JPH0634783B2 - Biomagnetic measurement method - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a biomagnetism measuring method for measuring minute magnetism in a living body.

[Prior art]

When a living body is stimulated, the polarization formed across the cell membrane breaks down and an action current flows. Such action currents are found in the brain, heart, skeletal muscle, retina, etc., and are called electroencephalogram, electrocardiogram, electromyogram, electroretinogram, etc., respectively. Further, the recording of the magnetic field generated by the flow of the current is called a magnetoencephalogram, a magnetocardiogram, a muscle magnetogram, a retina magnetogram, etc., respectively. In recent years, SQUID (Sup
erconducting Quantum Interference Device: A sensor using a superconducting quantum interference device has been developed to facilitate the measurement of minute magnetic fields in a living body (trigger separate volume p155-163, December 1987, parity separate volume No. 1, p26-38,
1986, Medical System News vol.9 No.4 100th
No. p26-27, 1988). This SQUID sensor needs to be cooled with liquid helium in order to maintain a superconducting state, and is usually immersed in liquid helium filled in a container called Dewar. When measuring the magnetism in a living body with such a SQUID sensor, the measured data is finally used for estimating the position, size, and direction of the current dipole in the living body related to the lesion. The current dipole is displayed on a tomographic image such as an X-ray CT image or MR image showing the structure inside the living body. Therefore, it is extremely important to accurately determine the positional relationship between the measurement point and the living body and the positional relationship between the measurement point and the tomographic image showing the cross section of the living body when performing magnetic measurement. Therefore, conventionally, a projector is attached to the dewar to irradiate a living body with a light beam to grasp the positional relationship, or the dewar is attached to a holding mechanism having absolute coordinates in the examination room to determine the position and direction of the dewar. Obtained on the basis of standard coordinates, and associate this with the position / orientation of the subject sitting in the examination room (“Integrated Biomagnetic Robotic Syste
m ”in Biomagnetism: Application Theory 1985) and so on.

[Problems to be Solved by the Invention]

However, the method using the light projector has a problem that it is difficult to accurately measure the position and direction of the SQUID sensor with respect to the subject, and this positional relationship cannot be measured in a short time. Further, in the method of attaching the dewar to the holding mechanism having absolute coordinates in the examination room, there is a problem in that a holding frame has to be provided in the entire examination room, resulting in a large scale, and it is not easy to correlate the measurement data with the lesion. . An object of the present invention is to provide a biomagnetism measuring method capable of performing magnetic measurement while easily and accurately grasping the relationship between the position and measurement direction of a magnetic measurement point and a living body and a living body image.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, in the biomagnetism measuring method according to the present invention, a transmitter for generating a three-dimensional magnetic field corresponding to a three-dimensional coordinate system is attached to a password housing a SQUID sensor to receive the three-dimensional magnetic field. By specifying the point related to the measurement position and direction of the SQUID sensor with the receiver that can specify the point, the S in the three-dimensional coordinate system by the above magnetic field
By inputting the measurement position and direction of the QUID sensor and designating a plurality of points on the subject by the receiver capable of designating the points, the relationship between the subject coordinate system and the three-dimensional coordinate system by the magnetic field is obtained. , The SQUID sensor measurement position / direction in the subject coordinate system is grasped from these, and the tomographic image in which the index related to the subject coordinate system appears is obtained and the subject coordinate system in the tomographic image coordinate system is obtained. And SQUID sensor measurement position / direction, and then biomagnetic measurement is performed by the SQUID sensor.

