JPH031839A - Brain magnetism measuring apparatus - Google Patents

Abstract

PURPOSE:To achieve a precise determination of a position of a cerebral active part without requiring time for measurement of brain magnetism by assuming positions, sizes and directions of a plurality of current dipoles in a model to determine a group of current dipoles so that a difference is minimized between a magnetic field distribution generated with the group of current dipoles at measuring points of a brain magnetic field and a magnetic field distribution obtained from multi-point brain magnetic field data measured simultaneously. CONSTITUTION:When a multi-point measuring data of a brain magnetic field obtained with a data sampling device 16 and an MRI image data obtained with an MRI device 17 are sent to a computer 18, with the determination of a positional relationship between the measuring points and an MRI image, a head approximate model selected and a coordinates system is selected. As a result, a coordinate system is determined and a brain magnetism measuring data subjected to a processing is used to determine a position, size and direction of each of a group of current bipoles on coordinates. This case, the position, size and direction of the current bipoles are assumed individually on the coordinates and the position, size and direction of the current bipoles are determined so that a least squared error is minimized in a magnetic field distribution generated at magnetic field measuring points by the current bipoles and a magnetic field distribution measured actually.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a device that measures magnetic fields generated in the brain of a human or the like and estimates active areas of the brain.

[Conventional technology]

Traditionally, determining the location of brain active areas by measuring magnetic fields generated in the human brain has been used in clinical medicine, such as estimating the location of epilepsy, research on spontaneous brain magnetism (especially alpha waves), and research on induced brain magnetism. (Ritta Ma
ri and R15to J, Ilmoniemi
. ”Cevebral Magnetic Fields
”CRCCriticalReviews in B
iomedical Engineering Vol.
, 14. No. 2 p93-126.1986. Kaufman, L.
and J, Williamson. Recent developments in new
uromagnetism” 1nThfrd Int
ernational Evoked Potenti
alsSymposium, Stoneham:
Butterworth, ploo-113°198
7). Further, USP No. 4,736,751 proposes a system for identifying brain activity areas by electroencephalogram measurement.

[Problem to be solved by the invention]

However, conventionally, when measuring magnetoencephalography,
Because a magnetic sensor with few measurement points is used, it is necessary to measure the required range of the skull while changing the location of the magnetic sensor to create a magnetoencephalogram, which takes time. By simply creating and displaying an isomagnetic field map, it is possible to grasp the overall magnetic field distribution or simply grasp the current dipoles using the isomagnetic field map, but it is not possible to accurately estimate a large number of current dipoles. The problem was that it was impossible. Further, USP No. 4,736,751 proposes a system suitable for electroencephalogram measurement, but magnetoencephalography requires special measures for the measurement system, sensor, and MRI head image position grasp. An object of the present invention is to provide a magnetoencephalography measurement device that does not take much time to measure magnetoencephalography and can accurately determine the position of a brain active area.

[Means to solve problem N]

In order to achieve the above object, the magnetoencephalography measurement device according to the present invention uses a multi-channel SQUID (Supe
rconducting Quantum Inter
means for simultaneously measuring brain magnetic fields at multiple points using a superconducting quantum interference device (superconducting quantum interference device) sensor, an MRI means for taking an MRI image of the head, and a means for determining the positional relationship between the multi-channel 5QUID sensor and the MRI image. and a means for creating a head approximation model from the MRI image, assuming the positions, sizes, and directions of a plurality of current dipoles in the model, and creating a group of current dipoles at the measurement point of the brain magnetic field. means for determining a current dipole group that minimizes the difference between the magnetic field distribution and the magnetic field distribution obtained from the simultaneously measured multi-point brain magnetic field data; means for displaying on the image.

[For production]

