MEASURING APPARATUS, MEASURING METHOD, AND PROGRAM

Abstract

To provide a measurement device having an estimation unit for estimating a current flowing in a living body or the conductivity in a living body on the basis of magnetic field measurement data and potential measurement data.SOLUTION: The measurement device includes: an electrode unit having a plurality of electrodes in contact with a living body 50; a magnetic sensor array having a plurality of magnetic sensor cells, the magnetic sensor array being capable of detecting an input magnetic field; a current control unit for flowing a current in the living body 50 by at least one pair of electrodes of a plurality of electrodes; a magnetic field measurement data acquisition unit for acquiring magnetic field measurement data based on an input magnetic field that the magnetic sensor array detected from the living body 50 while a current is being flown in the living body 50; and a potential measurement data acquisition unit for acquiring potential measurement data based on the potential difference between the at least one electrode pair of the plurality of electrodes while a current is being flown in the living body 50.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a measurement apparatus, a measurement method, and a program. [Background technology]

[0002] Conventionally, there are methods for obtaining cross-sectional 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 through the electrodes, 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 Summary of the Invention

[0003] 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.

[0004] The estimation unit may estimate the current flowing within the living body or the conductivity within the living body by weighting the magnetic field measurement data and the electric potential measurement data.

[0005] The estimation unit may perform weighting with a weighting factor based on the magnetic field measurement data and the electric potential measurement data.

[0006] The estimation unit may perform weighting with a weighting coefficient based on at least one of the magnetic field measurement data and the electric potential measurement data, the average value of the measurement amount, or the maximum value of the measurement amount.

[0007] The estimation unit may perform 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.

[0008] The estimation unit may perform weighting with a weighting coefficient based on at least one element of the magnetic field sensitivity matrix and the electric potential sensitivity matrix, the average value of the elements, or the maximum value of the elements.

[0009] The estimation unit may perform weighting with a weighting coefficient based on singular values ​​obtained by singular value decomposition of the magnetic field sensitivity matrix and the electric potential sensitivity matrix.

[0010] The estimation unit may perform weighting 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.

[0011] The current control unit may apply an alternating current to the living body through at least one electrode pair.

[0012] The measurement device may include a control unit that synchronizes a current flowing through a living body by 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.

[0013] The current control unit may apply a current to an electrode pair consisting of two adjacent electrodes among the plurality of electrodes while shifting the electrodes one by one, thereby passing a current through the living body.

[0014] 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 a current or conductivity in the living body based on the separated magnetic field to be measured and the potential measurement data.

[0015] The magnetic sensor cells may each include a magnetic sensor having a magnetic resistance element and a magnetic flux concentrator disposed at both ends of the magnetic resistance element. The signal spatial separation unit may separate the spatial distribution of the magnetic field by using, as basis vectors, signal vectors output by the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function.

[0016] The estimation unit may remove, from the magnetic field measurement data, magnetic field components arising from lead wires connected to the multiple electrodes.

[0017] In a second aspect of the present invention, there is provided a measurement method. The measurement method may include a step of passing a current through a living body 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 body by a magnetic sensor array while the current is passing through the living body. 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 the current is passing through the living body. The measurement method may include a step of 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.

[0018] In a third aspect of the present invention, a program is provided. The program may cause a computer to function as a signal space separator that separates a spatial distribution of a magnetic field indicated by magnetic field measurement data based on an input magnetic field detected from a living body by a magnetic sensor array while a current is passed through the living body by at least one electrode pair of a plurality of electrodes into a measurement target magnetic field from the living body and a disturbance magnetic field. The program may cause a computer to function as a calculation unit that calculates a current or a 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 a plurality of electrodes while a current is passed through the living body.

[0019] 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. [Brief description of the drawings]

[0020] [Figure 1] 1 shows the configuration of a measurement device 10 according to the present embodiment. [Diagram 2] 1 shows the configuration of a magnetic sensor unit 110 according to the present embodiment. [Diagram 3] 2 shows the configuration and arrangement of magnetic sensor cells 220 in a magnetic sensor array 210 according to the present embodiment. [Figure 4] 4 shows an example of input / output characteristics of a magnetic sensor having a magnetoresistive element according to the present embodiment. [Diagram 5] 2 shows an example of the configuration of a sensor unit 300 according to the present embodiment. [Figure 6] 2 shows an example of input / output characteristics of the sensor unit 300 according to the present embodiment. [Figure 7] 2 shows an example of the configuration of a magnetic sensor 520 according to the present embodiment. [Figure 8] 1 shows the configuration of a measurement device 10 according to the present embodiment. [Figure 9] An example in which the measurement device 10 of this embodiment measures a magnetic field using a magnetic sensor array 210 will be described. [Figure 10]2 shows an example of the arrangement of a plurality of electrodes 800 of the measurement device 10 of this embodiment. [Figure 11] The current distribution in a cross section of a living body 50 parallel to the XZ plane is shown. [Figure 12] 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. [Figure 13] 10A and 10B show schematic diagrams of separated regions in a living body 50 in a cross section parallel to the XZ plane when the conductivity is calculated by the measuring device 10 of the present embodiment. [Figure 14] 2 shows a measurement flow of the measurement device 10 according to the present embodiment. [Figure 15] 22 illustrates an example computer 2200 in which aspects of the present invention may be embodied, in whole or in part. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of 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.

