JPH10272111A - Apparatus for measuring organismic magnetism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organismic action current source capable of accurately superposing the organismic action current source on a diagnosing image. SOLUTION: Magnetic fields generated from respective oscillation coils C1-Cn are detected by fluxmeters S1-Sm and the relative positions of the oscillation coils C1-Cn are calculated. The magnetic field from an organismic action current source generated accompanying the stimulation applied to a subject M is inputted as magnetic field data through a data collection unit 2 and the relative position of the organismic action current source to the fluxmeters S1-Sm is calculated. A marker position for MRI on an MRI image for referring to a position is indicated by an operator and the marker position for MRI on an objective MRI image is calculated by a position converting part 6. By the contrast of the marker position for MRI on the obtained MRI image and the previously calculated positions of the oscillation coils C1-Cn, the position of the organismic action current source on the objective MRI image is specified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biomagnetic measurement for measuring a minute magnetic field generated with a living body current source in a subject and obtaining the living body current source in the subject based on the measurement data. Related to the device.

[0002]

2. Description of the Related Art With the development of superconducting device technology in recent years, SQUIDs (Superconducting Quantum Interferen
A biomagnetic measurement device using a highly sensitive magnetometer called ce Device) is being put to practical use as one of medical diagnostic devices, and is expected to be useful for elucidating brain functions and diagnosing cardiovascular diseases.

In such a biomagnetism measuring apparatus, the position, direction, and magnitude of a biological activity current source in a coordinate system based on a magnetometer are determined based on magnetic field data measured from a subject by, for example, a least square method or a minimum norm method. Is estimated (Jukka Sarvas "Basic mathematical and elec
tromagnetic concepts of the biomagnetic inverse pr
oblem ", Phys. Med. Biol., 1987, vol.32, No.1, 11-
22, Printedby the UK).

On the other hand, such an in-vivo magnetoencephalogram is an MR
By using it together with medical images such as I-images and X-ray CT images, it is possible to specify the physical position of an affected part or the like in a living body. It is important to accurately grasp the positional relationship between the position information and the medical image.

[0005] For this reason, an oscillation coil called a PROBE POSITIONINDICATOR is arranged at a clear position on the surface of the head, such as the root of the nose or under both ears, thereby obtaining the positional relationship between the biological activity current source and the subject. The methods shown in 1)-(5) have been proposed.

(1) Yamamoto T ,, SJ Williamson, et a
l., "Magnetic localization ofneuronal activity in
Natl. Acad. Sci. USA 85, p.
8732-8736 (2) S. Ahlfors, et al, "MAGNETOMETER POSITION INDIC
ATOR FOR MULTI CHANNELMEG ", Advances in Biomagneti
sm, Edited by SJWilliamson et al, PlenumPress, N
ew York 693-696, 1989 (3) Neuromag-122 Preliminary Technical Data, Augus
t 1991 (4) "Apparatus and method for performing biomagnetism measurement" (JP-A-1-503603) (5) "Position detection apparatus for biomagnetic field measurement apparatus" (Japanese Patent Publication No. 5-55)
No. 126) In these methods, a DC current is first applied to the first of three or more oscillation coils attached to a characteristic portion of the body surface of the subject, and the oscillation coil The magnetic field emitted from is detected by a plurality of magnetometers whose positional relationship is known to each other, and the strength of the current applied to the oscillation coil and the strength of the magnetic field detected by each magnetometer, and the positional relationship between the magnetometers, The position of the first oscillation coil with respect to the magnetometer group is obtained. Then, this operation is sequentially applied to the second and subsequent oscillation coils, and after the positions of all the oscillation coils are obtained, the position of the subject with respect to the magnetometer group is determined.

On the other hand, in the imaging of medical images, for example, MRI imaging, an MRI marker for generating a signal detectable by MRI imaging is attached to the same position as each oscillation coil of a subject, and imaging is performed, and the image is drawn on an image. By specifying the specified MRI marker, the MRI marker position in the image space can be obtained.

