JP2000325323A - Organism action current source estimating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly obtain a favorable estimation result by moving a lattice point with the minimum estimated current in each group to rearrange the lattice point group in a position estimated to enlarge a current source when the square error of a calculated magnetic field and a measured magnetic field data is not minimum. SOLUTION: A micro-magnetic field from an organism action current measured by in a diagnostic object area of a subject M is measured by a multi-channel SQUID sensor 1 and collected in a data collecting unit 5, and then the estimation processing for a current source is executed by a data analyzing unit 8. When it is judged that the square error of a magnetic field calculated from the current source and the magnetic field data actually measured and stored in the data collecting unit 5 is not minimum in the large, the lattice point group is divided into sub-groups by the respective apexes of plural polyhedrons. In each group, the lattice point with the minimum estimated current is moved to estimate the magnitude of a current source of the moved lattice point, and the lattice point group is rearranged in a position estimated to enlarge a current source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological activity current source estimating apparatus for estimating the position, orientation, and size of a biological activity current source, and quickly obtains a good estimation result of a physical quantity of the biological activity current source. For technology.

[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 sensor for measuring a minute magnetic field in a living body, a SQUID (Superconducting Quantum Int.)
erface Device: A sensor using a superconducting quantum interferometer) has been developed. This sensor is placed outside the head, and the sensor can non-invasively measure a small magnetic field generated by a current dipole (hereinafter simply referred to as a current source), which is a biological activity current source, generated in the brain. Estimate the position, direction, and size of the current source related to the lesion from the measured magnetic field data,
The estimated current source is displayed on a tomographic image obtained by an X-ray CT apparatus or an MRI apparatus and used for specifying a physical position of an affected part or the like.

Conventionally, as one of current source estimation methods, there is a method using a minimum norm method (for example, WHKullman
n, KDJandt, K. Rehm, HASchlitt, WJDallas and
WESmith, Advances in Biomagnetism, pp.571-574, P
lenum Pless, New York, 1989). Hereinafter, a conventional current source estimating method using the minimum norm method will be described with reference to FIG. As shown in FIG. 6, a multi-channel SQUID sensor 1 is provided near the subject M. The multi-channel SQUID sensor 1 includes a number of magnetic sensors (pickup coils) S _{1 to} S in a container called a dewar.
_m is immersed in a refrigerant such as liquid nitrogen and stored.

On the other hand, a large number of grid points (1) to (n) are set in, for example, the brain, which is a diagnosis target area of the subject M, and an unknown current source (current dipole) is assumed at each grid point. Each current source is represented by a three-dimensional vector VP _j (j = 1 to n). Then, S
Magnetic field B _i .about.B _m detected by the magnetic sensor S ₁ to S _m of QUID sensor 1 is expressed by the following equation (1).

[0006]

(Equation 1)

In equation (1), VP _j = (P _jx , P _jy , P
_jz ) α _ij = (α _ijx, α _ijy, α _ijz ). Note that α _ij is the magnetic sensors S ₁ to S ₁ when a current source having a unit size in the X, Y, and Z directions is placed on a grid point.
Is a known coefficient which represents the strength of the magnetic field detected by each position of the S _m.

[B] = (B ₁ , B ₂ ,...,
B _m ) [P] = (P _1x , P _1y , P _1z , P _2x , P _2y , P _2z ,...,
(P _nx , P _ny , P _nz ), the expression (1) can be rewritten into a linear relational expression like the expression (2). [B] = A [P] (2) In the equation (2), A is a matrix (lead field matrix) having 3n × m elements represented by the following equation (3).

[0009]

(Equation 2)

Here, when the inverse matrix of A is represented by A ⁻ ,
[P] is represented by the following equation (4). (P) = A ^- (B) ......... (4), where the minimum norm method, the number of the formula m (magnetic sensor S ₁
~S number of _m) than, assuming the case where X of the current source, which is assumed the number of unknowns 3n (each lattice point, Y, unknown in the case of considering the size of the Z-direction) is large, the current source [ P]
Of the current source [P] by adding a condition that the norm | [P] | Note that a solution can be uniquely obtained by making the number m of the above equations equal to the number 3n of unknowns. In such a case, however, the solution becomes very unstable, so the minimum norm method is used. Is used.

