JP2705067B2 - Magnetic susceptibility distribution measurement device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring magnetic susceptibility, and more particularly to a magnetic susceptibility distribution for measuring a non-destructive subject such as a living body whose internal magnetic susceptibility distribution needs to be measured. It relates to a measuring device. 2. Description of the Related Art Conventionally, a vibrating sample magnetometer (VSM) is often used for measuring the magnetic susceptibility of a substance because it can perform highly sensitive measurement. For example, it is described in detail in, for example, edited by Toshinobu Chikagaku, "Magnetic", Experimental Physics Course 17, Kyoritsu Shuppan Co., Ltd., pages 196 to P209. Hereinafter, a conventional sample vibration magnetometer will be described with reference to FIG. In FIG. 6, 601 is a sample to be a subject, 602 is a vibrator for vibrating the sample, 603 is a support rod connecting the vibrator 602 and the sample 601, 604 is a magnet for applying a static magnetic field Ho to the sample, 605 is sample
A magnetic field detector 601 detects the magnetic field generated by the magnetic field detector 601, an amplifier 606 amplifies the electric signal of the magnetic field detector, and a detector 607 detects the amplitude of the amplified AC signal. The operation of the above configuration will be described below. First, a sample 601 as a subject is vibrated at several tens to several hundreds Hz in the Z direction by a vibrator 602. Since a static magnetic field Ho is applied to the sample 601 in the x direction by the magnet 604, a magnetization of χHo is generated as the magnetic susceptibility χ of the sample. Since the magnetized sample 601 vibrates in the Z direction, the magnetic field detector 605 detects the oscillating magnetic field generated by the oscillating magnetization of the sample as an AC signal. Usually, a simple Z-oriented coil is used for the magnetic field detector, and an alternating voltage is generated in the coil by the oscillating magnetic field. AC signal is amplifier 60
The amplitude of the AC signal is amplified by the detector 6 and detected by the detector 607. Since the detected signal amplitude is proportional to the magnetization, that is, proportional to the magnetic susceptibility χ, the magnetic susceptibility of the sample 601 as the subject can be measured. With such an apparatus, a magnetic susceptibility of about 10 ⁻⁶ emu / cc of an object having a diameter of several mm can be measured with sufficient accuracy, and a magnetic susceptibility of a paramagnetic material can also be sufficiently measured. Problems to be Solved by the Invention However, the conventional magnetic susceptibility measuring apparatus as described above cannot measure the magnetic susceptibility distribution inside a large object due to the following problems. Measurement of the magnetic susceptibility distribution inside a large subject is important, for example, in the medical measurement field. Measuring the magnetic susceptibility distribution in a large living body such as a human has a great medical significance because the blood distribution of the living body can be measured.In other words, since blood contains iron ions of hemoglobin, it is a paramagnetic material. It has a relatively high magnetic susceptibility (number × 10 ⁻⁶ emu / cc), and it is considered that information on blood distribution can be obtained by measuring magnetic susceptibility distribution in a living body. It is useful for medical measurement to measure such a magnetic susceptibility distribution in a living body without adversely affecting the living body (non-invasively). However, the above-described conventional measurement system basically has two major problems. That is, first, the average magnetic susceptibility of the entire sample (test object) can be measured, but the magnetic susceptibility distribution inside the test object cannot be obtained. Second, in order to vibrate the subject, it is very difficult for a large subject (for example, a human body) to perform acceleration motion such as vibration due to a large mass. It is necessary to avoid giving acceleration motion because it has a bad effect on the living body. As described above, it is a problem of the conventional measurement system that the distribution cannot be measured and that the subject cannot be caused to perform acceleration motion such as vibration. The present invention solves the above problems of the prior art, and has an object to measure a magnetic susceptibility distribution inside a subject without applying strong acceleration motion such as vibration to the subject. . Means for solving the problem The present invention provides a magnetic field applying means for applying a magnetic field to a stationary subject by vibratingly displacing the magnetic field, and a fixed position relative to the applied magnetic field and around the stationary subject. The above object is achieved by a plurality of magnetic detecting means provided and an arithmetic processing unit for calculating a magnetic susceptibility distribution from a change signal corresponding to a change in the relative position of the magnetic detecting means. Operation The present invention changes the relative position with the applied magnetic field applied to the subject without giving a strong acceleration motion to the subject by the above configuration. 