[0008] Since the position of the MRI marker in the obtained image space corresponds to the position of the oscillation coil with respect to the magnetometer group,
Based on this relationship, a method is used in which the position of the biological activity current source with respect to the magnetometer group is superimposed on the MRI image.

Here, in general, in an imaging apparatus for obtaining a stereoscopic image by synthesizing each slice image, for example, an MRI imaging apparatus, when performing MRI imaging of a cerebral parenchyma as a diagnostic image, an S / N ratio, a spatial resolution, In consideration of the imaging time, a slice thickness of 5 mm is often used. Then, it is desirable from the viewpoint of diagnosis that the biological activity current source obtained by such a biomagnetic measurement apparatus is superimposed on the MRI image having the highest diagnostic capability.

Normally, when the positions of the biological activity current sources are superimposed, the MRI marker depicted on the MRI image itself to be superimposed is specified by a method such as clicking with a mouse. Direction accuracy is high.

[0011]

However, an image for diagnosis is not always an MR image showing a characteristic part of a subject.
For example, as described above, when an MRI image having a slice thickness of 5 mm is used for imaging a diagnostic image, display of an MRI marker having a thickness of 5 mm in the maximum slice thickness direction is not always described with high resolution. Errors may occur. In such a case, the superimposition on the MRI image is performed by MR
Since the position designation error of the marker for I is directly linked to the overlay error of the bioactivity current source (Okamura et al. "Improvement of position accuracy of brain surgery navigator" Medical Imaging Technology Vol12. No.
4 July 1994), a display error of 5 mm directly related to the position designation error is directly connected to the display error of the biological activity current source, and causes a problem in diagnosis.

In order to solve this problem, MRI imaging may be performed with a thin slice thickness of about 1 mm. However, even with the most popular permanent magnet MRI or superconducting MRI, a 0.5 T machine or the like has a thickness of 1 mm to 1 mm. Under conditions of a slice thickness of 0.5 mm, it is difficult to obtain an image quality that can be used for diagnosis.

In particular, recently, fMRI (functional MR)
Attempts have been made to directly image specific brain functions using a technique called I), but since this fMRI image requires a certain slice thickness from its principle, f
When using the MRI marker depicted in the MRI image itself to superimpose the biological activity current source determined by the biomagnetic measurement device, a larger error may occur.

For this reason, the conventional method of designating an MRI marker using the same image as the MRI image on which the position of the biological activity current source is to be superimposed has the above-mentioned problems in many clinical sites. there were.

The present invention has been made in order to solve these problems, and an object of the present invention is to provide a biomagnetism measuring apparatus capable of accurately superimposing a living activity current source on a diagnostic image.

[0016]

In order to achieve the above object, the present invention measures a minute magnetic field generated by a bioactive current source in the skull of a subject, and based on the measured data, measures the minute magnetic field. A biomagnetism measurement device for obtaining a biological activity current source of a specimen, and positional information of the magnetometer and the oscillation coil obtained by detecting a magnetic field generated by an oscillation coil attached to the subject with a magnetometer. The position information of the MRI marker in a spatial coordinate system of a position reference image obtained by imaging the subject with the MRI marker attached to the same position as the attachment position of the oscillation coil in a high-resolution image; Using the positional relationship information between the spatial coordinate system of the diagnostic image and the spatial coordinate system of the diagnostic image obtained by imaging the subject for diagnosis,
A computing unit is provided for superimposing the biological activity current source on a corresponding position of a diagnostic image.

