JP3365793B2 - Bird cage type RF coil capacitor and bird cage type RF coil - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a birdcage type RF.
The present invention relates to a coil capacitor and a birdcage type RF coil, and more particularly, to a capacitor interposed between conductors of a birdcage type RF coil of an MR device and a birdcage type RF coil having such a capacitor.

[0002]

2. Description of the Related Art FIG. 5 shows a birdcage type RF of an MR device.
It is a typical external view which shows an example of a coil. The birdcage type RF coil 501 includes an element Ea having a predetermined length,
Eb, ... are arranged in a substantially cylindrical shape, and these elements Ea, E are arranged.
The front end side and the rear end side of b, ...
The configuration is such that b, ... Are connected in a ring shape. Each element E
, and capacitors 51a, 51b, ... Are connected by link conductors L1, L2. α and β are
It is a power supply line.

FIG. 6 shows a birdcage type RF coil 501.
It is an external view of the conventional capacitor 51a used for. The capacitor 51a has a configuration in which several chip capacitors C1a and C2b are connected in parallel between the link conductors L1 and L2. Width of chip capacitors C1a and C2b is 5mm
A multilayer ceramic capacitor or mica capacitor having a size of about 5 mm in length and 1 mm in thickness. The capacitors 51b, ... Are similar to the capacitor 51a.

[0004]

The conventional capacitors 51a, 51b, ... Are small in size and easy to handle, and can be used in the conventional MR device of about 0.5T without any trouble. However, when an MR device with a high magnetic field of about 1.5 T has been developed in recent years, heat generation due to dielectric loss increases, while the chip capacitors C1a and C2b are less likely to radiate heat, so that the capacitors 51a, 51b ,. The rise in temperature has become a problem. Further, the capacitors 51a, 51b, ...
Since the voltage applied to the capacitor rises to several kV, dielectric breakdown of the chip capacitors C1a and C2b has become a problem. Therefore,
An object of the present invention is a birdcage type RF coil capacitor and a birdcage type RF coil capacitor, in which a temperature rise is small and dielectric breakdown does not occur even when used in an MR device having a high magnetic field of about 1.5T. It is to provide an RF coil.

[0005]

A birdcage type RF coil capacitor of the present invention is a capacitor interposed between elements of a birdcage type RF coil of an MR device, and is provided on the surface of a high frequency dielectric substrate. In addition to forming electrodes to form a capacitor, at least the outer edges of the electrodes connected to the element are covered with an insulator.

In the above structure, it is preferable to attach a heat sink to the electrode connected to the element. Further, it is preferable that an auxiliary electrode is formed outside the electrode connected to the element so that the electrode connected to the element and the auxiliary electrode can be connected or disconnected as necessary to adjust the capacitance.

[0007]

In the birdcage type RF coil capacitor of the present invention, electrodes are formed on the surface of a high frequency dielectric substrate to form a capacitor. As a result, the heat radiation area is increased as compared with the conventional one, so that the temperature rise can be reduced even when used in an MR device with a high magnetic field of about 1.5T. Further, in the birdcage type RF coil capacitor of the present invention, at least the outer edge of the electrode connected to the element is covered with an insulator. As a result, the edge of the electrode that is prone to corona discharge is shielded from the air, so that corona discharge can be prevented.

[0008]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this.

FIG. 1 is a schematic external view showing an example of a birdcage type RF coil of an MR device. The birdcage type RF coil 101 includes elements Ea, E having a predetermined length.
b, ... are arranged in a cylindrical shape, and these elements Ea, Eb,
The front end side and the rear end side of the capacitors 11a, 11b,
It is a structure that is connected in a circle by. Each element Ea, E
, and the capacitors 11a, 11b, ... Are connected by link conductors L1, L2. α and β are feeder lines.

FIG. 2 shows a birdcage type RF coil 101.
It is an external view of the capacitor 11a used for. Figure 3
[Fig. 3] is an exploded perspective view of the capacitor 11a. The capacitor 11a includes a capacitor board 1 and a cover layer 2
And a heat sink 3.

