JP3451190B2 - Biomagnetic measurement device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly sensitive quantum interference device (SQUID: Superconducting quan) for a biomagnetic field generated by cardiac muscle activity or the like.
tum interference devices (gane)
The present invention relates to a biomagnetic field measurement device that performs measurement using tomete). 2. Description of the Related Art The distribution of a weak magnetic field generated from a living body is measured using a superconducting quantum interference device (SQUID), which is a conventional magnetic sensor. A multi-channel biomagnetic imaging apparatus that estimates a position and images its distribution is known. Such a conventional example is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 4-3193.
No. 34 or JP-A-5-146416. [0003] The above-mentioned prior art relates to the operating principle of a biomagnetic imaging apparatus, and its disclosure does not disclose any technical problems or means for implementing the present invention. . [0004] Further, there is no disclosure of a specific device configuration in consideration of operability and the like for a subject and a doctor who operates the device. [0005] It is an object of the present invention to provide a biomagnetic field measuring apparatus which can easily perform a measurement for a subject and an operator of the apparatus. [0006] In order to achieve the above object, the present invention has the following features. A magnetic shield room for blocking the influence of magnetism, a bed movable in a three-dimensional direction and on which a subject is placed during measurement, and a magnetic sensor for measuring a magnetic field generated by the subject on the bed are provided. In the biomagnetism measuring device provided with the sensor means, the distance between the upper surface of the bed and the floor surface of the magnetically shielded room when the upper surface of the bed is lowered to the lowest position is 35 to 50 cm. Further, a biomagnetic field measuring apparatus in which the distance between the bottom surface of the sensor means and the floor surface of the magnetic shield room is set to 75 to 90 cm is proposed. Further, the bed is provided with adjusting means for adjusting the movement of the bed itself in the height direction of the subject, and the distance between the center line of the sensor means and the adjusting means is set to 0 to ++.
We propose a biomagnetic field measuring device with a length of 60 cm. [0010] Further, the bed serves as position adjustment means of the bed itself, the first adjustment means for adjusting the movement of the subject in the height direction, and the second adjustment means for adjusting the movement of the bed in the lateral direction. The present invention proposes a biomagnetic field measuring apparatus comprising: an adjusting means for adjusting the movement in the vertical direction; and a third adjusting means for performing a movable adjustment in the vertical direction, wherein the distance between the first to third adjusting means and the sensor means is at least 40 cm or more. . Further, the first to third adjusting means include:
In each case, a biomagnetic field measuring device is proposed which is installed at a position lower than the uppermost surface of the bed. [0012] These functions will be described in the following embodiments of the invention. An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an embodiment of a biomagnetic measurement apparatus (heart magnetic measurement apparatus) to which the present invention is applied.
As shown in FIG. 1, the biomagnetic measurement apparatus is installed in a magnetically shielded room 1 in order to remove the influence of environmental magnetic noise. The subject 2, which is a subject formed of a living body, is measured while lying on the bed 3. The subject's body plane (in the case of the chest, generally parallel to the chest wall) is assumed to be substantially parallel to the plane of the bed 3, and this plane is defined by a rectangular coordinate system (x, y,
z) is parallel to the xy plane. The chest of the subject is curved and tilted, but is assumed to be substantially parallel for ease of explanation. A dewar 4 filled with a liquid He serving as a refrigerant is arranged above the chest of the subject 2, and the dewar 4 is a superconducting quantum interference device (SQUID = Superconducting).
A plurality of magnetic sensors including a Quantum Interference Device and a detection coil connected to the SQUID are accommodated. The liquid He is continuously replenished from the automatic replenishing device 5 outside the magnetic shield 1. The output of the magnetic sensor outputs a voltage which has a specific relationship with the strength of the biomagnetic field generated from the subject 2 and which is detected by the detection coil (it can be considered as a magnetic flux density). The signal is input to a FLL (Flux Locked loop) circuit 6. The FLL circuit 6 cancels a change in the biomagnetic field (biomagnetism) input to the SQUID via a feedback coil so as to keep the output of the SQUID constant (this is called a magnetic field lock). By converting the current flowing through the feedback coil into a voltage, a voltage output having a specific relationship with a change in the biomagnetic signal can be obtained. Since the detection is performed via the feedback coil as described above, a weak magnetic field can be detected with high sensitivity. The output voltage is input to an amplifier / filter / amplifier (AFA) 7 whose output is sampled, A / D converted, and taken into a computer 8. The computer 8 comprises a personal computer, 8-1 denotes its display unit, 8-2 denotes a keyboard, and 8-3 denotes a mouse. The mouse 8-3 is used to select a processing target by moving a cursor on the screen. This operation can also be performed by operating the keyboard. AFA7 input gain (Igain)
And the output gain (Ogain) is adjustable.
