JP3298312B2 - Biological activity current source estimation 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 living activity current source estimating apparatus for estimating the position, orientation, and size of a living activity current source.

[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.

Recently, as a device for measuring a minute magnetic field in a living body, SQUID (Superconducting Quantum Inter
face 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. From the measured magnetic field data, the position, direction, and size of the current source related to the lesion are estimated, and the estimated current source is displayed on a tomographic image obtained by an X-ray CT or MRI device, and the physics of the affected part is displayed. It is used to identify the target position.

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).

A conventional current source estimation method using the minimum norm method will be described below with reference to FIG. As shown in FIG. 8, a multi-channel SQUID sensor 1 is provided near the subject M. Multichannel SQUID sensor 1 is accommodated by immersing a number of magnetic sensors (pickup coil) S ₁ to S _m in the refrigerant such as liquid nitrogen in a container called a dewar.

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).

[0007]

(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 having 3n × m elements represented by the following equation (3).

[0010]

(Equation 2)

Here, if 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 repeatedly obtaining a minimum norm solution while subdividing a grid point division in order to improve the position resolution of the minimum norm method (for example, Y.Oka).
da, J.Huang and C.Xu, 8th International Conference
on Biomagnetism, Munster, August 1991). Hereinafter, FIG.
This method will be described briefly with reference to FIG.

FIG. 9 is an enlarged view of a part of the lattice point group N shown in FIG. 8, and the symbol J in the figure represents a true current source estimated using the above-described minimum norm method. Is a grid point where a current source close to Around this grid point J, a subdivided grid point group M (indicated by small black dots in FIG. 9) is additionally set. Then, a current source closer to the true current source is estimated by using the same method as described above, with the newly set grid point group M included in the initially set grid point group N.

[0016]

However, the prior art having such a structure has the following problems. According to the conventional method shown in FIG. 9, since the subdivided grid point group M is newly set in addition to the initially set grid point group N, the number of grid points increases. for that reason,
There is a disadvantage 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 present applicant has previously filed Japanese Patent Application No. Hei.
No. 0450 and Japanese Patent Application No. 5-160451, a grid point moving minimum norm method for moving another group of grid points near a grid point where a current source having a large value exists among current sources estimated by the minimum norm method. Has been proposed. This method attempts to estimate the current source accurately while maintaining the accuracy of the minimum norm solution by estimating the current source with the number of grid points being the same as the previous time and narrowing only the grid point interval. Is what you do.

However, in the current source estimating method using the minimum norm method, the size of the current source in the X, Y, and Z directions assumed on each grid point is larger than the number m of magnetic sensors (the number of equations). Since it is assumed that the number of unknowns 3n (n is the number of lattice points) considered is large (3n> m), a coefficient matrix indicating the relationship between the unknown current source on each lattice point and the measured magnetic field is obtained. The rank may drop and the solution may become unstable. Further, in the process of specifying the optimal current source, whether or not the minimum grid point interval has become equal to or less than a preset value (convergence determination value) is used as a criterion, so that the estimation result depends on the value of this criterion. May be different.

Therefore, the present applicant further proposes Japanese Patent Application No. 6-47.
According to No. 220, the number of grid points smaller than the number of magnetic sensors is set, and the condition that the square error between the magnetic field exerted by the unknown current source on each of these grid points and the magnetic field measured by the magnetic sensor is minimized. The unknown current source is obtained by adding, and the square error between the magnetic field calculated from the obtained current source and the magnetic field measured by the magnetic sensor is calculated as follows.
When the movement of the grid points and the calculation of the current source, which will be described later, are repeated a plurality of times, the value is the smallest among the square errors determined for each grid point arrangement (see the specification of Japanese Patent Application No. Hei 6-47220). In the expression in the table, it is determined whether or not “globally minimum”), and if it is determined that the current source is not the minimum, it is located in the vicinity of a grid point where a current source having a large value exists among the obtained current sources. Another grid point group is moved, and a method has been proposed in which the above-described movement of the grid points and the current source calculation process are repeated a plurality of times.

