JPH0334898Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field This invention relates to a magnet device, and in particular to a magnet device that is equipped with a magnetic field generating means for generating a substantially uniform magnetic field along the main axis and a means for superimposing a gradient magnetic field across the main axis. Regarding equipment.

BACKGROUND OF THE INVENTION Such magnetic devices are used in a variety of fields, particularly in the field of magnetic resonance (NMR) imaging. In NMR imaging, a transverse principal axis gradient magnetic field is generated in a series of pulses to image the human body using magnetic resonance techniques.

Problems to be Solved by the Invention A conventional magnet device used in an NMR apparatus has two pairs of gradient coil sets arranged on both sides of a main shaft, and these pairs of gradient coil sets are separately controlled to control the coil set. Apply a gradient magnetic field between the pair. One of the problems with conventional devices is that the resulting gradient linearity is unacceptable under certain imaging conditions.

Means for Solving the Problems According to this invention, a magnet device includes a magnetic field generating means for generating a substantially uniform magnetic field along the main axis, and a pair of gradient coils arranged on both sides of the main axis. When current flows through the gradient coil pair, a gradient magnetic field is generated by the gradient coil pair along a second axis extending across the principal axis between the gradient coil pairs. Each gradient coil has a first and a second coil, the first,
The windings of the second coil are formed on respective surfaces substantially concentric with the main axis. A second coil is arranged in the central region of the magnet device, so that in use this central region has a higher current density than the remaining regions.

With this invention, the linearity of the generated gradient magnetic field is significantly improved compared to the conventional linearity of about 5% to about 2%. That is, at any point along the second axis, the maximum deviation of the magnetic field is less than 2% of the desired value.

Typically, two pairs of (gradient) coils are placed on either side of the main axis, with each coil set producing a gradient magnetic field along a respective second axis extending between each pair of coil sets.
These secondary axes intersect each other and the main axis. Further, typically, the main axis and each second axis are orthogonal to each other.

Preferably, the second coil of each coil set is arranged substantially coaxially or concentrically with the corresponding first coil.

Although the first and second coils can be energized separately, it is preferable to electrically connect each set of first and second coils in series. This connection particularly facilitates simultaneous energization of both coils during typical magnetic resonance imaging procedures where pulses are applied to both coils.

Three or more coils can be provided in each coil set to further improve linearity, but again it is preferable to arrange the coils coaxially with respect to each other.

Typically, the magnetic field generating means comprises at least one electrical coil approximately concentric with the main axis of the solenoid, for example, and these coils may be superconducting. On the other hand, gradient coil sets are typically resistive (non-superconducting).

EXAMPLES Hereinafter, this invention will be explained in detail based on examples.

The magnet device shown in FIGS. 1A, 1B, 2A, and 2B includes a superconducting coil (not shown) housed in a cryostat 1. The magnet device shown in FIGS. A cylindrical hole 2 with a main axis 3 is formed by a cryostat. A magnet arrangement housed in the cryostat 1 generates a uniform steady magnetic field extending in the direction z of the main axis 3. Hole 2 coaxial with main shaft 3
An aluminum winding form 4 is installed inside the winding form 4, and a large number of gradient coil sets are arranged on this winding form 4.

As shown in FIG. 1B, four substantially identical coils 5, 6, 50, 60 are arranged in a central plane 70 of the magnet arrangement.
Each coil set is arranged in pairs symmetrically with respect to the first coil 5A, 5B, 6A, 6B.
have. Each coil has a circumferential extent as shown in FIG. 1A. In use, a gradient magnetic field is created along a second axis extending between one of the opposing coil pairs, e.g., coil sets 5, 50.

Coils 5A, 5B, 6A, 6B each have a series of electrical conductor windings similar to those shown in FIG. As is clear from FIG. 3, a first area 7 consisting of six turns in the circumferential direction, a second area 8 consisting of four turns spaced apart from the first area,
A third area 9 of two turns separated from this second area
and is provided.