[0022] 1 shows the configuration of a measurement device according to this embodiment. The measurement device 10 measures a magnetic field generated by passing a current through a living body 50 such as a subject and a potential of the living body 50, and estimates parameters related to the 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.

[0023] 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 driving unit 125, a base unit 130, and a pole unit 140.

[0024] The current control unit 100 is arranged in contact with the surface of the living body 50 during measurement, and flows a current through the living body 50 and measures the potential of the surface of the living body 50. The magnetic sensor unit 110 is arranged at a position facing a measurement target part of the living body 50 (for example, the lungs of a subject) during measurement, and senses a 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 with respect 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. The magnetic sensor unit 110 may be further rotatable around the measurement target, centered on the Y axis in the figure.

[0025] The base unit 130 is a base that supports other components. The subject, which is the living body 50, may stand on the base unit 130 or may sit in front of the base unit 130 during measurement. The pole unit 140 supports the head 120 at the height of the measurement target of the living body 50. The pole unit 140 may be extendable in the vertical direction to adjust the height of the head 120.

[0026] The information processing unit 30 is a component for processing measurement data from the main body unit 20 and outputting the data by display, printing, etc. The information processing unit 30 may be a computer such as a PC (personal computer), a tablet computer, a smartphone, a workstation, a server computer, or a 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.

[0027] FIG. 2 shows the configuration of the magnetic sensor unit 110 according to this embodiment. The magnetic sensor unit 110 includes a magnetic sensor array 210 and a sensor data collector 230. The magnetic sensor array 210 includes a plurality of magnetic sensor cells 220 that can detect a magnetic field in three axial directions and are arranged three-dimensionally. As an example, the plurality of magnetic sensor cells 220 includes a plurality of magnetic sensors each having a magnetic resistance element and a magnetic flux concentrator arranged at least on one end and the other end of the magnetic resistance element. Note that it is preferable that the magnetic flux concentrator is arranged on both ends of the magnetic resistance element in that it is possible to improve the sampling accuracy of the spatial distribution of the magnetic field described later. In this figure, the magnetic sensor array 210 includes 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 plane in each of the X direction, Y direction, and Z direction.

[0028] 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.

[0029] FIG. 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 magnetic concentrator plates 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 the magnetic resistance element arranged in a narrow position sandwiched between the magnetic concentrator plates. The configuration of each sensor unit 300 will be described in detail later.

[0030] The 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 satisfying 0≦i≦Nx-1 (Nx indicates the number of magnetic sensor cells 220 arranged in the X-axis direction), j is an integer satisfying 0≦j≦Ny-1 (Ny indicates the number of magnetic sensor cells 220 arranged in the Y-axis direction), and k is an integer satisfying 0≦k≦Nz-1 (Nz indicates the number of magnetic sensor cells 220 arranged in the Z-axis direction).

[0031] 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 extends in each of the three axial directions away from the gap. As an example, in this figure, an example is shown in which a gap is provided in the lower left corner of the magnetic sensor cell 220 when viewed from the front, and the sensor units 300x, 300y, and 300z are provided so that one end is in contact with the gap and the other end extends 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 more easily grasp 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 algebraic 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 may be different from the three-dimensional direction in which the magnetic sensor cells 220 are arranged. When the two are different, there are no restrictions on the arrangement of the sensor units 300 in the magnetic sensor cells 220 or the arrangement direction of the magnetic sensor cells 220, and the degree of freedom in designing the magnetic sensor array 210 can be increased.

[0032] 4 shows an example of 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 a magnetic field in a predetermined uniaxial direction.

[0033] Such a magnetic sensor has high magnetic sensitivity, which is the gradient of the detection signal V_xMR0 relative to the input magnetic field B, and can detect a weak magnetic field 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.

[0034] 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 magnetic sensor cells 220, and includes a magnetic sensor 520, a magnetic field generating unit 530, and an output unit 540. Note that a part of the sensor unit 300, for example, an amplifier circuit 532 and the output unit 540, may be provided on the sensor data collecting unit 230 side instead of on the magnetic sensor cell 220 side.

[0035] The magnetic sensor 520 has a magnetoresistance element such as a GMR element or a TMR element, similarly to the magnetic sensor described in FIG. 4. The magnetic sensor 520 also has magnetic concentrators arranged at both ends of the magnetoresistance element. The magnetoresistance 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 magnetoresistance element of the magnetic sensor 520, the magnitude of the magnetic field B input to the magnetic sensor 520 can be detected. For example, when the magnetic sensitivity of the magnetic sensor 520 is S, the detection result of the magnetic sensor 520 with respect to 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 according to the change in the resistance value as the detection result of the input magnetic field. The configuration of the magnetic sensor 520 will be described in detail later.

