JPH0341966B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a uniform magnetic field coil for a nuclear magnetic resonance computer tomography apparatus (hereinafter referred to as NMR-CT), and particularly to a uniform magnetic field coil suitable for a superconducting magnet. .

[Prior art and its problems]

Uniform magnetic field coils for NMR-CT have a high flux density (magnetic field strength) in the uniform magnetic field space that houses the human subject, and the magnetic field strength is highly uniform. In order to prevent the uniformity of the magnetic field from being disturbed by objects, it is required to reduce leakage magnetic flux as much as possible.

FIG. 9 is an explanatory diagram showing the arrangement of coil conductors of a uniform magnetic field coil already proposed by the present inventors, and shows the cylindrical uniform magnetic field coil viewed in the axial direction. In the figure, on the circumference of radius R ₁ surrounding the cylindrical uniform magnetic field space 7,
For example, inner main conductor arrays 10A, 10B, 10C, 1 consisting of a plurality of coil conductors shown as 11 to 16
0D, and each of the inner main conductor rows has a center angle θ of the symmetry plane X ₁ −X ₂ passing through the center (axis).
= 0, and within the range of 0 to 90°, the ampere-turn density I ₁ in the circumferential direction (value obtained by dividing the product of the number of coil conductors and the current by the circumferential length or central angle) is proportional to the cosine of θ. They are distributed unevenly in the circumferential direction. Also, 20A, 20B, 20C, 20D are radius
It is an outer main conductor array arranged on the circumference of _R2 ,
For example, the ampere-turn density I ₂ in the circumferential direction of the outer main conductor row 20A decreases with respect to that of the inner main conductor row in inverse proportion to the square of the radius ratio (R ₂ /R ₁ ) (I ₂ =I ₁ / (R ₂ /R ₁ ) ² ) Coil conductors 21, 22,
23, 24 etc. are distributed in the circumferential direction,
Maintaining the relationship in the above formula, the corresponding inner and outer coil conductors are conductively connected using crossover wires 19A and 19B so that the current directions in the inner and outer coil conductors are opposite to each other as shown by the symbols in the figure, thereby achieving uniformity. By forming the magnetic field coils, a uniform magnetic field 6 in a direction perpendicular to the symmetry planes X ₁ and X ₂ is generated inside the cylindrical uniform magnetic field space 7 .

FIG. 10 is a magnetic flux distribution diagram of the uniform magnetic field coil configured as shown in FIG. Almost outer main conductor row 20
It is possible to prevent leakage magnetic flux from circulating in the space 8 inside the outer conductor array 20 and leaking into the outer space of the outer conductor row 20.

FIG. ₁₁ is a magnetic flux distribution diagram seen from the side in _FIG . A uniform magnetic field 6 is formed in the axial center of the enclosed cylindrical uniform magnetic field space 7, but the magnetic flux lines 100 bulge outward at the axial ends, as shown in the characteristic diagram in FIG. Since the strength of the magnetic field decreases, this change in the strength of the magnetic field affects the uniform magnetic field 6 at the center in the axial direction, and has the disadvantage that the uniformity of the magnetic field strength of the uniform magnetic field 6 is inhibited. . Furthermore, the uniformity of the uniform magnetic field 6 can be improved to some extent by increasing the lengths of the inner and outer main conductor arrays 10 and 20, but by taking such measures, the uniform magnetic field coil 1 becomes large and high. Not only does this increase the weight of the cryostat, but when it is applied to a superconducting magnet, the cryostat becomes larger and heat conduction loss from the outside increases.Therefore, improvements are needed.

[Purpose of the invention]

The present invention was made in view of the above-mentioned situation, and
It is an object of the present invention to provide a uniform magnetic field coil with an adjustment coil that can obtain a highly uniform magnetic field without increasing the axial dimension.

[Key points of the invention]

The present invention provides an adjustment coil portion consisting of inner and outer adjustment conductor rows each having a short axial length at both ends of a main coil surrounding a cylindrical uniform magnetic field space, at least on either the inner or outer side. By configuring the adjustment conductor array so that its radius is located on a different circumference from that of the main conductor array, the density of the magnetic flux generated by the main coil at both ends of the main coil is reduced. By compensating for this, the uniformity of the uniform magnetic field in the axial center portion is maintained to a high degree.