By adding the condition that the norm | [P] | of the current source [P] is minimized, the above equation (4) becomes the following equation (5).
It is represented as [P] = A ⁺ [B] (5) where A ⁺ is a generalized inverse matrix expressed by the following equation (6). ^{A + = A t (AA t} ) -1 ......... (6) However, A ^t is the transpose matrix of A.

By solving the above equation (5), the current sources VP _j on each grid point
Are estimated, and the one having the largest value among them is assumed to be close to the true current source. This is the principle of the current source estimation method using the minimum norm method.

Further, there has been proposed a method of estimating a current source that is closer to a true current source by repeatedly obtaining a minimum norm solution while subdividing grid points in order to improve the positional resolution of the minimum norm method. However, in this case, there is a problem that the number of elements of the vector [P] in the equation (5) increases and the calculation accuracy of the minimum norm solution decreases. Therefore, the applicant has
First, JP-A-6-343613 and JP-A-6-3436
According to No. 14, another group of grid points was moved to the vicinity of a grid point where a current source having a large value was present among the current sources estimated by the minimum norm method, and the number of grid points was changed to the same as the previous time. We propose a grid point moving minimum norm method that estimates the current source accurately while maintaining the accuracy of the minimum norm solution by estimating the current source with only the point interval narrowed. However, also in this case, there is a difficulty that a stable estimation result cannot be obtained due to difficulty in setting an appropriate value of the convergence determination value based on the grid point interval.

Therefore, the present applicant further proposes Japanese Patent Application No. 6-47.
According to No. 220, when calculating the current source, a condition that minimizes the square error between the magnetic field exerted by the current source on the grid point and the actual measured magnetic field is added, so that the convergence judgment value based on the grid point interval is unnecessary. A method for obtaining a stable estimation result is proposed. However, even in this method, the estimated moment of each current source tends to vary, and there is a problem that the discrete noise of the measurement magnetic field is estimated as a solution (current source). Kaihei 7
According to JP-A-327943, when calculating a current source, a square error (magnetic field square error term) between a magnetic field exerted by an unknown current source on each set grid point and an actual measured magnetic field (magnetic field data), and a current source A method of adding a condition of minimizing a sum with a square sum with a weighting factor λ (penalty function term) has been proposed.

[0015]

However, the conventional method has a problem that it is difficult to quickly obtain a good estimation result. When it is determined that the calculated current source is not appropriate, the grid points are rearranged and the calculation is repeated (iterated). However, it is not always easy to rearrange the grid points appropriately. There is a drawback in that the calculation process must be repeatedly performed. In the case of the conventional grid point group rearrangement, the grid point group is rearranged so that small current sources are concentrated toward larger current sources in the estimated current sources. Specifically, for example, it is assumed that the calculated magnitude of each current source is considered to be a mass, and that an attractive force acts between lattice points due to gravity. Then, each lattice point moves to a lattice point having a large mass, and a lattice group arrangement in which other lattice points are concentrated on a lattice point having a large mass. Further, as another grid point moving method, for example, eight grid points each having a small estimated current are moved to a vertex of a cube centered on a grid point having a large estimated current. Then, a lattice group arrangement in which lattice points having a small estimated current are concentrated on lattice points having a large estimated current is also obtained. However, if the true current source consists of multiple current sources of the same size, or if the current source is a non-intensive current source with a wide range of The way of rearranging the grid points that mechanically concentrate the sources according to simple rules is not suitable for the actual situation, and the calculation process is repeated many times.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and it is an object of the present invention to appropriately rearrange grid points when iteratively calculating a current source and to quickly obtain a good estimation result. It is an object of the present invention to provide a life activity current source estimating device capable of performing the above.