[Work]

An oscillator that generates a three-dimensional magnetic field corresponding to the three-dimensional coordinate system is attached to the Dewar that houses the SQUID sensor. The three-dimensional coordinate system based on this magnetic field serves as one reference coordinate system. The point related to the measurement position / direction of the SQUID sensor is designated by the point-designable receiver. This receiver receives the above-mentioned three-dimensional magnetic field, and from the received intensity of the specified point,
Since the position in the coordinate system regarding the three-dimensional magnetic field can be known, the measurement position / direction of the SQUID sensor can be obtained from this. Further, by specifying a plurality of points on the subject with this point-designable receiver, the relationship between the subject coordinate system and the coordinate system based on the magnetic field can be obtained. Thus, the SQUID sensor measurement position / direction in the subject coordinate system can be obtained with the coordinate system based on the magnetic field as a reference. Further, when a tomographic image of a subject is taken, an index associated with the subject coordinate system appears so that the relationship between the tomographic image coordinate system and the subject coordinate system is grasped. Then, the subject coordinate system in the tomographic image coordinate system and the SQUI
Since the measurement position / direction of the D sensor can be grasped, if the biomagnetic measurement is carried out by the SQUID sensor on it, the relation between the position / direction of the measurement data with respect to the tomographic image can be grasped accurately.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. First, the whole system of biomagnetic measurement adopted in this embodiment is as shown in FIG.
ID sensor 1, data collection device 2, and computer 3
And a three-dimensional coordinate input device 4, an MRI device 5 for taking a tomographic image, a display device 31 and a recording device 32 connected to the computer 3. This SQUID sensor 1 is housed in a dewar 11 as shown in FIG. 1, and the magnetism in its detection coil 12 is measured. Therefore, it is important to accurately grasp the position and direction of the detection coil 12. here,
The oscillator 41 of the three-dimensional coordinate input device 4 is attached to an appropriate position on the outer surface of the dewar 11. The oscillator 41 forms a magnetic field in each direction of the three-dimensional rectangular coordinates. Then, a point indicating the position and direction of the detection coil 12 (here, 6
Point) is designated by the tip of the stylus type receiver 42. This point is obtained by projecting the position of the detection coil 12 on the side surface as shown in FIG. 2 when viewed from the front end direction (direction A in the drawing) of the dewar 11. The stylus-type receiver 42 has coils oriented in orthogonal three-axis directions at the center thereof, and obtains a reception signal corresponding to each magnitude of the three-dimensional magnetic field emitted from the oscillator 41, Know the three-dimensional distance from the transmitter 41 to the coil, that is, the position in the three-dimensional coordinate system of the transmitter from the magnitude of the received signal, and exchange that value with the position of the designated point at the tip, It is something you can ask for. Thereby, as shown in FIG. 5, the detection point / direction by the detection coil 12 in the transmitter three-dimensional coordinate system x, y, z can be obtained. The variation in the mounting position / direction of the detection coil 12 in the dewar 11 can be prevented from being affected by measuring the data in advance by X-ray photography and correcting the data. Further, in the case of a multi-channel type SQUID sensor, since a large number of detection coils 12 are arranged, the dewar 1
The center point (axis) of 1 is input as described above, and the position of each detection coil 12 in the transmitter three-dimensional coordinate system x, y, z is determined by the coil positions measured in advance by X-ray photography.
Try to find the direction. When performing head magnetoencephalography, the tip of the dewar 11 is set at the measurement point on the head surface as shown in FIG. At this time, before starting the magnetoencephalography measurement, the stylus-type receiver 42 is used to detect three points on the head (for example, when measuring occipital area,
ION, 3 points on the left and right upper ears, and 3 points on the left side of the head, NASION, INION, and 3 points on the left upper ear, are specified, and the three-dimensional coordinates X, Y, Z of the head as shown in FIG.
Enter. As a result, the relationship between the three-dimensional coordinates x, y, z of the head with respect to the three-dimensional coordinates x, y, z of the transmitter can be grasped as shown in FIG. , Head 3D coordinates X, Y, Z
You can grasp the direction. Then, as shown in FIG. 3, the standard receiver 43 is attached to a predetermined portion of the head so that the positional relationship of the standard receiver 43 at the three-dimensional coordinates x, y, z of the transmitter can be grasped. By doing so, it is possible to detect the movement and rotation of the head three-dimensional coordinates X, Y, Z with respect to the transmitter coordinates x, y, z when the dewar 11 moves. That is, the movement / rotation of the detection point / direction on the three-dimensional coordinate X, Y, Z of the head can be known. In this way, magnetoencephalography is performed while setting the dewar 11 at each measurement point one after another. Then, the detection position / direction at each measurement point is always grasped as on the three-dimensional coordinate X, Y, Z of the head. On the other hand, prior to or after the magnetoencephalography measurement, the MRI apparatus 5 is used to photograph a sagittal image, a transverse image, and a coronal image of the head as shown in FIGS. 6A, 6B, and 6C. Head feature points appearing on these images (NAS
By specifying ION, INION, and four points of the left and right upper ears, the positional relationship of the three-dimensional coordinate of the head in the three-dimensional coordinate of the tomographic image is obtained. As for NASION, an index image taken by MR imaging is attached to the head, and the index image 5
1 (see FIG. 6A) is used. Then, the data obtained by the magnetoencephalography measurement will be positionally and accurately associated with the MR image. That is, S
The magnetoencephalography data obtained by the QUID sensor 1 is loaded into the computer 3 via the data collection device 2, and
The data representing the positional relationship from the three-dimensional coordinate input device 4 is also loaded into the computer 3, and the MR image from the MRI device 5 is also loaded into the computer 3, so that the magnetoencephalography data is intervened by the data representing the positional relationship. It is associated with the MR image. Therefore, the computer 3 calculates the current dipole and uses it for calculation in FIGS. 6A, 6B and 6C.
It is displayed on the MR image as indicated by the arrow. This current dipole is obtained as follows, for example. First, an appropriate model approximating the head is created from the MR image, the positional relationship between the model and the measured magnetoencephalographic data is captured, and the size, position, and direction of the current dipole are assumed in the approximate model. .
The current dipole is calculated so that the squared error between the magnetic flux density distribution created by the assumed current dipole on the approximate model and the measured magnetic flux density distribution is minimized.