By using a multi-channel SQUID sensor, brain magnetic fields can be measured simultaneously at multiple points. On the other hand, an MRI image of the head is taken by the MRI means. Then, the positional relationship between the multi-channel SQUID sensor and the MRI image is determined, and thereby the order-of-one relationship between the measurement point of the magnetoencephalogram measurement data and MR, 1 image is found. A head approximation model is created from the MRI images, and in this model, the positions, sizes, and directions of multiple current dipoles are assumed, and the magnetic field distribution created by these current dipole groups at the measurement points of the brain magnetic field and the above-mentioned simultaneous By finding the current dipole group that minimizes the difference from the magnetic field distribution obtained from the measured brain magnetic field data at multiple points, the position of each current dipole,
Know the size and direction. Each position of the current dipole group obtained in this way corresponds to the MRI image, so it is an image related to the MRI image (that is, the MRr image itself or an image made from it).
can be displayed on top. As a result, the brain active area is displayed on the MRI image as a group of current dipoles, and its position can be known precisely.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a subject 10 undergoes an examination in an examination room 8 (a shielded room or a room with little external magnetic field). All structures used in this examination room 8 are made of non-magnetic materials. A multi-channel SQUID sensor 11 is set on the head of the subject 10. A display device 12 such as a TV monitor device is arranged outside the examination room 8, and its image is displayed to the subject 10 via a mirror 12a.
A visual stimulus is given by having the person observe the object. Also,
An earphone 13 is placed outside the examination room 8, and the sound is guided to the ear of the subject 10 through a silicon tube 13a, etc., thereby providing auditory stimulation. Furthermore, somatosensory stimulation is provided using an electrical stimulation device (not shown). Alternatively, the motion detector 14 is used to perform the recognition motion. These are controlled by an experiment control device 15 to form a measurement system 9. The data collection device 16 collects brain magnetic field measurement data from multiple points from the multi-channel SQUID sensor 11. The head of the subject 10 is photographed by the MRI device 17 . The multi-point measurement data of the brain magnetic field obtained by the data collection device 16 and the MRI image data obtained by the MRI device 17 are sent to the computer 18 . In the computer 18, the magnetic field measurement data undergoes no special processing in the case of epileptic brain magnetism, undergoes FFT (fast Fourier transform) processing in the case of spontaneous brain magnetism such as alpha waves, and undergoes S/N ratio processing in the case of evoked brain waves. Addition (integration) processing is applied to improve the performance. In each of these cases, digital filter processing may be further performed to improve the S/N ratio. A head approximate model is created from the head MRI image. In addition, the relative positional relationship between the SQUID sensor and the head is determined, and this enables the magnetic brain measurement points and the head MRI.
The positional relationship with the image is determined. In this way, the measurement point and M
After understanding the positional relationship with the RI image, a head approximation model is selected and a coordinate system is selected. A coordinate system is thus determined, and the position, size, and direction of each current dipole group are determined using the magnetoencephalography measurement data that has undergone the above processing. This corresponds to solving a reverse problem, and here we assume the positions, sizes, and directions of multiple current dipoles on the above coordinates, and calculate the magnetic field distribution created by these current dipoles at the magnetic field measurement point. , the position, size, and direction of each current dipole group are determined so that the least squares error from the actually measured magnetic field distribution is minimized. The current dipoles determined in this way are displayed on the MRI image or a three-dimensional image created from the MRI image with marks such as arrows, or are displayed in coordinates on a single display device. The multi-channel SQUID sensor 11 is usually a dewar
It is cooled by being immersed in liquid helium in a container called a . Here, as shown in FIG. 2, three dewars 2 are used at the same time so that the bottom surfaces of their tips surround the subject's head. These three dewars 2 are each
It is held by a belt 24 via a shaft 23 at the tip of an arm 22 extending and contracting from the base 21 . The dewar 2 has a generally cylindrical shape, and the dewar 2 can be rotated about its central axis by loosening a fixing device (not shown) for the belt 24. Further, this belt 24 is rotatably attached to the tip of the arm 22 by a shaft 23. Further, the base 21 is movable along a rail (not shown) provided on the ceiling and is rotatable about a vertical axis. With such a suspension mechanism, each dewar 2 can be freely determined in its position in the horizontal and vertical directions, as well as in any direction in the horizontal plane, and in the inclination angle with respect to the vertical axis. It can also rotate around its own central axis. Further, the bottom surfaces of the dewars 2 located on both sides are inclined at about 45 degrees from the central axis, as shown in FIGS. 2 and 3. The bottom surface of the dewar 2 located in the center is approximately perpendicular to its central axis. Both of these bottom surfaces are spherical and concave, resembling the skull. The inside of the dewar 2 is constructed as shown in FIG. The dewar 2 consists of a liquid helium container 32 containing liquid helium 41 and an envelope 31 covering the outside thereof. The inside of this envelope 31 is a vacuum 33, and a super insulation layer 35 as a heat insulating material and a vapor cooling metal strip 34 surround the liquid helium container 32.
and are placed. A number of detection filters 42 are arranged at the bottom of the liquid helium container 32 . Each of the detection coils 42 is wound around a quartz bobbin. Since the bottom surface of this dewar 2 is inclined at 45 degrees and forms a spherical concave surface, a large number of detection coils 4 are arranged along this 45 degree concave surface.