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 does not change and the magnetization of the subject is changed. Only the component caused by the relative movement with respect to the magnetic detecting means is obtained from the magnetic detecting means as a change signal. Since a large number of magnetic detecting means are arranged around the subject, and the individual magnetic detecting means have different sensitivities depending on the location in the subject, the sensitivity corresponding to each location in the subject for each detecting means The susceptibility distribution in the subject is calculated by a calculation process from the obtained change signal of each detecting means using the coefficient. In addition, relative movement without subjecting the subject to strong acceleration motion can be easily performed by moving the applied magnetic field in an oscillatory manner while the subject is stationary or by moving the subject or the applied magnetic field linearly at a constant velocity. Can be achieved. Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing a magnetic susceptibility distribution measuring apparatus according to a first embodiment of the present invention, and FIG. 2 is a partially enlarged view for explaining the magnetic field distribution shown in FIG. In FIG. 1, 101
Is the subject, 102 is the subject holding means, 103 is the magnetic sensor, 10
4 is a movable magnetic pole, 105 is a vibration means, 106 is a magnet, 107 is a coil, 108 is a fixed magnetic pole, 109 is a magnetic sensor support frame, 110 is arithmetic processing means, 111 is a cable, 112 is processed data, 11
3 is a support bar. In FIG. 2, reference numeral 104 denotes a movable magnetic pole;
4a is a movable magnetic pole in a state where the movable magnetic pole is moved, 108 is a fixed magnetic pole, 114 is a magnetic field line, and 114a is a magnetic field line in a movable magnetic pole moving state. The operation of the above configuration will be described 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 held on the subject holding means 102 in a stopped state. A magnetic field Ho is applied to the subject 101 by the magnet 106 in the X-axis direction. The magnet 106 has a movable magnetic pole 104 in addition to the fixed magnetic pole 108, is connected to the vibration means 105 by a support rod 113, and the movable magnetic pole 104 performs a vibration motion in the Z-axis direction. A support frame 109 for holding the magnetic sensor 103 is fixed to the movable magnetic pole 104, and the magnetic sensors 103 arranged around the subject 101 have fixed positions relative to the movable magnetic pole 104, and vibrate in conjunction with the movable magnetic pole 104. Perform exercise. As shown in FIG. 2, when the left fixed magnetic pole 108 is an N pole, the magnetic flux from this magnetic pole flows into the left movable magnetic pole 104 and enters the space including the subject in the magnetic field distribution as shown by the magnetic field lines 114 on the right. The magnetic flux reaches the movable magnetic pole 104 and flows into the fixed magnetic pole 108 on the right side of the S pole. The moment when the movable magnetic pole 104 moves in the Z-axis direction by the vibration means 105 is defined as a movable magnetic pole 104a, and the magnetic force line at that time
Considering 114a, the magnetic field distribution, that is, the magnetic field
Similar to FIG. 4, the balance moves in the Z-axis direction. This is because you have sufficiently larger than the fixed magnetic pole 108 to the movable magnetic pole 104 facing the surface area S ₂ in S ₁ of the opposing surfaces of the area S ₁ opposite to the fixed magnetic pole 108 of the movable magnetic pole 104, the movable pole 104 Even when moving, all the magnetic flux from the fixed magnetic pole 108 reaches the movable magnetic pole 104,
This is because the distribution of the magnetic force lines 114 is fixed to the movable magnetic pole 104 and moves. That is, the applied magnetic field of the portion including the subject 101 moves in conjunction with the movable magnetic pole 104. Here the magnetic sensor 103
Is fixed to the movable magnetic pole 104, the multiple magnetic sensors 103 are linked with the movement of the applied magnetic field, and as a result, the output of the floor sensor does not change with the movement of the applied magnetic field. However, since the subject 101 is stationary, the subject 101 is relatively moving with respect to the applied magnetic field and the magnetic sensor 103.
A change signal corresponding to the oscillating motion of the movable magnetic pole 104 is obtained from the magnetic sensor 103 in accordance with the magnetization distribution inside. That is, in the sample vibration type magnetometer described in the conventional example, the sample vibrates, and the magnetic field and the magnetic sensor are stationary, whereas in the present embodiment, the subject stops and the magnetic field and the magnetic sensor are connected. Vibrating. In this case as well, the subject is relatively oscillating when viewed from the magnetic field or the magnetic sensor, so that a change signal corresponding to the relative motion can be obtained. Signals from a large number of magnetic sensors 103 arranged around the subject 101 are collectively sent to the arithmetic processing means 110 via the cable 111. The arithmetic processing means 110 uses the magnetic sensor 103 to detect the subject 10
The internal magnetization distribution, that is, the susceptibility distribution, is calculated from the change signal corresponding to the internal magnetization distribution of 1 by arithmetic processing. The magnetic sensor 103 uses a simple coil as used in a conventional vibrating sample magnetometer, and outputs a voltage corresponding to a time change of a magnetic flux generated by the magnetization of the subject 101 passing through the coil as a magnetic sensor output. Things are also possible. However, when the subject is a human body or the like, the entire apparatus becomes large. Naturally, the movable magnetic pole 104, the support frame 109, the magnetic sensor 103, the support rod 1
Since the entire 13 has a considerable mass, it is difficult to vibrate at several hundred Hz like a conventional vibrating sample magnetometer.
