JPS6316604A - Coil equipment - Google Patents

Abstract

PURPOSE:To eliminate anxiety of a patient and reduce the weight of a coil system and make the system compact by a method wherein circular coils are so arranged as to make an imaginery line connecting an origin of coordinates and the inside edge of the radial direction of the circular coil at the outermost side of the axial direction fall within the angle range of not less than about 34.5 deg. and not more than about 63.4 deg. from the center axis. CONSTITUTION:Circular coils 1, 1' and 2 are composed of a frame 3 and superconductors wound on the frame 3 and the coil 2 is provided at the middle part between the coils 1 and 1'. In this case, the coils 1, 1' and 2 are wound on the cylindrical frame 3 and the coils 1 and 1' are provided on both sides of the coil 2. An imaginery line L which connects the center of the coil 2, i.e. an origin 0 of coordinates and the inside edge 4 of the radial direction of the coil 1 at the outermost side along a Z-axis looking from the origin o is drawn and the angle theta between the imaginery line L and the Z-axis is defined. The coils 1 and 1' and the coil 2 are so arranged as to have an identical center axis and to be symmetrical with respect to the imaginery plane R and further the coils 1 and 1' are so arranged as to make the angle theta fall within the range of not less than about 34.5 deg. and of not more than about 63.4 deg..

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed to medical MRI (Magnetic Reaction MRI).
sonanceTmag ing ) device, N M
R-CT (Nuclear Hagne-tic
Resonance-Computer Tomogr
This invention relates to a coil device used in aphy) devices and the like.

(Prior art) Recently, in medical MRI equipment and NMR-CT equipment,
It has become possible to obtain tomographic images using a method different from that of the 12CT device, that is, a method that utilizes the nuclear magnetic resonance phenomenon of atomic nuclei, and it has begun to be used in actual diagnosis. In order to make this tomographic image clear and to obtain the best image in a short time, it is necessary to generate a highly uniform distributed magnetic field in a predetermined space. In this case, the uniformity of the distributed magnetic field varies depending on the diagnosis target, but
For example, 0.0 in a 1OcM sphere. lppm (1x10-7
) devices have also appeared.

By the way, circular coils are often used to generate this kind of distributed magnetic field, and if the central axis is the Z-axis, the magnetic field 82 on the Z-axis can be expressed by expanding as shown in the following equation. .

+ a 4 Z p+ ・・・・・・・・・(1)
a, = I-f (Z, θ)...
...(2) nCC However, I 2 Current z flowing through the circular coil: Measurement position Z in the z-axis direction: Position of the circular coil in 7 directions θ: Angle of the circular coil from the Z-axis.

Here, when a pair of circular coils are arranged symmetrically with respect to the imaginary plane of Z=O, and current is supplied in the same direction to these coil pairs, the magnetic field B7 near the central axis is calculated by the following equation. Represented by a function.

8 ・・・・・・・・・(3) +a8Z,+ Also, not only one pair of coils but also many coil pairs can be expressed in the same form as equation (3), and the coefficient a2n is expressed as the following equation become that way.

a = Σ ■,・f2n”'ci, θci)・(412
0, 1 1 = = square, M: coil logarithm.

By the way, the coefficient "2n" mentioned above is a function of the current flowing through the circular coil and the arrangement of the coil, so these two
By appropriately selecting two parameters, the coefficient a2n can be made zero. On the other hand, the coefficient a. is a constant term that is not related to position and represents a component of a uniform magnetic field, and the coefficient a2n of n to 0 represents an error component that disturbs the uniform magnetic field distribution.

Thus, in order to obtain a highly uniform distributed magnetic field, the coefficient a2. (n≧1) must be reduced to zero as high as possible.

On the other hand, the coefficient a2o with a higher degree is
Since C tends to decrease rapidly as C increases, it can be said that the longer the axial length of the coil, the less the influence of higher-order terms becomes, making it easier to realize a highly uniform distributed magnetic field.

From this point of view, there are known documents as conventional coil devices that obtain a highly uniform distributed magnetic field, such as JOURN^L DEPI.
IYSrQUE 8THINTERNATIONAL
C0NFERENCE ONMAGNET TECII
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．． There is one shown in 1983GR [N0BLE (FRANCE).

This coil device consists of a central coil arranged to include the origin of Z-0, and a coil arranged symmetrically to the imaginary plane of Z=0.
It consists of a pair of coils.