A biomagnetism measuring apparatus for measuring a minute magnetic field generated in accordance with a biological activity current source in a skull of a subject, and obtaining a biological activity current source of the subject based on the measurement data. Position calculation means for calculating the relative position of the oscillation coil with respect to the magnetometer from the detection data of the magnetic field generated by the oscillation coil attached to the magnetometer, and an MRI marker attached at the same position as the attachment position of the oscillation coil. A position reference image obtained by imaging the subject with high resolution, an image storage means for storing a diagnostic image obtained by imaging the subject for diagnosis, and a spatial coordinate system of the position reference image A position for obtaining a position in the spatial coordinate system of the diagnostic image corresponding to an MRI marker position depicted in the position reference image using positional relationship information of the diagnostic image with the spatial coordinate system. Switching means, and superimposing means for superimposing the biological activity current source on the diagnostic image by comparing the position of the oscillation coil with the position of the MRI marker in the spatial coordinate system of the diagnostic image. And

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a biomagnetism measuring apparatus according to one embodiment of the present invention. In FIG. 1, a sensor unit 1 includes a plurality of high-sensitivity magnetometers S1 to Sm each including a pickup coil and a SQUID sensor housed in a dewar together with a refrigerant. It is arranged near the head of the sample M. The oscillating coils C1 to Cn are adhered to characteristic parts such as the root of the nose of the subject M and the area under both ears.
For example, a coil formed by printing metal on a substrate such as a ceramic plate to form a coil portion, or a coil formed by winding a metal wire around a bobbin is used.

The acquisition controller 8 controls the stimulus applied to the subject M via the stimulator 11, and controls the current supplied to the oscillation coils C1 to Cn via the current supplier 10.

An AC magnetic field generated by supplying an AC current to each of the oscillating coils C1 to Cn is detected by magnetometers S1 to Sm in the sensor unit 1 and is subjected to A / D conversion by the data collection unit 2 before oscillation. It is sent to the coil position calculation unit 3.

On the other hand, the magnetic field generated from the biological activity current source due to the stimulation is detected by the magnetometers S1 to Sm in the sensor unit 1 like the magnetic fields generated from the oscillation coils C1 to Cn, After being subjected to the / D conversion, it is sent to the power analysis unit 4. MRI marker designation section 7
Designates an MRI marker displayed on a high-resolution MRI image for position reference based on an instruction from the operator. The designated MRI marker position is converted by the position conversion unit 6 into a position on the target MRI image captured for diagnosis.

The MRI superimposition unit 5 is provided with oscillation coils C1 to Sm for the magnetometers S1 to Sm obtained by the oscillation coil position calculation unit 3.
By associating the position of Cn with the position of the MRI marker on the target MRI image obtained by the position conversion unit 6, the position of the biological activity current source obtained by the power supply analysis unit 4 is superimposed on the target MRI image. It is displayed on the monitor 15.

The computer 9 calculates the position of the oscillation coil based on the A / D converted magnetic field data, calculates the position of the biological activity current source, designates the position of the MRI marker on the position reference MRI image, and refers to the position. Of the position of the MRI marker position on the target MRI on the target MRI image, and MRI
For superimposing the biological activity current source on the oscillating coil position, the above-described oscillation coil position calculation unit 3, power supply analysis unit 4, MRI marker designation unit 7, position conversion unit 6, MRI superposition unit 5,
And a collection control unit 8.

Next, the operation of this embodiment will be described with reference to a computer 9.
This operation will be described with reference to the flowchart of FIG.

First, the oscillation coil C1 for the magnetometers S1 to Sm
When measuring the relative positions of Cn to Cn, the collection control unit 8 supplies an alternating current to each of the oscillation coils C1 to Cn via the current supply unit 10 (S1).

The oscillating coil position calculator 3 includes an oscillating coil C1
To Cn and detected by the magnetometers S1 to Sm are input as magnetic field data via the data collection unit 2 (S2), and the respective oscillating coils for the magnetometers S1 to Sm are input.
The relative positions of C1 to Cn are calculated using a known least square method or the like (S3).

Next, when measuring the position of the biological activity current source with respect to the magnetometers S1 to Sm, the collection control unit 8 applies a stimulus to the subject M via the stimulating unit 11 (S4).

The power supply analyzer 5 inputs magnetic fields from the biological activity current source generated with the stimulus as magnetic field data through the magnetic fluxmeters S1 to Sm and the data collection unit 2 (S5), and the magnetic fluxmeters S1 to Sm. The relative position of the life activity current source with respect to is calculated (S6).