[0036] The magnetic field generating unit 530 applies to the magnetic sensor 520 a feedback magnetic field 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 substantially equal to that of the input magnetic field, thereby operating to cancel the input magnetic field. The magnetic field generating unit 530 includes an amplifier circuit 532 and a coil 534.

[0037] 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 by a bridge circuit including at least one magnetic resistance element, the outputs of the bridge circuit are 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 the feedback current I_FB according to the output voltage of the magnetic sensor 520. For example, when the voltage-current conversion coefficient of the amplifier circuit 532 is G, the feedback current I_FB can be calculated as G×S×B.

[0038] 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 by the following equation.

number

[0039] 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).

number

[0040] 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:

number

[0041] As described above, the sensor unit 300 generates a feedback magnetic field that reduces the magnetic field input from outside, thereby reducing the magnetic field that is substantially input to the magnetic sensor 520. As a result, the sensor unit 300 can prevent the detection signal V_xMR from being 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 of FIG. 4 as the magnetic sensor 520. The input / output characteristics of such a sensor unit 300 will be described next.

[0042] 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.

[0043] That is, the sensor unit 300 according to the present 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.

[0044] FIG. 7 shows a configuration example of the magnetic sensor 520 according to the present embodiment. As an example, the magnetic sensor 520 according to the present embodiment has a magnetoresistance element 702 and magnetic concentrators 704 and 706 arranged at one end and the other end of the magnetoresistance element 702. The magnetic concentrators 704 and 706 are arranged to sandwich the magnetoresistance element 702 between them. That is, the magnetic concentrators are arranged at both ends of the magnetoresistance element 702. In FIG. 7, the magnetic concentrator 704 arranged at the right end of the magnetoresistance 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 magnetoresistance 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 magnetoresistance element 702 may increase or decrease. The magnetic sensing axis may be along the direction of magnetization fixed by a magnetization fixed layer forming the magnetoresistance element 702. The magnetic concentrator plates 704 and 706 are made of a soft magnetic material such as iron. By disposing the magnetic concentrator plates 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, and the sensitivity of the magnetic sensor 520 can be increased.

[0045] In this figure, an example in which the magnetic flux concentrator is disposed at both one end and the other end of the magnetoresistance element 702 is shown, but the magnetic flux 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 the magnetic flux concentrator at both one end and the other end of the magnetoresistance element 702. Furthermore, when the magnetic flux concentrator is provided at both one end and the other end of the magnetoresistance element 702, the position of the magnetoresistance element 702 disposed at a narrow position between the two magnetic flux concentrators 704 and 706 becomes a magnetic sensing portion, i.e., a 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 increased. In this way, by using a magnetic sensor 520 in which magnetic concentrators 704 and 706 are arranged on both ends of a magnetic resistance element 702 in each sensor unit 300, the measuring device 10 of this embodiment can sample the spatial distribution of the magnetic field at an extremely narrow position (e.g., 100 μm or less) in each axial direction, with both ends sandwiched between the magnetic concentrators, as shown in Figure 3, so that 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.

[0046] 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 FIG. 1 has a plurality of electrodes 800, a lead wire 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 any one that includes at least a plurality of electrodes 800, and may be, for example, the current control unit 100.

[0047] The multiple electrodes 800 are each electrically connected to a current control unit 810 via a lead wire 805, and are arranged side by side at the same height position in the Y-axis direction corresponding to the measurement target site of the living body 50, in contact with the surface of the living body 50. Fig. 8 shows electrodes 800(1) to (5) out of the multiple electrodes 800. Note that 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.

[0048] The current control unit 810 is connected to the magnetic sensor unit 110 and the potential measurement data acquisition unit 815, and applies a current to 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 apply an AC current to 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 apply a current to 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 apply an AC current of 1 mA or less to the living body 50 in synchronization with the synchronization signal, for example.

[0049] 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.

[0050] The potential measurement data acquiring section 815 is connected to the control section 820 and the estimation section 870, and acquires from the current control section 810 potential measurement data based on a potential difference detected in at least one electrode pair among the plurality of electrodes while a current is flowing through the living body 50. The potential measurement data acquiring section 815 may acquire potential measurement data indicating the potential difference measured by the current control section 810 in response to a synchronization signal from the control section 820. The potential measurement data acquiring section 815 may execute processing such as AD conversion on the potential measurement data, and output the processed potential measurement data to the estimation section 870.

[0051] The magnetic sensor array 210 has a plurality of magnetic sensor cells 220 and can detect an input magnetic field in three-axis directions at a plurality of locations in a three-dimensional space. Each of the plurality of magnetic sensor cells 220 has a plurality of sensor units 300x to z as described above. In this figure, among the plurality of magnetic sensor cells 220 that the magnetic sensor array 210 has in each dimensional direction, portions related to positions [i,j,k], [i+1,j,k], [i,j+1,k], and [i,j,k+1] are shown.