As shown in the top view of FIG. 4A and the side view of FIG. 4B, the capacitor board 1 is a high frequency dielectric substrate having a thickness of 0.13 mm on the upper surface of a copper plate P having a thickness of 1 mm. εr
On the upper surface of the high frequency dielectric substrate εr.
It is configured by stacking 5 μm copper electrodes Ta, Tb, and Th. The copper plate P and the high frequency dielectric substrate εr have a size of width 80 mm × length 110 mm and an area of 8800 square mm. The electrodes Ta, Tb are the link conductors L1, L2.
It is a main electrode connected to. The electrode Th is an auxiliary electrode for adjusting the capacitance. The cover layer 2 is a film of the same size and of the same material as the high frequency dielectric substrate εr as shown in the top view of FIG. 4C and the side view of FIG. Windows 2a, 2b, 2h are provided to cover the edge portion and expose the central portion.

As shown in FIG. 3, the heat sink 3 is a radiating fin made of aluminum, and the nut N is connected to the electrodes Ta and Tb.
It is attached to the capacitor board 1 by soldering to the nut N and screwing the nut N with a screw B.

The capacitor 11a is fixed to a plastic body (not shown) of the birdcage type RF coil 101 with bolts, and as shown in FIG. 2, electrodes Ta and Tb are provided.
Are connected to the link conductors L1 and L2. Further, the electrode Th is connected to the electrodes Ta and Tb as necessary. The capacitors 11b, ... Have the same structure as the capacitor 11a.

According to the capacitors 11a, 11b, ..., Even when used in the birdcage type RF coil 101 of the 1.5T high magnetic field MR device, the temperature rise was small and no corona discharge occurred.

In another embodiment, the electrode and the high frequency dielectric substrate are multi-layered to obtain a large capacitance, or the element and the capacitor are integrally formed on one printed board by etching. The ones that have been done are listed.

[0016]

According to the present invention, even if heat is generated due to dielectric loss or the like, it has a sufficient heat radiation area.
The temperature rise can be suppressed. Further, since the edges of the electrodes are shielded from the air by the insulator, corona discharge can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic external view of a birdcage type RF coil of an MR device for high magnetic field.

FIG. 2 is a perspective view of a birdcage type RF coil capacitor according to an embodiment of the present invention.

FIG. 3 is an exploded perspective view of the capacitor shown in FIG.

4A and 4B are a top view and a side view of a capacitor board and a cover layer in the capacitor shown in FIG.

FIG. 5 is a schematic external view of a birdcage type RF coil.

FIG. 6 is a perspective view of a conventional birdcage-type RF coil capacitor.

[Explanation of symbols]

101 Bird Cage Type RF Coil 11a, 11b Bird Cage Type RF Coil Capacitor 1 Capacitor Board 2 Cover Layer 3 Heat Sink P Copper Plate εr High Frequency Dielectric Substrate Ta, Tb, Th Electrode L1, L2 Link Conductor

Front page continuation (72) Minor Nishiyama 127 Yokogawa Medical System Co., Ltd., 4-7 Asahigaoka, Hino City, Tokyo (56) Reference JP-A-2-95344 (JP, A) 52269 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) A61B 5/055 H01G 2/06 H05K 1/16

Claims (4)

(57) [Claims] 1. A capacitor interposed between conductors in a birdcage type RF coil of an MR device, wherein electrodes are formed on the surface of a high frequency dielectric substrate to form capacitors, and the capacitors are connected to the conductors. A birdcage type RF coil capacitor, characterized in that only an outer edge portion of an electrode is covered with an insulator. 2. The birdcage type RF coil capacitor according to claim 1, wherein a heat sink is attached to an electrode connected to the conductor. 3. The birdcage type RF coil capacitor according to claim 1, wherein the electrode has an auxiliary electrode in addition to the electrode connected to the conductor, and is connected to the conductor as necessary. A capacitor for a birdcage type RF coil, characterized in that the capacitance is adjusted by connecting or disconnecting an electrode that is connected to the auxiliary electrode. 4. A birdcage type RF coil capacitor according to any one of claims 1 to 3, wherein the birdcage type RF coil capacitor according to any one of claims 1 to 3 is interposed between conductors in a birdcage type RF coil of an MR device. RF coil.