JPS63311186A - Apparatus for measuring distribution of magnetic susceptibility - Google Patents

Abstract

PURPOSE:To measure the distribution of magnetic susceptibility in a specimen without destruction, by providing a magnetic-field applying apparatus, which can change its position with low acceleration relatively with respect to the specimen, and providing a magnetism detecting means, whose relative position with respect to the applied magnetic field is fixed. CONSTITUTION:A magnetism sensor 103 and a supporting frame 109 are fixed to a magnet 106. The magnet 106 is stationary. A specimen 101 is moved in the direction of a Z axis with a moving means 301, which is linked with a holding means 102 for the specimen. High acceleration cannot be applied to the specimen 101. When a sufficient air space is provided in the direction of Z, however, the body can be moved at weak acceleration. At the time of measurement, equal-speed movement without acceleration is performed, and the adverse effect of the acceleration can be avoided substantially. In detail, when a human body is specimen, acceleration of 1/10 G or less is recommended. The magnetism sensor is associatively moved with respect to the applied magnetic field. The specimen 101 is relatively moved with respect to the magnetism sensor. Thus a signal corresponding to the magnetic susceptibility of the specimen can be obtained in the magnetism sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an apparatus for measuring magnetic susceptibility, and in particular to a magnetic susceptibility distribution for measuring a subject such as a living body whose internal magnetic susceptibility distribution needs to be measured non-destructively. This relates to a measuring device.

3-vane conventional technology Traditionally, sample vibrating magnetometers (V
SM) is often used because it allows highly sensitive measurements. For example, it is described in detail in "Magnetism" edited by Satoshi Chikazumi, Experimental Physics Course 17, Kyoritsu Publishing Co., Ltd., pages 196 to 209.

A conventional sample vibrating magnetometer will be explained below with reference to FIG.

In FIG. 6, 601 is a sample to be examined, 602 is an exciter that vibrates the sample, 603 is a support rod that connects the exciter 602 and the sample 601, 604 is a magnet that applies a static magnetic field Ho to the sample, and 605 is a A magnetic field detector detects the magnetic field generated by the sample 601, 606 is an amplifier that amplifies the electric signal of the magnetic field detector, and 607 is a detector that detects the amplitude of the amplified alternating current signal.

The operation of the above configuration will be explained below.

First, a sample 601, which is an object to be inspected, is vibrated in the Z direction at several tens to several hundred Hz using a vibrator 60'2. Since a static magnetic field Ho is applied to the sample 601 in the X direction by the magnet 604, magnetization of χHo is generated as the magnetic susceptibility χ of the sample. Since the magnetized sample 601 vibrates in the Z direction, the oscillating magnetic field generated by the oscillating magnetization of the sample is detected by the magnetic field detector 605 as an alternating current signal. Usually, a magnetic field detector uses a simple coil oriented in the Z direction, and an alternating current voltage is generated in the coil by the oscillating magnetic field. The AC signal is amplified by an amplifier 606, and a detector 6
07 detects the amplitude of the AC signal.

The detected signal amplitude is proportional to the magnetization, i.e. the magnetic susceptibility χ
Since it is proportional to , the magnetic susceptibility of the sample 601, which is the object to be examined, can be measured.

With such a device, 1010-6e of a sample with several diameters can be measured.
A magnetic susceptibility of about /cc can be measured with sufficient accuracy, and the magnetic susceptibility of paramagnetic materials can also be measured with sufficient accuracy.

Problems to be Solved by the Invention However, the conventional magnetic susceptibility measuring device as described above was unable to measure the magnetic susceptibility distribution of a portion of a large object due to the problems detailed below. .

Measuring the magnetic susceptibility distribution inside a large object is important, for example, in the medical measurement field. Measuring the magnetic susceptibility distribution in a thick 5-page living body such as a human being has great medical significance because it enables the measurement of the blood distribution in the living body.In other words, blood is paramagnetic because it contains iron ions of hemoglobin. Inside the body, there is a relatively large magnetic susceptibility (several x 10' em
u/cc), and it is thought that information on blood distribution (loading amount) can be obtained by measuring the magnetic susceptibility distribution in living organisms.

Measuring the magnetic susceptibility distribution in a living body in this manner without adversely affecting the living body (non-invasively) is useful for medical measurements. However, the conventional measuring system described above basically has two major problems.

That is, first, although the average magnetic susceptibility of the entire sample (test object) can be measured, the magnetic susceptibility distribution inside the test object cannot be obtained.

