JPS60228944A - Hollow-core type magnet for nuclear magnetic resonance image pick-up apparatus - Google Patents

Abstract

PURPOSE:To make it possible to perform the correction of the uniformity degree of a magnetic field, by devising the arrangement and wiring of single coils each formed by single pan cake winding when the mutual wiring of said coils is performed. CONSTITUTION:Two pan cake shaped single coils (a), (b) [wherein the coil (b) is in backside-out state to the coil (a)] are used and superposed so as to be made symmetrical to a Y-axis while one terminals 2a of two coils are connected to each other. The wiring part 21 mutually connecting the coil terminals 2a becomes opposite to the other part in the direction of a current. A pair of thus formed single coils are further superposed on a plurality of other coils on the same axis so as to be connected thereto in series and four coils are arranged at predetermined intervals and these four coils are further connected in series to obtain the magnet for a nuclear magnetic resonance apparatus. Then, by appropriately adjusting the shift angle in the superposition of two similarly wound single pan cake shaped coils, the position of the part 21 coming to a linear shape is shifted and the uniformity degree of a magnetic field can be adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to improving the magnetic field uniformity of an air-core coil magnet used in a >m imaging apparatus for nuclear magnetic resonance (hereinafter referred to as NMR).

[Prior Art] NMR imaging devices have been well known as devices that can non-invasively obtain tomographic images of human bodies and the like. In such an NMR imaging device, an annular air-core coil is used to generate a necessary magnetic field (particularly a static magnetic field).

By the way, generally when winding an air-core coil in a single pancake or double pancake manner, a winding frame 1 (cylindrical or cylindrical) is used as shown in Figure 1.
However, when the first layer is rolled up, the winding frame 1
As a result, each layer of the coil does not form a perfect ring (the uniformity of NMR magnets is 10
Because a custom order is required, it cannot be handled as a toroidal coil, and some kind of correction is required. ).

An example of an air-core coil for an NMR imaging device has a configuration as shown in FIG. 2. That is, four air-core coils C81, O82, 0LI.

The OLs 2 are arranged on the same axis, and the uniformity of the internal space (within the imaging area) is several tens of ppwl. Then, each air-core coil is connected to a wire rod 2 as shown in FIG.
It is formed by stacking multiple coils wound around each other.

However, if these coils are designed as a complete ring, the magnetic field uniformity will be significantly worse than that at the design stage. Normally, as a means of correcting uniformity, for example, fine adjustment of each coil position and using shim coils are used, but such correction methods require complicated combinations of multiple sets of shim coils depending on the uniformity correction. It takes time because it has to be installed according to the layout.
Another problem is that an extra power source is required for the shim coil.

[Purpose of the Invention] In view of the above, the purpose of the present invention is to provide a method for correcting magnetic field uniformity by devising the arrangement and wiring of the coils when wiring single coils wound in single pancakes. An object of the present invention is to provide an air-core coil for a nuclear magnetic resonance imaging device.

[Summary of the Invention] The present invention to achieve such an object consists of two air-core coils with a large inner diameter and two air-core coils with a small inner diameter disposed outside of the air-core coils. In an air-core magnet for a nuclear magnetic resonance imaging device that is arranged concentrically at predetermined intervals on the Z-axis, each coil is constructed by stacking and connecting a plurality of pairs of single-layer coils wound in a Pankagi manner. , The pair of single coils is made by stacking the two single coils upside down, placing them so that the ends of each coil are offset from each other, and connecting the two coils. The two coils are connected so that the current direction in the wiring section is opposite to the current direction in the other winding sections, and the uniformity of the magnetic field changes depending on the angle at which the pair of single coils overlap. It is characterized by the following.

[Example] The present invention will be described in detail below with reference to the drawings. In Figure 3 (
A), (B) (However, (B) is the reverse relationship with the coil in (A).) A pancake-shaped coil wound as shown in (the part 2G that is wound one layer as in the conventional case) 2 single coils are stacked symmetrically with respect to the Y axis, and one end 28 of the two coils is used as shown in (c) in the same figure. connect them together. In the wiring portion 21 that connects the coil ends a, the direction of the current is opposite to that in other portions.

A plurality of pairs of single coils formed in this manner are further stacked coaxially and connected in series, and four of these are arranged at predetermined intervals as shown in Fig. 2, and these four coils are further connected in series. Connect in series to obtain a magnet for NMR equipment.

Figure 4 is a diagram showing the magnetic field uniformity inside a 4-coil magnet, where the horizontal axis shows the position on the Y axis at X=Z=O, and the vertical axis shows the position at the center (X=Y=Z=O). The uniformity of the magnetic field BO (
It is shown by taking ΔB/5o)ppIll. In this figure, in the case of broken line 41, the coil ends (the winding start and winding end parts) of each single coil of the four coils are YZ flat mutton (in Figure 2, the Z axis is perpendicular to the paper surface)
The solid line 42 shows the magnetic field uniformity characteristics when the coils OL1. The magnetic field uniformity is shown when a single coil arranged and connected as shown in FIG. 2 is used in OL2.

The reason why the uniformity deteriorates as shown by the broken line is that there is a portion 21 that does not form a circular ring but a straight line as shown in Fig. 2, and is rolled in the same way as shown in Fig. By appropriately adjusting the deviation angle in the superposition of the two single pancake-wound coils, the part 2 becomes straight.
1 can be shifted, and the magnetic field uniformity can be adjusted by such adjustment.

[Effects of the Invention] As explained above, according to the present invention, when wiring single pancake-wound single coils without using any other correction coils, the arrangement and wiring of the coils can be adjusted as appropriate. By adjusting, the magnetic field uniformity can be corrected.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the winding state of a pancake-wound coil, Fig. 2 is an external view of a magnet for an NMR imaging device, and Fig. 3 is an illustration of the procedure for creating a pair of single coils according to the present invention. FIG. 4 is a diagram showing the state of magnetic field uniformity inside the four-coil magnet. C3,1,O82,,,outer coil,CLl,C12,
,,inner coil, 1900 reel 1.2. ．． . Wire rod, 2a, 00 winding start, 2b, 0 winding end,
vj31 figure 2

Claims (1)

[Claims] Consisting of two air-core coils with a large inner diameter and two air-core coils with a small inner diameter placed outside the coils, these four coils are arranged concentrically at predetermined intervals on the Z-axis. In an air-core magnet for a nuclear magnetic resonance imaging device, each of the coils is configured by stacking and connecting a plurality of pairs of pancake-wound single coils, and each of the pair of single coils is composed of two single coils. The coils are placed one on top of the other in a reverse relationship, and the ends of each coil are placed at different positions, so that the current direction of the wiring section that connects the two coils is the same as the current direction of the other winding section. A coupling for a nuclear magnetic resonance imaging device, characterized in that two coils are connected in opposite directions, and the degree of magnetic field uniformity changes depending on the angle at which the pair of single coils are superimposed. mold magnet.