JPH0731768Y2 - RF antenna coil for MRI device - Google Patents

Description

[Detailed description of the device] [Industrial applications]

This invention relates to an RF antenna coil used in an MRI apparatus (an imaging apparatus using nuclear magnetic resonance).

[Prior art]

In order to perform local MR imaging of the human lower limbs and upper limbs,
A cylindrical RF antenna coil 5 as shown in FIG. 5 is used. That is, the cylindrical RF antenna coil 5 is inserted with an imaged region such as a lower limb for setting.

[Problems to be solved by the device]

However, since the conventional RF antenna coil has a cylindrical shape, there is a problem in that the subject is burdened when the imaging region is inserted therein. For example, when the knee is the imaging site and the ankle is fixed, setting is impossible. It is an object of the present invention to provide an RF antenna coil for an MRI apparatus, which is improved so as not to burden a subject.

[Means for Solving the Problems]

In order to achieve the above object, the RF of the MRI device according to the present invention
The entire antenna coil is formed in a cylindrical shape, and the outer conductor portion and the inner conductor portion, which are circular arcs and do not form a closed loop, are concentrically arranged at both ends of the cylinder with a dielectric spacer interposed therebetween. Of at least two first linear conductor portions extending from the arc-shaped outer conductor portion disposed at one end of the first linear conductor portion to the other end, and the first short-circuiting ends of the first linear conductor portions. A short-circuited portion, a first tuning variable capacitance element inserted between the first short-circuited portion and the arc-shaped outer conductor portion on the other end side, and an arc-shaped inner side arranged at one of the both ends At least two second linear conductor portions extending from the side opposite to the first linear portion of the conductor portion approximately 180 ° to the other end side, and the second linear conductor portions.
A second short-circuit portion that short-circuits the tips of the linear conductor portions of
A second tuning variable capacitance element inserted between the second short-circuit portion and the arcuate inner conductor portion on the other end side,
A plane that is parallel to the central axis of the cylinder and that passes between the first two linear conductor portions and between the second linear conductor portions, and has arcuate outer conductor portions and inner conductor portions at both ends. And the dielectric spacer and the first and second short-circuit parts are divided into two parts, and the two divided parts are mechanically and detachably joined by six joining jigs, and these six joints are joined together. Each of the jigs is configured so that the arc-shaped outer conductor portion, the inner conductor portion, and the first and second short-circuited portions at the six ends are electrically and detachably coupled.

[Action]