Second, since the object to be examined is vibrated, it is not only very difficult to perform acceleration motion such as vibration in a large object (such as a human body) due to its large mass, but also because it causes excessive vibration to the living body such as the human body. It is necessary to avoid applying accelerated motion because it has a negative effect on living organisms.

As mentioned on page 6 and above, problems with conventional measurement systems include the inability to measure distribution and the inability to cause the subject to undergo accelerated motion such as vibration.

The present invention solves the above-mentioned problems of the prior art, and aims to measure the magnetic susceptibility distribution inside a subject without applying strong acceleration motion such as vibration to the subject. It is.

Means for Solving the Problems The present invention provides a magnetic field applying device and a magnetic field application device configured so as to be able to change the position of a subject at a relatively low acceleration without applying strong acceleration motion to the subject. The above object is achieved by a plurality of magnetic detection means whose magnetic field and relative position are fixed, and an arithmetic processing device that calculates a magnetic susceptibility distribution from a change signal corresponding to a change in the relative position of the magnetic detection means. .

Function: With the above configuration, the present invention changes the relative position of the subject to the applied magnetic field without applying strong acceleration motion to the subject. Since the relative position between the applied magnetic field and the magnetic detection means is fixed, even if the relative position between the subject and the applied magnetic field changes, the component of the magnetic field sensed by the magnetic detection means due to the applied magnetic field does not change and the subject remains unchanged. Only the component caused by the relative movement of the magnetization with respect to the magnetic detection means is obtained as a change signal by the magnetic detection means. A large number of magnetic detection means are arranged around the subject, and each magnetic detection means is Since the sensitivity differs depending on the location inside the specimen, the sensitivity coefficient for each location in the specimen is used for each detection means, and the change signal of each detection means obtained is calculated. It is designed to calculate the magnetic susceptibility distribution inside the object.In addition, to make the object move relative to each other without making it move with strong acceleration, there are two methods: to move the applied magnetic field in an oscillatory manner while keeping the object stationary. This can be easily achieved by moving the subject or the applied magnetic field in a straight line at a constant velocity.

EXAMPLE A first example of the present invention will be described below with reference to the drawings.

FIG. 1 is an overview diagram showing a magnetic susceptibility distribution measuring device according to a first embodiment of the present invention, and FIG. 2 is a partially enlarged view illustrating the state of the magnetic field distribution in FIG. 1. In Figure 1, 101
102 is an object to be examined, 102 is an object holding means, 103 is a magnetic sensor, 104 is a movable magnetic pole, 105 is an excitation means, 106 is a magnet, 107 is a coil, 108 is a fixed magnetic pole, 109 is a magnetic sensor support frame, 110 is an operation Processing means, 111 is a cable, 112 is processed data, and 113 is a support rod.

In FIG. 2', 104 is a movable magnetic pole, 104a is a movable magnetic pole when the movable magnetic pole is moved, 108 is a fixed magnetic pole,
114 is a line of magnetic force, and 114a is a line of magnetic force in a moving state of the movable magnetic pole.

The operation of the above configuration will be explained below.

First, the subject 101 is, for example, a human body, and FIG. 1 will be described below assuming a human body. The subject 101 is the subject holding means 1
It is held stationary on the 02. A flux Ho is applied to the subject 101 in the X-axis direction by a magnet 106. The magnet 106 has a movable magnetic pole 104 in addition to a fixed magnetic pole 108, and is connected to an excitation means 105 by a support rod 113.
The movable magnetic pole 104 performs a vibrating motion in the nine-page direction of the Z-axis. Movable magnetic pole 10
A support frame 109 that holds magnetic sensors 103 is fixed to 4, and a large number of magnetic sensors 103 arranged around the subject 101 have their relative positions fixed to the movable magnetic pole 104, and vibrate in conjunction with the movable magnetic pole 104. Let's do it. As shown in FIG. 2, when the fixed magnetic pole 108 on the left side is set as the N pole, the magnetic flux from this magnetic pole flows into the movable magnetic pole 104 on the left side, and the magnetic field distribution as shown by the magnetic force lines 114 in the space containing the subject is created on the right side. The magnetic flux reaches the movable magnetic pole 104 and flows into the fixed magnetic pole 108 of the S pole on the right side. The moment when the movable magnetic pole 104 is moved in the Z-axis direction by the vibration means 105 is defined as the movable magnetic pole 104a,
Considering the magnetic force lines 114a at that time, the magnetic force line distribution, that is, the magnetic field, is also moving in parallel in the Z-axis direction similarly to the movable magnetic pole 104. This is opposite to the area S1 of the surface of the movable magnetic pole 104 facing the fixed magnetic pole 108.
Since the area S2 of the surface facing 4 is sufficiently larger than Sl, even when the movable magnetic pole 104 moves, the fixed magnetic pole 108
This is because all of the magnetic flux from the twist reaches the movable magnetic pole 10410 pages, so the distribution of the magnetic lines of force 114 is fixed to the movable magnetic pole 104 and moves. That is, the subject 101
The applied magnetic field in the portion including the movable magnetic pole 104 moves continuously. Here, since the magnetic sensors 103 are fixed to the movable magnetic pole 104, the multiple magnetic sensors 103 move in conjunction with the movement of the applied magnetic field, and as a result, the outputs of the magnetic sensors do not change with the movement of the applied magnetic field. However, since the subject 101 is stationary, it is moving relative to the applied magnetic field and the magnetic sensor 103, and the movable magnetic pole 104 is A change signal corresponding to the vibrational movement of is obtained from the magnetic sensor 103. In other words, in the sample vibrating magnetometer described in the conventional example, the sample vibrates and the magnetic field and magnetic sensor are stationary, whereas in this example, the object is stationary and the magnetic field and magnetic sensor are connected. It's vibrating. In this case, as seen from the magnetic field and magnetic sensor, the subject is still in relative vibrational motion, so a change signal corresponding to the C2 relative motion is similarly obtained.