[0052] The sensor data collection unit 230 includes a control unit 820 , a plurality of magnetic field measurement data acquisition units 830 , a plurality of AD converters 840 , a clock generator 842 , a calibration calculation unit 850 , and a memory unit 860 .

[0053] 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, 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. The control unit 820 outputs a synchronization signal having a frequency of, for example, 10 to 100 KHz.

[0054] Each of the magnetic field measurement data acquiring units 830 is connected to the corresponding sensor units 300x-z of the magnetic sensor cells 220 and the corresponding AD converter 840. The magnetic field measurement data acquiring unit 830 acquires magnetic field measurement data based on an 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 acquiring 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 acquiring unit 830 may multiply the magnetic field measurement data by the synchronization signal and output the result. The magnetic field measurement data acquiring unit 830 may acquire only frequency components equal to the reference signal from the magnetic field measurement data output by the corresponding sensor units 300x-z of the magnetic sensor cells 220, using the current signal applied by the current control unit 810 as a reference signal. The magnetic field measurement data acquiring unit 830 may perform processing such as low-pass filtering on the magnetic field measurement data.

[0055] Each of the AD converters 840 is connected to a clock generator 842 and a corresponding calibration calculation unit 850, and converts an 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 digitally converting the magnetic field measurement data from the sensor units 300x, 300y, and 300z.

[0056] The clock generator 842 generates a sampling clock and supplies the common sampling clock to each of the multiple AD converters 840. Then, each of the multiple AD converters 840 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.

[0057] 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 as follows. 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 characteristics of the three-axis magnetic sensor are represented by a matrix S, the detection result V of the three-axis magnetic sensor can be expressed as follows:

number

[0058] Here, Sxx, Syy, and Szz represent the sensitivities of the sensor units 300x, 300y, and 300z in the directions of the main axes, respectively, and Sxy, Sxz, Syx, Syz, Szx, and Szy represent the sensitivities in the directions of the other axes. Also, Vos,x, Vos,y, and Vos,z represent the offsets of the sensor units 300x, 300y, and 300z in the directions of the main axes, 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, these offsets can be ignored.

[0059] Since each of the sensor units 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 independent of the magnitude of the input magnetic field B. Even if the sensor unit 300 has other-axis sensitivity, as long as the detection result of the sensor unit 300 has linearity, each element of the matrix S has an approximately constant coefficient that is independent of the magnitude of the input magnetic field B.

[0060] Therefore, the calibration calculation unit 850 calculates the inverse matrix S of the matrix S. -1and offset (Vos,x,Vos,y,Vos,z), the magnetic field measurement data V (Vx,Vy,Vz) can be converted into magnetic field measurement data B (Bx,By,Bz) indicating the original input magnetic field as shown in the following formula. This conversion also holds when the sensor units 300x-z are equipped with the magnetic flux concentrator plates described above. This is because the magnetic sensor cell 220 is configured as a three-axis magnetic sensor using the sensor units 300x-z, and conversion using linear algebra is possible.

number

[0061] The calibration calculation unit 850 calculates the inverse matrix S of the matrix S using the environmental magnetic field measurement data. -1 and offset (Vos,x,Vos,y,Vos,z) are calculated, and the magnetic field measurement data acquired by the magnetic field measurement data acquisition unit 830 is converted into magnetic field measurement data B using these calibration parameters and supplied to the memory unit 860.

[0062] As described above, since each sensor unit 300 has linearity, the calibration calculation unit 850 can use the approximately constant coefficients to convert the magnetic field measurement data into the magnetic field measurement data B. That is, 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.

[0063] The storage 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 the data to the estimation unit 870 .

[0064] 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 storage unit 860 and the electric potential measurement data from the electric potential measurement data acquisition unit 815. The estimation unit 870 may estimate the current value or the conductivity for a plurality of regions in the living body 50 based on the magnetic field measurement data and the electric potential measurement data acquired at the same timing. The estimation unit 870 may estimate the current value or the conductivity by weighting the magnetic field measurement data and the electric potential measurement data. The estimation unit 870 may weight with a weighting factor based on the magnetic field measurement data and the electric potential measurement data. In addition, the estimation unit 870 may weight with a weighting factor 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 an electric potential sensitivity matrix (also called a lead field matrix) indicating the sensitivity of the electric 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. Furthermore, the estimation unit 870 may store a weighting coefficient optimized in advance and perform weighting with the weighting coefficient.

[0065] 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.

[0066] The basis vector storage unit 880 is connected to the signal space separation unit 890 , and stores in advance basis vectors necessary 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 .

[0067] 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 required 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 by suppressing the disturbance magnetic field. The signal space separating section 890 may calculate and output the magnetic fields to be measured at a plurality of magnetic field positions on the surface of the living body 50 where the magnetic sensor array 210 is not disposed.

