JPH04502982A - magnetic field generator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a magnetic field generating device.

Many types of magnetic field generators have been created for various purposes. child For these various purposes, magnetic fields are generated within the workspace where work is to be done. required to do so. For these purposes, e.g. magnetic resonance imaging (MHI) and nuclear magnetic resonance spectroscopy. However, these devices are quite complex .

- This is because superconducting magnets must be used to obtain the required high field strength. In addition to this, bulky cryogenic equipment is required to install it inside the bore of the oil. However, recently, new proposals have been made. The proposal is that at least the magnetic field The idea is to make the homogeneous region project outside the bore, making it easier to access. . However, these devices are still bulky and expensive. be.

German patent application GB-A-2174248 discloses a magnetohydrodynamic device. Ru. However, this device is not suitable for performing nuclear magnetic resonance experiments (on the human body). Not suitable.

A magnetic field generation device according to the present invention includes a magnetic field generator. Take this magnetic field generator Polar members are attached to the surrounding wall of magnetic material opposite to each other, creating a magnetic field generator. is located between the pole members and spaced apart from the pole members. The wall of magnetic material is almost closed. Furthermore, this wall of magnetic material forms a path for magnetic flux within this wall. The magnetic flux is arranged so that the force generated on the magnetic generator is almost balanced. Book The magnetic field generator according to the invention has the above configuration, in which the magnetic field generator is characterized in that it comprises at least two built-in coils running in opposite directions. Ma In addition, the spacing between the magnetic field generator and at least one of the pole members is sufficient to accommodate a human body. It is characterized by being a minute. Furthermore, the opposing pole members are not planar; The pole members are arranged so that a magnetic field is generated in the working area when the working current flows through the coil. will be placed in The working area consists of a magnetic field generator and a suitable level for performing nuclear magnetic resonance experiments. and at least one pole member having a quality.

Such a configuration introduces a new idea to the magnetic field generator. That is, magnetic material Extremely safe with a single short magnetic field generator by having a pronounced effect on the wall It is possible to provide a magnetomotive force generation source that can use a high-quality cryogenic chamber. Furthermore, the flatness of the wall Due to equilibrium effects, the net force in the cryostat is nearly zero. In addition, the wall is a magnetic field generator Blocks magnetism from the outside.

Preferably, the force balance is achieved by making the magnetic field generator symmetrical and placing the magnetic field generator inside the wall. This is achieved by symmetrically arranging the

Alternatively, a similar balancing effect can be achieved by arranging them asymmetrically. be. In this case, create a temporary pole on one side of the magnetic field generator and connect it to the other side. one pole closer to the magnetic field generator than the other pole.

Typically, the walls are made of iron or other ferromagnetic material.

In some configurations, the actuation between the magnetic field generator and at least one of the pole members The homogeneity of the magnetic field in the area must be large enough for the purpose of locating the magnetic field generator. It is. The homogeneity of the magnetic field is determined using the finite element method when designing the magnetic field generator. It can be controlled by considering wall effects and magnetic field generators. Special The wall itself can be contoured to achieve homogeneity within the working area. Wear. For example, the wall may be rectangular or square, and the magnetic field generator should be placed approximately on opposite sides of the wall. It is preferable to place them in parallel. In this case, the magnetic field generator should extend from the opposite wall. Preferably, the inner surface of the face of the wall is tapered towards the magnetic field generator. stomach.

However, if a new magnetic shim can be added, the magnetic field generator and wall The homogeneity created by this may not be very high. Such shims can be Iron, permanent magnets or coils formed on top or in a magnetic field generator. can form a file.

One of the major advantages of this device when applied to MHI is that it has at least a magnetic field generator. The space between the pole member and one pole member can be sufficiently wide, and the The patient should be able to sit or stand. By this during the confinement the patient feels when placed within the bore of the coil. The distance can be reduced considerably. For this reason, when performing a heart checkup, patients Allows sufficient freedom of movement within the working area. Furthermore, two If the magnetic field generator is placed symmetrically between the pole members, a pair of homogeneous In the case of MHI, two patients can be treated at the same time. It becomes possible to

Pole members can be part of the wall itself or formed by new elements attached to the wall. can be achieved. Typically, the pole members are centered approximately flat with respect to the magnetic field generator. The outer shape is determined so as to form a surface, and furthermore, it is placed radially outside of this central surface. The coil is formed to have a circular recess approximately concentric with the coil.

Hereinafter, an example of a magnet assembly for MRI according to the present invention will be described with reference to the drawings.

FIG. 1 is a side view of an example of a magnet assembly.

2 is a plan view of the magnet assembly of FIG. 1; FIG.

3 is an end view of the magnet assembly of FIG. 1; FIG.

FIG. 4 is a diagram showing the magnetic flux distribution inside the magnet assembly of FIG. 1.

FIG. 5 shows a quarter-section of the second assembly with the outer wall removed.

FIG. 6 is a schematic view of the second assembly with a portion of the outer wall.

