JPH07327943A - Biological activity current source estimating device - Google Patents

Abstract

PURPOSE:To provide a biological activity current source estimating device which suppresses the estimated dispersion of physical quantity of a current source and hard to receive the influence of a noise even when it is mixed in a measured magnetic field. CONSTITUTION:A micro magnetic field from the biological activity current source of an examinee M is measured by a multi-channel SQUID sensor 1, and magnetic field data is stored in a data collection unit 5. A data analysis unit 8 assumes a lattice point group in the diagnostic object area of the examinee M uniformly, and finds a current source on each lattice point by a method of linear least square using a condition to minimize the sum of the square error of a calculated magnetic field and a measured magnetic field and the sum of squares with weight of the current source. When such sum is shown in a value other than the minimum value in a global point of view, another lattice point is made to approach the lattice point in which a current source with large value out of calculated current sources exists, and the current source on each new lattice point is found similarly. When the sum is minimum, the current source in accordance with the sum is estimated as a true 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 estimation device for estimating the position, orientation and size of a biological activity current source.

[0002]

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

In recent years, as a device for measuring a minute magnetic field in a living body, SQUID (Superconducing Quantum Inter
face Device: A sensor using a superconducting quantum interferometer) has been developed. By placing this sensor outside the head, a minute magnetic field generated by a current dipole (hereinafter also simply referred to as a current source), which is a biological activity current source generated in the brain, can be noninvasively measured by the sensor. The position, orientation, and size of the current source associated with the lesion are estimated from the measured magnetic field data, and the estimated current source is displayed on a tomographic image obtained by an X-ray CT or MRI machine to display the physical properties of the affected area. It is used to specify the target position.

Conventionally, there is a method using the minimum norm method as one of the current source estimation methods (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, the multi-channel SQUID sensor 1 is provided in the vicinity of the subject M. In the multi-channel SQUID sensor 1, a large number of magnetic sensors (pickup coils) S _{1 to} S _m are immersed in a refrigerant such as liquid nitrogen and housed in a container called a Dewar.

On the other hand, a large number of grid points (1) to (n) are set in the diagnostic target region of the subject M, for example, the brain, 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
The magnetic fields B _{i to} B _m detected by the magnetic sensors S _{1 to} S _m of the QUID sensor 1 are represented 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 ) It should be noted that α _ij is the magnetic sensor S ₁ to when the current sources having unit sizes in the X, Y, and Z directions are placed on the grid points.
It is a known coefficient representing the strength of the magnetic field detected at each position of 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, expressed as P _nz), (1) formula can be rewritten to a linear relationship such as equation (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, 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]
The solution of the current source [P] is obtained by adding the condition that the norm | [P] | Note that the solution can be uniquely obtained by setting the number m in the above equation and the number 3n of unknowns to be equal. However, in such a case, the solution becomes very unstable. Is used.

By adding the condition that the norm | [P] | of the current source [P] is minimized, the above equation (4) is transformed into the following equation (5).
It is expressed as. [P] = A ⁺ [B] (5) Here, A ⁺ is a general inverse matrix expressed by the following equation (6). A ⁺ = A ^t (AA ^t ) ^-1 (6) where A ^t is a transposed matrix of A.

Solving the above equation (5), the current source VP _j on each lattice point
The direction and magnitude of the current source are estimated, and the one with the largest value is assumed to be closer to the true current source. This is the principle of the current source estimation method by the minimum norm method.

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

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

[0016]

However, the conventional example having such a structure has the following problems. According to the conventional method shown in FIG. 9, since the grid point group N that is initially set is added and the subdivided grid point group M is newly set, the number of grid points increases. for that reason,
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 present applicant previously filed Japanese Patent Application No. 5-16.
According to Japanese Patent Application No. 0450 and Japanese Patent Application No. 5-160451, among the current sources estimated by the minimum norm method, a grid point moving minimum norm method for moving another grid point group near a grid point where a current source with a large value exists Is proposed. This method tries 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 the same as the previous time and narrowing only the grid point spacing. To do.