[0017]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention detects a magnetic field generated by a biological activity current with a plurality of magnetic sensors, thereby detecting the position, size, and direction of the biological activity current source. A biological activity current source estimating apparatus for estimating a physical quantity such as: (a) a plurality of magnetic fields arranged close to a diagnosis target area of a subject and measuring a minute magnetic field by the biological activity current source in the diagnostic target area; Sensors and
(B) data conversion means for converting magnetic field data measured by each of the magnetic sensors into digital data, and (c)
Data collection means for collecting and storing the magnetic field data converted into the digital data; (d) grid point setting means for setting a plurality of grid points (grid point group) in the diagnosis target area; 2) the magnetic field exerted by the unknown current source on each of the grid points and the magnetic field data stored in the data collection means;
Current source calculating means for obtaining an unknown current source by adding a condition of minimizing a sum of a squared error and a weighted sum of squares of the current source; and (f) calculating from the obtained current source. Determining means for determining whether or not the square error between the magnetic field and the magnetic field data actually measured by the magnetic sensor and stored in the data collecting means is globally minimum;
(G) When it is determined that the square error is not globally minimum, the grid point group is grouped by each vertex of the plurality of polyhedrons, and the grid point having the smallest estimated current is moved for each group. Predict the size of the current source at the grid point after moving, determine the position where the current source is expected to be large from the result as the rearrangement position of the grid point, and rearrange the grid point group And (h) repeating the processing by the current source calculating means, the judging means, and the grid point group rearranging means, and reducing the magnetic field when the square error is judged to be globally minimum by the judging means. Current source specifying means for estimating the corresponding current source as a true current source; and (i) displaying the current source estimated by the current source specifying means so as to be superimposed on a tomographic image of the diagnosis target area of the subject. Display means.

[Operation] The operation of the present invention is as follows. The minute magnetic field measured by each magnetic sensor is converted into digital data by the data conversion unit, and then stored in the data collection unit. Then, a plurality of grid points are virtually set in the diagnosis target area by the grid point setting means. Usually, the number of the lattice points is set smaller than the number of the magnetic cesans. A condition is added that minimizes the sum of the square error between the magnetic field exerted by the unknown current source on each grid point and the magnetic field data stored in the data collection means, and the weighted sum of squares of the current source. Then, the current source on each grid point is obtained by the current source calculating means.

Subsequently, the square error between the magnetic field calculated from the current source calculated by the current source calculating means and the magnetic field data actually measured by the magnetic sensor and stored in the data collecting means is globally minimized. Is determined by the determining means. If it is determined that it is not the minimum, the grid point group rearrangement unit divides the grid point group into vertices of a plurality of polyhedrons, and moves the grid point having the smallest estimated current for each group to move the grid point. The size of the current source at the point is predicted, and a position where the current source is expected to be large is determined as a relocation position of the lattice point from the result, and the lattice point group is rearranged. The current source calculation means, the determination means, and the grid point group rearrangement means repeat the respective processes. When the determination means determines that the square error is globally minimum, the current source identification means applies the magnetic field to the magnetic field. The corresponding current source is estimated as a true current source. The current source estimated by the current source specifying unit is displayed by the display unit so as to be superimposed on the tomographic image of the diagnosis target region of the subject.

In the case of the rearrangement of the grid point group in the apparatus of the present invention, the grid point group is grouped at each vertex of a plurality of polyhedrons, and the rearrangement position is determined for each group. A situation where other current sources are uniformly concentrated on a current source having a large estimated current can be avoided. Furthermore, instead of moving the grid points according to the simple rules as in the past and determining the position for relocation of the grid points, the size of the current source accompanying the trial movement of the grid point with the smallest estimated current is determined. Is determined in accordance with the prediction result of the above, so that the grid point group can be accurately rearranged sufficiently reflecting the status of the true current source. That is, the grid point group rearrangement means of the present invention applies the simplex method, which is one of the direct search methods used for solving the minimization problem (as will be described in detail later), based on the algorithm of the simplex method. , Grid points are grouped,
Mirror image for each group of grid points
By performing each operation of expansion, contraction, and reduction, the grid point group is appropriately rearranged.