[Embodiments of the invention]

The present invention will be explained below based on examples.

FIG. 1 is a principle explanatory diagram showing an embodiment of the present invention. In the figure, 10 is an inner main conductor array arranged on the circumference of a radius R ₁ surrounding the cylindrical uniform magnetic field space 7, and 20 is an outer main conductor row arranged on the circumference of a radius R ₂ . , inner and outer conductor rows 1
The main coil 2 is formed by conductively connecting the wires 0 and 20 with the connecting wire 19 so that the current directions are opposite to each other. This is the uniform magnetic field coil already explained with reference to FIGS. 9 and 11. It is similar to Reference numeral 3 denotes an adjustment coil section, which is disposed at the end of the main coil 2 at a portion surrounded by the inner and outer main conductor rows 10 and 20, and is arranged on the circumference with radii r ₁ and r ₂ , respectively. An adjustment coil section 3 separate from the main coil 2 is formed by conductively connecting the inner and outer adjustment conductor rows 30 and 40 with a crossover wire 39 so that the directions of current flow are opposite to each other.

FIG. 2 is an explanatory diagram of the circumferential distribution (ampere turn density) of each coil conductor row in the embodiment shown in FIG. X ₁ is the plane of symmetry (θ=O)
In this figure, only the range where θ is 90° from 0 is shown. In addition, in the figure, assuming that equal currents are flowing through the main coil 2 and the adjustment coil section 3, the circumferential distribution of ampere-turn density is replaced with the distribution of the coil conductor, and the relative positions are indicated by circles. In addition, the direction of the flowing current is indicated by a cross or a dot within the circle. In the figure, on the circumference with radius R ₁ are the main coil conductor,
For example, an inner main conductor array 10 consisting of 11 to 16
A is the ampere-turn density in the circumferential direction. In other words, the coil conductors are distributed in the circumferential direction so as to be proportional to the cosine of the central angle θ. Further, the outer main conductor row 20A is on the circumference with radius R ₂ , and the inner and outer adjustment conductor rows 30A, 4 are on the circumference with radius r ₁ and r ₂ .
0A are distributed, and the angle Φ that each coil conductor of these conductor rows makes with the plane of symmetry, and the angle θ that the coil conductors 11 to 16 of conductor row 10A make with the plane of symmetry. By determining the position of the coil conductor in the circumferential direction so that the condition of the following formula is satisfied between
The ampere turn density in the circumferential direction of A etc. is determined by the conductor row 10
It can be formed such that it decreases in inverse proportion to the square of the radius ratio (r/R ₁ ) with respect to that of A.

sinΦ=(r/R ₁ ) sinθ ...(1) However, in the above formula, r and Φ are r ₁ , r ₂ , R ₂
The radius of a conductor array arranged on a circumference different from R ₁ and the central angle that the coil conductor makes with the plane of symmetry are representatively shown.

Therefore, in the coil conductor array configured as described above, the ampere turn density or the number of coil conductors in the circumferential direction decreases in inverse proportion to the increase in radius r. Therefore, the coil conductors located at positions that satisfy the above formula are conductively connected using curved crossover wires 19, 39, etc. so as to satisfy the above formula so that the direction of the current is opposite as shown by the cross and dot marks in the figure. , coil conductors 15, 16, etc., which do not have corresponding outer conductors, are electrically connected to coil conductors located at positions corresponding to the vertical axis in the figure, thereby forming the main coil 2 and the adjustment coil portion 3.

FIG. 3 is a characteristic diagram of the strength of the magnetic field on the O-Z axis in the above-mentioned embodiment, where the curve 102 represents the strength of the magnetic field due to the main coil 2, and the curve 103 represents the strength of the magnetic field due to the adjustment coil section 3. The curve 101 shows the strength of the total magnetic field obtained by adding both of them. As is clear from the figure, the adjustment coil section 3 is provided at both ends of the main coil 2, and the strength of the magnetic field generated by both coils is added, so that the strength of the magnetic field at both ends of the main coil is increased. It is possible to obtain a uniform magnetic field coil with an adjustment coil in which the decrease in magnetic field strength is compensated for and the uniform magnetic field (flat portion of the curve) has a large spread in the axial direction, as shown by curve 101, without increasing the axial length of the main coil. can.

