JPS6156947A - High frequency coil for nmr imaging apparatus - Google Patents

Abstract

PURPOSE:To improve the upper limit of a high frequency to be used, by electrically connecting two saddle-type signal coils in parallel, and making the distances between the corresponding points and power feeding points on two parallel straight-line parts equal. CONSTITUTION:Two saddle-type coils 1 and 2 are formed by conducting wire parts ABCDEF and A'B'C'D'E'F'. The coils are symmetrically arranged so that the centers of curvatures of the arc parts on the corresponding sides agree. Thus a coil pair having the saddle type as a whole is constituted. The central angle of the arc parts of both coils 1 and 2 is made to be 120 deg.. The length of the straight line part is made to be twice the radius of curvature at the arc part. Cut parts AF and A'F' are provided at the centers of the arc parts on the same side. The conducting parts A and A' and F and F' are connected. Power is fed in parallel symmetrically through terminals 3 and 4, which are connected to the central points of the connecting lines. Thus the maximum frequency limit of the high frequency to be used can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a high frequency coil for an NMR imaging device.

(b) Prior art In general, in order for a conductor wire wound into a coil to function as a pure inductance element, even if its DC resistance component can be ignored, the length of the conductor wire relative to the wavelength of the supplied alternating current must be It is necessary that the length be short enough to be approximately negligible. 'By the way, in medical NMR imaging equipment, it is necessary to insert a human body or a part of the human body as a subject into a DC magnetic field and a high-frequency magnetic field perpendicular to it. Saddle-shaped coils are often used as magnetic field coils and NMR signal detection coils (sometimes used for both). However, since the subject to be examined is a human body or a part thereof, the shape and dimensions of the coil must be much larger than those for physical and chemical NMR devices. Generally speaking, in order to increase the signal strength, it is desirable to increase the NMR frequency to a certain degree, that is, to shorten the wavelength of the high frequency used. conflict with the desired relationship.

Experiments and experience have shown that in practice, if the conductor is long,
It is necessary to keep it below /20 of the wavelength; if it exceeds this, the Q-value of the coil will drop significantly.

The above will be considered regarding a saddle-shaped coil for human head imaging. In this case, the radius of curvature of the arcuate portion of the saddle-shaped coil must be at least 15 (!7+1); on the other hand, according to the theoretically determined ideal shape of the saddle-shaped coil, the length of the straight portion is the radius of curvature above Therefore, the conductor length of one saddle-shaped coil is 123ffi, but
The high-frequency coil for NMR is used as a pair of saddle-shaped coils consisting of two such saddle-shaped coils, so when both coils are connected in series, the total length of the conductor part is 2'4'.
Reaches 6cm. On the other hand, the wavelength /20 is 246a
The frequency that becomes m is calculated as 6.1MH2J. Therefore :). . , 9ka, j-yo, Utsu O'am=l
When tvt[JIW=1, the NMR frequency is 6.
Must be selected below IMHz.

In order to overcome some of these drawbacks, as shown in Fig. 1, two saddle-shaped single coils 1 and 2 constituting a saddle-shaped coil pair are arranged so that the direction of the current is made additive. High-frequency coils have also been proposed in which the following are selected and configured to be electrically connected in parallel. In other words, the relationship between the coil conductor and the wavelength becomes a problem because when the length of the current path becomes negligible relative to the wavelength, a non-negligible deviation occurs in the time change of the current value in each part of the conductor. , shunting,
This is because the phase difference of the current along the conductor portion cannot be ignored. Therefore, if both single coils are connected in parallel, and it is only necessary to consider the length of the current path for each single coil, the limit wavelength of the high frequency used will be doubled, and the saddle-shaped coil pair illustrated above will be In this case, the parallel connection allows the NMR frequency to be selected as high as 12.2 MH2.
In a saddle-shaped coil pair, the magnetic field created at the center is mainly due to the current flowing through the straight section of the saddle-shaped coil, and although the contribution from the current in the arcuate section is small, it cannot be considered. Since the length of the current path includes the length of the arc, even if both single coils are connected in parallel, the upper limit of the high frequency that can be used is only twice as high as in the case of series connection, as described above. .

(C) Purpose The purpose of the present invention is to eliminate the above-mentioned drawbacks associated with the prior art, and to develop an NMR system that further increases the upper limit of the usable high frequency.
An object of the present invention is to provide a saddle-shaped coil pair for a device.