According to this method, the number of unknown current sources on each set grid point is made smaller than the number of magnetic sensors, and the current source on each grid point is set as a condition for obtaining a current source from a measured magnetic field. Since the condition that the square error between the magnetic field exerted by the source and the actual measured magnetic field is minimized is employed, the current source can be estimated more accurately. Further, regarding the square error, the current source when the value is the minimum among the square errors obtained for each grid point arrangement is estimated as a true current source. Thus, the setting of the convergence determination value becomes unnecessary, and the final current source can be uniquely specified.

However, it has been found that this technique has the following points to be improved. That is, according to the above-described method of estimating the current source using the linear least squares method, the moments (directions and magnitudes) of the current sources on each grid point are varied, and the magnetic fields of these current sources are canceled out. Current sources on each grid point are estimated such that the resulting magnetic field is the same as the measured magnetic field. That is,
Variations are likely to occur in the estimated moment of each current source. When noise is discretely mixed into the measurement magnetic field, the noise component may be calculated as a solution (current source).

The present invention has been made in view of such circumstances, and solves the above-mentioned drawbacks. In particular, the present invention suppresses the variation in the estimated physical quantity of the current source.
It is an object of the present invention to provide a living activity current source estimating device that is hardly affected by noise even if noise is mixed in a measurement magnetic field.

[0023]

The present invention has the following configuration to achieve the above object. That is, the present invention relates to 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. A plurality of magnetic sensors for measuring a minute magnetic field by a bioactive current source in the region; (b) data conversion means for converting magnetic field data measured by each of the magnetic sensors into digital data; and (c) the digital data. Data collection means for collecting and storing the converted magnetic field data; and (d) grid points for setting a plurality of grid points in the diagnosis target area so that the number thereof is smaller than the number of the magnetic sensors. Setting means; (e) calculating the sum of the square error between the magnetic field exerted by the unknown current source on each of the grid points, the magnetic field data stored in the data collection means, and the weighted sum of squares of the current source; minimum (F) a magnetic field calculated from the obtained current source and the magnetic field actually measured by the magnetic sensor and stored in the data collection means. Determining a function including a square error with the magnetic field data to determine whether or not the value is the minimum among the functions including the square error obtained for each lattice point arrangement; When it is determined that the value of the function including the square error is not the minimum among the functions including the square error obtained for each grid point arrangement, the value of each of the grid points calculated by the current source calculating means is determined. Grid point group rearrangement means for moving another group of grid points to the vicinity of a grid point where a current source having a large value exists, and rearranging the group of grid points, (h) the current source Calculation means, the judgment means, and the grid point group rearrangement As a result of repeating each processing by the means, the magnetic field when the value including the square error is determined to be the smallest among the functions including the square error obtained for each grid point arrangement by the determining means is obtained. Current source specifying means for estimating the current source corresponding to the true current source,
(I) display means for 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.

[0024]

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. The number of these grid points is
The number is set smaller than the number of 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. do it,
The current source on each grid point is determined by the current source calculation means.

Here, the penalty term, which is a weighted sum of squares of the current source, has the property that the value becomes smaller as the current source is more solidified (closer), so that the calculated current source In addition, the variation of the physical quantity is suppressed, and the noise that exists discretely as a solution is reduced.

Subsequently, regarding a function including a square error between the magnetic field calculated from the current source calculated by the current source calculation means and the magnetic field data actually measured by the magnetic sensor and stored in the data collection means, 2 obtained for each grid point arrangement
The determination means determines whether or not the value is the minimum among the functions including the squared error. If it is determined that it is not the minimum, the grid point group rearrangement means moves another grid point group to a vicinity of a grid point where a current source having a large value exists among the current sources obtained by the current source calculation means. Then, the grid point group is rearranged. As a result of repeating each processing by the current source calculation means, the judgment means, and the grid point group rearrangement means, the judgment means
When it is determined that the value of the function including the squared error is the smallest among the functions including the squared error obtained for each lattice point arrangement, the current source specifying unit determines that the current source corresponding to the magnetic field is true. It is estimated as a 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.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a living 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 in which the subject M is supine in the magnetically shielded room 2.
And a multi-channel SQUID sensor 1 which is arranged in close proximity to, for example, the brain of the subject M and non-invasively measures a small magnetic field generated by a biological activity current source generated in the brain. As described above, in the multi-channel SQUID sensor 1, a large number of magnetic sensors are immersed in the refrigerant in the dewar. In the present embodiment, when the brain of the subject M is 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 supplied 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 in which a projector is attached to a dewar and a light beam is applied to the subject M 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 SQUA
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.