However, in the method of estimating the current source using the minimum norm method, the size of the assumed current source on each lattice point in the X, Y, and Z directions 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), the coefficient matrix showing the relationship between the unknown current source on each lattice point and the measured magnetic field is The rank may drop and the solution may become unstable. In addition, in the process of specifying the optimum current source, whether or not the minimum grid point spacing is less than or equal to a preset value (convergence judgment value) is used as a judgment criterion. It can be different.

Therefore, the present applicant has further filed Japanese Patent Application No. 6-47.
No. 220 sets the number of grid points smaller than the number of magnetic sensors, and minimizes the square error between the magnetic field exerted by an unknown current source on each of these grid points and the magnetic field measured by the magnetic sensor. The unknown current source is obtained by adding, and it is determined whether or not the square error between the magnetic field calculated from the obtained current source and the magnetic field measured by the magnetic sensor has been globally minimized. In such a case, a method of moving another grid point group to the vicinity of a grid point where a current source with a large value exists among the obtained current sources is proposed. Here, the squared error is globally the minimum, which means that the minimum squared error obtained for each grid point arrangement is determined when the above-described grid point movement and current source calculation processing are repeated a plurality of times. It means that the value is the smallest.

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 on each grid point is set as a condition for obtaining the current source from the 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, the current source can be estimated more accurately. Further, since the current source when the squared error is globally minimized is estimated as the true current source, it is not necessary to set the convergence determination value in the process of specifying the final current source, and the final current is determined. The source can be uniquely identified.

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

The present invention has been made in view of the above circumstances, solves the above-mentioned drawbacks, and in particular suppresses the variation in the estimated physical quantity of the current source, and
It is an object of the present invention to provide a biological activity current source estimation device that is not easily affected by noise even if the measurement magnetic field contains noise.

[0023]

The present invention has the following constitution in order to achieve such an object. That is, the present invention is a biological activity current source estimation device for estimating a physical quantity such as a position, size, direction, etc. of a biological activity current source, which is (a) disposed in proximity to a diagnostic target region of a subject, A plurality of magnetic sensors for measuring a minute magnetic field by a biological activity 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 collecting means for collecting and storing the magnetic field data converted into the above, and (d) a grid point for setting a plurality of grid points in the diagnosis target region so that the number of the magnetic field data is smaller than the number of the magnetic sensors. Setting means, and (e) the sum of the squared error of the magnetic field exerted by the unknown current source on each grid point and the magnetic field data stored in the data collecting means, and the weighted sum of squares of the current source. minimum And (f) the magnetic field calculated from the obtained current source and the magnetic sensor actually measured and stored in the data collecting means. Determining means for determining whether or not the function including the squared error with the magnetic field data is globally minimized, and (g) when the function including the squared error is determined not to be the global minimum, Among the current sources on each grid point obtained by the current source calculation means, another grid point group is moved to the vicinity of the grid point where a current source with a large value exists, and the grid point is rearranged. Each processing by the group rearranging means, (h) the current source calculating means, the judging means, and the lattice point group rearranging means is repeated, and the judging means judges that the function including the square error is globally minimum. Current source corresponding to the magnetic field when exposed to A current source specifying unit that estimates a true current source; and (i) a display unit that displays the current source estimated by the current source specifying unit by superimposing the current source on the tomographic image of the diagnosis target region of the subject. Be prepared.

[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 means and then stored in the data collection means.
Then, the grid point setting means virtually sets a plurality of grid points in the diagnosis target area. The number of grid points is
Set less than the number of magnetic sesan. A condition is added to minimize the sum of the squared error between the magnetic field exerted by the unknown current source on each grid point and the magnetic field data stored in the data collecting means, and the weighted sum of squares of the current source. do it,
The current source on each grid point is obtained by the current source calculation means.

Here, the penalty term, which is the weighted sum of squares of the current source, has a property that its value becomes smaller as the current sources are clustered (closer together), and therefore the calculated current source. The variation in the physical quantity of is suppressed, and the noise that is discretely present as a solution is reduced.