Various methods such as a minimum norm method and a grid point moving method have been proposed as methods for calculating the relative position of the biological activity current source with respect to the magnetometers S1 to Sm. For example, the procedure of the minimum norm method is Hamarainen et al. Report (Matti Hamarainen, Ri
itta Hari, et al, "Magnetoencepharlography. Theor
y, instrumentation, and applications to noninvasiv
e studies of the human brain "Reviews of Modern Ph
The details are described in ysics, Vol.65 No.2 April 1993, p441).

When the relative position of the biological activity current source is calculated, the MRI marker designation unit 7 designates the position reference MRI image based on the designation of the MRI marker position drawn on the position reference MRI image by the operator. Recognizing the MRI marker position above, the position conversion unit 6 determines the position relationship between the position reference MRI image obtained in advance and the target MRI image,
An MRI marker position on the target MRI image is calculated (S7).

The MRI on the position reference MRI image
The operator can specify the marker position by clicking the marker position of the image displayed on the monitor 15 using a mouse or the like.

Further, the MRI image for position reference is indicated by a magnetometer S1.
To calculate the relative positional relationship between Sm and the subject M, an MRI marker is attached to the same place as the oscillation coils C1 to Cn attached to the subject M, and the MRI marker is MRI with high resolution, for example, 1 mm slice. It is obtained by imaging. Purpose MRI
The image shows the conditions for the original examination, for example, fMR
This is an image obtained by imaging using an I (functional MRI) method or the like.

Here, FIG. 3 shows the positional relationship between the spatial coordinate system of the position reference MRI image and the spatial coordinate system of the target MRI image. Based on the drawing, FIG. 3 shows the position reference MRI image and the target MRI image. A method of calculating the position of the MRI marker on the target MRI image from the positional relationship with the target will be described.

Since each position reference MRI image is a two-dimensional plane as a tomographic image, the position of the designated MRI marker M1 is given by two-dimensional coordinates, but includes the number of the slice used for position designation. The position reference M
Three-dimensional coordinates (a1, b) in the spatial coordinate system (a, b, c) of the RI image
1, c1) (not shown) is obtained (FIG. 3 (c)).

Normally, since the MRI image holds the positional relationship of the image in the magnetic field space in the MRI apparatus as header information or the like, the positional relationship in the magnetic field space of the MRI image for position reference specifying the MRI marker M1, for example, slices By using the center magnetic field space coordinate value (Xc ', Yc', Zc ') and the direction of the normal vector of the slice (θ', φ '), (a1, b1, c1
) Can be converted to magnetic field space coordinates (Xm1, Ym1, Zm1) (Fig. 3
(a)). Similarly, other MRI markers M2 and M3 (not shown)
Magnetic field space coordinates of (Xm2, Ym2, Zm2), (Xm3, Ym3, Zm3)
(Not shown) can also be obtained.

The marker position obtained in the magnetic field space coordinate system (Xm
(Ym1, Zm1) to (Xm3, Ym3, Zm3) are the positional relationship in the magnetic field space of the target MRI image, that is, the magnetic field space coordinate value (Xci, Yci, Zci) of the slice center of the target MRI image and the normal vector From the orientation (θ, φ) of the target MRI image and the slice number.

[0038] The MRI superimposition unit 5
The position of the biological activity current source on the target MRI image is specified by associating the MRI marker position on the RI image with the previously obtained positions of the oscillation coils C1 to Cn (S8). The image is superimposed on the superimposed target MRI image and displayed on the monitor 15 (S9).

In the present embodiment, the position of the biological activity current source is superimposed on the MRI image. However, the present invention is not limited to this, and an X-ray CT image or a nuclear medicine image is used instead of the MRI image. Is also good. In that case, the markers need to be made of the material depicted in each modality.

In the present invention, an image for specifying a marker and an image for superimposition may be captured by different modalities. In this case, the positional relationship between the two needs to be clear.

