JP2022153083A - Measurement device, method for measurement, and program - Google Patents

Abstract

To provide a measurement device that can estimate a current flowing in a living body or the conductivity in a living body on the basis of measurement data.SOLUTION: The measurement device includes: an electrode unit having a plurality of electrodes arranged laterally around a living body 50, the electrodes being longer in a vertical direction and being shorter in a circumferential direction of the 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 in three-axes directions in a plurality of positions in a three-dimensional space; a current application unit for flowing a current in the living body 50 by at least one pair of electrodes of the plurality of electrodes; and a measurement data acquisition unit for acquiring measurement data based on an input magnetic field that the magnetic sensor array detected from the living body 50 while a current was flowing in the living body 50.SELECTED DRAWING: Figure 1

Description

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

Conventionally, there is a method of acquiring a tomographic image or the like for diagnosis of a living body (see Patent Documents 1 to 3). As one of such methods, a plurality of electrodes are arranged around the living body, and the electrical conductivity distribution in the living body is detected from the potential difference between the other electrodes measured by applying an electric current. There is electrical impedance tomography (EIT), which obtains cross-sectional images of the tissue.
Patent Document 1 US 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 In a first aspect of the invention, a measurement device is provided. The measuring device may include an electrode unit having a plurality of vertically elongated electrodes arranged side by side around the living body, with the lateral direction being the circumferential direction of the living body. The measuring device may include a magnetic sensor array that has a plurality of magnetic sensor cells and is capable of detecting input magnetic fields in three axial directions at a plurality of locations in a three-dimensional space. The measuring device may include a current applying section that applies a current to the living body using at least one electrode pair of the plurality of electrodes. The measurement device may include a measurement data acquisition unit that acquires measurement data based on an input magnetic field detected from the living body by the magnetic sensor array while current is flowing through the living body. The measuring device may include an estimating unit that estimates the current flowing in the living body or the conductivity in the living body based on the measurement data.

Each of the plurality of electrodes may be longer in the longitudinal direction than the length of the measurement target site of the living body.

The plurality of electrodes may have the same length in the longitudinal direction.

The magnetic sensor array may be arranged without contact with the electrode unit.

The magnetic sensor array may be arranged facing the electrode unit.

The magnetic sensor array may be arranged in the longitudinal direction of the plurality of electrodes in a range shorter than the length of the plurality of electrodes.

The current applying section may apply alternating current to the living body using at least one electrode pair.

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

The measurement data acquisition unit may remove magnetic field components generated from lead wires connected to the plurality of electrodes from the measurement data.

The current applying unit may sequentially apply current to an electrode pair consisting of two adjacent electrodes while shifting the electrodes one by one, thereby causing the current to flow through the living body.

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

Each of the plurality of magnetic sensor cells may have a plurality of magnetic sensors each having a magnetoresistive element and magnetic concentrators positioned at opposite ends of the magnetoresistive element. The signal space separation unit may separate the spatial distribution of the magnetic field by using signal vectors output from each of the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function as a basis vector.

A second aspect of the present invention provides a measurement method. The measurement method may include applying current to the living body by at least one electrode pair among a plurality of longitudinally elongated electrodes arranged side by side around the living body and having a lateral direction in the circumferential direction of the living body. The measurement method may comprise detecting an input magnetic field in three axial directions at multiple locations in three-dimensional space with a magnetic sensor array having multiple magnetic sensor cells while an electrical current is flowing through the living body. The measurement method may comprise acquiring measurement data based on an input magnetic field detected from the living body by the magnetic sensor array. The measurement method may comprise estimating current flowing in the living body or conductivity in the living body based on the measured data.

A third aspect of the present invention provides a program. The program is executed by a computer, causing the computer to generate an electric current through at least one electrode pair of a plurality of longitudinally elongated electrodes arranged side by side around the living body, with the circumferential direction of the living body being the short side direction. The spatial distribution of the magnetic field indicated by the measurement data based on the input magnetic field detected from the living body by a magnetic sensor array capable of detecting the input magnetic field in the three-axis direction at multiple points in the three-dimensional space while the It may function as a signal space separating section that separates the magnetic field to be measured from the magnetic field and the disturbance magnetic field. The program may be executed by a computer to cause the computer to function as a calculator that calculates the current value of the current flowing in the living body or the conductivity in the living body based on the separated magnetic field to be measured.

It should be noted that the above summary of the invention does not list all the necessary features of the invention. Subcombinations of these feature groups can also be inventions.

1 shows the configuration of a measuring device 10 according to this embodiment. 2 shows the configuration of a magnetic sensor unit 110 according to this embodiment. The configuration and arrangement of magnetic sensor cells 220 in the magnetic sensor array 210 according to the present embodiment are shown. An example of input/output characteristics of a magnetic sensor having a magnetoresistive element according to this embodiment is shown. 3 shows a configuration example of a sensor unit 300 according to the present embodiment. An example of input/output characteristics of the sensor unit 300 according to the present embodiment is shown. 4 shows a configuration example of a magnetic sensor 520 according to the present embodiment. 1 shows the configuration of a measuring device 10 according to this embodiment. An example of arrangement of a plurality of electrodes 800 of the measuring device 10 of this embodiment is shown. An example in which the measurement device 10 of the present embodiment measures a magnetic field using a magnetic sensor array 210 is shown. FIG. 4 is an explanatory diagram for explaining the current distribution in the living body 50 during measurement by the measuring device 10 of the present embodiment; FIG. 8 is an explanatory diagram for explaining the current distribution in the living body 50 when current is applied to the electrode 807 of the comparative example; FIG. 4 is an explanatory diagram for explaining distribution of electric current inside the living body 50 during measurement by the measuring device 10 of the present embodiment; FIG. 4 is an explanatory diagram for explaining the current distribution and the magnetic field in the living body 50 during measurement by the measuring device 10 of the present embodiment; The measurement flow of the measuring device 10 according to this embodiment is shown. Another example of the arrangement of the plurality of electrodes 800 of the measuring device 10 of the embodiment is shown. An example computer 2200 is shown in which aspects of the present invention may be embodied in whole or in part.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution of the invention.

FIG. 1 shows the configuration of a measuring device according to this embodiment. The measuring device 10 measures a magnetic field generated by applying current to a living body 50 such as a subject, and estimates the current in the living body 50 using the measured magnetic field. The measuring device 10 may be used for acquiring internal images of the living body 50 .

The measuring device 10 includes a body section 20 and an information processing section 30 . The body portion 20 is a component for applying current to the living body 50 and sensing a magnetic field, and includes a current applying unit 100, a magnetic sensor unit 110, a head 120, a driving portion 125, a base portion 130, and a pole portion. 140.

The current applying unit 100 is placed in contact with the surface of the measurement target site (eg, the subject's stomach, etc.) of the living body 50 at the time of measurement, and applies current to the living body 50 . The magnetic sensor unit 110 is arranged at a position facing the measurement target site of the living body 50 during measurement, and senses the magnetic field from the living body 50 . The head 120 supports the magnetic sensor unit 110 and makes the magnetic sensor unit 110 face the living body 50 . The drive 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 drive unit 125 according to the present embodiment includes a first actuator capable of rotating the magnetic sensor unit 110 360 degrees around the Z-axis in the drawing, an axis perpendicular to the Z-axis (in the state in the drawing, the X-axis ), which are used to change the azimuth and zenith angles of the magnetic sensor unit 110 . Further, the magnetic sensor unit 110 may be rotatable around the object to be measured around the Y-axis in the figure.