FA7 is a low-pass filter (LPF) that passes a frequency signal lower than a first reference frequency, a high-pass filter (HPF) that passes a frequency signal higher than a second reference frequency lower than the first reference frequency, and a commercial power supply frequency. Includes a notch filter (BEF) to cut. The computer 8 can perform various processes, and the processing results can be displayed on the display unit 8-1. Note that the computer 8 shown in FIG. 1 shows one embodiment, and the present invention is not limited to this. For example, a device provided with a display having a touch panel, or a device using another coordinate pointing device such as a trackball or a joystick instead of a mouse may be used. In some cases, the computer may be connected via a public telephone line. As the SQUID, for example, a DC SQUID is used as an example. When an external magnetic field is applied to the SQUID, a DC bias current (Ibias) is supplied to the SQUID so that a voltage (V) corresponding to the external magnetic field is generated. When the external magnetic field is represented by a magnetic flux Φ, a characteristic curve of V with respect to Φ, that is, a Φ-V characteristic curve is given by a periodic function. Prior to measurement, the FLL circuit 6
Is adjusted to adjust the DC voltage of the Φ-V characteristic curve to the zero level by adjusting the offset voltage (VOFF). Furthermore,
The offset voltage (AOFF) of the AFA 7 is adjusted so that when the input of the AFA 7 is zero, the output becomes zero. When a large magnetic field is applied to the SQUID from the outside, the magnetic field is trapped by the SQUID and its normal operation cannot be performed. In that case, SQUID
Can be heated once to a normal state, and then the heating can be stopped to remove the trapped magnetic field. The SQUID heating operation in that case is called a heat flash. FIG. 2 shows the arrangement of the magnetic sensors. The detection coil of the magnetic sensor has a coil for detecting a tangential component of the biomagnetic field (a component substantially parallel to the living body plane, that is, an xy plane) and a normal component of the biomagnetic field (a component orthogonal to the living body plane, that is, the xy plane). There is a coil that detects As a coil for detecting the tangential component of the biomagnetic field, the coil surface is in the x direction and y direction.
Two coils, each oriented in the direction, are used,
As a coil for detecting a normal component of the biomagnetic field, a coil having a coil surface oriented in the z direction is used. Plurality of magnetic sensors 20-1 to 20-8, 21-1 to 21-8, 22-
1-22-8, 23-1 to 23-8, 241-1 to 24-
8, 25-1 to 25-8, 26-1 to 26-8 and 27
As shown in FIG. 2, -1 to 27-9 are arranged in a matrix on the body surface, that is, a surface substantially parallel to the xy plane. Although the number of magnetic sensors may be arbitrary, in FIG. 2, since the matrix of magnetic sensors has 8 rows and 8 columns, the number of magnetic sensors is 8 × 8 = 64. Each magnetic sensor, as shown in FIG.
It is arranged so that its longitudinal direction coincides with the direction perpendicular to the living body plane, that is, the xy plane (z direction). In addition,
In this embodiment, the bed surface and the XY surface of the sensor are parallel to each other. However, in order to improve the measurement accuracy, it is better to approach the body, and it is possible to tilt the bed. However, since the human body, which is the subject, is always moving, if the human body is brought into close contact with the human body, this movement will move the detection unit, and it will be difficult to perform highly accurate detection. FIG. 5 shows a positional relationship between the magnetic sensor and the chest 30 which is a measurement portion of the subject 2. The points shown are
An intersection of a row and a column on the matrix shown in FIG. 2, that is, a measurement point of the subject 2, that is, a measurement position is shown. Each of these measurement positions is also called a channel. As can be seen from the figure, in this embodiment, the height direction of the subject 2 is defined as the y direction, and the lateral direction of the subject 2 is defined as the x direction. FIG. 6 shows the measurement results of the biomagnetic field at the respective measurement positions shown in FIG. This measurement result shows the time-varying biomagnetic field waveform obtained by performing the above-described processing based on the signals detected by the magnetic sensors corresponding to the respective measurement positions, for each corresponding channel in the matrix. Things. In this embodiment, since each channel is provided at a position where a magnetic field generated by the heart muscle can be detected, the waveform in FIG. 6 shows a magnetocardiogram waveform. A waveform obtained by measuring a magnetic field generated from the heart muscle is called a magnetocardiogram waveform. As shown in FIG. 6, when the measurement data measured for each channel is displayed corresponding to the position for each channel, this is called a grid map display.