[0068] 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 a current value or conductivity in the living body 50 based on the magnetic field measurement data and the electric potential measurement data. The calculation unit 895 may calculate a distribution of current values ​​or a distribution of conductivity in the living body 50 through which a current is passed by the electrode pair.

[0069] The calculation unit 895 may remove the magnetic field components generated from the lead wires 805 connected to the electrodes 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 a plurality of electrode pairs through which a current flows during measurement. The calculation unit 895 may store the magnetic field generated by the lead wires 805 and cancel the stored magnetic field components from the magnetic field measurement data. For example, the magnetic field generated by the lead wires 805 may be calculated from the path of the lead wires connected to each electrode (for example, at least one of the length and the position of the lead wires 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 wires 805 may be acquired by measuring in advance the magnetic field generated by the lead wires 805 when a current flows for each electrode pair. Furthermore, the magnetic field generated by the lead wire 805 may be estimated from the path of the lead wire 805 by performing a simulation.

[0070] 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.

[0071] 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 on a curved surface 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 surface shape in a three-dimensional lattice space. Note that 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 having 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 having 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, for example, 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 predetermined curved surface having a convex in the positive direction of the Z axis.

[0072] The measurement device 10 measures the magnetic field by arranging 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 portion, and the center position in the X-axis direction of the measurement target portion of the living body 50 is located at the center of the curved surface. This allows the measurement device 10 to perform signal space separation using the 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. In this case, it is preferable that the curvature of the curved surface of the magnetic sensor array 210 is approximately equal to the curvature around the subject's chest, since the magnetic field can be measured at a position closer to the living body 50, which is the source of the magnetic field to be measured.

[0073] FIG. 10 shows an example of the arrangement of the multiple electrodes 800 of the measurement device 10 of this embodiment. Note that FIG. 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, so as to surround the measurement target on the cross section (XZ plane) of the living body 50.

[0074] The electrodes 800 may be, for example, independent electrodes attached to the surface of the living body 50 by a seal or the like. The electrodes 800 may 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 electrodes 800 may have the same shape. Each of the electrodes 800 may be circular, elliptical, polygonal, or the like.

[0075] FIG. 11 shows a cross section parallel to the XZ plane of a part of the measuring device 10 of this embodiment. In FIG. 11, the dotted arrow in the living body 50 shows the flow of the secondary current in the living body 50. When the measuring device 10 passes a current through a plurality of 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 an 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 passes an AC current with the magnetic sensor array 210, detects the potential with the plurality of electrodes 800, and can calculate the distribution of the current or conductivity in the living body 50 from the detected magnetic field and potential.

[0076] FIG. 12 shows the distribution of the magnetic field and current 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 field 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 at the same positions as the positions where the electrodes 800 are arranged. 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 field and potential of the M detection positions 1200. Note that the detection position 1200 may be approximately the same as the center position of the measurement target part in the Y-axis direction, and may be approximately the same as the center position or within the length range of the electrode 800.

[0077] 13 shows a schematic diagram of regions divided in a living body 50 in a cross section parallel to the XZ plane when the conductivity is calculated by the measuring device 10 of this embodiment. 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 ~Ω k=9 The measurement device 10 can calculate the conductivity distribution within the living body 50 by calculating the conductivity in each region Ω.

[0078] FIG. 14 shows a measurement flow of the measuring device 10 according to this embodiment.

[0079] 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 of 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 by simulation results or the like.

[0080] Next, in step 1310, the measuring device 10 acquires potential measurement data together with magnetic field measurement data based on an input magnetic field detected while a 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 having a frequency set by the user or a predetermined frequency.

[0081] The current control unit 810 may pass an AC current having the same frequency as the synchronization signal through the living body 50 via the electrode pair during a 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 a 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 among 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.

[0082] Specifically, the current control unit 810 may pass a current through 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 cycles 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 of the electrodes 800(2) to 800(5) with the electrode 800(1) as the reference potential. The current control unit 810 may also output a potential difference of one electrode 800 of the electrode pair to which the current is applied, with the other electrode 800 being set as a reference potential. The current control unit 810 may also detect a potential difference between a specific electrode 800 and a plurality of other electrodes 800, and output the difference between the detected potential differences as the potential difference of the electrode pair consisting of the plurality of 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).

[0083] The potential measurement data acquiring unit 815 may acquire one or more pieces of potential measurement data measured for each electrode pair to which the signal is applied by multiplying the synchronization signal. The potential measurement data acquiring unit 815 may acquire only frequency components of the potential measurement data equal to the reference signal, using the current signal applied by the current control unit 810 as a reference signal. The potential measurement data acquiring 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.

[0084] The magnetic field measurement data acquiring section 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 acquiring section 830 may filter the magnetic field measurement data multiplied by the synchronization signal using an analog low-pass filter and output the filtered data.

