JPH05119136A - Position and direction measuring method of detection coil of SQUID sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] To accurately determine the position and direction of the detection coil installed inside the dewar. [Arrangement] An X-ray magazine 6 containing an X-ray film is arranged just below the front end of the dewar 2, and X-ray imaged detection coil images are collected from a plurality of directions. The transmitter 1 is attached to the outer wall of the dewar 2, three points of the X-ray magazine 6 are designated by the stylus type receiver 3, and the positional relationship of the three-dimensional coordinates of the imaging surface with respect to the three-dimensional coordinates of the dewar 2 is obtained. The detection coil image and the X-ray focal point are connected by a straight line, and the position and direction in the three-dimensional coordinates of the imaging surface of the detection coil formed at the intersection of each straight line are obtained. The position and direction of the detection coil in the Dewar three-dimensional coordinate system can be obtained from the above positional relationship.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the position and direction of a detection coil of an SQUID sensor which measures a minute magnetic field formed by a living body current source.

[0002]

2. Description of the Related Art When an external stimulus such as light or sound is given to a living body, a signal (active current) is generated in a sensory nerve.
The magnetic field formed by this biological activity current is SQUI
A sensor using a D (Superconducting Quantum Interference Device) is used to measure the position, size, and direction of the biological activity current source from the measured data. The estimated biological activity current source (hereinafter simply referred to as current source) is displayed on a tomographic image in the body taken by an X-ray CT apparatus or MRI apparatus, and is used for specifying the physical position of the affected area or the like. It

Therefore, it is an extremely important factor to accurately obtain the positional relationship between the measurement point of the SQUID sensor and the living body. The SQUID sensor is configured by housing the SQUID, the detection coil and the compensation coil in a container called a dewar, and the dewar is filled with liquid helium in order to maintain the superconducting state of the SQUID.

In order to obtain the positional relationship between the position and direction of the detection coil, which is the measurement point of the SQUID sensor, and the living body, first, a design drawing of the position and direction of the detection coil with respect to the three-dimensional coordinate system with Dewar as a reference is drawn. See and understand. Next, a projector is attached to the dewar to irradiate the living body with a light beam, or small coils are attached to a plurality of parts of the living body, and the magnetic field generated from the small coils is detected by the SQUID sensor. Understand the positional relationship of the living body to the system. The positional relationship between the detection coil and the living body is obtained from these pieces of information, that is, the relationship between the dewar and the position and direction of the detecting coil, and the positional relationship between the dewar and the living body.

[0005]

However, since the detection coil is immersed in the liquid helium filled in the dewar and is in a cryogenic state, the detection coil contracts, and the position as designed is practically used. ， There is a problem that the direction is not maintained. Further, a similar problem occurs due to an error in manufacturing the detection coil, an error in attaching to the dewar, or the like. If an error occurs in the positional relationship between the dewar and the detection coil, even if the positional relationship between the dewar and the living body is accurately grasped, the positional relationship between the measurement point to be finally obtained and the living body will be incorrect, and the estimated living body The position of the active current source may not be accurately displayed on the tomographic image of the living body, which may cause a misdiagnosis.

The present invention has been made in view of such circumstances, and provides a method for measuring the position and direction of the detection coil of the SQUID sensor, which can accurately grasp the position and direction of the detection coil of the SQUID sensor. The purpose is to do.

[0007]

The present invention adopts the following method in order to achieve the above object. That is, according to the present invention, the dewar accommodating the detection coil of the SQUID sensor is imaged in X-rays from a plurality of directions to collect detection coil images in a plurality of directions, and the dewar 3 is provided on the X-ray imaging surface with respect to the three-dimensional coordinate system. An image pickup surface of a detection coil formed by intersections of straight lines connecting a plurality of points of a detection coil image obtained by X-ray imaging from the plurality of directions and an X-ray focal point at each X-ray imaging Is obtained in the three-dimensional coordinate system, and the position and direction of the detection coil in the Dewar's three-dimensional coordinate system are obtained from them.