Subsequently, a function including a square error between the magnetic field calculated from the current source obtained 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 in a global range. The determination means determines whether or not it has become minimum. When it is determined that the grid point group is not the minimum, the grid point group rearrangement means moves another grid point group to the vicinity of the grid point in which the current source having the larger value exists among the current sources calculated by the current source calculation means. Then, the grid point group is rearranged. When the function including the squared error is globally minimized by the determining means by repeating the respective processes by the current source calculating means, the determining means, and the lattice point group rearranging means, the magnetic field of the magnetic field is determined by the current source identifying means. The current source corresponding to is estimated as the true current source. The current source estimated by the current source specifying means is displayed by the display means 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 the biological activity current source estimation apparatus according to the present invention. In the figure, reference numeral 2 is a magnetically shielded room, and a bed 3 on which the subject M is supine in the magnetically shielded room 2.
And a multi-channel SQUID sensor 1 provided near the brain of the subject M, for non-invasively measuring a minute 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 and housed in the dewar. In the present embodiment, each magnetic sensor is composed of a pair of coils that detect a magnetic field component in the radial direction when the brain of the subject M is a sphere.

The magnetic field data detected by the multi-channel SQUID sensor 1 is given to the data conversion unit 4 and converted into digital data, and then collected in the data collection unit 5. The stimulator 6 is for applying electrical stimulation (or sound, optical stimulation, etc.) 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 the three-dimensional coordinate system based on the QUID sensor 1. For example, small coils are attached to a plurality of positions of the subject M, and the positioning unit 7 supplies power to these small coils.
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. Other than this, a method for grasping the positional relationship of the subject M with respect to the SQUID sensor 1 is to attach a light projector to the dewar and irradiate the subject M with a light beam to grasp the positional relation between the two. Alternatively, various methods disclosed in JP-A-5-237065 and JP-A-6-788925 are used.

The data analysis unit 8 is for estimating the current source in the diagnosis target region 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 means, a current source calculating means, a judging means, a grid point group rearranging means, and a current source specifying means in the present invention, as will be apparent from the description below. . 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 the current source estimated by the data analysis unit 8 is Color monitor 1 superimposed on these tomographic images
It is displayed at 0 or printed out on the color printer 11. An X-ray CT system and M
The tomographic image obtained by the RI apparatus may be directly transmitted to the data analysis unit 8 via the communication line 12 shown in FIG.

As mentioned 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 detects a region to be examined by the subject M, for example, from a biological activity current source in the brain. After measuring the minute magnetic field and collecting the magnetic field data in the data collection unit 5, the data analysis unit 8 executes the 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. 8, a three-dimensional lattice point group N is assumed in the diagnosis target area, for example, the brain (step S1). Here, the unknown number 3n for the grid point group N (the number of current sources expected in the X, Y, Z directions for each grid point) is the same as that of each magnetic sensor 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) by using Biot-Savart's law (each coefficient of the matrix A is calculated for each movement of the lattice points described later). ,
The current source on each grid point is obtained by the linear least squares method with a penalty term (step S2). Hereafter, this step S2
The process 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 represented by the above equation (3), 3n
It is a matrix with × m elements. In equation (4), the solution cannot be obtained because the number m of equations (the number of magnetic sensors S _{1 to} S _m ) is larger than the unknown number 3n. Therefore, the squared error | [Bd]-[B] | of the measured magnetic field [Bd] and the magnetic field [B] exerted on the magnetic sensors S _{1 to} S _m by the current source [P] assumed on each lattice point. And the condition that the evaluation function f represented by the sum of the following penalty term is minimized, the current source [P] is calculated using the linear least squares method. This evaluation function is shown in formula (7)).

[0035]

[Equation 3]

The first term of the evaluation function is the square error of the magnetic field, and the second term is
The term is a penalty term. Λ in the penalty term is a 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. The penalty term has a property that its value becomes smaller as the current source is solidified. Therefore, the current source was 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 sources are likely to vary is suppressed, and the noise component that exists discretely is reduced as a solution.