[0021]

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 a life activity current source estimating apparatus according to the present invention. In the figure, reference numeral 2 denotes a magnetically shielded room, and a bed 3 on which the subject M is supine, and a living activity current source which is disposed in the brain of the subject M and is placed in the magnetically shielded room 2. And a multi-channel SQUID sensor 1 for non-invasively measuring a minute magnetic field due to.
As described above, the multi-channel SQUID sensor 1
Has a large number of magnetic sensors immersed in a coolant in a Dewar. In the present embodiment, when the brain of the subject M is assumed to be a sphere, each magnetic sensor is constituted by a pair of coils for detecting a magnetic field component in the radial direction.

The magnetic field data detected by the multi-channel SQUID sensor 1 is provided to a data conversion unit 4 and converted into digital data, and then collected in a 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 multi-channel S
This is a device for grasping the positional relationship of the subject M with respect to a three-dimensional coordinate system based on the QUID sensor 1. For example, small coils are attached to a plurality of locations of the subject M, and 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 1 to grasp the positional relationship of the subject M with respect to the multi-channel SQUID sensor 1. In addition, other methods for grasping the positional relationship of the subject M with respect to the SQUID sensor 1 include a method of attaching a projector to a dewar and irradiating the subject M with a light beam to grasp the positional relationship between the two. Alternatively, various methods disclosed in Japanese Patent Application Laid-Open Nos. 5-237065 and 6-788925 are used.

The data analysis unit 8 is for estimating the current source in the diagnosis target area of the subject M based on the magnetic field data collected by the data collection unit 5.
The data analysis unit 8 has functions as a grid point setting unit, a current source calculation unit, a determination unit, a grid point group rearrangement unit, and a current source identification unit according to the present invention, as will be apparent from the following description. . The magneto-optical disk 9 provided in association with the data analysis unit 8 stores, for example, a tomographic image obtained by an X-ray CT apparatus or an MRI apparatus, and a current source estimated by the data analysis unit 8 is The color monitor 1 is superimposed on these tomographic images.
0 or printed out on the color printer 11. Note that an X-ray CT device or M
The tomographic image obtained by the RI device may be configured to be directly transmitted to the data analysis unit 8 via the communication line 12 shown in FIG.

As described above, the multi-channel SKU
The positional relationship of the subject M with respect to the three-dimensional coordinate system based on the ID sensor 1 is measured and stored, and the multi-channel SQUID sensor 1 is used to detect a diagnosis target region of the subject M from a biological activity current source in the brain, for example. After collecting the magnetic field data in the data collection unit 5, the data analysis unit 8 executes a current source estimation process. Hereinafter, description will be given with reference to the flowchart shown in FIG.

Similar to the conventional example shown in FIG. 6, a three-dimensional grid point group N is assumed in a diagnosis target area, for example, the brain (step S1). Here, the unknown number 3n (the number of current sources assumed in the X, Y, and Z directions for each grid point) for the grid point group N is the number of magnetic sensors S _{1 to} S _m constituting the multi-channel SQUID sensor 1. The number of grid points of the grid point group N is set so as to be smaller than the number m. Here, the total number of grid points in the three-dimensional grid point group is 32, and the number of magnetic sensors is 129.

Then, each coefficient of the lead field matrix A represented by the equation (3) is calculated using Biot-Savart's law (each coefficient of the matrix A is calculated every time a lattice point described later is moved). I do. Here, the diagnosis target area is assumed to be a sphere, and the magnetic field of the radial component of the sphere is detected by each sensor. Therefore, there are 32 current sources having 2 elements and 129 generated magnetic fields. Therefore, the lead field matrix A
Is 129 rows and 64 columns. When the lead field matrix A is obtained, current sources on each grid point are obtained by a linear least squares method with a penalty term (step S2). Hereinafter, the process of step S2 will be described in detail.