[0008]

The operation of the method of the present invention is as follows. When a plurality of points of a detection coil image obtained by X-ray imaging the detection coil housed in the dewar from a plurality of directions and the X-ray focal point at the time of each X-ray imaging are connected by a straight line, The intersection forms a plane that represents the detection coil. By obtaining the position and direction of this plane with respect to the image pickup surface, the position and direction of the detection coil in the three-dimensional coordinate system of the image pickup surface can be obtained. Then, the position and direction of the detection coil in the Dewar coordinate system are obtained from the positional relationship between the Dewar three-dimensional coordinate system and the coordinate system of the imaging surface. As described above, since the position and direction of the detection coil in the state of being housed in the dewar can be obtained, the accurate position and direction can be obtained regardless of contraction due to liquid helium, manufacturing error, and the like.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. [1] As shown in FIG. 1, a transmitter 1 that forms a magnetic field in each of the three orthogonal x, y, and z axes is attached to an appropriate position on the outer surface of the dewar 2, and a detection coil 4 and a compensation coil 5 are incorporated. The index point D made of, for example, lead is attached to the tip of the dewar 2.
Install 1, D2, D3 and D4. An X-ray magazine 6 containing an X-ray film is arranged just below the front end of the dewar 2, and similar index points F1, F2, F3 are attached to appropriate three positions of this X-ray magazine 6.

Index points F1 and F attached to the X-ray magazine 6 at the tip of the stylus type receiver 3 having a coil for receiving the magnitude of each magnetic field from the transmitter 1 respectively.
2 and F3 are designated, and the three-dimensional coordinates of the imaging surface with respect to the three-dimensional coordinate system of the transmitter 1 are input. The stylus-type receiver 3 knows the distance from the transmitter 1 to the built-in coil, that is, the position of the transmitter 1 in the three-dimensional coordinate system, based on the magnitude of the received magnetic field in each direction. The position of the specified point can be obtained by converting it to the position of the specified point. As a result, 3 on the X-ray magazine 6 in the three-dimensional coordinate system of the transmitter 1 (coordinate system xyz of the Dewar 2).
The positions of the three points F1, F2, F3, that is, the positional relationship of the coordinate system XYZ of the imaging surface is obtained.

Similarly, the index points D1, D2, D3 and D4 attached to the tip of the dewar 2 are designated by the stylus type receiver 3, and the index points D1 in the coordinate system xyz of the dewar 2 are designated. , D2, D3, D4 are obtained.
Then, the coordinate system xy of the Dewar 2 that was previously obtained
An index point D on the dewar 2 in the coordinate system X-Y-Z of the imaging surface is determined from the positional relationship between z and the coordinate system X-Y-Z of the imaging surface.
The positions of 1, D2, D3 and D4 are obtained.

A standard receiver 7 for receiving the magnitudes of the magnetic fields in the three axial directions from the transmitter 1 is attached to an appropriate position of the magazine 6, and the coordinates of the dewar 2 when the dewar 2 moves or rotates. The position of the standard receiver 7 with respect to the system xyz is to be known. By doing so, from the three-dimensional position information of the standard receiver 7, the coordinate system x- of the dewar 2 when the dewar 2 moves or rotates.
It is possible to detect the movement and rotation of the coordinate system XYZ of the imaging surface with respect to yz.

[2] X-rays are radiated from an X-ray tube (not shown) arranged to face the magazine 6 so as to sandwich the tip of the dewar 2, and the dewar 2 in the posture shown in FIG.
The X-ray fluoroscopic image of is captured on the X-ray film contained in the magazine 6. Index point D1, attached to Dewar 2
Since D2, D3, D4 and the index points F1, F2, F3 attached to the magazine 6 are made of lead as described above, they are projected on the X-ray film as black dots together with the detection coil 4 and the compensation coil 5. (See Figure 2).

Since the positional relationship between the X-ray film 8 and the X-ray magazine 6 is fixed and known, the X-ray film 8
The X-ray film 8 by correcting the distance between the X-ray magazine 6 and
The image D1 ', D2', D3 'of the index points projected above,
The coordinate position in the coordinate system XYZ of the image pickup surface of D4 'is obtained. Then, as shown in FIG. 3, the images D1 ′, D2 ′, D3 ′, and D4 ′ of these index points and the index point D1 on the dewar 2 in the coordinate system XYZ of the imaging surface obtained above. , D2, D3, D4 are connected by a straight line, and the three-dimensional position coordinates of the intersection of each straight line are obtained. This intersection point becomes the X-ray focal point in the coordinate system XYZ of the imaging surface.

[3] The dewar 2 shown in FIG. 1 is rotated by approximately 90 ° along the direction of the symbol R in the figure, and the magnitudes of the magnetic fields emitted from the oscillator 1 in the xyz directions are expressed as follows. The standard receiver 7 attached to the X-ray magazine 6 receives it. As described above, from this received signal, the dewar 2 coordinate system xy
The positional relationship of the coordinate system XYZ of the imaging surface with respect to −z is obtained. That is, it can be obtained that the three-dimensional coordinates X-Y-Z of the imaging surface are rotated by 90 ° with reference to the coordinate system x-yz of the Dewar 2.