The base portion 130 is a base that supports other components. The subject who is the living body 50 may stand on the base section 130 or sit in front of the base section 130 during measurement. The pole portion 140 supports the head 120 at the height of the living body 50 to be measured. The pole portion 140 may be vertically extendable to adjust the height of the head 120 .

The information processing section 30 is a component for processing data measured by the main body section 20 and outputting the data by display, printing, or the like. The information processing unit 30 may be a computer such as a PC (personal computer), a tablet computer, a smart phone, 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 section 30 may be a dedicated computer designed for specific information processing, or may be dedicated hardware realized by dedicated circuitry.

FIG. 2 shows the configuration of the magnetic sensor unit 110 according to this embodiment. The magnetic sensor unit 110 has a magnetic sensor array 210 and a sensor data acquisition section 230 . The magnetic sensor array 210 is configured by three-dimensionally arranging a plurality of magnetic sensor cells 220 capable of detecting magnetic fields in three axial directions. As an example, the plurality of magnetic sensor cells 220 have a plurality of magnetic sensors each having a magnetoresistive element and a magnetic flux concentrator arranged at least one of one end and the other end of the magnetoresistive element. It is preferable that the magnetic flux concentrators are arranged at both ends of the magnetoresistive element in that the sampling accuracy of the spatial distribution of the magnetic field, which will be described later, can be increased. In this figure, the magnetic sensor array 210 includes a plurality of magnetic sensor cells 220 in each of the X, Y, and Z directions (e.g., 8 in the X direction, 8 in the Y direction, and 2 in the Z direction, totaling 128 cells). magnetic sensor cells 220) are arranged in a plane.

The sensor data collection unit 230 is electrically connected (not shown) to the plurality of magnetic sensor cells 220 included in the magnetic sensor array 210, and collects and processes measurement data (detection signals) from the plurality of magnetic sensor cells 220. It is supplied to the information processing section 30 .

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 sections 300x-z (hereinafter collectively referred to as "sensor sections 300") each having a magnetoresistive 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. Further, the sensor unit 300y is arranged along the Y-axis direction and can detect a magnetic field in the Y-axis direction. Also, 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-dotted line in this figure, in this embodiment, each sensor unit 300 has a magnetic flux concentrator arranged at both ends of the magnetoresistive element. Therefore, each sensor unit 300 samples the spatial distribution of the magnetic field using a magnetoresistive element arranged at a narrow position sandwiched between the magnetic flux concentrators, thereby clarifying sampling points in space in each axial direction. be able to. The details of the configuration of each sensor unit 300 will be described later.

The plurality of magnetic sensor cells 220 are arranged at regular 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 the set [i,j,k] of position i in the X direction, position j in the Y direction, and position k in the Z direction. Here, i is an integer satisfying 0≤i≤Nx-1 (Nx indicates the number of magnetic sensor cells 220 arranged in the X direction), and j is an integer satisfying 0≤j≤Ny-1 ( Ny indicates the number of magnetic sensor cells 220 arranged in the Y direction), k is an integer satisfying 0≦k≦Nz−1 (Nz indicates the number of magnetic sensor cells 220 arranged in the Z direction).

In this figure, the three-axis directions of the magnetic fields detected by the sensor units 300x, 300y, and 300z are the same as the three-dimensional directions in which the magnetic sensor cells 220 are arranged. This facilitates understanding of each component of the distribution of the measured magnetic field. In each magnetic sensor cell 220, the sensor units 300x, 300y, and 300z do not overlap with each other when viewed from each of the three-dimensional directions in which the magnetic sensor cells 220 are arranged, and the gap side provided between the plurality of sensor units 300 It is preferable that one end is provided at the end and the other end is arranged extending in each of the three axial directions so as to be separated from the gap. As an example, in this figure, a gap is provided in the lower left corner of the magnetic sensor cell 220 when viewed from the front. An example of extending in each of the X-axis, Y-axis, and Z-axis directions so as to separate from the gap is shown. In this figure, sensor units 300x, 300y, and 300z are arranged from one corner of a cubic magnetic sensor cell 220 along three sides perpendicular to each other, and a gap is provided in the one corner. In addition, it is preferable that coils or magnetic bodies of sensor units 300x, 300y, and 300z, which will be described later, are arranged so as not to overlap each other. As a result, the measurement point can be clarified, and each component of the magnetic field to be measured can be grasped more easily. Further, the sensitivities of the sensor units 300x, 300y, and 300z can be regarded as equivalent to each other, which facilitates the calibration calculation of linear algebra, which will be described later. This cross-axis sensitivity is caused by mutual interference by the coils or magnetic bodies of the sensor units 300x, 300y, and 300z. However, the three-axis directions of the magnetic field to be detected and the three-dimensional directions in which the magnetic sensor cells 220 are arranged may be different. When both are different, the arrangement of the sensor units 300 in the magnetic sensor cells 220 and the arrangement direction of the magnetic sensor cells 220 are not restricted, and the degree of freedom in designing the magnetic sensor array 210 can be increased.

FIG. 4 shows an example of input/output characteristics of a magnetic sensor having a magnetoresistive 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 magnetoresistance (GMR) element or a tunnel magnetoresistance (TMR) element, and detects the magnitude of a predetermined uniaxial magnetic field. .

Such a magnetic sensor has high magnetic sensitivity, which is the gradient of the detection signal V_xMR0 with respect to the input magnetic field B, and can detect a minute magnetic field of about 10 pT. On the other hand, in the magnetic sensor, for example, the detection signal V_xMR0 is saturated when the absolute value of the input magnetic field B is about 1 μT, and the range in which the linearity of the input/output characteristics is good is narrow. Therefore, by adding a closed loop that generates a feedback magnetic field to such a magnetic sensor, the linearity of the magnetic sensor can be improved. Such a magnetic sensor will be described below.

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

The magnetic sensor 520 has a magnetoresistive element such as a GMR element or a TMR element, like the magnetic sensor described with reference to FIG. The magnetic sensor 520 also has magnetic concentrators arranged at both ends of the magnetoresistive element. When the positive direction of the magnetosensitive axis is the +X direction, the magnetoresistive element of the magnetic sensor 520 increases in resistance when a magnetic field in the +X direction is input, and decreases in resistance when a magnetic field in the −X direction is input. may be configured to That is, the magnitude of the magnetic field B input to the magnetic sensor 520 can be detected by observing the change in the resistance value of the magnetoresistive element of the magnetic sensor 520 . For example, if the magnetic sensitivity of the magnetic sensor 520 is S, the detection result for the input magnetic field B of the magnetic sensor 520 can be calculated as S×B. As an example, the magnetic sensor 520 is connected to a power supply or the like, and outputs a voltage drop corresponding to a change in resistance value as a detection result of the input magnetic field. The details of the configuration of the magnetic sensor 520 will be described later.

The magnetic field generator 530 provides the magnetic sensor 520 with a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor 520 . The magnetic field generator 530 operates to, for example, generate a feedback magnetic field B_FB that is opposite in direction to the magnetic field B input to the magnetic sensor 520 and has substantially the same absolute value as the input magnetic field, thereby canceling out the input magnetic field. Magnetic field generator 530 includes an amplifier circuit 532 and a coil 534 .