Using the above equation (4), the magnetic sensor S ₁
Measured by to S _m, determine the magnetic field data stored in the data collecting unit 5 current sources on each grid point from [Bd] [P]. Equation (4) is shown below again. (P) = A ^- [Bd] ......... (4)

The matrix A is expressed by the above-mentioned equation (3).
It is a matrix of n × m elements, but here 129 rows × 6
This is a matrix having four columns of elements. In equation (4), no solution is obtained because the number of equations (the number of magnetic sensors S _{1 to} S _m ) is greater than the number of unknowns. Therefore, the measured field [Bd], the square error between the magnetic field assumed current sources on each grid point (P) is on the magnetic sensor S ₁ to S _m (B) | [Bd] - [B] By adding a condition to minimize the evaluation function f expressed by adding a penalty term shown below to |, the current source [P] is calculated using the linear least squares method. This evaluation function is shown in equation (7).

[0029]

(Equation 3)

The first term of the evaluation function is the square error of the magnetic field,
The term is a penalty term. In the penalty term, λ is a weight coefficient of the penalty term, and wi is a coefficient for canceling the influence of the distance from the magnetic sensor to the magnetic field measurement surface. Since the penalty term has a property that its value becomes smaller as the current source is solidified, the current source is obtained under the condition that only the square error of the magnetic field of the first term in the evaluation function is minimized. In this case, the tendency that the current source is likely to vary is suppressed, and the adoption of discrete noise components as solutions is reduced.

By adding the condition of minimizing the evaluation function f, equation (4) is represented by [P] = A ⁺ [Bd] (8). Here, A ⁺ is obtained by the following equation (9). A ⁺ = (A ^t A + λ · W) ⁻¹ · A ^t (9) (9) W in the equation is a penalty function matrix represented by the following equation (10). Here, since the number of elements of the current source is 2, W is 64
It is a matrix with 64 rows.

[0032]

(Equation 4)

Here, in general, as the current source Pi is closer to the magnetic field measurement surface, a larger magnetic field is measured.
By performing as in (11), for the current source Pi to be obtained,
The effect of the distance to the magnetic field measurement surface (ie, the current source Pi
Tend to be estimated close to the magnetic field measurement plane).

[0034]

(Equation 5)

Further, by setting the weight λ of the penalty term as in the following equation (12), the terms of the square error of the magnetic field (A ^t A) and the penalty term (W) can be set to the same magnitude. Can be. λ = | A ^t A | / | W | ............ (12)

[0036] When the above-mentioned (8) and (9) current source by formula (P) is obtained, the process proceeds to step S3, the magnetic field estimated current source (P) is on the magnetic sensor S ₁ to S _m [ It is determined whether or not the square error between B] and the measured magnetic field [Bd] is globally minimum. Here, it is determined that the square error of the magnetic field is globally minimum when the grid point group is moved a plurality of times in the process of repeating step S4, which will be described later, at each grid point position by the above-described method. Among the square errors of the applied magnetic field, those having the smallest value. The determination as to whether or not the square error of the magnetic field is globally minimum was obtained by performing the above-described processing in steps S2 and S3 for the rearranged grid point group in the process of repeating step S4 described below. The square error of the magnetic field may be stored, and the respective values may be compared to determine the minimum value as the global minimum value.

If it is determined that it is not the minimum, step S
Proceeding to No. 4, the rearrangement of the three-dimensional grid point group having 32 grid points is performed. In step S4, based on the simplex method, which is one of the direct search methods used for solving the minimization problem,
The rearrangement of the lattice point group is performed. Usually, in the case of the simplex method, a set of (n + 1) points in an n-dimensional space forms a simplex (simplex) to be minimized. Here, since the lattice point group is three-dimensional, the number of lattice points constituting one simplex is four. Therefore, in this case, 32 lattice points are defined as triangular pyramids (4
The eight simplexes SP1 to SP8 are set by grouping them into eight groups at the vertices of the (hedron).