Then, an X-ray fluoroscopic image of the tip of the dewar 2 is picked up by the same method as described in [2] above, and X in the coordinate system X'-Y'-Z 'of the image pickup surface rotated 90 °. The three-dimensional position coordinates of the line focus S2 are obtained (see FIG. 4).

[4] The positions of the respective detection coil images on the two X-ray films obtained thus far in the respective image pickup plane coordinate systems are obtained. As described above, since the positional relationship between the X-ray film and the X-ray magazine 6 is fixed and known,
By correcting these distances, the coordinate position in the coordinate system of the image pickup surface of the plurality of point sequences of the detection coil image projected on the X-ray film is obtained. That is, the coordinate system X of the imaging plane of the plurality of point arrays of the detection coil image captured before the dewar 2 is rotated.
-Determining the three-dimensional position coordinates in YZ,
Three-dimensional position coordinates in the coordinate system X'-Y'-Z 'of the image pickup surface in a plurality of point sequences of the detection coil image picked up after 90 ° rotation are obtained.

Next, as shown in FIG. 5, the coordinate systems of these two image pickup planes are combined to form a plurality of point sequences of the detection coil image of each coordinate system and the X-ray in each coordinate system previously obtained. The focal points S1 and S2 are connected by a straight line. Then, the plane H formed by the intersections of these straight lines is obtained. The position and direction in the coordinate system XYZ of the image pickup surface of the plane H is the position and direction in the coordinate system XYZ of the image pickup surface of the detection coil 4. Image plane coordinate system XYZ
And the positional relationship between the dewar 2 and the coordinate system xyz of the image pickup surface are obtained from the positions of the index points F1, F2, F3 attached to the X-ray magazine 6 as described above.
From these, the position and direction of the detection coil 4 in the coordinate system xyz of the Dewar 2 are obtained.

The position and direction of the dewar 2 in the coordinate system xyz are obtained by performing the same processing on the detection coil 4 and the compensation coil 5 projected on each X-ray film. it can.

Also, for a multi-channel SQUID sensor having a plurality of SQUIDs and detection coils,
By individually capturing the X-ray fluoroscopic image of each detection coil, the position and direction of the detection coil when attached to the dewar 2 can be obtained.

[0021]

As is apparent from the above description, according to the method of measuring the position and the direction of the detecting coil of the SQUID sensor of the present invention, the position of the detecting coil in the Dewar coordinate system from the X-ray image of the detecting coil. Since the detection coil and the direction are obtained, it is possible to perform measurement with the detection coil housed in the dewar, and therefore, regardless of contraction of the detection coil due to liquid helium inside the dewar, manufacturing error of the detection coil, installation error, etc. The position and orientation of the detection coil can be measured. This allows
Accurate grasping of the estimated positional relationship between the position of the biological activity current source and the living body can improve the accuracy of diagnosis, and the safety of treatment and surgery.

[Brief description of drawings]

FIG. 1 is a perspective view showing a measurement example of a position and a direction of a detection coil of an SQUID sensor of the present invention.

FIG. 2 is a diagram showing an example of an X-ray fluoroscopic image of a dewar tip portion.

FIG. 3 is a diagram illustrating a method of obtaining a position of an X-ray focal point.

FIG. 4 is a diagram illustrating a method of obtaining a position of an X-ray focal point when X-ray imaging is performed from another angle.

FIG. 5 is a diagram illustrating how to determine the position and direction of the detection coil in the coordinate system of the imaging surface.

[Explanation of symbols]

 2 ... Dewar 4 ... Detection coil

Claims (1)

[Claims] 1. A three-dimensional X-ray imaging surface with respect to the three-dimensional coordinate system of the dewar by collecting X-ray images of the dewar housing the detection coil of the SQUID sensor from a plurality of directions and collecting detection coil images in the plurality of directions. Find the positional relationship of the coordinate system,
Position and direction in the three-dimensional coordinate system of the imaging surface of the detection coil formed by intersections of straight lines connecting the plurality of points of the detection coil image captured by X-ray imaging from the plurality of directions and the X-ray focal point at the time of each X-ray imaging Then, the position and direction of the detection coil in the Dewar three-dimensional coordinate system are calculated from these values, and the position and direction of the detection coil of the SQUID sensor are measured.