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

Coil 534 generates a feedback magnetic field B_FB corresponding to feedback current I_FB. The coil 534 is wound so as to surround the magnetoresistive element of the magnetic sensor 520 and the magnetic flux concentrators arranged at both ends of the magnetoresistive element. Coil 534 preferably generates a uniform feedback magnetic field B_FB across 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, since the feedback magnetic field B_FB is generated in a direction to cancel the input magnetic field B, the magnetic field input to the magnetic sensor 520 is reduced to BB_FB. Therefore, the feedback current I_FB is given by the following equation.

By solving the equation (1) for the feedback current I_FB, the value of the feedback current I_FB in the steady state of the sensor unit 300 can be calculated. Assuming 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 is calculated from the equation (1).

The output unit 540 outputs an output signal V_xMR corresponding to the feedback current I_FB that the magnetic field generation 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 an output signal V_xMR. In this case, the output signal V_xMR is calculated from the equation (2) as follows.

As described above, the sensor unit 300 generates a feedback magnetic field that reduces the magnetic field that is input from the outside, so that the magnetic field that is substantially input to the magnetic sensor 520 is reduced. As a result, the sensor unit 300 can prevent the detection signal V_xMR from being saturated even when the absolute value of the input magnetic field B exceeds 1 μT, for example, using a magnetoresistive element having the characteristics of FIG. 4 as the magnetic sensor 520 . Input/output characteristics of the sensor unit 300 will be described below.

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

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

FIG. 7 shows a configuration example of a magnetic sensor 520 according to this embodiment. As an example, the magnetic sensor 520 according to this embodiment has a magnetoresistive element 702 and magnetic flux concentrators 704 and 706 arranged at one end and the other end of the magnetoresistive element 702 . The magnetic concentrator plates 704 and 706 are arranged so as to sandwich the magnetoresistive element 702 therebetween. That is, magnetic flux concentrators are arranged at both ends of the magnetoresistive element 702 . In FIG. 7, the magnetic flux concentrating plate 704 arranged at the right end of the magnetoresistive element 702 along the magnetic sensing axis in front view is the magnetic flux concentrating plate provided on the positive side of the magnetic sensing axis. A magnetic flux concentrator 706 arranged at the left end of is a magnetic flux concentrator provided on the negative side of the magnetosensitive axis. As the magnetic field is input to the magnetic flux concentrators 704, 706 from the negative side to the positive side of the magnetosensitive axis, the resistance of the magnetoresistive element 702 may increase or decrease. Note that the magneto-sensitive axis may be along the magnetization direction fixed by the magnetization fixed layer forming the magnetoresistive element 702 . The magnetic flux concentrators 704 and 706 are made of a soft magnetic material such as iron. By arranging the magnetic flux concentrators 704 and 706 made of a soft magnetic material at one end and the other end of the magnetoresistive element 702, the lines of magnetic force passing through the magnetoresistive element 702 can be increased, thereby increasing the magnetic force of the magnetic sensor 520. Sensitivity can be increased.

Although this figure shows an example in which the magnetic flux concentrating plate is arranged at both one end and the other end of the magnetoresistive element 702, the magnetic flux concentrating plate may be provided only in However, in order to further increase the sensitivity of the magnetic sensor 520, it is preferable to provide magnetic flux concentrators at both one end and the other end of the magnetoresistive element 702. FIG. Further, when magnetic flux concentrators are provided at both one end and the other end of the magnetoresistive element 702, the position of the magnetoresistive element 702 arranged in a narrow position sandwiched between the two magnetic flux concentrators 704 and 706 becomes the magnetic sensing part, That is, since it becomes a spatial sampling point, the magnetically sensitive portion becomes clear, and affinity with the signal spatial separation technique described later can be further enhanced. In this way, by using the magnetic sensor 520 in which the magnetic flux converging plates 704 and 706 are arranged at both ends of the magnetoresistive element 702 for each sensor unit 300, the measuring device 10 according to the present embodiment can be configured as shown in FIG. Furthermore, in each axial direction, the spatial distribution of the magnetic field can be sampled at extremely narrow (for example, 100 μm or less) positions sandwiched between magnetic flux concentrators at both ends. Sampling accuracy (positional accuracy) is higher than when sampling the spatial distribution of the magnetic field using a magnetic field.

FIG. 8 shows the configuration of the measuring device 10 according to this embodiment. As an example, the current application unit 100 of the main body 20 shown in FIG. The data collection unit 230 is provided, and the information processing unit 30 has an estimation unit 870 . Note that the electrode unit of the present application may include at least a plurality of electrodes 800, and may be the current application unit 100, for example.

The plurality of electrodes 800 are electrically connected to a current applying section 810 via lead wires 805 and arranged in contact with the surface surrounding the living body 50 . In FIG. 8, electrodes 800(1)-(5) of the plurality of electrodes 800 are shown. Note that the number of electrodes 800 is not particularly limited as long as it is two or more.

The current applying section 810 is connected to the magnetic sensor unit 110 and applies current to the living body 50 through at least one electrode pair of the plurality of electrodes 800 . The current applying section 810 may apply alternating current to the living body 50 using at least one electrode pair. The current application unit 810 may have an AC power supply for supplying AC current to the electrode pair, or may be connected to an external AC power supply. The current applying section 810 may apply current to the electrode pairs of the plurality of electrodes 800 according to the synchronization signal from the control section 820 of the magnetic sensor unit 110 . As an example, the current applying section 810 may apply an alternating current of 1 mA or less to the living body 50 in synchronization with the synchronization signal.

The magnetic sensor array 210 has a plurality of magnetic sensor cells 220 and is capable of detecting input magnetic fields in three axial directions at a plurality of locations within a three-dimensional space. Each of the plurality of magnetic sensor cells 220 has a plurality of sensor portions 300x-z as described above. In this figure, among the plurality of magnetic sensor cells 220 that the magnetic sensor array 210 has in each dimension, positions [i, j, k], [i+1, j, k], [i, j+1, k], and The part for [i,j,k+1] is shown.

The sensor data collection section 230 has a control section 820 , a plurality of measurement data acquisition sections 830 , a plurality of AD converters 840 , a clock generator 842 , a calibration calculation section 850 and a storage section 860 .

Control section 820 is connected to current application section 810 and a plurality of measurement data acquisition sections 830 , and controls synchronous detection of current application section 810 and measurement data acquisition section 830 . The control unit 820 synchronizes the current flowing through the living body 50 through at least one electrode pair and the acquisition of measurement data by the measurement data acquisition unit 830 . Control section 820 outputs a common synchronization signal to current application section 810 and each measurement data acquisition section 830 . The control unit 820 may cause the current application unit 810 to apply a current at the same timing as the plurality of measurement data acquisition units 830 acquiring measurement data from each sensor cell using a common synchronization signal. Control unit 820 outputs a synchronization signal with a frequency of 10 to 100 KHz, for example.