Although the following vibration and low frequency occur, the sensitivity of a simple coil magnetic sensor decreases at low frequency because the time derivative dφ / dt of the magnetic flux is output. To eliminate this drawback, it is desirable to use a superconducting quantum interferometer (SQUID) that has essentially high magnetic sensitivity and measures magnetic flux instead of time derivative of the magnetic flux. Next, a method of calculating the magnetization distribution in the subject from the signal of the magnetic sensor by arithmetic processing according to the present embodiment will be described with reference to FIG. FIG. 3 is an explanatory diagram of the arithmetic processing, where 101 is a subject, and 103 is a magnetic sensor. The magnetic sensor 103 is denoted by 1,
2, 3,..., N−1, n are configured by n magnetic sensors 103. The subject 101 is virtually classified into 1, 2, 3, ...
It is divided as shown by n−1, n. Since the subject 101 has an applied magnetic field of Ho in the X-axis direction, the susceptibility of the k-th section is set to χ
The magnetization I k and the magnetic moment M k are given by Equation (1), where k is the volume of the section and 1 / k is the volume. Mk = Ik1 / k = χkHo1 / k (1) Further, assuming that a magnetic flux perceived by the i-th magnetic sensor 103 when a unit magnetic moment is assumed in the k-th section is fik, fik is i-th. Is a coefficient depending on the position of the magnetic sensor and the position of the k-th section. From this, the magnetic flux φi felt by the i-th magnetic sensor when the magnetic moment of the k-th section is Mk in equation (1) is given by equation (2). φi = fikMk = fikχoVkHo (2) Therefore, the time change dφi / dt of the magnetic flux φi is given by the following equation (3). Here, ∂fik / ∂z indicates that the object 101 is the magnetic sensor 1 in the Z direction.
This is a fine powder having a coefficient fik when displaced relative to 03, and is a coefficient depending on the position of the i-th magnetic sensor and the position of the k-th section. dz / dt is, of course, the velocity ^v z in the Z direction of the subject 101 relative to the magnetic sensor 103. From the above, if the new coefficient Fix is expressed by equation (4), the magnetic flux φ
The time change dφi / dt of i is given by equation (5). Here, the time change of the magnetic flux given to the i-th magnetic sensor by the k-th section is considered, and the time change of the magnetic flux given to the i-th magnetic sensor of all the sections from 1 to n is obtained by adding the sections, It is given by equation (6). Here, equation (6) considers the i-th magnetic sensor.
Expression (7) is given for all of the nth to nth magnetic sensors. Here, dφ1 / dt, dφ2 / dt..., Dφn / dt on the left side are actually measured from the time change of each output of the magnetic sensor 103.
Since the relative velocity ^ν z and the coefficient Fix are also known quantities, equation (7) is a simultaneous equation relating to χk, and χk is obtained by arithmetic processing. That is, the susceptibility distribution Δk in the subject is obtained. Returning to FIG. 1, the arithmetic processing means 110 performs the above-described arithmetic operation, and calculates the relative speed ^v z of the signal of the magnetic sensor 103 of the subject 101.
From the time-varying signal component according to
A magnetization distribution Δk is calculated in 101 and output as processed data 112. The processed data 112 is generally displayed or recorded as an image, but is not particularly shown in FIG. In the above calculation, the applied magnetic field Ho is calculated as being spatially uniform for simplicity. However, in general, the calculation can be performed in substantially the same manner when the magnetic field has a spatial distribution. That is, if a large number of magnetic sensors 103 are used, the magnetic susceptibilities of many places in the subject 101 can be calculated by arithmetic processing. In this embodiment, as shown in FIG. 1, the movable magnetic pole 104 is used to cause the applied magnetic field to vibrate, but if the size of the subject is small, the entire magnet 106 is displaced. It is natural that you may let them. However, since the magnet is generally heavy in all of the electromagnet, the permanent magnet, and the superconducting magnet, the use of the movable magnetic pole 104 facilitates the excitation. Next, a second embodiment of the present invention will be described. FIG. 4 is a schematic view of a magnetic susceptibility distribution measuring apparatus according to a second embodiment of the present invention, wherein (A) is a front view and (B) is a side view. 4, the same parts as those in FIG. 1 of the first embodiment are denoted by the same reference numerals. In FIG. 4, 201 is a moving means of the magnet 106, 202 is a rail, 203 is a motor, and 204 is a wheel. In this embodiment, the magnetic sensor 103 and the support frame 109 are fixed to the magnet 106, and the entire magnet 106 can be moved linearly on the rail 202 by the moving device 201. The subject 101 is stationary on the subject holding means 102, and the magnet 106 is
The measurement is performed while the magnet 106 moves in a state in which the magnetic sensor 103 is moved relatively in the Z direction due to 1 and the subject 101 is around the magnetic sensor 103. The principle of measurement is the same as that of the first embodiment, and the applied magnetic field Ho
The magnetic sensor 103 performs an interlocking movement, the subject 101 moves relative to the magnetic sensor 103, and the magnetic sensor 103 obtains a signal corresponding to the magnetic susceptibility χk of the subject 101 to measure. The signal processing is almost the same as in the first embodiment,
In this embodiment, since the spatial distribution of the applied magnetic field Ho cannot be ignored, the expression (3) becomes the expression (3) '. Therefore, equation (4) becomes equation (4) ′. The other expressions are not changed, and the expression (7) is calculated by the arithmetic processing unit at χk
By solving, the susceptibility distribution χk is obtained. In the present embodiment, the three-dimensional distribution of the magnetization of the subject 101 can be obtained by analyzing the data of the magnet 106 while moving each location of the subject 101. In this embodiment, the movement of the magnet 106 does not necessarily have to be a constant velocity movement.