B) Structure To achieve the above object, the saddle-shaped coil pair according to the present invention is a saddle-shaped high-frequency coil pair for an NMR apparatus, which comprises:
The two saddle-shaped single coils constituting this coil pair are electrically connected to each other in parallel, and the two corresponding points on the two parallel straight sections of each saddle-shaped single coil are connected to the saddle-shaped single coil. It is characterized by the fact that the distance between the power supply point to the coil and the power supply point is the same.

(e) Examples Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a perspective view schematically showing the configuration of a saddle-shaped coil pair according to an embodiment of the present invention. In the same figure, two saddle-shaped coils 1 and 2 each consist of conductor parts ABCDEF and AIB/C/D/E7F/, and are arranged symmetrically so that the centers of curvature of the circular arc parts on the corresponding sides coincide with each other. They are arranged to form a whole saddle-shaped coil pair. For both type coils 1 and 2, the central angle of the arc part is 1
20°, and the length of the straight section is chosen to be twice the radius of curvature of the arc section. In addition, both type coils 1 and 2 are, respectively,
It has cutting AF and A'F' in the center of the arc part on the same side,
A and A' and F and F' are connected, and terminals 3 and 4 are connected to the midpoint of A and A' and the midpoint of F and F', respectively.
This allows them to be symmetrically fed in parallel.

Due to this structure of the saddle-shaped coil pair, each saddle-shaped coil has a feeding point at a symmetrical force position with respect to its straight section, so that the current (( There is no phase difference between the absolute values. Moreover, as mentioned earlier, regarding the magnetic field created at the center of the saddle-shaped coil pair, we only need to consider the magnetic field caused by the current in the straight section, so the relationship between the length of the coil conductor and the wavelength is similar to that of the saddle-shaped coil pair. It is replaced by the relationship between the length of the straight part of the type coil and the wavelength. In the ideally shaped saddle-shaped coil where the central angle of the arc part is 120° and the length of the straight part is twice the radius of curvature of the arc part as described above, the length of the arc part is equal to the length of the saddle-shaped coil - circumference. Since there is no need to consider the length of the arc portion, the maximum frequency limit of the high frequency used is greatly increased.

The present invention also provides, as shown in FIG.
It is also possible to insert a capacitance K into the center of the non-power feeding side circular arc portion. By inserting into the capacitance of the entire saddle-shaped coil pair i,! The inductance is smaller than in the embodiment shown in FIG. 2, and the Q-value is improved.

The present invention can also be modified into a structure as shown in FIG. In this example, four rectangular coils a+
4+ 5. Although it cannot be called a saddle-shaped coil pair, the inner sides of coils 13 and 14 correspond to the straight part of saddle-shaped coil 1 shown in FIG. This corresponds to the straight portion of the saddle-shaped coil 2 shown in FIG. In FIG. 4, the same symbols and numbers as used in FIG. 2 are given to the parts corresponding to the parts in FIG. 2.

(F) Effect As is clear from the above explanation, according to the present invention, if the external dimensions are the same, the maximum frequency limit of the high frequency used can be selected to be much higher than in the case of the conventional saddle-shaped coil pair. However, if the maximum frequency limit is the same, the shape of the saddle-shaped coil pair can be made larger than that of the conventional t↑.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a saddle-shaped coil pair according to the prior art. FIG. 2 is a perspective view of a saddle-shaped coil pair according to an embodiment of the present invention. FIG. 3 is a perspective view of a saddle-shaped coil pair according to another embodiment of the present invention. FIG. 4 shows a modified embodiment having the same effect as the saddle coil pair shown in FIG. 2 in terms of magnetic field generation. 1.2...Saddle type single coil, 3.4...Current supply terminal,

Claims (2)

[Claims] (1) A pair of saddle-shaped high-frequency coils for NMR equipment,
The two saddle-shaped single coils constituting this coil pair are electrically connected to each other in parallel, and the two corresponding points on the two parallel straight sections of each saddle-shaped single coil are connected to the saddle-shaped single coil. A high-frequency coil for an NMR imaging device, characterized in that the distances between the coil and a power feeding point are equal. (2) A high-frequency coil for an NMR imaging apparatus according to claim 1, characterized in that a capacitance is connected in series at the center of the arc-shaped portion in each of the saddle-shaped single coils.