[0085] Each of the AD converters 840 performs analog-to-digital conversion on the acquired magnetic field measurement data and outputs the data. The calibration calculation unit 850 may calibrate the acquired magnetic field measurement data and output the data 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.

[0086] In step 1320, the signal space separating unit 890 acquires from the basis vector storage unit 880 the signal vectors that the basis vector storage unit 880 stored as basis vectors in step 1300. Note that in this flow, either step 1310 or step 1320 may be performed first.

[0087] 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 a measurement target magnetic field and a disturbance magnetic field, based on the vector obtained by series expansion. Note that the orthogonal function may be a spherical harmonic function. In addition, the signal space separation unit 890 calculates the coefficients of the basis vectors by the least squares method when performing signal separation.

[0088] Then, in step 1340, the signal space separation section 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 section 895. This will be described in detail below.

[0089] 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 Δ·V(r) = 0, as shown in the following equation: Here, r is the position vector representing the position from the coordinate origin, Δ is the Laplacian, μ is the magnetic permeability, and ∇ is the operator representing a vector differential operation.

number

[0090] 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 function systems, so that 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.

number

[0091] 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.

number

[0092] When the solution of 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 in a series of about 10 terms. Also, for example, it is said that the series of signal space separation in the 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 these, 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.

[0093] 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 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, as components. 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 a dimension that is three times the number of magnetic sensor cells 220. Also, the vectors nx, ny, and nz representing the magnetic sensing axis directions and magnetic sensitivity of each sensor unit 300 may be vectors 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.

number

[0094] Then, the sensor output vector Φ outputted from the magnetic sensor array 210 at a certain time can be expressed by the following equation.

number

[0095] Furthermore, Sin, Sout, Xin, and Xout are defined as follows. That is, Sin is defined as a vector with Lin (Lin+2) columns in total, 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 Lout (Lout+2) columns in total, 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 Lin (Lin+2) rows in total, transposed vectors 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, let Xout be defined as a vector with a total of Lout (Lout+2) rows, obtained by transposing the vectors in which the multipole moments β for l=1 to l=Lin, where m=-1 to l are integers for each l, are arranged in order.

number

[0096] 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. Moreover, the column vector X indicates a coefficient related to the basis vector.

number

[0097] Based on the model formula of the sensor output vector Φ obtained by (Equation 12), the following formula is used to determine the column vector X that satisfies Φ=S·X in a least squares approximation. This enables the signal space separation section 890 to solve the spatial distribution of the magnetic field.

number

[0098] 12, in the case of calculating the magnetic field at a plurality of detection positions 1200 on the surface of the living body 50, the magnetic field at vector r of the plurality of 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.

[0099]

number

[0100] The signal space separating section 890 according to this embodiment can calculate the magnetic field for each of the multiple detection positions 1200 using (Equation 14). The signal space separating section 890 outputs a 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 separating section 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).

[0101] The measurement device 10 may obtain the difference ΔB of the magnetic flux density at the time of measurement from the magnetic flux density at a predetermined reference state as magnetic field measurement data. The magnetic flux density at the reference state may be a magnetic flux density obtained by simulating the inside of the living body 50 as uniform, or a magnetic flux density measured in a previous measurement. The measurement method and calculation method of the magnetic flux density at the reference state and the magnetic flux density at the time of measurement may be the same as described above.

[0102] Next, in step 1350, the calculation unit 895 may calculate 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) is expressed as the potential sensitivity matrix J E The equation for calculating the elements of is given, and the forward problem showing the relationship between the conductivity Δσ and the potential ΔV is the potential sensitivity matrix J E Using this, it can be expressed as (Equation 16). In (Equation 15), Φ ddenotes the potential of the electrode pair to which the current is applied, and Φ m indicates the potential of the electrode pair for measuring the potential measurement data. As shown in Fig. 13, i indicates the detection position of the potential, and k indicates the area in the living body 50. The calculation unit 895 may calculate the conductivity Δσ in the same manner 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.

[0103]

number

number

[0104] Next, (Equation 17) is the magnetic field sensitivity matrix J M The equation for calculating the elements of is shown, and the forward problem showing the relationship between the conductivity Δσ and the magnetic field ΔB is the magnetic field sensitivity matrix J M 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 area Ω k As shown in FIG. 13, i indicates a detection position, k indicates an area in the living body 50, and the magnetic field sensitivity matrix J M The rows of indicate the values ​​corresponding to each detection position i, and the magnetic field sensitivity matrix J M The columns of each region Ω k Refers to the value corresponding to.

[0105]

number

number

[0106] The calculation unit 895 calculates the potential sensitivity matrix J E and the magnetic field sensitivity matrix J M The combined sensitivity matrix J EM Generate J EMThe conductivity Δσ may be calculated by a forward problem such as (Equation 20) which expresses the relationship between Δy, which indicates the magnetic field measurement data and the electric potential measurement data, and the conductivity Δσ, using the above equation. Here, the magnetic field measurement data ΔB, the electric potential measurement data ΔV, and the conductivity Δσ are each a three-dimensional vector.