2 is placed. In the case of the central dewar 2, the bottom surface is a substantially right-angled spherical concave surface, and a large number of detection coils are arranged along the bottom surface. In either case, when the detection coils 42 are viewed from the front, they are arranged at equal intervals as shown in FIG. 4, and are oriented toward the center of the curvature of the spherical concave surface. Here, the detection coil 42
As shown in FIG. 4, 19 units are arranged per dewar, and each of them is connected to 19 DCSQUID units 43. These detection coils 42 and DC
The SQUID unit 43 is supported by a support tube 44. A heat radiation shield 45 is attached to the upper part of the support tube 44. The magnetic flux detected by the detection coil 42 is transmitted to the DCSQUID unit 43 by a magnetic flux transformer, and the magnetic flux is converted into voltage by the operation of a FLL (Flux Lock Loop). preamplifier unit 4
It is output to the outside via 6. Since each dewar 2 has such a concave bottom surface and the position and direction of the dewar 2 can be determined freely as described above, the detection coil 4
The position No. 2, that is, the magnetic field measurement point, can be placed on a spherical surface that approximates the skull. These 57 (=19×3) measurement signals are sent to the computer 18 via the data collection device 16. That is, as shown in FIG. 5, it is sent to the CPU bus 52, stored in the CPU memory (not shown), and
The data is sent via the disk interface 53 to the hard disk drive unit 254 and stored therein. After that, C.P.
After the processing by U51 is performed and the obtained image is stored in the image memory 58, the color image monitor device 5
9, and the image will be displayed. Further, a character monitor device 56 and a keyboard device 57 are connected to the CPU bus 52 via a console controller 55, so that data processing procedures and the like can be input. The data collection device 16 is configured as shown in FIG. SQ
The signal (analog) sent from the FLL of the UID sensor 11 is first taken in via the amplifier 61, and then sent to the filter 62,
It is input to the A/D converter 65 via the sample hold circuit 63 and the multiplexer 64, where it is converted into a digital signal in real time, and then F I F O (First
In First Out) circuit 66 and output. On the other hand, the positional relationship between the magnetic field measurement point and the MRI image is determined as follows. As shown in FIG. 7, several small coils 71 are attached to characteristic positions on the skull of the subject 10. Three points among the nasal root, the preauricular notch, and the external occipital eminence point are desirable as the characteristic positions.A known current pulse is sequentially applied to each of the small coils 71 installed in this way, and the multiple SQUID sensors 11. The computer 1 calculates the magnetic field measured by the small coil 71 placed on known coordinates.
By storing the information in advance in step 8, the position of the small coil 71 attached to the skull can be determined. Thereby, the positional relationship on the magnetic field measurement coordinates of the cranial feature point to which the small coil 71 is attached can be known. Note that instead of using the small coil 71 in this way, three
It is also possible to determine the positional relationship between the measurement point by the SQUID sensor 11 and the head using a dimensional digitizer. This is done by attaching an orthogonal coil to the head side, generating an orthogonal magnetic field with the orthogonal coil, and detecting it with the orthogonal coil provided on the SQUID sensor 11 side.
The positional relationship with the sensor 11 is detected three-dimensionally. On the other hand, in the MRI apparatus 17, as shown in FIG. (x-y
(lined up in two directions perpendicular to the plane). Since this image data is sent to the computer 18, it is possible to match the positional relationship between the MRI image and the magnetic field measurement data. The computer 18 identifies the boundaries of the head epidermis, cranium, and brain from this three-dimensional MRI image data, and creates an approximate model by using these boundaries. This approximate model is, for example, the 9th
10 and 11. 9th
The figure represents the cerebral cortex with homogeneous lines. Figures 10 and 11 show the head epidermis, head epidermis-cranial boundary, cranial-cerebral cortex boundary,
Represented by multilayer spheres and triangular elements, respectively. The triangular element representation is the most accurate model. Regarding these models, assuming the positions, sizes, and directions of multiple current dipoles, the so-called reverse direction problem is solved. The magnetic field Bir created by the current dipoles at the measurement point is a spherical model (Figure 9).
If , the analytic expression has already been found (B, NEI
L CUFFIN et al, “MagneticF
fields of a Dipole in 5pec
ial Volume Conductor 5hape
s”IEEE Trans, Bion+ed, En
g, , Vol. BME-24, No. 4. ρ372-381.197
7) can be obtained using this. In the case of the multilayer sphere model (Figure 10) and the precision model (Figure 11),
The model is expressed with triangular elements, and three-dimensional potential problems can be solved using the boundary element method (C, A, Previa "Introduction to the Boundary Element Method" Baifukan), the boundary integral equation method (A, C, L, Barnard
et al. ”The application of select
romagnetic theory of select
"rocardiology"
Journal. Vol, 7. p443-491.1967). Then, the positions, sizes, and directions of the plurality of current dipoles are determined so that the least squares error with the measured value Bie is minimized as follows. Once the position, size, and direction of each current dipole are determined in this way, they are superimposed using marks such as arrows on a 3D MRI image or a 3D image obtained by transforming the 3D MRI image. . In this way, for example, arrows representing current dipoles are displayed on the three-dimensional head cut image as shown in Fig. 12, or on coronal, sagittal, and transverse cross-sectional views as shown in Fig. 13 A, B, and C. An arrow will be displayed. Further, the distance and coordinates of the current dipole from an arbitrary point on the head skin may be displayed. Furthermore, in addition to displaying the current dipole corresponding to the brain activity at a certain point based on the magnetoencephalography measurement data at a certain point, it also measures the brain magnetism continuously over a long period of time and then calculates the current dipole at regular intervals. It is also possible to understand temporal changes in brain activity and dynamically understand brain activity by displaying it as a graph or by changing the color of the current dipole over time.