Then, the set simplex SP1
For each of SP8, according to each operation of mirror image, expansion, contraction, and reduction in the simplex algorithm,
By moving only the grid point with the smallest estimated current for each group, the size of the current source at the grid point after movement is predicted, and the position where the current source is expected to be large is determined as the relocation position of the grid point from the result. Will decide. In other words, the grid point having the smallest estimated current is moved according to the simplex algorithm out of the four grid points to predict and calculate whether or not the estimated current increases after the movement, and the current source is expected to increase according to the prediction result. To determine the location where

On the other hand, each operation in the algorithm of the simplex method requires an objective function, and fs = the reciprocal of the magnitude of the moved current source P ′ = (Psa, Psb).
[√ (Psa ² , Psb ² )] ⁻¹ is the objective function fs. Here, the current source is a vector of the element 2, and it is desired to find a position where the current source becomes large. Therefore, the current source P ′ (Psa, Psb) is set so that the current source becomes larger as the value of the objective function fs becomes smaller. Is set as the objective function fs.

In the following, the positions of the four grid points of the simplex SP1, the current source and the value of its objective function fs are:
Lattice point position r1 (current source Ps1, objective function value fs1), lattice point position r2 (current source Ps2, objective function value fs2), lattice point position r3 (current source Ps3, objective function value fs3), lattice point Position of
r4 (current source Ps4, objective function value fs4), and fs1> f
Description will be made on the assumption that s2>fs3> fs4. That is, the current source Ps1 at the grid point position r1 is the smallest, and the current source Ps4 at the grid point position r4 is the largest.

In the case of the embodiment, the current source P 'is given by the following equation:
Approximation is calculated by (13). P ′ = (A ′ ^t A ′ + λW ′) ⁻¹ A ′ ^t (Bd−A ″ P ″) (13) where A ′ is a lead field matrix (1
A ″ is the lead field matrix of the non-moving current source (129 rows and 62 columns), P ″ is the magnitude vector of the non-moving current source (62 elements), and W ′ is the penalty for the moving current source. Function matrix (2 rows 2
Column), Bd is the measured magnetic field vector (129 elements), λ is a weighting factor] In the case of equation (9), it is necessary to calculate an inverse matrix of 64 rows and 64 columns, but in the case of equation (13), 2 rows Since the calculation is an inverse matrix of two columns, the amount of calculation is small. The position after the movement is included in A 'and W' as factors. Everything else is known.

Next, the process of determining the relocation position of the lattice point in each simplex according to each operation of mirror image, expansion, contraction, and reduction will be described with reference to FIGS. FIG. 3 is a schematic diagram showing the movement position of the current source when the search for the rearrangement of the grid point group is performed in the embodiment. FIG. It is. [Step F1] The position ra of the mirror image of the position r1 of the lattice point having the largest objective function value fs1 (the smallest current source Ps1) is determined, and the objective function value fr of the position ra of the mirror image is determined. As shown in FIG. 3, the position ra of the mirror image is on a perpendicular line from the position r1 to the triangle formed by the other three grid points, and is a position having the same distance to the triangle.

[Step F2] It is checked whether or not the objective function value fra at the mirror image position ra is equal to or smaller than the second largest objective function value fs2. Proceed to.

[Step F3] It is checked whether or not the objective function value fra of the mirror image position ra is less than the minimum objective function value fs4. If the objective function value fra is less than the minimum objective function value fs4, the mirror image position ra is determined as the relocation position of the lattice point. . If no, the process proceeds to the next step F4.

[Step F4] The extension position rb is determined, and the objective function value frb of the extension position rb is determined. As shown in FIG. 3, the extended position rb is on a perpendicular line from the position r1 to the triangle formed by the other three grid points, and is a position of the mirror image.
This is a position ahead of ra by an appropriate distance.