Note that the central coil placed to include the origin has a shape that is symmetrical to the imaginary plane of Z=0, so
It is estimated that these coils also form a pair, and in the end, it is estimated that the two pairs of coils are arranged symmetrically with respect to the imaginary plane of Z=O. In this coil device, the coil arrangement is such that the imaginary line segment connecting the radially inner edge of the outermost circular coil in the ZIN1 direction and the origin is approximately 30.8 degrees with respect to the Z axis. There is.

Generally, the angle that the above-mentioned virtual line segment makes with the Z axis is O,
If the coil is arranged so that θ is -63.44 degrees, it becomes a so-called Helm-Holtz type coil arrangement, and the coefficient a
It is known that 2=o.

However, considering that the θ of the conventional coil device mentioned above is approximately 30.8 degrees, this device increases the axial length of the coil to eliminate the influence of higher-order terms and achieves a highly uniform distributed magnetic field. It seems that it was done.

(Problems to be Solved by the Invention) In an MRI apparatus, a superconducting coil is usually used as the circular coil, and the patient is diagnosed in a highly uniform magnetic field at the center of the superconducting coil. The shorter the axial length, the less anxiety the patient will feel.

However, the conventional coil device has a problem in that the length of the coil in the axial direction is large, giving the patient a sense of anxiety.

Further, in the conventional coil device, since the length of the coil in the axial direction is large, there is also a problem that the ff1fa of the coil increases.

The present invention was made to solve the above-mentioned problems, and eliminates patients' feelings of anxiety. ? The purpose of the present invention is to provide a coil device that can significantly reduce the occurrence of small coil claws.

[Structure of the invention]

(Means for Solving the Problem) The present invention is arranged such that their central axes coincide with each other, and the assumed origin is aligned with the central axis and is symmetrical with respect to a virtual plane perpendicular to the central axis. In a coil device including a plurality of circular coils arranged, an imaginary line segment connecting the radially inner edge of the circular coil at the outermost end in the axial direction when viewed from the origin and the origin is relative to the central axis. te 34.5
The present invention is characterized in that the circular coils are arranged so as to fall within an angular range of 63.4 degrees or more.

(Function) Generally, a coil is provided with a plurality of circular coils that are arranged so that their central axes coincide, that include an assumed origin on the central axis, and that are symmetrically arranged on a virtual plane perpendicular to the central axis. In the device, the uniformity of the distributed magnetic field differs depending on the angle range of the virtual line connecting the radially inner coil edge of the axially outer end and the origin with respect to the central axis. The sign of the coefficient a2n in the expansion equation may be reversed.

Now, the angle that the virtual line segment makes with the Z axis is θ, and the angle θ is the horizontal axis,
The relationship between the two is shown in FIG. 2, with the vertical axis representing the error that disturbs the magnetic field distribution. In other words, when the angle θ is 34°, the error is approximately -5 ppm (ppm is the value obtained by multiplying the error magnetic field/center magnetic field by 106), and when the angle α0 is 35°, the error is approximately 5 ppm, and the error in the magnetic field is Experiments conducted by the inventors have revealed that the error changes along a straight line connecting two points, and that the error becomes zero when the angle θ is close to 34.5°.

Therefore, although it is best to set the angle O to 34.5°, making it at least less than this angle is nothing but an unnecessarily long axial length of the coil.

On the other hand, when the angle θ exceeds 63.4°, the above-mentioned coefficient a
2 becomes negative, it becomes necessary to reverse the direction of the current supplied to the coil, and the t of the wire increases by that amount.

Therefore, in the present invention, the angle θ is approximately 34.5° or more, 63.
By arranging the circular coils within an angular range of 4 degrees or less, the patient's sense of anxiety is eliminated and the coil surroundings are reduced.

(Embodiment) FIG. 1 is a longitudinal sectional view showing the configuration of an embodiment of the present invention. In the same figure, circular coils (hereinafter simply referred to as coils) 1.1' and 2 are superconductors wound on a winding frame 3, and among these, coil 2 is a coil 1.1'.
is placed in the middle.

In this case, the coils 1, 1' and 2 are wound on a cylindrical bobbin 3, the coils 1.1' being arranged symmetrically on both sides of the coil 2.