4 and 5 are explanatory diagrams showing different embodiments of the present invention. FIG. 4 shows one turn of the coil three-dimensionally, and FIG. 5 shows a plan view. In the figure, 17 is an inner main coil conductor arranged on a circumference with a radius of R ₁ , 27 is an outer main coil conductor arranged on a circumference with a radius of R ₂ , and 47 is a larger radius than the outer main coil conductor 27. The outer adjustment coil conductor is arranged on the inner circumference with radius R ₃ , and by passing a current i in series through the main coil conductors 17, 27 and the outer adjustment coil conductor 47 as shown by the arrow in the figure, the radius R ₂ Position 2 indicated by the dashed line on the circumference
7A has an inner adjustment coil conductor and an outer main coil conductor in which currents flow in opposite directions to each other, so as to provide the same function.

As described above, the uniform magnetic field coil with adjustment coil is integrated with the main coil and the adjustment coil part, and is located at position 2.
By omitting the coil conductor that should be in 7A, the structure of the uniform magnetic field coil with adjustment coil can be simplified, and the peak value of the adjustment magnetic field 103 shown in FIG. 3 can be lowered and the axial direction Since the spread can be increased, the uniformity of the magnetic field of the total magnetic field 101 can be controlled in consideration of the characteristics of the main coil magnetic field 102.

FIG. 6 is an explanatory diagram showing still another embodiment of the present invention, in which the inner main coil conductor 18 is shown among the inner and outer main coil conductors 18 and 28 arranged on the circumference with radii R ₁ and R ₂ . It differs from the previous embodiment in that it is formed shorter and the adjustment coil conductor 48 is provided on the circumference of a circle with a radius r ₄ smaller than the radius R ₁ , and the main coil and adjustment coil part are integrated. As a result, the structure can be simplified, and the adjustment magnetic field 103 in FIG.
Since the peak value of can be increased and the axial spread can be narrowed, it is possible to concentrate the compensation of the magnetic field in a narrow axial range at both ends of the main coil. Compensation characteristics for different magnetic field strengths can be obtained.

FIG. 7 is an explanatory diagram showing another embodiment of the present invention, in which the outer main coil conductor 29 is of the inner and main outer coil conductors 19 and 29 arranged on the circumference with radii R ₁ and R ₂ . Extend both ends of
This differs from the previous embodiment in that an outer adjustment coil conductor 49 is provided that is inclined in the radial direction, and both ends of the inner main coil conductor 19 overlap with the adjustment coil. This can be further simplified, and by selecting the inclination of the coil conductor 49, the uniformity of the uniform magnetic field can be adjusted more precisely.

FIG. 8 is an explanatory diagram showing still another embodiment of the present invention, and in the embodiment shown in FIG _.
This differs from the previous embodiments in that the axial position of the outer adjustment coil conductor 47 arranged on the circumference is slightly shifted toward the center in the axial direction. By selecting the position where the magnetic field is best, the uniformity of the magnetic field can be adjusted more precisely.

The embodiments shown in FIGS. 5 to 8 may be used alone, but by combining a plurality of embodiments as necessary, the axial center portion of the cylindrical uniform magnetic field space 7 can be It goes without saying that the uniformity of the magnetic field strength of the uniform magnetic field 6 formed can be further improved.