[Step F5] It is checked whether the objective function value frb at the extended position rb is less than the objective function value fra at the mirror image position ra. If less, the extension position rb is determined as the relocation position of the lattice point. If not, mirror image position ra
Is determined as the relocation position of the lattice point.

[Step F6] If it is determined in step F2 that the objective function value fr of the mirror image position ra is larger than the second largest objective function value fs2, the mirror image position ra
Is checked whether or not the objective function value fra is less than the maximum objective function value fs1. If less than, the position ra of the mirror image is determined as the relocation position of the lattice point. If no, the process proceeds to the next step F7.

[Step F7] The shrink position rc is obtained, and the objective function value frc of the shrink position rc is obtained. As shown in FIG. 3, the contraction position rc is on a perpendicular line from the position r1 to the triangle formed by the other three grid points, and is a position closer to the position r1 by an appropriate distance from the triangle.

[Step F8] It is checked whether the objective function value frc at the contraction position rc is less than the maximum objective function value fs1. If less than, the contraction position rc is determined as the relocation position of the lattice point. If no, the process proceeds to the next step F9.

[Step F9] The position r1 is obtained by the reduction operation.
The intermediate position between the position r4 and the position r4 is the relocation position of the lattice point corresponding to the position r1m, the intermediate position r2m between the position r2 and the position r4 is the relocation position of the lattice point corresponding to the position r2, and the position between the positions r3 and r4. The position r3m is determined as the relocation position of the grid point corresponding to the position r3. Above, simplex SP1
Will end.

Further, the remaining seven simplex SPs
The same processing as that of the simplex SP1 is performed for 2 to SP8. Therefore, once step S4 is performed, processing is performed for a total of eight current sources, one for each simplex.

After moving the grid points, the process returns to step S2, and the condition that the above-mentioned evaluation function is minimized is added to the moved grid point group, and the current source [P] is calculated by the linear least square method. Ask for a new one. Since the current source P 'is a value approximately obtained, the current source is accurately recalculated after the rearrangement of the lattice point group. And step S
In step 3, it is again determined whether or not the square error is globally minimum.
Steps 2 to S4 are repeated.

If it is determined in step S3 that the current is the minimum, the current source [P] for the globally minimum magnetic field [B] in step S5 is estimated as a true current source.
The current source [P] estimated as a true current source is superimposed on the X-ray CT image or MR tomographic image stored in the magneto-optical disk 9 shown in FIG. .

[Simulation] A simulation example for visually confirming the current source estimating function of the life activity current source estimating apparatus of the embodiment will be described with reference to the drawings. FIG. 5 is a diagram showing a situation of the simulation, in which a true current source (current dipole) is placed at a position indicated by a white cross mark. S / N which is the signal-to-noise ratio of the measured magnetic field
The ratio was 10. FIG. 5A shows the calculation state of the first current source without rearranging the grid point group. After the first grid point group rearrangement, as shown in FIG. 5B, the calculated current source is slightly closer to the true current source. As shown in FIG. 5 (c), the calculated current source is much closer to the true current source, and after the third rearrangement of the lattice point group, as shown in FIG. It can be clearly understood that the calculated current sources almost coincide with each other, and the relocation of the grid point group in the life activity current source estimating apparatus of the embodiment is accurate, and a good estimation result can be obtained quickly.

The present invention is not limited to the above embodiment, but can be modified as follows. (1) In the case of the embodiment, the operation of mirror image, expansion, contraction, and reduction is performed once for one simplex.
As a modified example, an apparatus having a configuration in which mirror image / expansion / shrinkage / reduction operation processing is repeatedly performed on individual simplexes until a predetermined stop condition is satisfied.

(2) The specific algorithm of the simplex method used for rearranging the grid points in the living activity current source estimating apparatus of the present invention is not limited to the algorithm shown in the embodiment.