As in the conventional example shown in FIG. 8, 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.

Then, after calculating each coefficient of the matrix A represented by the equation (3) using the Biot-Savart law (each coefficient of the matrix A is calculated for each movement of a lattice point described later). ,
A current source on each grid point is obtained by a linear least squares method with a penalty term (step S2). Hereinafter, this 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 having × m elements. In equation (4), no solution is obtained because the number m of equations (the number of magnetic sensors S _{1 to} S _m ) is greater than the number of unknowns 3n. Therefore, the square error between the magnetic field (B) which assumed current source and the measured field [Bd] on each grid point (P) is on the magnetic sensor S ₁ to S _m | [Bd] - [B] | A current source [P] is calculated using the linear least squares method by adding a condition of minimizing the evaluation function f expressed by the sum of the following and a penalty term. This evaluation function is shown in equation (7).

[0035]

(Equation 3)

The first term of the evaluation function is the square error of the magnetic field,
The term is a penalty term. Λ in the penalty term is the weight 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 matrix represented by the following equation (10).

[0038]

(Equation 4)

Here, in general, a larger magnetic field is measured as the current source Pi is closer to the magnetic field measuring surface.
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).

[0040]

(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)

[0042] 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 [ B] and the sum of the squared error between the measured magnetic field [Bd] and the above-mentioned penalty term, which will be described later in step S
When the grid point group is moved a plurality of times in the process of repeating step 4, the value is the smallest of the sum of the square error of the magnetic field and the penalty term obtained by the above-described method at each grid point position. It is determined whether or not. The determination as to whether or not the sum of the square error of the magnetic field and the penalty term is the minimum is performed by repeating the above-described steps S2 and S3 for the rearranged lattice points in the process of repeating step S4 described below. The sum of the square error of the magnetic field obtained and the penalty term may be stored, and the respective values may be compared to minimize the minimum value.

If it is determined that it is not the minimum, step S
Proceeding to 4, the current source on another grid point is moved around the grid point where the current source having a large value exists among the current sources [P] obtained in step S2. As a result, a new lattice point group having the same number of lattice points as the original lattice point group N and a close interval is obtained. It should be noted that the current source having a large value is not necessarily one, and there are usually a plurality of current sources.

A method for bringing another group of grid points closer to a grid point where a current source having a large value exists is not particularly limited.
For example, the following method is exemplified. The magnitude of the current source at each grid point obtained in step S2 is considered as a mass, and it is assumed that an attractive force acts between each grid point due to gravity. Then, each lattice point approaches a lattice point having a large mass, and a lattice point group having a higher density is obtained as the lattice point is closer to a lattice point having a large mass. The moving distance of each grid point is set appropriately.
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. At this time, the size of the cube is, for example, half the distance between a grid point having a large estimated current and the closest grid point.

After moving the grid points, the process returns to step S2, and the condition that the above-described evaluation function is minimized is added to the moved grid point group, and the current source [P] is calculated by the linear least squares method. Ask for a new one. Then, in step S3, it is determined again whether or not the sum of the square error and the penalty term is minimum. If it is determined that the sum is not minimum, steps S2 to S4 described above are repeated.