FIG. 4 is a perspective view of the coil 5. Coil group 5
is the first coil 5A extending over a circumferential angle of approximately 160 degrees.
and has a winding similar to that shown in FIG.
Extending by a smaller circumferential angle of about 87 degrees, the coil 5A
and a coaxial second coil 10. For clarity of illustration, the coil 10 has been omitted from FIG. 1B. The coil 10 serves to increase the current density in the central region of the coil set, resulting in a significant improvement in the linearity of the gradient field extending between the opposing coil pairs.

The circumferential angles of the coils 5A and 10 (as well as the corresponding coils among the other coils) can take various values. The circumferential angle values are determined empirically, but are preferably 132° 12° 156° 84°.

In the illustrated example, the smaller coil 10 is arranged radially outward from the coil 5A. However, the coil 10 may be arranged radially inward from the coil 5A.

The two coils of each coil set are connected in series to a remote power source (not shown) to energize each coil simultaneously. Furthermore, coil sets 5, 6, 50, 6
0 are also interconnected in series.

In addition to the X gradient coil sets 5, 6, 50, 60, a similar set of Y gradient coil sets are arranged on the former 4. FIG. 2B shows two Y-direction gradient coil sets 11, 12. Further, FIG. 2A shows the above-mentioned coil set 11 and another Y-direction coil set 1 opposite thereto.
10 is shown. These coil sets are No. 1A
1B, while the X-direction coil set is omitted in FIGS. 2A and 2B. Coil sets 11 and 12 are identical to coil sets 5 and 6, except that they are arranged on the former 4 so as to generate a gradient magnetic field orthogonal to the gradient field generated by the X-direction coils. . Therefore, each of the coil assemblies 11, 12 has a first coil 13, which is equivalent to the coil 5A, for example, and a second coil 14, which is similar to the coil 10 and superimposed concentrically on each coil 13. The Y-direction coils are also interconnected in series.

The various coils described above do not necessarily have to have the configuration shown in Figure 3; for example, each coil may have a different number of turns and the arrangement of turns may be the same as that shown in Figure 3 (3).
arcuate portions).

[Brief explanation of drawings]

Figures 1A and 1B are schematic partial end and side views of the magnet device showing the coil set for generating a gradient magnetic field in the X direction, and Figures 2A and 2B show the coil set for generating a gradient magnetic field in the Y direction. Figures 1A and 1B shown.
3 is a diagram showing a typical coil structure in one coil set, and FIG. 4 is a schematic perspective view showing details of one coil set. 3... Main shaft, 5, 50... Gradient coil set pair, 5
A, 5B...First coil, 6,60...Gradient coil pair, 10...Second coil, X...Second axis, Y
...Second axis.

Claims (1)

[Claims for Utility Model Registration] 1. Comprising a magnetic field generating means that generates a substantially uniform magnetic field along the main axis, and a pair of gradient coils arranged on both sides of the main axis, when a current flows through the pair of gradient coils, A gradient magnetic field is generated by the pair of gradient coil sets along a second axis extending across the main axis between the pairs of gradient coil sets, each gradient coil set having a first and a second coil, the first , the windings of the second coil are formed on respective planes substantially concentric with the main axis, and the second coil is arranged in a central region of the magnet arrangement such that in use this central region carries a higher current density than the remaining regions. A magnet device comprising: 2. The magnet device according to claim 1, characterized in that the second axes cross each other and the main axis. 3 Utility Model Registration The magnet device according to claim 1 or 2, characterized in that the second coil of each gradient coil set is substantially coaxial with the corresponding first coil. 4. In any one of claims 1 to 3 of the claims for utility model registration, the first and second
A magnet device characterized in that the coils are electrically connected in series. 5 Utility Model Registration The magnet device according to any one of claims 1 to 4, characterized in that the magnetic field generating means includes at least one electric coil substantially coaxial with the main axis.