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

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

A clock generator 842 generates a sampling clock and supplies a common sampling clock to each of the AD converters 840 . Each of the AD converters 840 performs analog-to-digital conversion according to the common sampling clock supplied from the clock generator 842 . Therefore, all of the plurality of AD converters 840 that analog-to-digital convert the outputs of the 3-axis sensor units 300x to 300z provided at different positions perform synchronous operation. Thereby, the plurality of AD converters 840 can simultaneously sample the detection results of the three-axis sensor units 300x to z provided in different spaces.

Each of the plurality of calibration calculation units 850 is connected to a corresponding storage unit 860 , calibrates the measurement data from the AD converter 840 using calibration parameters, and outputs the calibrated data to the storage unit 860 . The outline of the calibration of the measurement data by the calibration calculator 850 is 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 triaxial magnetic sensor by the sensor units 300x, 300y, and 300z is V (Vx, Vy , Vz). In this case, assuming that the magnetic sensor characteristics of the triaxial magnetic sensor are a matrix S, the detection result V of the triaxial magnetic sensor can be expressed by the following equation.

Here, Sxx, Syy, and Szz represent the sensitivities of the sensor units 300x, 300y, and 300z in the main axis direction, respectively, and Sxy, Sxz, Syx, Syz, Szx, and Szy represent the sensitivities in the other axis directions. Vos,x, Vos,y, and Vos,z represent offsets in the main axis direction of the sensor units 300x, 300y, and 300z, respectively. Note that 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, so these offsets can be ignored. be.

Each of the sensor units 300 has linearity in the detection result for the input magnetic field in the range of the input magnetic field to be detected. Become. Further, even if the sensor unit 300 has multi-axis sensitivity, if the detection result of the sensor unit 300 has linearity, each element of the matrix S is an approximation irrelevant to the magnitude of the input magnetic field B. constant coefficient.

Therefore, the calibration calculation unit 850 uses the inverse matrix S ⁻¹ of the matrix S and the offset (Vos, x, Vos, y, Vos, z) to obtain the measurement data V (Vx, Vy , Vz) can be converted into magnetic field measurement data B (Bx, By, Bz) representing the original input magnetic field. Note that this conversion is also established when the sensor units 300x to 300z are provided with the magnetic flux concentrators described above. This is because the magnetic sensor cell 220 is configured as a three-axis magnetic sensor using the sensor units 300x to 300z, and conversion using linear algebra is possible.

The calibration calculation unit 850 uses the environmental magnetic field measurement data to calculate the inverse matrix S ⁻¹ of the matrix S and the offset (Vos, x, Vos, y, Vos, z), and the measurement data acquired by the measurement data acquisition unit 830 is converted into measurement data B using these calibration parameters and supplied to the storage unit 860 .

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

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

The estimation unit 870 estimates the current flowing through the living body 50 based on the measurement data from the storage unit 860 . The estimation unit 870 has a basis vector storage unit 880 , a signal space separation unit 890 and a calculation unit 895 .

The basis vector storage unit 880 is connected to the signal space separation unit 890, stores in advance the basis vectors necessary for the signal space separation unit 890 to separate the magnetic field measurement data B, and supplies them to the signal space separation unit 890. do.

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 measurement data output from the storage unit 860 into the magnetic field to be measured from the living body 50 and the disturbance magnetic field. . For example, the signal space separation unit 890 outputs the spatial distribution of the magnetic field indicated by the measurement data B when each of the plurality of magnetic sensors 520 detects a magnetic field having a spatial distribution of an orthonormal function with the magnetic sensor array 210. Signal separation is performed using the signal vectors as basis vectors. The signal space separation unit 890 acquires basis vectors necessary for signal separation from the basis vector storage unit 880 . Then, the signal space separation unit 890 uses the basis vectors acquired from the basis vector storage unit 880 to separate the spatial distribution of the magnetic field indicated by the measurement data B into the measurement target magnetic field and the disturbance magnetic field, and separates the disturbance magnetic field. Suppress and calculate the magnetic field to be measured. The signal space separating section 890 may calculate and output 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 arranged.

The calculator 895 receives data indicating the magnetic field to be measured from the signal space separator 890, and calculates the current value or conductivity in the living body 50 based on the magnetic field to be measured. The calculation unit 895 may calculate the distribution of current values or the distribution of conductivity in the living body 50 through which current is applied by the electrode pairs, from the magnetic fields to be measured at a plurality of positions on the surface of the living body 50 .

The calculation unit 895 may remove the magnetic field component generated from the lead wire 805 connected from the current application unit 810 to the electrode 800 from the measurement data before calculating the current value. The calculation unit 895 may store in advance magnetic field components caused by different lead wires 805 for each of a plurality of electrode pairs through which current flows during measurement. The calculator 895 may store the magnetic field generated by the lead wire 805 and cancel the stored magnetic field components from the measurement data. For example, the magnetic field generated by the lead wires is applied to the path of the lead wires connected to each electrode (eg, the lead wire 805 located on the living body 50, particularly in the region on the living body 50 facing the magnetic sensor array 210 during measurement). at least one of the length and position of ) and calculated from the path. Also, the magnetic field generated by the lead wire 805 may be obtained by pre-measuring the magnetic field generated by the lead wire 805 when current flows for each of the electrode pairs. Also, the magnetic field generated by the lead wire 805 may be estimated from the path of the lead wire 805 by performing a simulation.

FIG. 9 shows an arrangement example of a plurality of electrodes 800 of the measuring device 10 of this embodiment. In addition, FIG. 9 shows an example in which a current is passed through an electrode pair consisting of electrodes (3) and (4), and a measurement target site (for example, a tissue such as the stomach) is indicated by a dotted line. A plurality of electrodes 800(1) to (5) may be arranged on the surface of the living body 50 facing the measurement target site. The plurality of electrodes 800 are arranged side by side around the living body 50, and each has a vertically long shape with the circumferential direction (the X-axis direction in FIG. 9) of the living body 50 being the lateral direction. The length a of the plurality of electrodes 800 may each be longer than the length c of the measurement target region of the living body 50 in the longitudinal direction. Each electrode 800 has a horizontal length b smaller than a vertical length a, and the aspect ratio a/b may be in the range of 6-10, for example, the vertical length a is 200-300 mm and the horizontal length a is 200-300 mm. The width b may be 20-50 mm. The plurality of electrodes 800 may have the same length a in the longitudinal direction, and the plurality of electrodes 800 may have a shape such as a vertically long oval or rectangle, or may have the same shape as each other. For example, 8 to 16 electrodes 800 are in contact with the surface of the living body 50 on the side where the magnetic sensor array 210 is arranged, and are arranged side by side at regular intervals so as to surround the measurement target in the cross section (XZ plane) of the living body 50. may be placed.

The plurality of electrodes 800 may be attached to the surface of the living body 50 by, for example, using a seal or the like as an independent electrode. In addition, the plurality of electrodes 800 may be fixed to a waistband-shaped belt (fixing portion) in a state in which the contact surface is exposed. may

FIG. 10 shows an example in which the measurement apparatus 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 placed facing the electrodes 800 of the current application unit 100 at a position separated from the living body 50 by 20 to 50 mm, for example, without contacting the electrodes 800 of the current application unit 100 . The magnetic sensor array 210 may be arranged in a range shorter than the length of the plurality of electrodes 800 (length a in FIG. 9) in the longitudinal direction of the electrodes 800 . For example, the length between the magnetic sensor cells 220 at both ends in the Y-axis direction in the magnetic sensor array 210 may be shorter than the length of the electrode 800 in the Y-axis direction (length a in FIG. 9).