FIG. 7A is a cross-sectional view of the third assembly.

FIG. 7B is a sectional view taken along the line X--X of FIG. 7A.

The assembly shown in FIG. 1 is placed inside the cryostat 2 and is made of superconducting wire. It is equipped with a pair of coils running in opposite directions. From cryostat 2 A pair of pole pieces 3.4 of iron are provided which are shaped axially outwards. low The temperature keeping device 2 is formed by a square iron wall 5 and is made of iron with an open side. is placed inside the box. The coils l have their axes located at opposite ends 6 of the wall 5. 7 and the ends 6.7 of the wall 5 are shaped iron pole members. 8.9 is supported concentrically with the coil 1.

Conventionally, coils used in magnet assemblies for MRI are as shown in Figures 1 and 2. A coil with a relatively short axial length as shown in Figure 2 was unsuitable. This kind of This is because the magnetic field causes considerable inhomogeneity in the magnetic field. Such magnetic field inhomogeneity The problem can be solved at least partially by the iron wall 5. Iron wall 5 is this Due to the magnetic flux passing through the iron wall of This is because it can contribute to the magnetic field in the formed region 1O111. . However, in general, the degree of homogeneity achieved is still insufficient for MRT applications. shim members 12 to 15 are newly attached to the inner surface of the wall 5. Ru.

The size, location and strength of these permanent magnet shims are determined while designing the magnet assembly. can be determined empirically.

FIG. 4 shows the distribution of magnetic flux in a quarter-shaped magnet assembly. this The magnet assembly is similar to that in Figure 1, but with three coils and only the passive side. The iron frame has a pole surface and no shims are provided on the iron frame. 4 minutes shown in Figure 4 One shape is plane symmetric with the other three quarter shapes. this computer stain Due to modeling, the effect of the shaped pole member 8.9 and shims 12 to 15 is null I am watching. In this case, the vertical axis in FIG. 4 corresponds to the axis of coil 1, and the vertical axis in FIG. The horizontal axis extends in the vertical direction of the first ffi. As shown in Figure 4 , the magnetic flux lines are concentrated inside the iron wall 5, and a very small amount of magnetic flux leaks out from the wall 5. There is.

This is because the iron wall 5 acts as a shield and protects most of the magnetic flux. This indicates that it forms a return path for the area.

Figure 4 shows the contours of 5 Gauss and 1 Gauss on the outside of wall 5. The bone magnetic field is 5338. It is considered to have a magnitude of ilGauss. Figure 4 also shows that the magnetic field is ±11 It shows the position of the volume that varies in the range of 000pp, and this volume is located on the axis of the coil. located at a radius of approximately 50 cm along the coil radius and approximately 50 cm along the coil radius. It can be seen that it is located at a radius of m.

In reality, each area 1O111 is used to simultaneously assign different patients to each area 1O111. separate MRI experiments.

Typically, one patient is examined in one area while the other area is examined. Preparations for the other patient can be made at the same time. This is a compilation This means that only one computer system is required. between two areas. This is because multiple computer systems can be shared. Area 10.11 The size is large enough for the patient to lie down, stand up, or assume any intermediate position. The size is determined so that it can be used. Intermediate positions include sitting, lying or, for example, to achieve a specific response to a medication or disease condition. It is a good attitude. In fact, the patient can easily walk into the area.

Note that the coil 1 and wall 5 are arranged symmetrically. Because this This is because such an arrangement makes the forces in the coil 1 almost symmetrical, thus This is because there is no need to use a complicated and expensive support structure. In addition, thin carp By using a cryostat, the volume of the cryostat can be made relatively small; This reduces heat leakage into the system and requires very little cryogen. Become.

More complex coil systems for magnetic field generators to reduce the need for shims and other can be used. For example, European patent application EP-A-0160350 It is possible to use a coil running in the opposite direction of the pre-insertion as described in No. Ru. A portion of such a coil system is shown in FIG. In the same figure, A four-coil system consisting of coils 20-23 is shown. coil 20 The comparative number of turns of ~23 is indicated graphically by the radial thickness of each coil. Fifth The direction of the operating current flowing through the coils 21 and 23 (with time) is indicated by the arrows shown in the figure. counterclockwise direction) is opposite to the direction of the current flowing through the coil 22 (counterclockwise direction). moreover In this case, a ring-shaped iron shim 24 (only a quarter of the shape is shown in Figure 5) is used. ) is placed between the coils 21 and 22, acting as a shim and further to homogenize the magnetic field within the working area.

The pre-coil is placed in such a way that the center of the homogeneous area protrudes outward from the volume formed by the coil. It can be formed as follows. This is also described in the European patent application mentioned above. That's true. Preferably, the center of the homogeneous region is the coil and the remote or passive pole member. projecting into the interior of the space between the Optimize as a thing.