Now, the central axis of winding frame 3, that is, the central axis of coils 1°1' and 2, is 7, and the center of coil 2, that is, the origin, is 7.
A virtual plane that includes this origin O and is perpendicular to ZIIlIl is R
shall be. Also, when viewed from the origin 0, there is a J on the outermost side in the Z-axis direction.
The line segment connecting the inner edge 4 of the coil 1 in the 3rd direction and the origin O is defined as an imaginary line segment, and the angle between this imaginary line segment and the Z-axis is defined as θ.

Here, the coils 1.1' and 2 are arranged so that their central axes coincide with each other, and furthermore, they are arranged symmetrically about the virtual plane R. Also, the angle θ is approximately 34.5' or more, 63
．． The coil 1.1' is arranged so as to fall within a range of 4 degrees or less.

With this configuration, it is possible to prevent negative error components from being included in the magnetic field in the predetermined space 5 including the origin O, and it is possible to prevent the current from being included in the magnetic field in the predetermined space 5 including the origin O. Eliminating the need to reverse orientation.

As a result, the length of the coil in the axial direction is suppressed to eliminate the patient's sense of anxiety, and the weight of the coil is reduced.

Although three coils were used in Example 1-1, even if there are a large number of coils, the key is to align the central axes and arrange them symmetrically with respect to the virtual plane R, so that the angle θ is approximately 34. It is clear that the same effect as described above can be obtained by arranging the angle within the range of .5° or more and 63.4° or less.

FIG. 3 is a longitudinal cross-sectional view showing the configuration of another embodiment of the present invention, in which coil 2, coil 6.6'
, the coils 1 and 1' are arranged symmetrically, but the inner diameter of the coil 2, which is arranged so as to surround the origin O, is the smallest, and the inner diameter of the coil 2 that surrounds the origin O is the smallest.
If you look closely, the inner diameter of the outer coil in the Z-axis direction is narrower. In this case as well, the coil shape and coil arrangement are such that the angle θ is approximately 34.5° or more and 63.4° or less.

According to such a configuration, it is possible to further reduce the lit by reducing the inner diameter of the central coil.

Next, FIG. 4 is a longitudinal sectional view showing the structure of another embodiment of the present invention. In the same figure, coil 2, coil 6
．． 6' and coils 1.1' are arranged symmetrically with respect to the virtual plane R, but coil 2, which is arranged so as to surround the origin 0, has the largest inner diameter, and the outer coil in the Z-axis direction has the largest inner diameter. The inner diameter is smaller. In this case as well, the coil shape and coil arrangement are such that the angle θ is approximately 34.5' or more and 63.4° or less.

Compared to the coil device shown in Fig. 1 above, this coil device has a shape in which the inner diameter of the central coil 2 is increased by the smaller inner diameter of the outer coil 1.1' in the Z-axis direction. Even if the coils ff1ffl are the same, the surrounding space in which the patient is placed is significantly expanded, thereby reliably eliminating the patient's sense of anxiety.

Note that when the angle θ is the same, the axial length of the coil device shown in FIG. 4 is the shortest compared to the coil devices shown in FIGS. 1 and 3, respectively. Therefore, in this aspect as well, the patient's anxiety can be alleviated.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the virtual line segment connecting the radially inner edge of the circular coil at the axially outer end and the origin is approximately 34.5 degrees or more with respect to the central axis.
Since the circular coil is arranged within an angle range of 63.4 degrees or less, when this device is applied to MRI neck straps for medical treatment, it can reliably eliminate the feeling of anxiety caused to patients. This has the effect of reducing the number of coil limbs and making it more compact.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the angle formed by a virtual line segment drawn so as to be in contact with a circular coil and the error in the magnetic field, in order to explain the present invention in detail. FIG. 3 is a longitudinal cross-sectional view of another embodiment of the present invention, and FIG. 4 is a longitudinal cross-sectional view of another embodiment of the present invention. 1.1', 2.2', 6.6'...Circular coil, 3...Reeling frame, O...Origin, Z...Center axis, R...
...Virtual plane, L...Virtual line segment. Applicant's agent Yuchi Sato 1 Figure

Claims (1)

[Claims] They are arranged so that their central axes coincide, and
In a coil device comprising a plurality of circular coils that include a hypothetical origin on the central axis and are arranged symmetrically on a virtual plane perpendicular to the central axis, the circular coil at the outermost end in the axial direction when viewed from the origin The circular coil is arranged such that a virtual line connecting the radially inner edge of the coil and the origin falls within an angle range of approximately 34.5 degrees or more and 63.4 degrees or less with respect to the central axis. Characteristic coil device.