The magnetic sensor array 210 includes a plurality of magnetic sensor cells 220 in each of the X, Y, and Z directions (for example, 12 in the X direction, 8 in the Y direction, and 2 in the Z direction, for a total of 192 magnetic sensor cells). 220) are arranged on a curved surface. Each magnetic sensor cell 220 is arranged at each lattice point included in the curved shape in the three-dimensional lattice space. Here, the grid points are grid-like points provided at predetermined intervals (for example, intervals of 5 to 15 mm) in the X, Y, and Z directions. As an example, each magnetic sensor cell 220 is arranged along a curved surface that is convex in a direction orthogonal to one direction when viewed from any one of the X, Y, and Z directions. This figure shows an example in which each magnetic sensor cell 220 is arranged along a curved surface that is convex in the positive direction of the Z axis when viewed from the Y direction. At this time, the magnetic sensor array 210 is arranged, for example, in the negative direction of the Z axis as much as possible within a range in which each vertex of each magnetic sensor cell 220 does not exceed a predetermined curved surface having a convexity in the positive direction of the Z axis. By arranging each magnetic sensor cell 220 at each lattice point in the three-dimensional lattice space, a curved surface shape convex in the positive direction of the Z-axis may be formed.

The measuring apparatus 10 is configured such that the center position in the Y-axis direction coincides with the center position of the plurality of electrodes 800 and/or the measurement target region, and the center position of the measurement target region of the living body 50 in the X-axis direction is positioned at the center of the curved surface. , the magnetic sensor array 210 is arranged to measure the magnetic field. As a result, the measurement apparatus 10 performs 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, so that the magnetic field to be measured and the disturbance magnetic field can be separated with high accuracy. can. At this time, it is preferable that the curvature of the curved surface of the magnetic sensor array 210 is approximately the same as the curvature around the chest of the subject, because 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.

FIG. 11 shows the current distribution in the living body 50 during measurement by the measuring device 10 of this embodiment. In FIG. 11, current flow is indicated by dotted lines. Since the electrodes 800 of the measuring device 10 have a vertically long shape, it is possible to reduce the three-dimensional diffusion of the current between the electrodes 800 (3) and (4) serving as the electrode pair, and the current around the measurement target site can be reduced. Density can be increased. Therefore, the measuring device 10 can accurately detect the magnetic field from the measurement target site.

FIG. 12 shows the current distribution between the electrodes 807 of the comparative example. In FIG. 12, current flow is indicated by dotted lines. In FIG. 12, electrodes 807(1), 807(2), 807(3) are each square and current is passed between electrode 807(1) and electrode 807(2). As shown in FIG. 12, the current flows while diffusing three-dimensionally in the living body 50, resulting in a low current density around the measurement target site.

FIG. 13 shows a cross section parallel to the XZ plane of part of the measuring device 10 of this embodiment. In FIG. 13 , dotted arrows in the living body 50 schematically indicate secondary current flows in the living body 50 . The measuring device 10 has the plurality of electrodes 800 in contact with the living body 50 and the magnetic sensor array 210 detects an input magnetic field on one side of the living body 50 . The measuring device 10 causes an alternating current to flow through an electrode pair consisting of, for example, two electrodes 800 ( 3 ) and ( 4 ), thereby causing a secondary current to flow within the living body 50 . The measuring device 10 can detect the magnetic field generated while the alternating current is flowing through the electrode pair with the magnetic sensor array 210, and calculate the current distribution in the living body 50 from the detected magnetic field.

FIG. 14 shows the distribution of the magnetic field and current detected by the measuring device 10 of this embodiment in a cross section parallel to the XZ plane. The signal space separation unit 890 of the measurement apparatus 10 of the present embodiment calculates the magnetic field to be measured at M (M≧1) magnetic field positions 1200 on the surface of the living body 50 based on the magnetic field detected by the magnetic sensor array 210. be able to. Accordingly, the calculation unit 895 can calculate the currents J1 to JN at N (N≧1) positions (voxels) in the living body 50 using the magnetic fields of the M magnetic field positions 1200 . The magnetic field position 1200 may be substantially the same as the center position of the measurement target region in the Y-axis direction, and may be within the length range of the electrode 800 or substantially the same as the center position.

FIG. 15 shows a measurement flow of the measuring device 10 according to this embodiment.

At step 1300, the basis vector storage unit 880 stores the basis vectors. As an example, the basis vector storage unit 880 stores signal vectors output by each of the plurality of magnetic sensors 520 when a magnetic field having a spatial distribution of spherical harmonics is detected by the magnetic sensor array 210 before measurement of the magnetic field to be measured. Store as basis vectors. That is, the basis vector storage unit 880 stores, as basis vectors, magnetic field signal vectors obtained by spatially sampling the spherical harmonics when a predetermined point in space is specified as the coordinate origin. Here, the spherical harmonic function is a function obtained by restricting a homogeneous polynomial, which is a solution of the n-dimensional Laplace's equation, to the 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 (step 1330) by the measuring device 10. FIG. Also, the basis vector storage unit 880 may store signal vectors that are predetermined based on simulation results or the like as basis vectors.

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

The current applying unit 810 applies an alternating current having the same frequency as the synchronization signal to the living body 50 through the electrode pair during the period during which the synchronization signal is received. Measurement data may be acquired at The current applying section 810 may apply a current to an electrode pair consisting of two adjacent electrodes among the plurality of electrodes 800 to flow the current through the living body 50 . For example, the current applying unit 810 may sequentially apply a current to an electrode pair consisting of two adjacent electrodes 800 while shifting the electrodes 800 one by one, thereby causing the current to flow through the living body 50 .

Specifically, the current applying unit 810 includes electrodes 800(1) and (2), electrodes 800(2) and (3), electrodes 800(3) and (4), and electrode 800(4) in FIG. and (5), electrodes 800 (5) and (6), electrodes 800 (6) and (7), electrodes 800 (7) and (8), electrodes 800 (8) and (9), electrodes 800 (9) and (10) in the order of the electrode pairs, by switching the electrode pairs with a relay or the like every one or a plurality of periods of the synchronization signal to flow the current, the current may flow to the living body 50 from all combinations of the electrode pairs.

The measurement data acquisition section 830 may acquire only the same frequency as the synchronization signal for the measurement data measured for each electrode pair. The measurement data acquisition section 830 may filter the measurement data with an analog low-pass filter and output the filtered data.

The plurality of AD converters 840 each analog-to-digital converts the acquired measurement data and outputs them. The calibration calculation section 850 may calibrate the acquired measurement data and output it to the storage section 860 . Calibration calculator 850 may filter the measurement data with a digital low-pass filter before calibration. The signal space separation section 890 acquires the calibrated measurement data B from the storage section 860 .

At step 1320 , the signal space separation section 890 acquires from the basis vector storage section 880 the signal vectors stored as basis vectors by the basis vector storage section 880 at step 1300 . In this flow, either step 1310 or step 1320 may be performed first.

In step 1330, the signal space separator 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 vectors acquired in step 1320 as basis vectors. Then, the signal space separation unit 890 separates the spatial distribution of the magnetic field into the magnetic field to be measured and the disturbance magnetic field from the vector obtained by the series expansion. Note that the orthonormal functions may be spherical harmonic functions. Further, the signal space separation unit 890 calculates the coefficients of the basis vectors by the method of least squares when separating the signals.

