JPH0446727Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Industrial application field]

This invention relates to an RF antenna coil for an MRI apparatus that uses nuclear magnetic resonance to take cross-sectional images of the human body.

[Conventional technology]

The RF antenna coil of an MRI device transmits high-frequency power for excitation to a subject such as a human body,
It is used to receive NMR signals from a subject. A saddle-shaped coil 20 as shown in FIG. 5 is usually used as an RF antenna coil in a conventional MRI apparatus. A frequency tuning variable capacitor 8 and an impedance matching variable capacitor 9 are connected near a feeding point from the signal source 11. Further, a split saddle-shaped coil 20 is also used, as shown in FIG. 6, in which the antenna element portion of a conductor is cut at several places and combined with a coupling capacitor 21.

[Problem that the invention attempts to solve]

By the way, in an MRI apparatus, the frequency used increases as the static magnetic field becomes stronger. Therefore, in the conventionally used saddle-shaped coil, the spatial coupling of each element cannot be ignored due to its shape.
As a result, the frequency characteristics of the RF antenna coil have become extremely complex, making it difficult to tune to the frequency of the NMR signal or match the characteristic impedance to the transmission line. Furthermore, spatial coupling causes an undesirable peak on the frequency spectrum, and this peak overlaps with the desired frequency, resulting in a decrease in the Q value and sensitivity. This invention has simple and easy-to-understand frequency characteristics, allows easy adjustment of frequency tuning and impedance matching, improves sensitivity and Q value, and minimizes inductance to increase resonant frequency. The purpose of the present invention is to provide an improved RF antenna coil for an MRI apparatus.

[Means for solving the problem] The RF antenna coil of the MRI apparatus according to this invention is formed by two conductor ring plates each formed by arranging two conductor ring plates sandwiching a dielectric ring.
first and second linear antenna elements that connect the conductor ring plates on one side and the conductor ring plates on the other side between the two distributed capacitance elements; It has a coupling capacitor inserted in series in one of the two linear antenna elements, and a variable capacitor for frequency tuning inserted in series in the other.

[Effect]

The two linear antenna elements are coupled in a loop by the distributed capacitance element, and this linear element acts as an antenna element and contributes to the generation of a magnetic field. Since the linear elements are connected by the distributed capacitance element to form a loop in this way, the overall inductance of the RF antenna coil is effective only in the linear element portion and can be minimized. Furthermore, since spatial coupling is reduced, frequency characteristics become straightforward, frequency tuning and impedance matching adjustment become easier, and at the same time sensitivity and Q value are improved.

【Example】

FIG. 1 is an exploded perspective view showing an embodiment of this invention. In FIG. 1, a conductor ring plate 1,
5 are placed outside and inside the dielectric ring 12 with the dielectric ring 12 in between, and the conductor ring plates 2 and 6 are also placed outside and inside the dielectric ring 13 with the dielectric ring 13 in between. A straight conductor flat plate 3 extends from the outer conductor ring plate 1 and is coupled to the conductor ring plate 2 via a coupling capacitor 4. A linear conductor flat plate 7 also extends from the inner conductor ring plate 5 and is coupled to the conductor ring plate 6 by a variable capacitor 8. These conductor ring plates 1, 2, 5, and 6 are cut at one location so as not to form one loop. These conductor ring plates 1, 2, 5, 6 and conductor flat plates 3, 7 are
It is formed of a copper plate or the like, and the outer part (conductor ring plates 1, 2, conductor flat plate 3) and the inner part (conductor ring plates 5, 6, conductor flat plate 7) are mirror symmetrical. The dielectric rings 12 and 13 are made of, for example, a Teflon sheet. Power is supplied to the outer conductor ring plate 1 and the inner conductor ring plate 5 from a signal source 11 via a variable capacitor 9 and a fixed capacitor 10. An equivalent circuit diagram of this configuration is shown in FIG.
In other words, the dielectric ring 12 is formed by the conductor ring plates 1 and 5.
By sandwiching the dielectric ring 13 between the conductor ring plates 2 and 6, a distributed capacitance element is formed. The linear conductor plates 3 and 7 connect these distributed capacitance elements and the capacitor 4,
8 forms one loop. Therefore,
The straight conductor flat plates 3 and 7 act as an antenna element that generates a high frequency magnetic field. Therefore, the conductor flat plates 3 and 7 have a somewhat large width (angle) so that the generated magnetic field becomes a uniform magnetic field inside the RF coil. Here, the coupling capacitors 4 and 8 are for adjusting the resonance frequency, and one of them (here 8)
is used as a variable capacitor. Furthermore, one of the capacitors 9 and 10 (9) is a variable capacitor in order to adjust the characteristic impedance of the antenna. The straight conductor flat plates 3 and 7 act as antenna elements, and the other ring-shaped parts act as distributed capacitance elements, so the overall inductance of the RF antenna coil is that of the straight conductor. It depends only on the flat plates 3 and 7 and can be kept to a minimum. As a result, it is possible to increase the resonant frequency of this antenna coil. In addition, as shown in FIG. 3, coupling capacitors 4 and 8
The place where the conductor is inserted in series is the straight conductor flat plate 3,
Any part of 7 is fine. Further, instead of the straight conductor flat plates 3 and 7, strip-shaped conductor flat plates 31 and 71 may be used as shown in FIG. In this way, it may be constructed by arranging narrow conductor flat plates in the form of strips, or by arranging a number of pipe-shaped conductors (not shown).

[Effect of the idea]

According to the RF antenna coil of the MRI device of this invention, spatial coupling is reduced and unnecessary resonance peaks do not occur, so the frequency characteristics are simple and easy to understand, and frequency tuning and impedance matching adjustment is easy. Become. Additionally, compared to a saddle-shaped coil, both the Q value and the sensitivity are improved. Furthermore, since the inductance is reduced, the resonant frequency can be increased.

[Brief explanation of the drawing]

Figure 1 is an exploded perspective view of one embodiment of this invention, Figure 2 is an equivalent circuit diagram of Figure 1, Figures 3 and 4 are exploded perspective views of modified examples, and Figures 5 and 6. FIG. 2 is a schematic perspective view of a conventional example. 1, 2... Outer conductor ring plate, 3, 7... Conductor flat plate, 4, 10, 21... Coupling capacitor, 5,
6... Inner conductor ring plate, 8... Variable capacitor for frequency tuning, 9... Variable capacitor for impedance matching, 11... Signal source, 12, 13... Dielectric ring, 20... Saddle-shaped coil, 31, 71...
...Rectangular conductor flat plate.

Claims (1)

[Scope of utility model registration request] Two distributed capacitance elements are each formed by arranging two conductor ring plates to sandwich a dielectric ring, and two distributed capacitance elements are formed by connecting the conductor ring plates on one side and the conductor ring plates on the other side. first and second linear antenna elements connected between the elements; a coupling capacitor inserted in series with one of the first and second linear antenna elements; and a frequency tuning capacitor inserted in series with the other. An RF antenna coil for an MRI apparatus having a variable capacitor for use.