If it is determined in step S3 that the current is the minimum, the current source [P] corresponding to the 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 was performed to visually confirm the operation of the above-described method.
Fig. 3 shows (-10 / 1 / 6.0) at the position of (16.0, 16.0, 48.0) [mm].
Assuming that there is a current source of (√2, -10 / √2,0) [nAm], this current source is added to 32 magnetic fields (signal-to-noise ratio S / N = 20) measured by 129 magnetic sensors. Is set, and an evaluation function without adding a penalty term (that is, 2
It is a simulation result of estimating the current source under the condition that the squared error only) is minimized. According to this comparative example,
It can be seen that the current sources are required to be separated due to the influence of noise. In each of the figures showing the simulation results, open circles indicate assumed current sources, arrows or black points indicate grid points (estimated current sources), and those with a large current value have larger black points, Larger values are indicated by arrows. In addition, since the grid point having a small current value does not appear in the figure, what is shown is smaller than the actually set number of grid points.

FIG. 4 shows (0, 10.0, 69.0) [m
m], the current source of (10, 0, 0) [nAm] is (0, 0, 0).
-10.0, 49.0) [mm], it is assumed that there are (10, 0, 0) [nAm] current sources, respectively, and this current source has a magnetic field (signal-to-noise ratio S) measured by 129 magnetic sensors. / N = 2
This is a simulation result estimated in the first embodiment by setting 32 grid points in (0). According to the present embodiment,
It can be seen that even when noise is mixed in the measurement magnetic field, the current source is accurately estimated.

<Second Embodiment> The method described in the first embodiment can perform a good estimation when the magnetic field source is assumed to be a current dipole. In step S3), a penalty term is added, and the estimated current source tends to solidify (locally concentrate). Therefore, when the current sources are distributed with a certain degree of spread, there is a problem that it is difficult to correctly estimate these current sources. In the present embodiment, in view of this point, a current source having a spread can be correctly estimated. Since the schematic configuration of the apparatus is the same as that of the first embodiment shown in FIG. 1, the description is omitted here.

Hereinafter, referring to the flowchart of FIG.
The current source estimating process in the data analysis unit 8 will be described. In step S11, as in the first embodiment, a grid point group is set evenly in the diagnosis target area. In step S12, Upon current source from the magnetic field measured by the magnetic sensor S ₁ to S _m [Bd] a [P] obtained by linear least squares method, as in step S2 of the first embodiment, the measured magnetic field [ Bd] the square error between the magnetic field assumed current sources (P) is on the magnetic sensor S ₁ to S _m on each lattice point [B] | [Bd] - [B] | and the sum of the penalty term The condition that the evaluation function f represented by is minimized is added.

Here, the weight λ of the penalty term in equation (7)
Is determined according to the distance between grid points. Specifically, for each grid point, the distance between that grid point and the closest grid point is determined. Then, using the average value of each distance as a parameter, the weight λ is determined so that the smaller the average value, the smaller λ. As a result, when the lattice points are disjointed, the weight λ increases, and as a result, the influence of the penalty term in the equation (7) increases, and the variation of the estimated current source due to the influence of the noise component can be suppressed. on the other hand,
When the lattice points are locally gathered, the weight λ becomes small, and as a result, the influence of the penalty term in the equation (7) becomes small, so that unnecessary concentration of the current source can be avoided.

When the current source [P] is obtained, step S13 is performed.
The willing, the estimated current source (P) is the magnetic sensors S ₁ ~
For square error between the magnetic field measured with the magnetic field (B) on S _m [Bd], the value in the square error obtained for each place each lattice point to determine whether the minimum. That is,
In this step S13, the penalty term is removed from the specific reference of the optimal current source, so that it is possible to prevent the unnecessary solidified current source from being adopted as the optimal current source.

If it is determined that the current source is not the minimum, the process proceeds to step S14 as in the first embodiment, and the current sources on the other grid points are moved around the grid point where the maximum current source exists. Returning to step S12, a current source [P] is newly obtained for the moved lattice point group by the linear least squares method to which a penalty term is similarly added. Then, it is determined again in step S13 whether or not the square error is minimum. If it is determined that the square error is not minimum, steps S12 to S14 described above are performed.
Is repeated. If it is determined in step S13 that the current source is the minimum, the current source [P] for the minimum magnetic field [B] in step S15 is estimated as a true current source, and the current source is superimposed on the tomographic region in the region of interest. Display together and finish the process.