The magnetocardiogram waveform in FIG. 6 shows the waveform of the measurement result of the magnetocardiogram for a certain healthy person. Here, (a) shows the magnetocardiogram waveform of the tangential component Bx, (b) shows the magnetocardiogram waveform of the tangential component By, and (c) shows the magnetocardiogram waveform of the normal component Bz. The specific structure of the biomagnetism measuring device described above will be described in more detail with reference to FIGS. FIG. 3 is a plan view of the biomagnetism measuring apparatus according to the present embodiment as viewed from above the magnetic shield room 1, and FIG. 4 is a side view thereof. The bed 3 is provided with a bed top 106 on which the subject 2 is placed, and as a position adjusting means for the bed itself, a handle for adjusting the front and rear position of the bed top for performing movable adjustment in the height direction of the subject (first handle). Adjusting means) 108 and second adjusting means (not shown) for performing the movable adjustment of the subject in the lateral direction.
And a bed top plate lifting / lowering lever (third adjusting means) 107 for vertically adjusting the movable state. These adjusting means are provided on the side surface of the bed 3. The dewar 4 is supported by a gantry 102, and liquid He is supplied from the liquid He automatic supply device 5 via a transfer tube 104 for He supply.
105 is an exhaust pipe of evaporating He, 111 is a signal cable, 1
12 is a He level meter cable, and 113 is a measurement circuit rack. Among these components, the bed top plate 106, Dewar 4, bed top plate front / rear position adjustment handle 108 and the like are set as follows. The setting conditions will be described with reference to FIG. (1) Regarding the height i of the lowest position of the bed top 106, the height from the floor of the magnetically shielded room 1 when the top 106 of the bed 3 is lowered to the lowest position (ie, the height of the bed top 106) The distance (i) between the upper surface of the bed and the floor surface of the magnetically shielded room is set to a value between 35 and 50 cm. This value is a value that allows the adult to take a posture of sitting on the bed 3 smoothly. As a result, when the subject gets on the bed, he or she once sits on the bed and then lays down on the bed, thereby reducing the accident and the burden on the subject when the subject gets on or off the bed. This is important for subjects with heart disease. In the case of 35 cm or less, it is necessary to take a posture of squatting down once or sitting down once on the top plate and lowering the leg. In addition, if it is 50 cm or more, it is necessary to once lift the body with toes or arms, and in extreme cases, it is dangerous to climb up. In any case, the burden is heavy on the elderly and subjects with heart disease. (2) Height j of the bottom surface of liquid He Dewar 4 Height from the floor surface of magnetic shield room 1 to the bottom surface of liquid He Dewar 4 (ie, the height between the bottom surface of sensor means and the floor surface of magnetic shield room). The interval j is set to a value between 75 and 90 cm. This value is obtained as an optimal value necessary and sufficient for the measurement in consideration of the thickness of the adult chest, with the adult lying on the bed designed based on the above item (1) in a supine or prone position. That is, it is considered that the thickness of the adult chest varies depending on the body shape, but falls within a range of approximately 30 to 40 cm. From this viewpoint, the bed minimum height i
It is enough if there is a value obtained by adding 40 cm to the above. Further, a doctor or other person who adjusts the bed (adjuster) adjusts the height of the subject 2 using the lever 107 provided on the bed 3 when the dewar 4 bottom height j Is a value at which the height of the liquid He dewar 4 can be precisely and safely adjusted because the bottom surface of the liquid He dewar 4 is exactly at the level of the adjuster's line of sight in the state of the adjustment posture (warped state). This is most desirable in terms of operability and safety. (3) The center line O of the liquid He Dewar 4 and the position interval e between the front and rear position adjusting handles 108 of the bed top plate The center line O of the liquid He Dewar 4 and the front and rear position adjusting handle 108 of the bed top (first adjusting means) 108 0 to +
The value is within a range of 60 cm. To adjust the heart measurement position of the subject 2 to the center position of the liquid He Dewar 4, the coordinator is positioned in front of or slightly to the right of the liquid He Dewar 4 toward the subject 2, and the right and left sides of the bed top plate are used. The most direct alignment method is to visually check the position of the subject 2 / the liquid He Dewar 4 while rotating the position adjustment handle 108. For this reason, the above-mentioned position interval 0 to +60 cm is defined as the optimum range of the work efficiency of the adjuster. As a result, it is possible to achieve the highest operability, high accuracy, and minimize measurement errors. (4) Arrangement of metal control device Bed top plate front / back position adjustment handle (first adjustment means) 1
08, bed top plate lifting / lowering cylinder 107 composed of a bed top plate lifting / lowering lever 107 (third adjusting means) and a hydraulic cylinder
Metallic control members such as 15 (part of the third adjusting means) and the second adjusting means generate magnetic noise when moving. To avoid this effect, each metallic control member must be at least 40c from any magnetic sensor in the liquid He Dewar 4.
