JP2795211B2 - Biomagnetic measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biomagnetism measuring apparatus for detecting weak magnetism generated from a living body and forming an image of the weak magnetism to provide medically useful diagnostic information.

[0002]

2. Description of the Related Art When a living body is stimulated, the polarization formed across a cell membrane is broken and a living activity current flows. This biological activity current appears in the brain and heart, and is recorded as an electroencephalogram and an electrocardiogram. The magnetic field generated by the biological activity current is recorded as a magnetoencephalogram and a magnetocardiogram.

In recent years, as a device for measuring a minute magnetic field in a living body, a SQUID (Superconducting Quantum Interf
(ace Device: superconducting quantum interferometer). By placing this sensor outside the head, it is possible to non-invasively measure a minute magnetic field due to a biological activity current generated in the brain. Such measurement is performed at many measurement points, and the magnetic field strength of many points on the measurement surface including the measurement points is obtained by spline interpolation or the like, and the points having the same magnetic field strength are connected as shown in FIG. A simple isomagnetic field diagram can be obtained. The isomagnetic field diagram shown in this figure is obtained by detecting the magnetic field intensity generated by a single current dipole (current source). In the figure, white circles indicate measurement points, and black circles indicate magnetic fields obtained by interpolation. There are a number of grid points on the measurement plane for which the intensity is calculated. Such an isomagnetic field map provides medically useful diagnostic information such as a rough positional relationship of the biological activity current source.

[0004]

However, the prior art having such a structure has the following problems. That is, according to the conventional example, since the magnetic field strengths on a large number of grid points on the measurement surface are obtained by interpolation, for each grid point located outside the area where the measurement points (magnetic sensors) are arranged, Actual measurement data referenced during the interpolation processing is reduced. Therefore, the magnetic field strength obtained by interpolation for the grid points outside the measurement area contains many errors. As a result, for example, a diagram may appear as if a current source that does not actually exist is present in a region outside the measurement region in the obtained isomagnetic field diagram.

[0005] The present invention has been made in view of such circumstances, and a magnetic field intensity is accurately obtained even in a region outside a region where a magnetic sensor is arranged, so that a highly reliable isomagnetic field diagram is obtained. It is an object of the present invention to provide a biomagnetism measurement device capable of obtaining the above.

[0006]

The present invention has the following configuration to achieve the above object. That is, the biomagnetism measuring apparatus according to the present invention is (a) disposed at each position (measurement point) of the subject close to the diagnosis target area, and measures a minute magnetic field by a biological activity current source in the diagnosis target area. A plurality of magnetic sensors; (b) measured magnetic field intensities at each measurement point measured by each of the magnetic sensors; and a unit size on a number of lattice points (lattice points in the subject) assumed in the diagnosis target area. And a known coefficient group related to the magnetic field strength detected by each of the magnetic sensors when the current source is placed, based on the magnitude and direction of the current source on each of the lattice points in the subject. Current source calculating means for calculating a physical quantity; and (c) a physical quantity of a current source on each intra-subject grid point obtained by the current source calculating means, and a unit-size current source on each intra-subject grid point. Each magnetic sensor Field strength calculation for calculating the magnetic field strength on each measurement plane grid point based on a known group of coefficients related to the magnetic field strength generated at each of a large number of grid points (measurement plane grid points) on the measurement plane Means; and (d) image processing means for obtaining an isomagnetic field map by sequentially connecting grid points having the same magnetic field strength among the grid points of the measurement plane obtained by the magnetic field strength calculating means. It is characterized by.

[0007]

The operation of the present invention is as follows. The known magnetic field intensity at each measurement point measured by each magnetic sensor and the magnetic field intensity detected by each magnetic sensor when assuming that a unit-sized current source is placed on a number of lattice points in the subject Based on these coefficient groups, physical quantities such as the size and direction of the current source on each intra-subject grid point are calculated. Then, the magnetic field intensity at each measurement plane lattice point generated by each current source on these intra-subject lattice points is obtained by the magnetic field intensity calculation means. That is, the magnetic field strength at each measurement plane grid point is not calculated by interpolation of the magnetic field strength at each measurement point.
This is obtained by calculating the magnetic field strength at each measurement plane lattice point generated by these current sources. Therefore, since the magnetic field strength of each measurement plane grid point in the area deviating from the area where the magnetic sensor is placed can be obtained relatively accurately, the isomagnetic field map created by the image processing means is highly reliable. Become.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the biomagnetism measuring apparatus according to the present invention.