Further, in the present embodiment, a stimulus is applied to a subject, and a biological activity current source induced by the stimulus is used for the purpose M.
Although the present invention is superimposed on the RI image, the present invention is not limited thereto, and a spontaneously generated bioactive current source that does not give a stimulus such as epilepsy may be superimposed. In this case, measurement is performed without performing stimulus output .

In this embodiment, the MRI for position reference is used.
The position of the MRI marker specified in the image is converted into position information in the spatial coordinate system of the diagnostic image, and the bioactivity current source is converted to the diagnostic image by comparison with the position information of the oscillation coil obtained by biomagnetic measurement. Although it was configured to be superimposed, by comparing the position of the MRI marker specified in the position reference MRI image with the position information of the oscillation coil obtained by the biomagnetic measurement, the biological activity in the spatial coordinate system of the position reference MRI image was obtained. The position of the current source may be obtained, converted into position information of the diagnostic image in the spatial coordinate system, and superimposed.

[0043]

According to the present invention, an MRI image for obtaining position information of an MRI marker is captured at a high resolution, and the position of a bioactive current source is superimposed on an MRI image for diagnosis separately. As a result, the bioactivity current source can be accurately superimposed on the target MRI image, and the bioactivity current source can be accurately superimposed on an MRI image having a large slice thickness such as an fMRI (functional MRI) or a brain surface image. Can be matched.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a biomagnetism measuring apparatus according to one embodiment of the present invention.

FIG. 2 is a flowchart illustrating the operation of the present embodiment.

FIG. 3 is a diagram showing a positional relationship in a spatial coordinate system between a position reference MRI image and a target MRI image.

[Explanation of symbols]

 M subject S1 to Sm magnetometer C1 to Cn oscillation coil 1 sensor unit 2 data collection unit 3 oscillation coil position calculation unit 4 power supply analysis unit 5 MRI superposition unit 6 position conversion unit 7 MRI marker designation unit 8 collection control unit 9 computer DESCRIPTION OF SYMBOLS 10 Current supply part 11 Stimulation part 12 Stimulator 13 Target MRI 14 MRI for position reference 15 Monitor

Claims (2)

[Claims] 1. A biomagnetism measuring apparatus which measures a micro magnetic field generated with a biological activity current source in a skull of a subject and obtains the biological activity current source of the subject based on the measurement data. The position information of the magnetometer and the oscillation coil obtained by detecting the magnetic field generated by the oscillation coil attached to the magnetism by the magnetometer, and the MRI marker attached to the same position as the attachment position of the oscillation coil. The MR in a spatial coordinate system of a position reference image obtained by imaging a specimen with high resolution
Using the position information of the marker for I, and the positional relationship information between the spatial coordinate system of the position reference image and the spatial coordinate system of the diagnostic image obtained by imaging the subject for diagnosis, the biological activity current A biomagnetism measurement apparatus comprising a calculation unit for superimposing a source on a corresponding position of a diagnostic image. 2. A biomagnetism measuring apparatus for measuring a micro magnetic field generated with a biological activity current source in a skull of a subject and obtaining a biological activity current source of the subject based on the measurement data. Position calculation means for calculating the relative position of the oscillation coil with respect to the magnetometer from detection data of the magnetic field generated by the oscillation coil attached to the magnetometer, and an MRI marker attached to the same position as the attachment position of the oscillation coil. A position reference image obtained by imaging the subject with high resolution, an image storage unit that stores a diagnostic image obtained by imaging the subject for diagnosis, and a spatial coordinate system of the position reference image A position for obtaining a position in the spatial coordinate system of the diagnostic image corresponding to an MRI marker position depicted in the position reference image using positional relationship information of the diagnostic image with the spatial coordinate system. And a superposition means for superimposing a biological activity current source on the diagnostic image by comparing the position of the oscillation coil with the position of the MRI marker in the spatial coordinate system of the diagnostic image. Characteristic biomagnetic measurement device.