Signals from a large number of magnetic sensors 11 and pagers 103 arranged around the subject 101 are collectively sent to the arithmetic processing means 110 via a cable 111. The arithmetic processing means 110 uses the magnetic sensor 103 to calculate the internal magnetization distribution, that is, the magnetic susceptibility distribution, by arithmetic processing from a change signal corresponding to the magnetization distribution inside the subject 101 .

The magnetic sensor 103 uses a simple coil similar to that used in conventional vibrating sample magnetometers, and outputs a voltage corresponding to the time change in the magnetic flux generated by the magnetization of the object 101 passing through the coil as the magnetic sensor output. It is also possible to do so. However, when the subject to be examined is a human body, the entire device becomes large.
Naturally, the movable magnetic pole 104, the support frame 109, the magnetic sensor 10
3. Since the entire support rod 113 has a considerable mass, it is difficult to vibrate at several hundred Hz like in a conventional vibrating sample magnetometer, and the vibration is at a low frequency of several tens of Hz or less. In a magnetic sensor with a coil, the output is the time differential dφ/dt of the magnetic flux, so the sensitivity decreases at low frequencies. In order to eliminate this drawback, a superconducting quantum interferometer (SQUI), which has essentially high magnetic sensitivity and measures magnetic flux rather than the time derivative of magnetic flux, is needed.
It is desirable to use D).

Next, the method of calculating the magnetization distribution in the object according to this embodiment from the signal of the magnetic sensor by calculation processing (the two will be explained using FIG. 3. FIG. , 103 is a magnetic sensor.The magnetic sensor 103 is composed of n magnetic sensors 103 as shown in 1.2.3...n-1,n in the figure.Subject 1
01 is virtually divided into categories 1. 2. 3.・・・・・・n
-1, n. Since there is a magnetic field Ho applied to the object 101 in the X-axis direction, the magnetization Ik and the magnetic moment Mk are given by equation (1), where the magnetic susceptibility of the th section is χ and the volume of the section is 1/.

Mk = I k 1/ to −Zk Ho 1/k ・・
-(1) Also, if fik is the magnetic flux sensed by the i-th magnetic sensor 103 when assuming a unit magnetic moment in the k-th section, then fik is the position of the i-th magnetic sensor and the magnetic flux of the i-th section. It is a coefficient that depends on the position. As a result, when the magnetic moment of the th division is Mk in equation (1) on page 13, the magnetic flux φi felt by the i-th magnetic sensor is given by equation (2).

φi = f ikMk = f ikχoVkHo・
......(2) Therefore, the time change dφ of the magnetic flux φi
i/dt is expressed as equation (3).

d df ikdφi/dt
= (fikχoVkHo)−χoVkHocort −χkVkHogaeigon・・・・・・・・・・・・(5)
δz dt Here, afik/θ2 is the partial differential of the coefficient fik when the subject 101 is displaced relative to the magnetic sensor 103 in the Z direction, and the position of the i-th magnetic sensor and the position of the th division (Two dependent coefficients.

Naturally, dz/dt is the magnetic sensor 10 of the subject 101.
3 (the relative velocity νZ in the Z direction between the two).