m or more. This enables stable measurement without magnetic noise from the metal control member. (5) Position of the Operating Handle The protrusion on the bed elevating side becomes an obstacle when getting on and off the bed. In order to avoid this, the operating parts such as the bed top plate front / back position adjustment handle (first adjustment means) 108, bed top plate lifting / lowering lever 107 (third adjustment means), and second adjustment means are all tested. Is placed under the bed top 106 for the patient. Accordingly, even a subject having a heart disease can easily and safely get on and off the bed. According to the biomagnetism measuring apparatus of the present invention described above, the measurement can be performed easily and safely even by an elderly person or a subject having a heart disease. In addition, since the arrangement of the members that generate the magnetic noise is arranged at a distance where the magnetic field is sufficiently attenuated, there is no influence of the magnetic noise on the dewar, and high-precision measurement is possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of an embodiment of a biomagnetic field measuring apparatus to which the present invention is applied. FIG. 2 is a perspective view showing an arrangement configuration of a magnetic sensor used in the biomagnetic field measurement device of FIG. 1; FIG. 3 is a top view of the biomagnetic field measuring apparatus of the present invention. FIG. 4 is a side view of the biomagnetic field measuring apparatus of the present invention. FIG. 5 is a diagram showing a positional relationship between a magnetic sensor and a chest of a subject in the biomagnetic field measuring apparatus. FIG. 6 is a time waveform chart of each component of a healthy person's biomagnetic field (cardiac magnetism) measured by each magnetic sensor in the biomagnetic field measuring apparatus. [Description of Signs] 1 ... magnetic shield room, 2 ... subject, 3 ... bed, 4
... Liquid He dewar, 5 ... Liquid He automatic replenishing device, 6 ... F
LL circuit, 7: amplifier / filter / amplifier, 8: computer, 8-1: display unit, 8-2: keyboard, 8
-3: mouse, 20-1 to 20-8, 21-1 to 21-
8, 22-1 to 22-8, 23-1 to 23-8, 24-
1-24-8, 25-1 to 25-8, 26-1 to 26-
8 and 27-1 to 27-8: magnetic sensor, 30: chest,
104: transfer tube for replenishing liquid He, 10
5: Evaporated He gas exhaust pipe, 106: Bed top plate, 107
... Lever for raising and lowering the bed top plate (third adjusting means), 108
... Handle for adjusting the top and bottom position of the bed top (first adjusting means), 111... Signal cable, 112... He level meter cable, 113... Measurement circuit rack, 115.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Kamtori 1-280 Higashi Koigabo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-4-164271 (JP, A) JP-A-5 −341025 (JP, A) JP-A-8-191807 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/05

Claims (1)

(57) [Claims] [Claim 1] A magnetically shielded room for shielding the influence of magnetism, a bed movable in a three-dimensional direction, on which a subject is placed during measurement, and a bed on the bed. A biomagnetic measurement apparatus comprising: a sensor having a magnetic sensor for measuring a magnetic field generated by an examiner ; wherein the bed is movable in a height direction of the subject.
First adjusting means for performing dynamic adjustment, and in the lateral direction of the subject
Second adjustment means for performing movable adjustment, and movable adjustment in the vertical direction
And a third adjusting means for performing the operation , wherein the first to third adjusting means have a metal operating portion,
The distance between these operating units and the sensor means is small.
Both are 40 cm or more, and the operation units of the first to third adjustment units are all
The bed is located lower than the top of the bed
Biomagnetic measurement apparatus, characterized in that that.