<Simulation> A simulation was performed to visually confirm the operation of the above-described method.
FIG. 6 shows that one side is centered on (0, 20, 60) [mm].
Assuming that a 10 nA current source is uniformly distributed in a 20 mm cube, 32 grid points are set from the magnetic field (S / N = 20) measured by 129 magnetic sensors for this uniformly distributed current source. 9 is a simulation result estimated by the method of the first embodiment described above. According to the method of the first embodiment, it can be understood that the estimated current source is too hard than necessary.
FIG. 7 is a simulation result obtained by estimating the same equally distributed current source by the method of the second embodiment. According to the second embodiment, it can be seen that the equally distributed current sources are estimated in a correct form.

[0055]

As is apparent from the above description, according to the present invention, the square error between the magnetic field exerted by the unknown current source on each grid point and the measured magnetic field data, and the weighting of the current source Since a current source on each grid point is obtained by adding a condition of minimizing the sum of the sum of squares, variations in the physical quantity of the obtained current source are suppressed and discretely exist. Noise is less likely to be found as a solution.

Further, in order to improve the estimation accuracy of the current source,
Without increasing the number of grid points, the current source is estimated again by moving another grid point group to the vicinity of the grid point where the current source with a large value exists among the current sources obtained earlier. . That is, since the number of unknowns is constant, the calculation accuracy of the current source calculation can be maintained.

Furthermore, the sum of the square error of the magnetic field and the weighted sum of the squares of the current source is determined as the current source when the value is the minimum among the square errors obtained for each grid point arrangement. Is estimated as a true current source, so that it is not necessary to set a convergence determination value in the process of specifying the final current source, and the final current source can be uniquely specified.

[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 estimation process according to the first embodiment.

FIG. 3 is a simulation result of an estimation process shown for comparison with the first embodiment.

FIG. 4 is a simulation result of an estimation process according to the first embodiment.

FIG. 5 is a flowchart of an estimation process according to a second embodiment.

FIG. 6 is a simulation result of an estimation process shown for comparison with the second embodiment.

FIG. 7 is a simulation result of an estimation process according to the second embodiment.

FIG. 8 is an explanatory diagram of an estimation process according to a conventional example.

FIG. 9 is an explanatory diagram of an estimation process according to another 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

Claims (1)

(57) [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,
(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 bioactive current source in the diagnosis target area; and (b) magnetic field data measured by each of the magnetic sensors. (C) data collecting 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 in the diagnosis target area such that the number is smaller than the number of magnetic sensors; and (e) an unknown current source on each of the grid points. Current for obtaining an unknown current source by adding a condition that minimizes the sum of the square error between the magnetic field exerted by the magnetic field and the magnetic field data stored in the data collection means and the weighted sum of squares of the current source. Source calculation means, and (f) a function including a square error between a magnetic field calculated from the obtained current source and magnetic field data actually measured by the magnetic sensor and stored in the data collection means. Determining means for determining whether or not the value is the smallest among the functions including the square error obtained for each arrangement; and (g) obtaining the function including the square error for each grid point arrangement. Of the function containing the square error When it is determined that the value is not the minimum in the above, among the current sources on each grid point obtained by the current source calculating means, another grid point group is moved to the vicinity of the grid point where the current source having a large value exists. (H) repeating the respective processes by the current source calculating means, the determining means, and the grid point group relocating means; In the function including the square error, the current source corresponding to the magnetic field when the value is determined to be the minimum among the functions including the square error obtained for each grid point arrangement is estimated to be a true current source. Current source specifying means for performing (i)
A biological activity current source estimating device, comprising: a display unit configured to display the current source estimated by the current source specifying unit on a tomographic image of a diagnosis target region of the subject.