【The invention's effect】

According to the biomagnetic measurement method of the present invention, SQ for a living body is
The position / direction of the UID sensor can be accurately and easily grasped, and the biomagnetism measurement data can be accurately associated with the tomographic image of the living body. Therefore, the accuracy of the current dipole or the like calculated using the biomagnetism measurement data and the tomographic image data is also improved, which is useful for the diagnosis of lesions.

[Brief description of drawings]

1 is a schematic perspective view near the tip of the dewar, FIG. 2 is a plan view showing the positional relationship as seen from the direction A in FIG. 1, and FIG. 3 is a schematic perspective view showing the input of head feature points. FIG. 4 is a diagram showing three-dimensional coordinates of the head, FIG. 5 is a diagram showing the positional relationship of each coordinate, and FIGS. 6A, 6B, 6C are diagrams showing examples of MR images, and FIG.
The figure is a block diagram showing a system configuration example. 1 ... SQUID sensor, 2 ... Data collection device, 3 ...
… Computer, 4 …… 3D coordinate input device, 5 …… M
RI device, 11 ... Dewar, 12 ... Detection coil, 3
1 ... Display device, 32 ... Recording device, 41 ... Transmitter of three-dimensional coordinate input device, 42 ... Stylus type receiver of three-dimensional coordinate input device, 43 ... Standard receiver of three-dimensional coordinate input device, 51 ... Index image.

Claims (1)

[Claims] 1. A measuring device for measuring the position of a SQUID sensor with a point-designable receiver for receiving a three-dimensional magnetic field, wherein a transmitter for generating a three-dimensional magnetic field corresponding to a three-dimensional coordinate system is attached to a dewar containing the SQUID sensor. SQU in the three-dimensional coordinate system by the above magnetic field by specifying the point related to the direction
By inputting the measurement position and direction of the ID sensor and designating a plurality of points on the subject by the receiver capable of designating the points, the relationship between the subject coordinate system and the three-dimensional coordinate system by the magnetic field is obtained. , The SQUID sensor measurement position / direction in the subject coordinate system is grasped from these, and the tomographic image in which the index related to the subject coordinate system appears is obtained and the subject coordinate system in the tomographic image coordinate system is obtained. And the SQUID sensor measurement position / direction, and then the biomagnetic measurement is performed by the SQUID sensor.