In FIG. 1, reference numeral 1 denotes a magnetically shielded room, in which a bed 2 on which a subject M is supine and a diagnosis target area of the subject M, for example, a brain, are arranged in close proximity. Multi-channel SQ for non-invasive measurement of minute magnetic field generated by a biological activity current source generated inside
A UID sensor 3 is provided. In the multi-channel SQUID sensor 3, a plurality of magnetic sensors arranged two-dimensionally are immersed in a refrigerant such as liquid nitrogen and stored in a container called a Dewar. Each magnetic sensor is composed of a coil body in which a pair of coils consisting of a detection coil and a compensation coil are arranged one-dimensionally or three-dimensionally, and a SQUID element connected thereto. In this embodiment, each magnetic sensor (particularly, the coil body) is arranged on a spherical surface, and this surface is hereinafter referred to as a measurement surface.
The position of each magnetic sensor on the measurement surface is referred to as a measurement point.

The magnetic field data at each measurement point detected by the multi-channel SQUID sensor 3 is
Is converted into digital data and collected by the data collection unit 5. The stimulating device 6 is for giving an electrical stimulus (or a sound, a light stimulus, or the like) to the subject M. The positioning unit 7 is a device for grasping the positional relationship of the subject M with respect to the three-dimensional coordinate system with reference to the multi-channel SQUID sensor 3. For example, small coils are attached to a plurality of locations of the subject M,
Power is supplied to these small coils from the positioning unit 7. Then, the magnetic field generated from each coil is detected by the multi-channel SQUID sensor 3 to grasp the positional relationship of the subject M with respect to the multi-channel SQUID sensor 3. In addition, multi-channel SQUID
Other methods for ascertaining the positional relationship of the subject M with respect to the sensor 3 include a method in which a projector is attached to a dewar to irradiate the subject M with a light beam and the relationship between the two is grasped. No.-237065, JP-A-6-7
Various techniques disclosed in, for example, US Pat.

A data analysis unit 8, which is a main part of the present embodiment, includes a current source calculation unit 9 which calculates a current source in a diagnosis target area of the subject M based on magnetic field data collected by the data collection unit 5. And a magnetic field strength calculating unit 10 for calculating a magnetic field strength on the measurement surface based on the current source, an image processing unit 11 for creating an isomagnetic field map from a calculation result of the magnetic field strength on the measurement surface, and the like. I have. The color monitor 12 and the color printer 13 are for displaying or printing out the isomagnetic field diagram and the like obtained by the data analysis unit 8.

Hereinafter, a description will be given centering on the processing for creating an isomagnetic field map executed by the data analysis unit 8 with reference to the flowchart shown in FIG.

Step S1: Multi-channel SQUI
After the positional relationship between the D sensor 3 and the subject M is set, the multi-channel SQUID sensor 3 measures a minute magnetic field (magnetic field intensity at each measurement point) generated by a biological activity current source in the diagnosis target area of the subject M. Then, the obtained magnetic field data of each measurement point is collected in the data collection unit 5.
When the data collection is completed, the process proceeds to the process of the current source calculation unit 9 shown in step S2.

Step S2: As shown in FIG.
A large number of grid points (grid points in the subject) N _j (j = 1 to n) are set in the diagnosis target area (for example, the brain M ′). The symbol P ₀ in FIG. 3 is a true current source existing in the brain M ′, and S _i (i = 1 to m) is a multi-channel SQUID.
Plural (m) magnetic sensors constituting sensor 3, PL
Is a measurement surface. An unknown current source (current dipole) P _j (j = 1 to n) is placed on these lattice points Nj as shown in FIG.
And each current source Pj is calculated by the following arithmetic processing.

Assuming that a current source P _j is present on each in-subject lattice point N _j , a magnetic field Bi (i = 1) detected by each magnetic sensor Si of the multi-channel SQUID sensor 3
To m) are represented by the following equation (1).

[0016]

(Equation 1)

In the above equation (1), α _ij (i = 1 to m,
j = 1 to n) is a known coefficient group that represents the magnetic field intensity detected at each position of the magnetic sensor S _i when placing the current source unit magnitude on each subject in the lattice point N _j is there. here,
Each element of the above equation (1) is represented as follows.

[0018]

(Equation 2)

Then, the above equation (1) can be expressed by a linear relational equation such as the following equation (2). [B] = A [P] (2)

Here, when the inverse matrix of A is represented by A ⁻ ,
[P] is represented by the following equation (3). [P] = A ^- [B] ... (3)

In the simultaneous equations represented by the above equation (3), the number of unknowns n (the number of current sources) is larger than the number m of equations (the number of magnetic sensors), and therefore no solution is obtained. Therefore,
A condition is added to minimize the norm | P | of the vector [P]. Then, the above equation (3) is expressed as the following equation (4). [P] = A ⁺ [B] (4)

In the above equation (4), A ⁺ is a generalized inverse matrix represented by the following equation (5). A ⁺ = A ^t (AA ^t ) ^-1 (5)

By solving the above equations (4) and (5), the physical quantity (magnitude, direction) of each current source P _{j at} the intra-subject lattice point N _j set inside the diagnosis target area of the subject M is obtained. Can be requested. The obtained current source P _j is close to the true current source P ₀ .