[0107]

number

number

[0108] As shown in (Equation 21), the calculation unit 895 calculates the magnetic field measurement data and the potential measurement data, or the potential sensitivity matrix J E and the magnetic field sensitivity matrix J M The calculation unit 895 may multiply the weighting coefficient w E and the weighting factor for the magnetic field measurement data w M and a diagonal matrix (W=diag(w E , . E , w M , . M ) may be used as the weighting coefficient W. The calculation unit 895 may optimize the weighting coefficient 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 coefficient W based on the measurement data or the sensitivity matrix.

[0109]

number

[0110] The calculation unit 895 may weight the data with a weighting coefficient based on at least one of the magnetic field measurement data and the electric potential measurement data, the average of all the measurement data, or the maximum of all the measurement data. For example, the calculation unit 895 may calculate the weighting coefficient w MThe reciprocal of the average value of all the potential measurement data (potential measurement data at all potential detection positions) is used as the weighting coefficient w E It is acceptable to do so.

[0111] The calculation unit 895 may perform weighting using a weighting coefficient 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. M The inverse of the average value of all elements (values) is used as the weighting coefficient w M Then, the potential sensitivity matrix J E The inverse of the average value of all elements (values) is used as the weighting coefficient w E It is acceptable to do so.

[0112] The calculation unit 895 calculates the magnetic field sensitivity matrix J M and the potential sensitivity matrix J E The weighting may be performed by a weighting coefficient based on singular values ​​obtained by singular value decomposition from the above, and the weighting coefficient may be set based on at least one singular value of the singular values, the average value of all singular values, or the maximum value of all singular values. M The weighting coefficient w is the inverse of the average value of all singular values ​​obtained by singular value decomposition of M Then, the potential sensitivity matrix J E The weighting coefficient w is the inverse of the average value of all singular values ​​obtained by singular value decomposition of E It is acceptable to do so.

[0113] In step 1350, the calculation unit 895 may calculate a 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 a three-dimensional vector. 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 manner using the detected magnetic field B of the magnetic sensor array 210 instead of the measured magnetic field B at the detection position 1200.

[0114]

number

[0115] The calculation unit 895 calculates the potential sensitivity matrix J E The forward problem ΔV=J that shows the relationship between the potential ΔV and the current value J using E ·J, and similarly, the potential sensitivity matrix for the current value J E may be calculated.

[0116] The calculation unit 895 calculates the magnetic field sensitivity matrix L and the electric potential sensitivity matrix J calculated above. E and may be used to calculate the current values ​​J1 to JN by weighting in the same manner as above.

[0117] 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 reverse calculation of the above-mentioned current calculation. The calculation unit 895 may calculate the magnetic field components caused by the lead wire 805 from the determined path of the lead wire 805 and the current value, for example, using the Biot-Savart equation.

[0118] 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 acquiring the potential measurement data and magnetic field measurement data in the current application of all electrode pairs, acquisition of measurement data for each current pair may be repeated in the same manner. 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 together 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 result by using a part of the EIT technology, for example, by the display of the information processing unit 30, and display it in multi-value.

[0119] The measurement device 10 of this embodiment can suppress disturbance magnetic fields by the signal space separation unit 890 and 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 result and the electric potential detection result of the magnetic sensor array 210, so that the accuracy can be improved compared to the case where only one of the results is used.

[0120] The magnetic sensor array 210 (or the magnetic sensor cell 220) is not limited to one capable of detecting an input magnetic field in three axial directions, and may be one capable of detecting an input magnetic field in one axial direction or two axial directions. The electrodes 800 may be arranged in a plurality of rows on the living body 50, or may be arranged in a row only on one surface side of the living body 50. All of the electrodes 800 do not need to have both the function of applying a current and the function of measuring a potential, and the electrodes 800 for applying a current and the electrodes 800 for measuring a potential may be separate.

[0121] Various embodiments of the present invention may be described with reference to flow charts and block diagrams, where the blocks may represent (1) stages of a process in which operations are performed or (2) sections of an apparatus responsible for performing the operations. 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.

[0122] 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 flowcharts or block diagrams. 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.

[0123] 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.

[0124] Computer readable instructions may be provided to a processor or programmable circuitry of a general purpose computer, special purpose computer, or other programmable data processing apparatus, either locally or over a local area network (LAN), a wide area network (WAN), such as 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.

[0125] 15 illustrates an example of a computer 2200 in which aspects of the present invention may be embodied in whole or in part. Programs 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 a process according to an embodiment of the present invention. Such programs may be executed by the CPU 2212 to cause the computer 2200 to perform specific operations associated with some or all of the blocks of the flowcharts and block diagrams described herein.

[0126] The computer 2200 according to this embodiment includes a CPU 2212, a RAM 2214, a graphic controller 2216, and a display device 2218, which are connected to each other 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.

