnected by a host controller 2210. The computer 2200 also includes input/output units such as a communication interface 2222, a hard disk drive 2224, a DVD-ROM drive 2226, and an IC card drive, which are connected to the host controller 2210 via an input/output controller 2220. The computer also includes legacy input/output units such as a ROM 2230 and a keyboard 2242, which are connected to the input/output controller 2220 via an input/output chip 2240.

The CPU 2212 operates according to the programs stored in the ROM 2230 and the RAM 2214, thereby controlling each unit. The graphics controller 2216 retrieves image data generated by the CPU 2212 into a frame buffer or the like provided in the RAM 2214 or into itself, and causes the image data to be displayed on the display device 2218.

The communication interface 2222 communicates with other electronic devices via a network. The hard disk drive 2224 stores programs and data used by the CPU 2212 in the computer 2200. The DVD-ROM drive 2226 reads programs or data from the DVD-ROM 2201 and provides the programs or data to the hard disk drive 2224 via the RAM 2214. The IC card drive reads programs and data from an IC card and/or writes programs and data to an IC card.

ROM 2230 stores therein a boot program, etc., executed by computer 2200 upon activation, and/or a program that depends on the hardware of computer 2200. Input/output chip 2240 may also connect various input/output units to input/output controller 2220 via a parallel port, a serial port, a keyboard port, a mouse port, etc.

The programs are provided by a computer-readable medium such as a DVD-ROM 2201 or an IC card. The programs are read from the computer-readable medium, installed in the hard disk drive 2224, RAM 2214, or ROM 2230, which are also examples of computer-readable media, and executed by the CPU 2212. The information processing described in these programs is read by the computer 2200, and brings about cooperation between the programs and the various types of hardware resources described above. An apparatus or method may be constructed by realizing the manipulation or processing of information according to the use of the computer 2200.

For example, when communication is performed between computer 2200 and an external device, CPU 2212 may execute a communication program loaded into RAM 2214 and instruct communication interface 2222 to perform communication processing based on the processing described in the communication program. Under the control of CPU 2212, communication interface 2222 reads transmission data stored in a transmission buffer processing area provided in RAM 2214, hard disk drive 2224, DVD-ROM 2201, or a recording medium such as an IC card, and transmits the read transmission data to the network, or writes reception data received from the network to a reception buffer processing area or the like provided on the recording medium.

The CPU 2212 may also cause all or a necessary portion of a file or database stored on an external recording medium such as the hard disk drive 2224, the DVD-ROM drive 2226 (DVD-ROM 2201), an IC card, etc. to be read into the RAM 2214, and perform various types of processing on the data on the RAM 2214. The CPU 2212 then writes back the processed data to the external recording medium.

Various types of information, such as various types of programs, data, tables, and databases, may be stored in the recording medium and may undergo information processing. CPU 2212 may perform various types of processing on data read from RAM 2214, including various types of operations, information processing, conditional judgment, conditional branching, unconditional branching, information search/replacement, etc., as described throughout this disclosure and specified by the instruction sequence of the program, and write back the results to RAM 2214. CPU 2212 may also search for information in a file, database, etc. in the recording medium. For example, if multiple entries each having an attribute value of a first attribute associated with an attribute value of a second attribute are stored in the recording medium, CPU 2212 may search for an entry that matches a condition, in which an attribute value of the first attribute is specified, from among the multiple entries, read the attribute value of the second attribute stored in the entry, and thereby obtain the attribute value of the second attribute associated with the first attribute that satisfies a predetermined condition.

The above-described program or software module may be stored on a computer-readable medium on or near the computer 2200. Also, a recording medium such as a hard disk or RAM provided in a server system connected to a dedicated communication network or the Internet can be used as a computer-readable medium, thereby providing the program to the computer 2200 via the network.

The present invention has been described above using an embodiment, but the technical scope of the present invention is not limited to the scope described in the above embodiment. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiment. It is clear from the claims that forms incorporating such modifications or improvements can also be included in the technical scope of the present invention.

The order of execution of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not specifically stated as "before" or "prior to," and it should be noted that the processes may be performed in any order, unless the output of a previous process is used in a later process. Even if the operational flow in the claims, specifications, and drawings is explained using "first," "next," etc. for convenience, it does not mean that it is necessary to perform the processes in this order.

10 Measuring device 20 Main body 30 Information processing unit 50 Living body 100 Current control unit 110 Magnetic sensor unit 120 Head 125 Driving unit 130 Base unit 140 Pole unit 210 Magnetic sensor array 220 Magnetic sensor cell 230 Sensor data collection unit 300 Sensor unit 520 Magnetic sensor 530 Magnetic field generation unit 532 Amplification circuit 534 Coil 540 Output unit 702 Magnetic resistance element 704 Magnetic concentrator 706 Magnetic concentrator 800 Electrode 810 Current control unit 815 Potential measurement data acquisition unit 820 Control unit 830 Magnetic field measurement data acquisition unit 840 AD converter 842 Clock generator 850 Calibration calculation unit 860 Memory unit 870 Estimation unit 880 Basis vector memory unit 890 Signal space separation unit 895 Calculation unit 1200 Detection position 2200 Computer 2201 DVD-ROM
2210 host controller 2212 CPU
2214 RAM
2216 Graphics controller 2218 Display device 2220 Input/output controller 2222 Communication interface 2224 Hard disk drive 2226 DVD-ROM drive 2230 ROM
2240 Input/Output Chip 2242 Keyboard