By adding the condition that the evaluation function f is minimized, the equation (4) is expressed by [P] = A ⁺ [Bd] (8). Here, A ⁺ is ^calculated 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 measurement surface.
By doing as in (11), for the desired current source Pi,
Effect of distance to the magnetic field measurement plane (ie current source Pi
The tendency that is estimated near the magnetic field measurement plane) can be canceled.

[0040]

[Equation 5]

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

When the current source [P] is obtained by the equations (9) and (9), the process proceeds to step S3, where the estimated current source [P] exerts a magnetic field [B] on the magnetic sensors S _{1 to} S _m. Then, it is determined whether or not the sum of the squared error of the measured magnetic field [Bd] and the above-mentioned penalty term is globally minimum. Here, the sum of the squared error of the magnetic field and the penalty term is globally minimum, which means that step S4 described later is performed.
When the grid point group is moved multiple times in the process of repeating,
The sum of the squared error of the magnetic field and the penalty term obtained by the above-mentioned method at the position of each lattice point has the smallest value. Whether the sum of the square error of the magnetic field and the penalty term is globally minimum is determined in step S described later.
In the process of repeating 4, for the rearranged grid point group,
If the sum of the squared error of the magnetic field and the penalty term obtained respectively by the processing of steps S2 and S3 described above is stored, and the respective values are compared and the minimum value is set to the global minimum value. Good.

If it is determined that the value is not the minimum, step S
In step 4, the current sources on the other grid points are 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 grid point group having the same number of grid points as that of the original grid point group N and a close spacing can be obtained. It should be noted that the number of current sources having a large value is not always one, and there are usually a plurality of current sources.

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

After moving the lattice points, the process returns to step S2, and the condition that the above evaluation function is minimized is added to the moved lattice point group, and the current source [P] is applied by the linear least squares method. Is newly requested. Then, in step S3, it is again determined whether or not the sum of the squared error and the penalty term is globally minimum. If it is determined that the sum is not the minimum, steps S2 to S4 described above are repeated.

When it is determined in step S3 that it is the minimum, the current source [P] for the magnetic field [B] that is globally minimized in step S5 is estimated to be the 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. 1 and displayed on the color monitor 10, for example. .

<Simulation> A simulation was performed in order to visually confirm the operation of the above method.
Fig. 3 shows the position of (-16.0, 16.0, 48.0) [mm] (-10 /
Assuming that there is a current source of √2, -10 / √2,0) [nAm], this current source is measured by 129 magnetic sensors and the magnetic field (signal to noise ratio S / N = 20) is 32. Of the evaluation function (that is, the magnetic field 2
This is a simulation result of estimating the current source under the condition that the multiplication 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 figure showing the simulation results, white circles are assumed current sources, arrows or black dots are grid points (estimated current sources), and those with large current values have larger black dots and more current. Larger values are indicated by arrows. Further, among the grid points, those having a small current value do not appear in the figure, and therefore the number shown is smaller than the number of grid points actually set.

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

<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, but it is a criterion for identifying the optimum current source (see FIG. 2). The estimated current source has a tendency to be solidified (locally concentrated) due to the relationship in which the penalty term is added to the step S3). Therefore, when the current sources are distributed with a certain spread, it is difficult to correctly estimate these current sources. In view of this point, the present embodiment has made it possible to correctly estimate a current source having a spread. Since the schematic structure of the apparatus is the same as that of the first embodiment shown in FIG. 1, its description is omitted here.

Hereinafter, with reference to the flowchart of FIG.
The current source estimation process in the data analysis unit 8 will be described. In step S11, similarly to the first embodiment, the grid point group is uniformly set in the diagnosis target area. In step S12, when the current source [P] is obtained from the magnetic field [Bd] measured by the magnetic sensors S _{1 to} S _m by the linear least squares method, the measured magnetic field [P] is obtained as in step S2 of the first embodiment. Bd] and the squared error | [Bd]-[B] | between the magnetic field [B] exerted on the magnetic sensors S _{1 to} S _m by the assumed current source [P] on each lattice point, and the sum of the penalty term. A condition of minimizing the evaluation function f represented by is added.