[0127] The CPU 2212 operates according to a program stored in the ROM 2230 and the RAM 2214, thereby controlling each unit. The graphic controller 2216 retrieves image data generated by the CPU 2212 into a frame buffer or the like provided in the RAM 2214 or into the graphic controller 2216 itself, and causes the image data to be displayed on the display device 2218.

[0128] 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.

[0129] The ROM 2230 stores therein a boot program or the like executed by the computer 2200 upon activation, and / or a program that depends on the hardware of the computer 2200. The input / output chip 2240 may also connect various input / output units to the input / output controller 2220 via a parallel port, a serial port, a keyboard port, a mouse port, and the like.

[0130] 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, the RAM 2214, or the ROM 2230, which are also examples of computer-readable media, and executed by the CPU 2212. 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 information manipulation or processing according to the use of the computer 2200.

[0131] For example, when communication is performed between the computer 2200 and an external device, the CPU 2212 may execute a communication program loaded in the RAM 2214 and instruct the communication interface 2222 to perform communication processing based on the processing described in the communication program. Under the control of the CPU 2212, the communication interface 2222 reads transmission data stored in a transmission buffer processing area provided in the RAM 2214, the hard disk drive 2224, the 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.

[0132] Furthermore, the CPU 2212 may cause all or a necessary portion of a file or database stored in 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.

[0133] Various types of information, such as various types of programs, data, tables, and databases, may be stored in the recording medium and undergo information processing. The CPU 2212 may perform various types of processing on the data read from the 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 the RAM 2214. The CPU 2212 may also search for information in a file, database, etc. in the recording medium. For example, when a plurality of 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, the 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 plurality of 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.

[0134] The above-described programs or software modules may be stored in a computer-readable medium on the computer 2200 or in the vicinity of the computer 2200. Also, a recording medium such as a hard disk or a 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 programs to the computer 2200 via the network.

[0135] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the claims that such modifications and improvements can also be included in the technical scope of the present invention.

[0136] It should be noted that 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," "prior to," etc., and may be realized 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 essential to perform the process in this order. [Explanation of symbols]

[0137] 10. Measurement Equipment 20 Main body 30 Information Processing Section 50 Living organisms 100 Current Control Unit 110 Magnetic sensor unit 120 Head 125 Drive unit 130 Base 140 Pole section 210 Magnetic Sensor Array 220 Magnetic Sensor Cell 230 Sensor Data Collection Unit 300 Sensor section 520 Magnetic Sensor 530 Magnetic field generation section 532 Amplification circuit 534 Coil 540 Output section 702 Magnetoresistance element 704 Magnetic Concentrator 706 Magnetic Concentrator 800 electrodes 810 Current control section 815 Electric potential measurement data acquisition unit 820 Control section 830 Magnetic field measurement data acquisition unit 840 A / D converter 842 Clock Generator 850 Calibration Calculation Unit 860 Storage section 870 Estimation part 880 Basis Vector Storage Unit 890 Signal Space Separation Unit 895 Calculation Department 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

1. 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.

2. 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 1 .

3. 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 2 .

4. The estimation unit performs weighting using a weighting factor based on a magnetic field sensitivity matrix indicating the sensitivity of the magnetic field measurement data to the current or conductivity in the living body and a potential sensitivity matrix indicating the sensitivity of the potential measurement data to the current or conductivity in the living body. The measurement device according to claim 1 .

5. The estimation unit weights the magnetic field sensitivity matrix and the electric potential sensitivity matrix with a weighting coefficient based on at least one of the elements, the average value of the elements, or the maximum value of the elements. The measurement device according to claim 4.

6. The estimation unit performs weighting using a weighting coefficient based on a singular value obtained by singular value decomposition from the magnetic field sensitivity matrix and the electric potential sensitivity matrix. The measurement device according to claim 4.

7. 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 6.

8. The current control unit applies an alternating current to the living body through the at least one electrode pair. The measuring device according to any one of claims 1 to 7.

9. 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 any one of claims 1 to 8.

10. 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, thereby passing a current through the living body. The measurement device according to any one of claims 1 to 9.

11. 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 measurement target magnetic field 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 measurement target magnetic field and the potential measurement data. The measurement device according to any one of claims 1 to 10.

12. 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 signal space separation unit separates the spatial distribution of the magnetic field using signal vectors output by each of the magnetic sensors as basis vectors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function. The measurement device according to claim 11.

13. The estimation unit removes, from the magnetic field measurement data, a magnetic field component generated from lead wires connected to the plurality of electrodes. The measurement device according to any one of claims 1 to 12.

14. 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 by a magnetic sensor array from the living body while a current is being passed through the living body; acquiring potential measurement data based on a potential difference detected between 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.

15. 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 measurement target magnetic field 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 flowing through the living body; The calculation unit weights the separated measurement target magnetic field and the potential measurement data to calculate a current or a conductivity in the living body. program.

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