[0057]

As is apparent from the above description, according to the biological activity current source estimating apparatus of the present invention, the rearrangement of the grid points performed before the calculation of the current source is repeated is one of the so-called direct search methods. The grid points are grouped into groups based on the simplex algorithm, and mirror image, expansion, contraction, and reduction operations are performed on each group of grid points according to the simplex algorithm. Since the position for relocating the grid points is determined for each group according to the prediction result of the size of the current source accompanying the test movement, another current source is used for the current source having a large estimated estimated current. This avoids a situation where the user concentrates uniformly, and at the same time, the position for relocation is determined based on experimental predictions instead of uniform movement using simple rules as in the past. Since is because, so repositioning of exact grid point group was sufficiently reflects the situation of the true current source is made. As a result, even if the true current source in the diagnosis target area is composed of a plurality of current sources of the same size or a non-intensive current source in which the current sources are distributed over a wide range, Since the rearrangement of the point cloud is performed accurately,
The number of repetitions of the current source calculation is reduced, and a good estimation result can be obtained quickly.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a life activity current source estimating apparatus according to the present invention.

FIG. 2 is a flowchart of an entire estimation process according to the embodiment.

FIG. 3 is a schematic diagram showing a movement position of a current source when a process of obtaining a rearrangement of a lattice point group in the embodiment is progressed.

FIG. 4 is a flowchart illustrating a process of obtaining a lattice point group rearrangement position in the embodiment.

FIG. 5 is a graph illustrating a simulation result of an estimation process according to the embodiment.

FIG. 6 is an explanatory diagram of an estimation process according to a conventional example.

[Explanation of symbols]

1 ... multichannel SQUID sensor 2 ... magnetic shield room 4 ... data conversion unit 5 ... data collection unit 8 ... data analysis unit 10 ... color monitor M ... subject S ₁ to S _m ... magnetic sensor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naoichi Yamaki 3-5-1 Jokita, Hamamatsu-shi, Shizuoka Pref. Shizuoka University Faculty of Engineering F-term (reference) HH11 HH13 HH16 JJ01 KK00 KK05

Claims (1)

[Claims] 1. A biological activity current source estimating apparatus for estimating a physical quantity such as a position, a size, and a direction of a biological activity current source by detecting a magnetic field generated by the biological activity current with a plurality of magnetic sensors, (A) a plurality of magnetic sensors arranged in proximity to a diagnosis target area of a subject and measuring a minute magnetic field by a biological activity current source in the diagnosis target area;
(B) data conversion means for converting magnetic field data measured by each of the magnetic sensors into digital data, and (c)
Data collection means for collecting and storing the magnetic field data converted into the digital data; (d) grid point setting means for setting a plurality of grid points (grid point group) in the diagnosis target area; 2) the magnetic field exerted by the unknown current source on each of the grid points and the magnetic field data stored in the data collection means;
Current source calculating means for obtaining an unknown current source by adding a condition of minimizing the sum of the squared error and the weighted sum of squares of the current source; and (f) calculating from the obtained current source. Determining means for determining whether or not the square error between the magnetic field and the magnetic field data actually measured by the magnetic sensor and stored in the data collecting means is globally minimum;
(G) When it is determined that the square error is not globally minimum, the grid point group is grouped by each vertex of the plurality of polyhedrons, and the grid point having the smallest estimated current is moved for each group. Predict the size of the current source at the grid point after moving, determine the position where the current source is expected to be large from the result as the rearrangement position of the grid point, and rearrange the grid point group And (h) repeating the processing by the current source calculating means, the judging means, and the grid point group rearranging means, and reducing the magnetic field when the square error is judged to be globally minimum by the judging means. Current source specifying means for estimating the corresponding current source as a true current source; and (i) displaying the current source estimated by the current source specifying means so as to be superimposed on a tomographic image of the diagnosis target area of the subject. Display means. Bioelectric current source estimating apparatus.