Since the mass is too large, the measurement is actually in a state close to a uniform motion. As described above, this embodiment has a feature that the magnet 106 having a large mass can be moved with a small acceleration because the movement is a linear movement. Next, a third embodiment of the present invention will be described. FIG. 5 is a schematic view of a magnetic susceptibility distribution measuring apparatus according to a third embodiment of the present invention, wherein (A) is a front view and (B) is a side view. 5, the same parts as those in FIG. 1 of the first embodiment are denoted by the same reference numerals. In FIG. 5, reference numeral 301 denotes a moving unit for moving the subject, 302 denotes a rail, and 303 denotes wheels. In the present 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 moved in the Z-axis direction by the moving means 301 connected to the subject holding means 102. Subject 101, of course
Although it is not possible to give a large acceleration to the object, it is possible to move with a small acceleration by taking a sufficient space in the Z direction (lengthening the rail 302). It is possible to avoid the adverse effect of acceleration. Specifically, 1/10 if the human body is the subject
It is considered that the acceleration should be less than G. With such a configuration, by performing the same signal processing as described in the second embodiment,
The susceptibility distribution Δk of the subject 101 can be obtained. In this embodiment, as in the second embodiment, the specimen 10
A three-dimensional magnetization distribution is also required. In this case, since the magnet 106 having a large mass can be stopped, there is an advantage that the moving means 301 is simplified. In addition, the subject 101 of the first to third embodiments is not limited to a living body, and has a relatively large mass and is difficult to vibrate,
When the subject is affected by acceleration motion,
If the internal susceptibility distribution is to be examined nondestructively, it can be used as a subject. The number of the magnetic sensors 103 in the first to third embodiments is preferably as large as possible in order to increase the resolution of the magnetic susceptibility distribution of the subject 104. It is desirable to do. Effect of the Invention As described above, the present invention provides a magnetic field applying unit whose relative position can be changed with respect to a subject without applying a strong acceleration motion to the subject, and a plurality of magnetic detection units arranged around the subject. In addition, the susceptibility distribution in the subject can be measured nondestructively (non-invasively), and the effect is great.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a magnetic susceptibility distribution measuring device according to an embodiment of the present invention, FIG. 2 is an enlarged view of a main part of the first embodiment, and FIG. FIG. 4 is a schematic view illustrating a distribution calculation process, FIG. 4 is a schematic view of a magnetic susceptibility distribution measuring apparatus according to a second embodiment of the present invention, FIG. 4 (A) is a front view, and FIG. 4 (B) is a side view. FIG. 5 is a schematic view of a susceptibility distribution measuring apparatus according to a third embodiment of the present invention. FIG. 5 (A) is a front view, FIG. 5 (B) is a side view, and FIG. FIG. 2 is a schematic view of a sample vibration magnetometer. 101: subject, 102: subject holding means, 103: magnetic sensor, 104: movable magnetic pole, 105: vibrating device, 106:
Magnet, 110... Arithmetic processing means.

Claims (1)

(57) [Claims] A magnetic field applying means for applying a magnetic field by vibratingly displacing the magnetic field with respect to a stationary object, and a spatial relative position fixed with respect to a magnetic field from the magnetic field applying means, being installed around the stationary object; A plurality of magnetic detecting means, and an arithmetic processing means for calculating a magnetic susceptibility distribution in the subject based on a change signal of a magnetic field change based on a relative position change between the magnetic field and the subject detected by the magnetic detecting means. A magnetic susceptibility distribution measuring device comprising: 2. 2. The magnetic susceptibility according to claim 1, wherein the magnetic field applying means comprises a fixed magnetic pole and a movable magnetic pole, and the movable magnetic pole is fixed in a spatial relative position to the magnetic detecting means and is caused to vibrate. Distribution measuring device.