Then, in step 1340 , the signal space separation section 890 suppresses the disturbance magnetic field based on the result of 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.

The static magnetic field B(r) is determined as the spatial gradient of the potential V(r) as follows using the potential V(r) that satisfies the Laplace equation Δ·V(r)=0. Here, r is a position vector representing a position from the coordinate origin, Δ is the Laplacian, μ is magnetic permeability, and ∇ is an operator representing vector differential operation.

Since the solution of Laplace's equation generally has a solution in the form of a series expansion using spherical harmonic functions Yl,m(θ,φ), which is an orthonormal function system, the potential V(r) is given by the following equation: can be represented. where |r| is the absolute value of the position vector r (distance from the coordinate origin), θ and φ are the two declination angles in spherical coordinates, l is the azimuthal quantum number, and m is the magnetic quantum number. , α and β are multipolar moments, and Lin and Lout are series numbers for the space in front of and behind the magnetic sensor array 210 when viewed from the living body 50 , respectively. The azimuthal quantum number l takes a positive integer, and the magnetic quantum number m takes 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 from 0. The first term in (Equation 7) is a term that is inversely proportional to the distance from the coordinate origin, and indicates the potential that exists in the space in front of the magnetic sensor array 210 when viewed from the living body 50 . The second term in (Equation 7) is a term that is proportional to the distance from the coordinate origin, and indicates the potential that exists in the space behind the magnetic sensor array 210 as viewed from the living body 50 .

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

When the solution of Laplace's equation is expressed in the form of a series expansion using spherical harmonics, the general solution is an infinite series, but the SNR (signal-to-noise ratio, i.e., It is sufficient to obtain the ratio of the magnetic field signal to be measured to the disturbance magnetic field and the sensor noise, and in fact, it is said that a series of about 10 terms is sufficient. In addition, it is said that about Lin=8 and Lout=3 are sufficient for the series of spatial signal separation in magnetoencephalography, for example. Therefore, also 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 values sufficient to sufficiently suppress the disturbance magnetic field and calculate only the magnetic field to be measured.

Here, let nx, ny, and nz be vectors representing the magnetosensitive axis directions and magnetic sensitivities of sensor units 300x, y, and z in each magnetic sensor cell 220, respectively, and subscript t be a transposed matrix, and al, m, and bl,m are defined as follows. That is, al, m and bl, m are the respective vectors nx, ny, and nz representing the magnetosensitive axis directions and magnetic sensitivities of the sensor units 300 x, y, and z, and spherical harmonic functions that are three-dimensional vector signals. is defined as a vector whose components are inner products of . This means that in each magnetic sensor cell 220 the spherical harmonics are sampled in a Cartesian coordinate system. Note that the al, m and bl, m are vectors having dimensions that are three times the number of the magnetic sensor cells 220 . The vectors nx, ny, and nz representing the magnetosensitive axis direction and the magnetic sensitivity of each sensor unit 300 may be vectors corresponding to the above-described sensitivity in the main axis direction and the sensitivity in the other axis direction. nx may correspond to Sxx, Sxy, Sxz. ny may correspond to Syx, Syy, Syz. nz may correspond to Szx, Szy, Szz. Thus, the values of al,m and bl,m calculated including the principal axis sensitivities and the other axis sensitivities corrections of the sensor units 300 x, y, and z are stored in the basis vector storage unit 880 . The magnetic measurement device 10 according to the present 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), during operation By correcting the acquired measurement data in the calibration calculation section 850, the magnetic sensitivity (main axis sensitivity, other axis sensitivity) of each magnetic sensor cell 220 can be corrected.

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

Further, Sin, Sout, Xin, and Xout are defined as follows. That is, a total of Lin·(Lin+2) columns of vectors, in which each vector a when Sin is an integer from l=1 to l=Lin and m=-l to l is arranged in order in each l defined as In addition, Sout is a vector of Lout (Lout+2) columns in which each vector b when taking an integer from l = 1 to L = Lout and m = -l to l for each l is arranged in order. defined as In addition, Xin is a total of Lin· Define a vector with (Lin+2) rows. In addition, Xout is a total of Lout· Define a vector with (Lout+2) rows.

Then, the sensor output vector Φ can be expressed in the form of the inner product of the matrix S and the column vector X as shown in the following equation. Here, the matrix S indicates the basis vectors, which the signal space separator 890 obtained from the basis vector storage 880 in step 1320, for example. A vertical vector X indicates coefficients related to basis vectors.

Based on the model formula of the sensor output vector Φ obtained by (Equation 12), the following equation is used to determine the vertical vector X that satisfies Φ=S·X by least-squares approximation. Thereby, the signal space separating section 890 can solve the spatial distribution of the magnetic field.

In this embodiment, as shown in FIG. 14, when calculating the magnetic field at a plurality of magnetic field positions 1200 on the surface of the living body 50, the sensor Based on the output vector Φ, the magnetic field at vector r at the plurality of magnetic field positions 1200 can be calculated. In (Equation 14), the first term indicates the magnetic field to be measured at the magnetic field position 1200 on the surface of the living body 50, and the second term indicates the disturbance magnetic field.

The signal space separator 890 according to the present embodiment can calculate the magnetic field using (Formula 14) for each of the plurality of magnetic field positions 1200(1) to (M). The signal space separator 890 outputs the result of suppressing the disturbance magnetic field component (that is, the component of the second term in (Formula 14)). The signal space separator 890 may output only the magnetic field to be measured in the vector r of the magnetic field position 1200, that is, the first term component in (Equation 14).

Next, at step 1350 , the calculator 895 calculates the current flowing in the living body 50 based on the magnetic field data B of the magnetic field component to be measured from the signal space separator 890 . The calculator 895 may obtain N currents J1 to JN as shown in FIG. 11 from the M magnetic field data B1 to BM from the signal space separator 890 . First, the forward problem of converting a current into a magnetic field can be expressed using the lead field matrix L as shown in (Equation 15). Here, the magnetic fields B1-BM and the currents J1-JN are respectively three-dimensional vectors. The values of the matrix elements of the lead field matrix L may be calculated by finite element method (FEM) modeling the living body 50 . Note that the calculation unit 895 may similarly calculate the current based on the detected magnetic field B of the magnetic sensor array 210 instead of the magnetic field B to be measured at the magnetic field position 1200 .

After calculating the lead field matrix by the forward problem, the calculator 895 may calculate the N currents J1 to JN as the inverse problem. Calculation unit 895 can calculate currents J1 to JN according to equation (17) so as to minimize the squared error as shown in (16) in the inverse problem.

Further, in step 1350, the calculation unit 895 calculates the conductivity σ in the living body 50 based on the magnetic field data B of the magnetic field component to be measured from the signal space separation unit 890 instead of or in addition to the current value J. good. From the M magnetic field data B1 to BM from the signal space separation unit 890, the calculation unit 895 calculates the conductivities σ1 to σN may be determined. First, the forward problem of transforming the conductivity σ into the magnetic field B can be expressed as (Equation 18) using the lead field matrix A for estimating the conductivity distribution. Here, each of the magnetic fields B1 to BM is a three-dimensional vector. The values of the matrix elements of the lead field matrix A may be calculated by a finite element method (FEM) modeling the living body 50 . Note that the calculation unit 895 may similarly calculate the conductivity σ based on the magnetic field B detected by the magnetic sensor array 210 instead of the magnetic field B to be measured at the magnetic field position 1200 .