From the above, if the new coefficient Fix is expressed as (4), the magnetic flux φ
The time change dφi/dt of i is given by equation (5).

dφi /d t =χkFi kν2 ・・・・・・
・・・・・・・・・・・・・・・(5) 14be〉' Here, we considered the time change of the magnetic flux given to the i-th magnetic sensor by the k-th division, and from 1 to n The time change in the magnetic flux applied to the i-th magnetic sensor in all the sections is given by equation (6) by adding up the sections.

Here, equation (6) considers the i-th magnetic sensor, but
For all n-th magnetic sensors, equation (7) is obtained.

Here, dφ1/dt on the left side, dφ2/dt ・−−
-, dφn/dt are actually measured from the time change of each output of the magnetic sensor 103, and the relative velocity ν2 of the subject 101 and the coefficient Fix are also known quantities, so equation (7) becomes a simultaneous equation regarding χk, and the calculation process χ is required.

That is, the magnetic susceptibility distribution χk in the subject is obtained.

Returning to FIG. 1, the arithmetic processing means 110 performs the above-mentioned calculation, and calculates the magnetization distribution of the object 101 from the time-varying signal component of the signal from the magnetic sensor 103 according to the relative velocity νZ of the object 101 using equation (7). χk is calculated and output as processed data 112.

Processed data 112 is generally displayed as an image or recorded, but is not particularly illustrated in FIG.

In addition, in the above calculation, for simplicity, the applied magnetic field HO was calculated assuming that it is spatially uniform, but in general, calculations can be made in almost the same way even when the applied magnetic field HO has a spatial distribution. That is, by using a large number of magnetic sensors 103, it becomes possible to calculate the magnetic susceptibility of many locations in the subject 101 through arithmetic processing.

In this embodiment, as shown in FIG. 1, the movable magnetic pole 104 is used to oscillally displace the applied magnetic field, but if the object to be examined is small, the entire magnet 106 may be displaced. Of course it's okay to let them do it. However, since magnets such as electromagnets, permanent magnets, and superconducting magnets are generally heavy, it is easier to excite using the movable magnetic pole 104.

Next, a second embodiment of the present invention will be described.

FIG. 4 is an overview diagram of a magnetic susceptibility distribution measuring device according to a second embodiment of the present invention, in which (A) is a front view and (B) is a side view. In FIG. 4, the same parts as in FIG. 1 of the first embodiment are given the same numbers. In FIG. 4, 201 is a magnet 106
transportation means, 202 is a light novel, 203 is a motor, 20
4 is a wheel.

In this embodiment, the magnetic sensor +103 and the support frame 109 are
is fixed to the magnet 106, and the entire magnet 106 is attached to the moving device 2.
01 enables linear movement on the rail 202.

The subject 101 is stationary on the subject holding means 102, and the magnet 106 is relatively moved in the Z direction by the moving means 201, and a magnetic sensor is placed around the subject 101.
Measurement is performed while the magnet 106 is moving in the state where the magnet 106 has arrived.

The principle of measurement is the same as in the first embodiment, and the applied magnetic field Ho
The magnetic sensor +103 moves in conjunction with the subject 101.
The measurement is performed by obtaining a signal corresponding to the magnetic susceptibility χk of the subject 101 from the magnetic sensor 103 by moving 17 pages relative to the magnetic sensor 103.

The signal arithmetic processing is almost the same as in the first embodiment, but in this embodiment, the spatial distribution of the applied magnetic field Ho cannot be ignored, so Equation (3) becomes Equation (3)7.

dφi/dt −χoVk (Ho anorin+”f
ik ) dt dt −χoVk (Ho “” + j rainbow f ik ) −”
-(3)'aX δx dt Therefore, equation (4) becomes equation (4)7.

afik aH.

Fik3vk (Ho] Ma + - Mu f1k)...
(4)' The magnetic susceptibility distribution χk is determined by solving the equation (7) for χk using an arithmetic processing device, without changing the other equations.

In addition, in this embodiment, by analyzing data while the magnet 106 is moving from place to place on the subject 101,
The three-dimensional magnetic susceptibility distribution is also determined.

In addition, in this embodiment, the movement of the magnet 106 does not necessarily have to be a uniform movement, but if the movement is too rapid, the movement of the magnet 106 may not be uniform.
Since the mass of 6 is large and unreasonable, the actual measurement of 18 vanes will be in a state close to uniform motion.

In this way, this embodiment has the advantage that the motion is linear, so the acceleration is small, and the magnet 106, which has a large mass, can be moved.

Next, a third embodiment of the present invention will be described.

FIG. 5 is an overview diagram of a magnetic susceptibility distribution measuring device according to a third embodiment of the present invention, in which (A) is a front view and (B) is a side view. In FIG. 5, the same parts as in FIG. 1 of the first embodiment are given the same numbers. In FIG. 5, 301 is a moving means for moving the subject, 302 is a light novel, and 303 is a wheel.