This can be determined by determining the required coil and iron wall shapes using the growth factor method described above. What we found is that the optimal shape for an iron wall is the part of the wall facing away from the coil position. It has a taper extending radially inward. This is shown in Figure 6. The same figure shows the coils 20 to 23 shown in Fig. 5 together with a part of the iron wall. ing. As can be seen from FIG. 6, the upper part of the iron wall 25 has an inner surface 26. The inner surface 26 of the pole member 28 tapers toward the vertical portion 27 of the wall supporting the pole member 28. There is. Moreover, as can be seen from FIG. 6, the pole 28 has a substantially circular outer peripheral portion 29 and a concave shape. It has a shape that allows it to grow with a flat central portion 30.

Another embodiment is shown in FIGS. 7A and 7B. In this embodiment, the magnetic field generator is attached to each winding form inside the helium container 34 of the cryostat 35. It includes three concentric superconducting coils 31 to 33. The following table shows shaft 45 and amperage It shows the positions of the coils 31 to 33 with respect to the number of turns.

Center radius (cm) Ampere turns Coil 31 35.5 -4700 Coil 32 51.5 +30000 Coil 33 109 -300000 As mentioned above, the cryostat 35 has the helium container 34, and its shape is a general shape for growing a window element container and an outer casing surrounding the helium container 34. It is. The cryostat 35 has a pore 36 having a diameter of 64.7 cm. Ru.

The low temperature holding device 35 and the coils 31 to 33 are placed inside an iron wall 37. The iron wall 37 consists of two upright walls 38, 39, a nearly horizontal top wall 40, and a bottom wall 41. It forms a box with open ends. Walls 38 to 41 are approximately 20 cm long. The walls 38,39 have a height of approximately 560 cm. open end The total width of the wall between sections (see Figure 7B) is approximately 420 cm, with a wall width of 40.4 cm. 1 has a length of approximately 230 cm.

On the side of the wall 38, 39 facing towards the coils 31-33, a pair of iron pole members 42 are provided. ．． 43 is attached. As can be seen from FIG. 7A, the pole members 42 and 43 are , a central part 44 concentric with the axis 45 of the coil and raised in a circular shape, and a semi-circular part 44 concentric with the axis 45 of the coil. A concave portion 46 that is recessed outward in the radial direction, and a circularly raised circumferential portion that is concentric with the shaft 45. 47. The exact shape of the pole members 42 and 43 can be determined by calculation. The magnetism generated by the coils 31 to 33 combined with the effects of the iron box and pole members 48.4 between the coils 31-33 and each pole member 42.43. A substantially homogeneous magnetic field is generated inside the magnetic field 9.

Typically, the coil arrangement shown in FIGS. 7A and 7B results in a diameter of 26 cm. A magnetic field with a homogeneity in the range of ±1100 pp inside a sphere of m has an operating area of 48.4 Occurs inside 9. The operating area is the plane 50 of the coils 31-33 and the pole member 42.4. It is located midway between the 3rd plane and the 3rd plane.

The distance between the side surface of the cryostat 35 and the adjacent pole member is approximately 57.5 cm. , the working area 48,49 can be arranged to be located in the center of these intervals. Wear.

International search report. , 7,8°. . /I’H7QG international search report GB 8901296 S^32304

Claims (7)

[Claims] (1) Mutual opposing devices located within a wall of magnetic material surrounding the magnetic field generator. a magnetic field generator disposed between the facing pole members and spaced from the pole members; The wall forms a substantially closed magnetic flux path, and the magnetic flux inside the wall causes the magnetic field generator to In a magnetic field generator in which the forces acting on the magnetic field are almost balanced, The field generator has at least two built-in coils running in opposite directions; The spacing between the magnetic field generator and at least one of the pole members is large enough to accommodate a human body. sufficient that the opposing pole members are not planar and these pole members are are arranged so that a magnetic field is generated in the actuating region when the actuating current flows through the coil. and the working area includes the magnetic field generator and a uniform area suitable for conducting nuclear magnetic resonance experiments. and the at least one pole member having a polarity. A magnetic field generator with a characteristic feature. (2) The magnetic field generator is arranged symmetrically within the wall. A magnetic field generating device according to claim (1). (3) Claim (1) characterized in that the wall is made of a ferromagnetic material. Or the magnetic field generator described in (2). (4) The pole member has a substantially flat center surface facing the magnetic field generator, and a radius of the center surface. characterized by comprising a circular recess located outward in the direction and concentric with the coil. The magnetic field generating device according to any one of claims (1) to (3). (5) The inner surface of the wall extending from the magnetic field generator to the opposing wall faces the magnetic field generator. According to any one of claims (1) to (4), the material has a taper. Magnetic field generator. (6) one or more for controlling the homogeneity of the magnetic flux inside the working region; Claims (1) to (5) characterized in that a shim member is attached to the inner surface of the wall. The magnetic field generator according to any one of the above. (7) A pair of operating regions are provided on each side of the magnetic field generator. The magnetic field generating device according to any one of claims (1) to (6).