After calculating the lead field matrix by the forward problem, the calculator 895 may calculate N conductivities σ1 to σN as the inverse problem. The calculation unit 895 can calculate the conductivities σ1 to σN using the equations shown in (20) so as to minimize the square error as shown in (19) in the inverse problem.

The calculation unit 895 may remove the magnetic field component caused by the lead wire 805 from the measurement data measured for each electrode pair before calculating the current or conductivity. The calculation unit 895 may determine the path of the lead wire 805 and acquire the component of the magnetic field caused by the lead wire 805 from the determined path by performing inverse calculation of the current calculation described above. The calculator 895 may, for example, calculate the component of the magnetic field caused by the lead wire 805 using the Biot-Savart equation from the determined path of the lead wire 805 and the current value. Further, the calculator 895 may, for example, calculate back the components of the magnetic field detected by the magnetic sensor array 210 using (Equation 15) to (Equation 17) from the value of the current flowing through the determined path. The calculation unit 895 further calculates the components of the magnetic field generated from the electrodes 800 (in particular, the electrodes 800 placed on the region of the living body 50 facing the magnetic sensor array 210) as well as the components of the magnetic field generated from the lead wire 805. It may be calculated and removed from the measurement data.

As described above, the calculation unit 895 can calculate currents or conductivities at a plurality of positions within the living body 50 and output current density distributions or conductance distributions within the living body 50 . Step 1310 may be repeatedly performed, and similarly, acquisition of measurement data for each current pair may be repeated after acquisition of measurement data corresponding to all electrode pairs. Steps 1330-1350 may be performed in parallel with step 1310, and calculation results can be output in real time while applying current and measuring the magnetic field. In addition, the measurement apparatus 10 of the present embodiment uses a part of the EIT technology on the display of the information processing unit 30, for example, to display an image ( For example, an xz-plane cross-sectional image of the living body 50 surrounded by the electrodes 800 or a cylindrical three-dimensional image including the cross-section can be generated and displayed in a multivalued manner.

The measurement apparatus 10 of the present embodiment can suppress the disturbance magnetic field by the signal space separating section 890 and detect the magnetic field on the outer surface of the living body 50 with high accuracy. Since the measuring device 10 of the present embodiment can calculate the magnetic fields at many positions on the outer surface of the living body 50 based on the magnetic field detection results of the magnetic sensor array 210, the resolution can be improved. Moreover, since the measurement apparatus 10 of the present embodiment uses the magnetic field detection result of the magnetic sensor array 210 , it is possible to perform measurement independent of the surface state and movement of the living body 50 .

FIG. 16 shows another example of arrangement of the current applying unit 100 and the magnetic sensor unit 110 in the measuring device 10 of this embodiment. The plurality of vertically elongated electrodes 800 of the current applying unit 100 of FIG. 16 are arranged only on one side of the living body 50, unlike the plurality of electrodes 800 arranged all around the living body 50 in FIGS. be done. The plurality of electrodes 800 of the current applying unit 100 are arranged so as to contact the surface of the living body 50 opposite to the side on which the magnetic sensor unit 110 is arranged. The current applying unit 100 and the magnetic sensor unit 110 are attached to a waistband-shaped fixing portion 1500 and fixed to the living body 50 . Fixing part 1500 may have a cylindrical shape in which the diameter of the hollow portion can be changed. may be fixed in positional relationship with at least a portion of 16 may not have the head 120, the drive section 125, the base section 130, and the pole section 140 shown in FIG.

The measuring device 10 acquires the difference ΔB in the magnetic field data at the time of measurement from the magnetic flux density in a predetermined reference state, and uses the lead field matrix L or A to calculate the difference ΔJ in current or the difference Δσ in conductivity. It may be calculated by the formula ΔB=LΔJ or ΔB=AΔσ. The magnetic flux density in the reference state may be the magnetic flux density obtained by simulating the inside of the living body 50 as uniform, or the magnetic flux density measured in a previous measurement. The method of measuring the magnetic flux density in the reference state and the magnetic flux density during measurement may be the same as described above, and the method of calculating the current or conductivity may also be the same as described above. Further, the current or conductivity is calculated from the magnetic flux density in the reference state and the magnetic field data at the time of measurement, and the current or conductivity at the time of measurement is subtracted from the current or conductivity in the reference state to obtain ΔJ or Δσ. can be calculated. By calculating the change in the current density distribution or conductivity distribution in the living body from such a change in the magnetic flux density, it is possible to reduce disturbance factors such as the magnetic field caused by the lead wire 805 connected to the electrode 800, and the calculated current Alternatively, a highly accurate image can be generated from the conductivity.

The plurality of electrodes 800 of the current application unit 100 and the magnetic sensor unit 110 may be arranged only on the same side of the living body 50. In this case, the plurality of electrodes 800 are arranged on the surface of the living body 50 It may be arranged between the magnetic sensor unit 110 and in contact with the surface.

Various embodiments of the invention may be described with reference to flowchart illustrations and block diagrams, where blocks refer to (1) steps in a process in which operations are performed or (2) devices responsible for performing the operations. may represent a section of Certain steps and sections may be implemented by dedicated circuitry, programmable circuitry provided with computer readable instructions stored on a computer readable medium, and/or processor provided with computer readable instructions stored on a computer readable medium. you can Dedicated circuitry may include digital and/or analog hardware circuitry, and may include integrated circuits (ICs) and/or discrete circuitry. Programmable circuits include logic AND, logic OR, logic XOR, logic NAND, logic NOR, and other logic operations, memory elements such as flip-flops, registers, field programmable gate arrays (FPGAs), programmable logic arrays (PLAs), etc. and the like.

Computer-readable media may include any tangible device capable of storing instructions to be executed by a suitable device, such that computer-readable media having instructions stored thereon may be designated in flowcharts or block diagrams. It will comprise an article of manufacture containing instructions that can be executed to create means for performing the operations described above. 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 include floppy disks, diskettes, hard disks, random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM or flash memory), Electrically Erasable Programmable Read Only Memory (EEPROM), Static Random Access Memory (SRAM), Compact Disc Read Only Memory (CD-ROM), Digital Versatile Disc (DVD), Blu-ray (RTM) Disc, Memory Stick, Integration Circuit cards and the like may be included.

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

Computer readable instructions may be transferred 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 wide area network (WAN), such as a local area network (LAN), the Internet, or the like. ) and may be executed 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, and the like.

FIG. 17 illustrates an example computer 2200 upon which aspects of the invention may be implemented in whole or in part. Programs installed on the computer 2200 may cause the computer 2200 to function as one or more sections of an operation or apparatus associated with an apparatus according to embodiments of the invention, or may Sections may be executed and/or computer 2200 may be caused to execute processes or steps of such processes according to embodiments of the present invention. Such programs may be executed by CPU 2212 to cause computer 2200 to perform certain operations associated with some or all of the blocks in the flowcharts and block diagrams described herein.