In this embodiment, similarly to the second embodiment, the magnetic sensor 10
3 and the support frame 109 are fixed to the magnet 106, and the magnet 106
is stationary. The subject 101 is the subject holding means 102
1: Move in the Z-axis direction by the connected moving means 301. Naturally, large acceleration cannot be applied to the subject 101, but sufficient spatial space is taken up in the Z direction (rail 3
02), it is possible to move with weak acceleration, and by moving at a constant speed without acceleration during measurement, it is possible to substantially avoid the adverse effects of acceleration on the 19 vanes.

Specifically, if the subject is a human body, it is considered that the acceleration should be less than ^G. With such a configuration, the magnetic susceptibility distribution χk of the subject 101 can be obtained by signal processing similar to that described in the second embodiment.

Note that in this embodiment, as in the second embodiment, the subject 10
The three-dimensional magnetization distribution of 1 is also determined. In this case, since the magnet 106 having a large mass can be kept stationary, the moving means 3
01 has the advantage of being simple.

Note that the subject 101 in the first to third embodiments is not limited to a living body, but may have a relatively large mass and have difficulty in vibrating motion, or
It can be used as a test object if the internal magnetic susceptibility distribution is to be non-destructively investigated in cases where accelerated motion has an adverse effect on the test object.

The number of magnetic sensors 103 in the first to third embodiments is preferably 10 or more in order to improve the resolution of the magnetic susceptibility distribution of the subject 104, so to obtain an image-like magnetic susceptibility distribution. It is desirable to use it.

Effects of the Invention As described above, the present invention comprises a magnetic field applying means whose relative position can be changed with respect to the subject without applying strong acceleration motion to the subject, and a plurality of magnetic detection means disposed around the subject. This allows non-destructive (non-invasive) measurement of the magnetic susceptibility distribution in the subject, and its effectiveness is significant.

[Brief explanation of drawings]

Fig. 1 is an overview diagram of a magnetic susceptibility distribution measuring device according to an embodiment of the present invention, Fig. 2 is an enlarged view of main parts of the first embodiment, and Fig. 3 is an overview diagram illustrating the magnetic susceptibility distribution calculation process of the invention. , FIG. 4 is an overview diagram of a magnetic susceptibility distribution measuring device according to a second embodiment of the present invention, FIG. 4(A) is a front view, FIG. 4(B) is a side view,
FIG. 5 is an overview diagram of the magnetic susceptibility distribution measuring device according to the third embodiment of the present invention, FIG. 5(A) is a front view, and FIG. 5(B) is a front view.
is a side view, and FIG. 6 is an overview of a conventional sample vibrating magnetometer. 101... Subject, 102... Subject holding means, 1
03... Magnetic sensor, 104... Movable magnetic pole, 105
... Vibration device, 106 ... Magnet, 110 ... Arithmetic processing unit 21 Page stage. Name of agent: Patent attorney Toshio Nakao (1st person, 2nd person)
Figure 3 Figure 103 Night air Bimbu

Claims (6)

[Claims] (1) A magnetic field applying means configured to apply a magnetic field at least across the subject and to make a low acceleration position change relative to the subject, and a space with respect to the magnetic field from the magnetic field applying means. The relative position of the object is fixed, and the object is detected by a plurality of magnetic detection means installed around the object, and a change signal of the magnetic field based on a change in the relative position between the magnetic field and the object detected by the magnetic detection means. 1. A magnetic susceptibility distribution measuring device comprising: arithmetic processing means for calculating a magnetic susceptibility distribution in a specimen. (2) The magnetic susceptibility distribution measuring device according to claim 1, characterized in that the subject is kept stationary and the position of the magnetic field applying means is vibrated relative to the subject. (3) The magnetic susceptibility distribution measuring device according to claim 1, characterized in that the subject is kept stationary and the position of the magnetic field applying means is changed linearly with respect to the subject. (4) The magnetic susceptibility distribution measuring device according to claim 1, characterized in that the magnetic field applying means is kept stationary and the position of the object to be examined is changed linearly relative to the magnetic field applying means. (5) Magnetic detection means is a superconducting quantum interferometer (SQUID)
A magnetic susceptibility distribution measuring device according to claim 1, characterized in that: (6) The magnetic field applying means includes a fixed magnetic pole and a movable magnetic pole, and the movable magnetic pole is fixed in a spatial relative position with the magnetic detection means and is caused to vibrate. magnetic susceptibility distribution measuring device.