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

When the current source [P] is obtained, step S13
And the estimated current source [P] is moved to the magnetic sensor S ₁ ~.
It is judged whether or not the squared error between the magnetic field [B] exerted on S _m and the measured magnetic field [Bd] is globally minimum. That is, in this step S13, since the penalty term is removed from the identification standard of the optimum current source, it is possible to avoid adopting an unnecessary fixed current source as the optimum 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 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 grid point group by the linear least squares method with a penalty term added. Then, in step S13, it is again determined whether or not the squared error is globally minimum. If it is determined that the squared error is not minimum, step S1 described above is performed.
2 to S14 are repeated. When it is determined in step S13 that it is the minimum, the current source [P] for the magnetic field [B] that is globally minimized in step S15 is estimated to be a true current source, and the current source is a slice in the region of interest. The process is overlaid and displayed on top.

<Simulation> A simulation was performed in order to visually confirm the operation of the above method.
In Fig. 6, one side is centered around (0, 20, 60) [mm].
Assuming that a current source of 10 nA is evenly distributed in a cube of 20 mm, set 32 grid points from the magnetic field (S / N = 20) measured by 129 magnetic sensors for this evenly distributed current source. The simulation result is estimated by the method of the first embodiment described above. According to the method of the first embodiment, it is understood that the estimated current source is excessively hardened.
FIG. 7 is a simulation result in which the same uniform distribution current source is estimated by the method of the second embodiment. According to the second embodiment, it is understood that the current sources having the uniform distribution are estimated in the 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 lattice point and the measured magnetic field data, and the weighting of the current source. Since the current source on each lattice point is obtained by adding the condition that the sum of squares to the minimum is added, the variation in the obtained physical quantity of the current source is suppressed and the current sources exist discretely. Noise is reduced as a solution.

In order to improve the estimation accuracy of the current source,
Without increasing the grid point group, move the other 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, and estimate the current source again. . That is, since the number of unknowns is constant, the calculation accuracy of the current source calculation can be maintained.

Further, the current source when the sum of the squared error of the magnetic field and the weighted square sum of the current sources is globally minimized is estimated as the true current source, so that the final current source is specified. In the process, there is no need to set the convergence judgment value, and the final current source can be uniquely specified.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a biological activity current source estimation device according to the present invention.

FIG. 2 is a flowchart of an estimation process according to the first example.

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

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

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

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

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

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)

[Claims] 1. A biological activity current source estimation device for estimating a physical quantity such as a position, size, direction, etc. of a biological activity current source, comprising:
(A) A plurality of magnetic sensors that are arranged in the vicinity of the diagnosis target region of the subject and measure a minute magnetic field by the biological activity current source in the diagnosis target region; and (b) magnetic field data measured by each of the magnetic sensors. Data conversion means for converting the data into digital data, and (c) data collection means for collecting and storing the magnetic field data converted into the digital data,
(D) Lattice point setting means for setting a plurality of lattice points in the diagnosis target region so that the number thereof is smaller than the number of the magnetic sensors; and (e) Unknown current source on each lattice point. Current for obtaining an unknown current source by adding the condition that the sum of the square error of the magnetic field exerted by the current source, the square error of the magnetic field data stored in the data collecting means, and the weighted square sum of the current source is minimized. The source calculation means, and (f) the function including the square error between the magnetic field calculated from the obtained current source and the magnetic field data actually measured by the magnetic sensor and stored in the data collection means is globally minimum. And (g) a current source on each grid point obtained by the current source calculating means when it is determined that the function including the squared error is not globally minimum. There is a current source with a large value Lattice point group rearrangement means for rearranging the grid point group by moving the other grid point group to the vicinity of the child points,
(H) The magnetic field when the function including the square error is judged to be globally minimum by the judging means by repeating each processing by the current source calculating means, the judging means, and the lattice point group rearranging means A current source identification unit that estimates the corresponding current source as a true current source, and (i) the current source estimated by the current source identification unit are displayed in a superimposed manner on the tomographic image of the diagnosis target region of the subject. A biological activity current source estimation device comprising: a display means.