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

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

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

ROM 2230 stores therein programs that are dependent on the hardware of computer 2200, such as a boot program that is executed by computer 2200 upon activation. Input/output chip 2240 may also connect various input/output units to input/output controller 2220 via parallel ports, serial ports, keyboard ports, mouse ports, and the like.

A program is provided by a computer-readable medium such as a DVD-ROM 2201 or an IC card. The program is read from a computer-readable medium, installed in hard disk drive 2224 , RAM 2214 , or ROM 2230 , which are also examples of computer-readable medium, and executed by CPU 2212 . The information processing described within these programs is read by computer 2200 to provide coordination between the programs and the various types of hardware resources described above. An apparatus or method may be configured by implementing the manipulation or processing of information in accordance with the use of computer 2200 .

For example, when communication is performed between the computer 2200 and an external device, the CPU 2212 executes a communication program loaded into the RAM 2214 and sends communication processing to the communication interface 2222 based on the processing described in the communication program. you can command. The communication interface 2222 reads transmission data stored in a transmission buffer processing area provided in a recording medium such as the RAM 2214, the hard disk drive 2224, the DVD-ROM 2201, or an IC card under the control of the CPU 2212, and transmits the read transmission data. Data is transmitted to the network, or received data received from the network is written to a receive buffer processing area or the like provided on the recording medium.

In addition, the CPU 2212 causes the RAM 2214 to read all or necessary portions of files or databases stored in external recording media such as a hard disk drive 2224, a DVD-ROM drive 2226 (DVD-ROM 2201), an IC card, etc. Various types of processing may be performed on the data in RAM 2214 . CPU 2212 then writes back the processed data to the external recording medium.

Various types of information, such as various types of programs, data, tables, and databases, may be stored on recording media and subjected to information processing. CPU 2212 performs various types of operations on data read from RAM 2214, information processing, conditional decision making, conditional branching, unconditional branching, and information retrieval, as specified throughout this disclosure and by instruction sequences of programs. Various types of processing may be performed, including /replace, etc., and the results written back to RAM 2214 . In addition, the CPU 2212 may search for information in a file in a recording medium, a database, or the like. For example, if 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 determines that the attribute value of the first attribute is specified. search the plurality of entries for an entry that matches the condition, read the attribute value of the second attribute stored in the entry, and thereby associate it with the first attribute that satisfies the predetermined condition. an attribute value of the second attribute obtained.

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

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 obvious 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 scope of claims that forms with such modifications or improvements can also be included in the technical scope of the present invention.

The execution order of each process such as actions, procedures, steps, and stages in the devices, systems, programs, and methods shown in the claims, the specification, and the drawings is particularly "before", "before etc., and it should be noted that they can be implemented in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the specification, and the drawings, even if the description is made using "first," "next," etc. for the sake of convenience, it means that it is essential to carry out in this order. not a thing

10 Measurement device 20 Main unit 30 Information processing unit 50 Living body 100 Current application unit 110 Magnetic sensor unit 120 Head 125 Driving unit 130 Base unit 140 Pole unit 210 Magnetic sensor array 220 Magnetic sensor cell 230 Sensor data collecting unit 300 Sensor unit 520 Magnetic sensor 530 Magnetic field generation unit 532 Amplifier circuit 534 Coil 540 Output unit 702 Magnetoresistive element 704 Magnetic converging plate 706 Magnetic concentrating plate 800 Electrode 805 Lead wire 807 Electrode 810 Current application unit 820 Control unit 830 Measurement data acquisition unit 840 AD converter 842 Clock generator 850 Calibration calculation unit 860 Storage unit 870 Estimation unit 880 Basis vector storage unit 890 Signal space separation unit 895 Calculation unit 1200 Magnetic field position 1500 Fixed unit 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 (14)

an electrode unit having a plurality of vertically elongated electrodes arranged side by side around a living body and having a lateral direction in the circumferential direction of the living body;
a magnetic sensor array having a plurality of magnetic sensor cells and capable of detecting input magnetic fields in three axial directions at a plurality of locations in a three-dimensional space;
a current applying unit that applies a current to the living body using at least one electrode pair of the plurality of electrodes;
a measurement data acquisition unit that acquires measurement data based on the input magnetic field detected from the living body by the magnetic sensor array while current is flowing through the living body;
An estimating unit that estimates current flowing in the living body or conductivity in the living body based on the measurement data. The measuring device according to claim 1, wherein each of the plurality of electrodes is longer in the longitudinal direction than the length of the measurement target site of the living body. The measuring device according to claim 1 or 2, wherein the plurality of electrodes have the same longitudinal length. The measuring device according to any one of claims 1 to 3, wherein the magnetic sensor array is arranged without contact with the electrode unit. The measuring device according to claim 4, wherein the magnetic sensor array is arranged to face the electrode unit. The measuring device according to any one of claims 1 to 5, wherein the magnetic sensor array is arranged in a range shorter than the length of the plurality of electrodes in the longitudinal direction of the plurality of electrodes. The measuring device according to any one of claims 1 to 6, wherein the current applying section 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, further comprising a control section that synchronizes current flowing through the living body by the at least one electrode pair and acquisition of the measurement data by the measurement data acquisition section. The measurement apparatus according to any one of claims 1 to 8, wherein the measurement data acquisition unit removes magnetic field components generated from lead wires connected to the plurality of electrodes from the measurement data. 10. The current applying unit according to any one of claims 1 to 9, wherein the current applying unit sequentially applies a current to an electrode pair consisting of two adjacent electrodes while shifting the electrodes one by one to pass the current to the living body. measuring device. The estimation unit
A signal space separation unit that separates the spatial distribution of the magnetic field indicated by the measurement data into a magnetic field to be measured from the living body and a disturbance magnetic field;
11. The measuring device according to any one of claims 1 to 10, further comprising a calculation unit that calculates a current value of current flowing in the living body or a conductivity in the living body based on the separated magnetic field to be measured. each of the plurality of magnetic sensor cells has a plurality of magnetic sensors each having a magnetoresistive element and a magnetic flux converging plate disposed at both ends of the magnetoresistive element;
The signal space separation unit separates the spatial distribution of the magnetic field from signal vectors output by each of the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function as a basis vector. Item 12. The measuring device according to item 11. applying a current to the living body by at least one electrode pair of a plurality of vertically elongated electrodes arranged side by side around the living body and having a lateral direction in the circumferential direction of the living body;
detecting an input magnetic field in three axial directions at a plurality of locations in a three-dimensional space with a magnetic sensor array having a plurality of magnetic sensor cells while current is flowing through the living body;
obtaining measurement data based on the input magnetic field detected from the living body by the magnetic sensor array;
and estimating current flowing in the living body or conductivity in the living body based on the measurement data. executed by a computer to cause said computer to:
A three-dimensional space is generated while an electric current is being supplied to the living body by at least one electrode pair among a plurality of vertically elongated electrodes arranged side by side around the living body and having a lateral direction in the circumferential direction of the living body. The spatial distribution of the magnetic field indicated by the measurement data based on the input magnetic field detected from the living body by a magnetic sensor array capable of detecting the input magnetic field in three axial directions at multiple points in the living body, and the magnetic field to be measured and the disturbance magnetic field from the living body. a signal space separation unit that separates into
a calculation unit that calculates the current value of the current flowing in the living body or the conductivity in the living body based on the separated magnetic field to be measured;
A program to function as

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