〔Effect of the invention〕

As described above, the present invention provides adjustment coil sections at both ends of a main coil consisting of inner and outer main conductor rows arranged on a circumference of different radii surrounding a cylindrical uniform magnetic field space. Based on the inner main conductor row distributed in the circumferential direction so that the ampere turn density is proportional to the cosine of the central angle made with respect to the plane of symmetry, the ampere turn density of the other conductor rows is the square of the radius ratio. The main coil and the adjustment coil are formed so as to be inversely proportional to each other, and are electrically connected to each other so that the magnetic flux generated by each of the main coil and the adjustment coil is added. As a result, the problem that the magnetic field strength at both axial ends of the conventional structure consisting only of the main coil decreases can be compensated for by the magnetic flux generated in the adjustment coil section without increasing the axial length of the coil. Therefore, it is possible to economically advantageously provide a uniform magnetic field coil with a compensation coil that is small and has a highly uniform magnetic field strength. In addition, by reducing the ampere turn density in inverse proportion to the square of the radius ratio, it is possible to provide the outer conductor row with a magnetic field shielding function, making it possible to block leakage magnetic fields without using a core-shaped magnetic shield. Since it does not contain any magnetically saturated parts, it is highly applicable to superconducting homogeneous magnetic field magnets with high magnetic field strength, and by housing the uniform magnetic field coil with integrated adjustment coil in one cryostat, High strength, uniform, and small installation area.
Moreover, it can contribute to providing a uniform magnetic field magnet for NMR-CT with less leakage magnetic flux. moreover,
By omitting part of the main coil and the adjustment coil, there is an advantage that the structure of the coil can be simplified.

[Brief explanation of drawings]

FIG. 1 is a principle explanatory diagram showing an embodiment of the present invention,
FIG. 2 is an explanatory diagram showing the circumferential distribution of the coil conductor in FIG. 1, FIG. 3 is a characteristic diagram of the strength of the axial magnetic field in the above embodiment, and FIGS.
The figures are explanatory diagrams showing different embodiments, FIG. 6 is an explanatory diagram showing a further different embodiment, FIG. 7 is an explanatory diagram showing another embodiment, FIG. 8 is an explanatory diagram showing still another embodiment, Fig. 9 is an explanatory diagram of the already proposed uniform magnetic field coil, Fig. 10 is a magnetic flux distribution diagram in the uniform magnetic field coil of Fig. 9, and Fig. 11 is an axial magnetic flux distribution diagram when Fig. 10 is viewed from the side. , FIG. 12 is a characteristic diagram of the strength of the magnetic field on the axis of FIG. 2... Main coil, 3... Adjustment coil, 6... Uniform magnetic field, 7... Uniform magnetic field space, 10, 10A, 1
0B, 10C, 10D...Inner (main) conductor row, 1
1 to 19...Inner (main) coil conductor, 19, 39
...crossover wire, 20, 20A, 20B, 20C, 2
0D...Outer (main) coil conductor row, 21 to 24,
27-29...Outer (main) coil conductor, 30A...
...Inner adjustment conductor row, 40A...Outer adjustment conductor row,
47, 48, 49...Adjustment coil conductor, X ₁ -X ₂
... Symmetry plane, R ₁ , R ₂ , r ₁ , r ₂ , r ₃ ... Radius, θ,
Φ...Central angle.

Claims (1)

[Claims] 1. An inner side and It consists of a main coil in which the outer main conductor rows are conductively connected so that the current directions are opposite to each other, and the ampere turn density in the circumferential direction of the inner main conductor row is proportional to the central angle and cosine of the plane of symmetry passing through the axis. The coil conductors are distributed in the circumferential direction, and the ampere turn density of the outer main conductor row decreases in inverse proportion to the square of the radius ratio. Adjustment conductor rows in which adjustment coil conductors shorter than the coil conductor are distributed in the circumferential direction so as to overlap in the axial direction at both ends of the main coil so that the ampere turn density maintains the same relationship as the main coil. A uniform magnetic field coil with an adjusting coil, characterized in that the adjusting coil part is electrically connected so that the generated magnetic flux is added to that of the main coil. 2. In what is stated in claim 1,
The adjustment coil consists of an inner and outer adjustment conductor row, and the two adjustment conductor rows are arranged on different circumferences between the inner and outer main conductor rows, forming an adjustment coil section separate from the main coil. Uniform magnetic field coil with adjustment coil featuring: 3 In what is stated in claim 1,
A uniform magnetic field coil with an adjustment coil, characterized in that an adjustment coil section and a main coil are connected in series between turns and integrated. 4 In what is stated in claim 1,
The adjustment conductor row of the adjustment coil section consists of one adjustment conductor row arranged on the circumference of either the inside of the inner main conductor row or the outside of the outer main conductor, and the coil conductors of both coils are arranged between the turns. A uniform magnetic field coil with an adjustment coil, characterized in that the coils are connected in series with each other.