【Effect of the invention】

According to the magnetoencephalography measuring device of the present invention, the multi-channel S
Because magnetoencephalography is measured using a QUID sensor, testing time can be shortened. Furthermore, it is possible to determine the precise position of a brain active area, and in the case of epilepsy, for example, it becomes clear how much π corresponds between an abnormal biological function area on an MRI image and a current dipole generated by epilepsy.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an overall system according to an embodiment of the present invention, FIG. 2 is a front view showing the arrangement of a dewar in which a SQUID sensor is housed, and FIG. 3 is a sectional view showing the inside of the dewar. Figure 4 is a diagram showing the positional relationship of the detection coils;
FIG. 5 is a block diagram showing the hardware configuration of the computer, FIG. 6 is a block diagram showing the hardware configuration of the data collection device, and FIG. 7 is a diagram showing the position of the small coil attached to the subject's skull. Figure 8 shows a slice plane of an MRI image, Figure 9 shows a spherical model of the cranium, Figure 10 shows a multilayered spherical model of the cranium, and Figures 11 A, B, and C show precision of the cranium. FIG. 12 is a diagram showing a simulated homogeneous model, FIG. 12 is a diagram showing a three-dimensional cut-off image of the head, and FIG. 13 A, B, and C are diagrams showing three-directional cross-sectional images of the head. 8... Examination room, 9... Measurement system, 10... Subject,
11...SQUID sensor, 12.19...Display device, 12a...Mirror 13...Earphone, 13a
... Silicon tube 14 ... Motion detector, 15.
...Experiment control equipment, 16...Data acquisition device, 17.
... MRI device, 18... Computer, 2... Dewar-221... Base, 22... Arm, 23...
・・Shaft, 24・Belt, 31・Envelope, 32・
...Liquid helium, 33...Vacuum, 34...Vapor-cooled metal strip, 35...Super insulation layer, 41...Liquid helium, 42...Detection coil, 43...DCSQUID unit, 44... Support cylinder, 45... Heat radiation shield, 46... Preamplifier unit, 51... CPU, 52... CPU bus, 53... Disk interface, 54... Hard disk driver device, 55... Console controller, 56... Character monitor device, 57.
・・Keyboard device, 58 ・・Image memory, 59
...Color' image monitor device, 61...Amplifier, 62...Filter, 63...Sample hold circuit, 64...Multiplexer, 65...A/D converter, 66...FIFO Circuit, 71...small coil. Paper I'? Trouble paper 8th note No. U own chopsticks, 13 piles A, B Sacycle Y Runsno (゛-

Claims (1)

[Claims] (1) A means for simultaneously measuring brain magnetic fields at multiple points using a multi-channel SQUID sensor, an MRI means for taking an MRI image of the head, and the multi-channel SQUID sensor.
means for determining the positional relationship between the ID sensor and the MRI image;
means for creating a head approximation model from the MRI image;
In this model, the positions, sizes, and directions of multiple current dipoles are assumed, and the magnetic field distribution created by these current dipole groups at the above-mentioned brain magnetic field measurement points and the above-mentioned simultaneously measured multi-point brain magnetic field data are calculated. A magnetoencephalography measuring device comprising means for determining a current dipole group that minimizes the difference from the magnetic field distribution obtained by the current dipole group, and means for displaying the current dipole group on an image related to the above-mentioned MRI surface image.