Note that the current source P _j on the lattice point N _j in the subject is
Is not limited to the method described above (generally called the minimum norm method). For example, for example, an actually measured magnetic field data and a virtual current source having a different size and direction at each lattice point in the subject are sequentially placed. The physical quantity of each current source may be calculated using the condition that the root mean square error with the simulation magnetic field data measured in this case is minimized. Current source P _i
Is calculated, the process proceeds to the process of the magnetic field strength calculation unit 10 shown in step S3.

[0025] Step S3: generated by the current source P _j on the subject in the lattice points, a number of lattice points assumed on a measurement surface PL (measurement surface grid point: code Q _{k (k} = 1~ in FIG
The magnetic field strength B _k at each position indicated by q)) is calculated by the following equation (6).

[0026]

(Equation 3)

In the above equation (6), β _kj is a magnetic field generated at each position of each grid point Q _k on the measurement surface when a current source having a unit size is placed on each in-subject grid point N _j. This is a group of known coefficients representing the intensity. When the magnetic field strength in the subject lattice point N _j is obtained, proceeds to the processing of the image processing unit 11 shown in step S4.

[0028] Step S4: the magnetic field intensity of each measuring surface grid point Q _k, for example 10fT to draw isomagnetic diagram of (femto Tesla) intervals, the point of 10fT near the magnetic field intensity of each measuring surface grid point Q _k , All the search points are connected by a line, all the points near 20 fT are searched out and connected by a line, and the same process is repeatedly executed every 10 fT. It is not always necessary to draw the isomagnetic field diagram with lines. For example, the isomagnetic field intensity is 0 ft or more and less than 10 fT, 10 fT or more and less than 20 ft,. , An isomagnetic field map may be created. The data of the isomagnetic field map obtained in this manner is stored in the color monitor 12 or the color printer 13.
Is output to

The isomagnetic field diagram obtained as described above is
Since it is obtained from the magnetic field strength generated by the estimated current source in the subject, an isomagnetic field diagram is drawn with relatively high accuracy even in a region outside the region where the magnetic sensor is installed. Also, when the above-described method of estimating the current source by the minimum norm method is used, an isomagnetic field diagram is obtained by performing two operations of calculating the magnetic field strength between the current source on the grid point in the subject and the grid point on the measurement plane. Therefore, the number of arithmetic processes is reduced as compared with the conventional example in which the magnetic field strengths at a large number of grid points on the measurement surface are obtained by one-by-one interpolation.

[0030]

As is apparent from the above description, according to the present invention, the magnetic field strength at each grid point on each measurement surface is not determined by interpolating the magnetic field strength at each measurement point.
Once the current sources on the grid points in the subject are calculated and the magnetic field strength at each position of each measurement plane grid point generated by these current sources is obtained, the area where the magnetic sensor is placed The magnetic field strength of each measurement plane grid point in a region deviated from the distance is also determined relatively accurately, and as a result, a highly reliable isomagnetic field diagram can be created.

[0031]

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a biomagnetism measurement device according to an embodiment.

FIG. 2 is a flowchart illustrating a processing procedure of the apparatus according to the embodiment.

FIG. 3 is a schematic diagram of an intra-subject lattice point group set in a diagnosis target region;

FIG. 4 is a schematic diagram of a current source assumed on a lattice point in a subject.

FIG. 5 is a diagram showing an example of a magnetic field diagram.

[Explanation of symbols]

 3 Multi-channel SQUID sensor 8 Data analysis unit 9 Current source calculation unit 10 Magnetic field intensity calculation unit 11 Image processing unit

Claims (1)

(57) [Claims] (A) a plurality of magnetic sensors arranged at respective positions (measurement points) of a subject in proximity to a diagnosis target region and measuring a minute magnetic field by a biological activity current source in the diagnosis target region; (B) The measured magnetic field strength at each measurement point measured by each of the magnetic sensors and a current source having a unit size placed on a large number of grid points (lattice points in the subject) assumed within the diagnosis target area. Current source calculation for calculating physical quantities such as the magnitude and direction of the current source on each of the lattice points in the subject based on a known group of coefficients related to the magnetic field strength detected by each of the magnetic sensors when assumed. Means, and (c) the physical quantities of the current sources on each intra-subject grid point obtained by the current source calculating means, and the case where a unit-sized current source is placed on each intra-subject grid point. A number of grid points (measurement points) on the measurement surface on which the magnetic sensors are placed Based on the known coefficient group associated with the magnetic field intensity generated at each position of the surface grid points), and the magnetic field intensity calculating means for calculating the magnetic field intensity on the measurement plane lattice points,
(D) image processing means for obtaining an isomagnetic field diagram by sequentially connecting grid points having the same magnetic field strength among the grid points of the measurement plane obtained by the magnetic field strength calculating means. Biomagnetic measurement device.