Claims (15)

an electrode unit having a plurality of electrodes that come into contact with a living body;
a magnetic sensor array having a plurality of magnetic sensor cells and capable of detecting an input magnetic field;
a current control unit that applies a current to the living body through at least one electrode pair of the plurality of electrodes;
a magnetic field measurement data acquisition unit that acquires magnetic field measurement data based on the input magnetic field detected from the living body by the magnetic sensor array while a current is being passed through the living body;
a potential measurement data acquiring unit that acquires potential measurement data based on a potential difference detected in at least one electrode pair among the plurality of electrodes while a current is being passed through the living body;
an estimation unit that estimates a current flowing in the living body or a conductivity in the living body based on the magnetic field measurement data and the electric potential measurement data ,
The estimation unit estimates a current flowing in the living body or a conductivity in the living body by weighting the magnetic field measurement data and the electric potential measurement data.
Measuring equipment. The measurement device according to claim 1 , wherein the estimation unit performs weighting with a weighting factor based on the magnetic field measurement data and the electric potential measurement data. The measurement device according to claim 2 , wherein the estimation unit weights the magnetic field measurement data and the electric potential measurement data with a weighting coefficient based on at least one of a measurement amount, an average value of the measurement amount, or a maximum value of the measurement amount. The measurement device according to claim 1 , wherein the estimation unit performs weighting using a weighting coefficient based on a magnetic field sensitivity matrix indicating the sensitivity of the magnetic field measurement data to current or conductivity in the living body and a potential sensitivity matrix indicating the sensitivity of the potential measurement data to current or conductivity in the living body. The measurement device according to claim 4 , wherein the estimation unit performs weighting with a weighting coefficient based on at least one element, an average value of elements, or a maximum value of elements of the magnetic field sensitivity matrix and the electric potential sensitivity matrix. The measurement device according to claim 4 , wherein the estimation unit performs weighting with a weighting coefficient based on a singular value obtained by singular value decomposition of the magnetic field sensitivity matrix and the electric potential sensitivity matrix. The measurement apparatus according to claim 6 , wherein the estimation unit performs weighting with a weighting coefficient based on at least one of the singular values, an average value of the singular values, or a maximum value of the singular values. The measurement device according to claim 1 , wherein the current control unit applies an alternating current to the living body through the at least one electrode pair. The measurement device according to claim 1 , further comprising a control unit that synchronizes the current flowing through the living body by the at least one electrode pair with the acquisition of the magnetic field measurement data by the magnetic field measurement data acquisition unit and the acquisition of the electric potential measurement data by the electric potential measurement data acquisition unit. The measurement device according to claim 1 , wherein the current control unit applies a current to an electrode pair consisting of two adjacent electrodes among the plurality of electrodes while shifting the electrodes one by one in sequence to pass a current through the living body. The estimation unit is
a signal space separation unit that separates the spatial distribution of the magnetic field indicated by the magnetic field measurement data into a magnetic field to be measured from the living body and a disturbance magnetic field;
The measurement device according to claim 1 , further comprising: a calculation unit that calculates a current or a conductivity in the living body based on the separated measurement data of the magnetic field to be measured and the potential measurement data. each of the plurality of magnetic sensor cells includes a plurality of magnetic sensors each having a magnetic resistance element and a magnetic flux concentrator disposed on both ends of the magnetic resistance element;
The measurement device according to claim 11 , wherein the signal space separation unit separates the spatial distribution of the magnetic field by using, as basis vectors, signal vectors output by each of the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function. The measurement device according to claim 1 , wherein the estimation unit removes a component of a magnetic field generated from lead wires connected to the plurality of electrodes from the magnetic field measurement data. applying a current to the living body through at least one electrode pair of the plurality of electrodes;
acquiring magnetic field measurement data based on an input magnetic field detected from the living body by a magnetic sensor array while a current is being passed through the living body;
acquiring potential measurement data based on a potential difference detected at at least one electrode pair among the plurality of electrodes while a current is being passed through the living body;
and estimating a current flowing in the living body or a conductivity in the living body based on the magnetic field measurement data and the electric potential measurement data .
The estimating step includes a step of weighting the magnetic field measurement data and the electric potential measurement data to estimate a current flowing in the living body or a conductivity in the living body.
Measurement method. Computer,
a signal space separation unit that separates a spatial distribution of a magnetic field indicated by magnetic field measurement data based on an input magnetic field detected from the living body by a magnetic sensor array while a current is being passed through the living body by at least one electrode pair among a plurality of electrodes into a magnetic field to be measured from the living body and a disturbance magnetic field;
a calculation unit that calculates a current or a conductivity in the living body based on the separated magnetic field to be measured and potential measurement data based on a potential difference detected by at least one electrode pair among the plurality of electrodes while a current is being passed through the living body;
The calculation unit calculates a current or a conductivity in the living body by weighting the separated measurement target magnetic field and the potential measurement data.
program.

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