Since the dielectric spacer is sandwiched between the arcuate outer conductor portion and the inner conductor portion arranged at each of both ends of the cylinder, the outer conductor portion and the inner conductor portion are coupled at high frequency. The first linear conductor portion extending from the arc-shaped outer conductor portion disposed on one side of both ends is the first
Is connected to the arc-shaped outer conductor portion at the other end via the tuning variable capacitance element, and the second linear conductor portion extending from the arc-shaped inner conductor portion arranged on one side of both ends is the second Is connected to the arc-shaped inner conductor portion at the other end via the tuning variable capacitance element. Therefore, in terms of high frequency, from the first linear conductor portion to the first tuning variable capacitance element, the arc-shaped outer conductor portion at the other end, the arc-shaped inner conductor portion at the other end, the second tuning element, and the second tuning element. , A one-turn closed loop passing through the linear conductor portion, the arc-shaped inner conductor portion at one end, and the arc-shaped outer conductor portion at one end is formed. As a result, the function as an RF antenna coil is fulfilled. Although it is formed into a cylindrical shape as a whole, it is divided into two parallel to the central axis of the cylinder and is detachably connected both mechanically and electrically by a connecting jig, so that it can be set on the imaging site. The degree of freedom is increased and there is no burden on the subject. Further, when divided into two, only one of them can form a closed loop coil, so that only one side thereof can be set in the imaging region to fulfill the function as an RF antenna coil. Furthermore, it is possible to tune to the high-frequency excitation signal and the NMR signal by the first and second tuning variable capacitance elements. Moreover, since the arc-shaped outer and inner conductors are arranged so as to sandwich the dielectric spacer, a capacitance is formed between them and the resonance frequency of the coil is increased, which causes resonance for a high-frequency signal. It can be easily taken. Further, since the arc-shaped outer conductor portion and the inner conductor portion arranged at both ends of the cylinder are all formed in an arc shape so as not to form a closed loop, a gradient magnetic field pulse at the time of imaging is applied to this RF antenna coil. Can be prevented from being induced. As a result, high-frequency excitation and reception of NMR signals can be performed without being affected by the gradient magnetic field pulse.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, MRI according to the present invention
The RF antenna coil 1 of the device has a cylindrical shape as a whole, and is divided into two semi-cylindrical parts in a plane parallel to the central axis.
It is divided into 11 and 12. A window 13 is provided in one of the semi-cylindrical portions 11. These two semi-cylindrical parts 11, 12 are
The joint portion 15 provided on the 14 is detachably connected. That is, each of the semi-cylindrical parts 11 and 12 is provided with a projecting piece 14, and as shown in FIG. 2, a pin 16 is formed on one projecting piece 14 and a slot 17 is formed on the other projecting piece 14. , The pin 16 is inserted into the slot 17 to be coupled. By this mechanical connection, 2
The two protruding pieces 14 are also electrically connected to each other. The projecting piece 14 and the joint portion 15 are provided at three locations on one side and at six locations on both sides, and mechanical coupling is performed at six locations as well as electrical connection. As shown in FIG. 3, the RF antenna coil 1 has a conductive outer element 2, a conductive inner element 3, and a spacer 4 arranged between them embedded therein for insulation. Molded with a synthetic resin. The outer element 2 is formed of a copper plate or the like, and has circular arc portions 21 and 22 of about 350 ° and the circular arc portion 22 to the circular arc portion 2
It is composed of straight line portions 23 and 24 extending in one direction and a short-circuit portion 25 that short-circuits the tips of these straight line portions 23 and 24. The inner element 3 is formed of a copper plate or the like, and has arc portions 31 and 32 of about 350 ° and a straight portion extending from the arc portion 32 in the direction of the arc portion 31.
33, 34 and a short-circuit part that short-circuits the ends of these straight parts 33, 34
It consists of 35 and. A spacer 4 made of a dielectric material such as fluororesin is arranged between the circular arc portions 21 and 22 of the outer element 2 and the circular arc portions 31 and 32 of the inner element 3. The opening direction of arcuate parts 21, 22 and the opening direction of arcuate parts 31, 32 are 180 °
In the opposite direction. The outer element 2, the inner element 3 and the spacer 4 are divided into two parts, but the arc elements 21, 22, 31, 32 and the short-circuit parts 25, 35 of the outer element 2 and the inner element 3 are divided into a total of 6 parts. Is bent outward to form a protruding piece 14. Then, in the lower semi-cylindrical portion 12, a variable capacitor 26 that connects the arc portion 21 and the short-circuit portion 25, and a variable capacitor 36 that connects the cylindrical portion 31 and the short-circuit portion 35.
And. Since the dielectric spacers 4 and 4 are arranged between the circular arc portions 21 and 31 and between the circular arc portions 22 and 32, respectively, a capacitance is formed between them and they are coupled at high frequency. become. Therefore, these elements 2, 3, the spacer 4,
A one-turn closed loop is formed by the variable capacitors 26 and 36, so that a coil whose magnetic flux direction is the vertical direction of FIGS. 1 and 3 is formed. This variable capacitor 2
6 and 36 are for tuning to a high frequency excitation signal and an NMR signal, and the capacitance formed in the arc portions 21, 31, 22, and 32 increases the resonance frequency of this coil to a high frequency signal. This is to facilitate resonance. The straight line portions 23, 24, 33, 34 are two arc portions 21, 22, 3 respectively.
Since it is for connecting 1 and 32, it is not limited to 2 and 1
The number of wires may be three or more (in the case of one, one straight portion is arranged in the lower semi-cylindrical portion so that only the lower semi-cylindrical portion forms a closed loop of the coil). The reason why the circular arc portions 21, 22, 31, 32 are not closed loop is that the gradient magnetic field pulse at the time of imaging is due to the RF antenna coil 1
This is because it does not cause induction. Although not shown, the signal cable is connected to any position of the lower half cylindrical portion 12 with the outer element 2 on the ground side and the inner element 3 on the signal side. The RF antenna coil 1 thus formed is, for example, as shown in FIG. 4A, the rear joint portion 15 which is set on the imaging site such as the lower limb in a state where the two semi-cylindrical portions 11 and 12 are divided.
Used by combining with. Further, even in the lower half cylinder portion 12 alone, since the variable capacitors 26 and 36 are arranged in this lower portion to form a closed loop, the function as an RF antenna coil is fulfilled, as shown in FIG. 4B. Since it is possible to set only the lower cylindrical portion 12 to the photographing part and use it, it is possible to set it on the shoulder or the like. In the above, the copper plate elements 2 and 3 and the spacer 4 are used.
And are integrated by molding with a synthetic resin, but conductors may be printed and formed on both surfaces of the flexible substrate. Variable capacitors 26 and 36 may be variable capacitance diodes. Further, a variable capacitor for impedance matching can be inserted in series at the connection point with the signal cable.

[Effect of device]

The RF antenna coil of the MRI apparatus of the present invention has a cylindrical shape as a whole, and is divided into two parts so that it can be freely attached and detached. It can be set on the shooting site. Furthermore, the function as the RF antenna coil can be achieved by only one of the two divided parts. In addition, high frequency excitation signal and NM
It is easy to tune to the R signal, and high frequency excitation and reception of the NMR signal can be performed without being affected by the gradient magnetic field pulse.

[Brief description of drawings]

1 is a perspective view showing the overall appearance of an RF antenna coil of an MRI apparatus according to an embodiment of the present invention, FIG. 2 is an enlarged front view of a joint portion, and FIG. 3 is the inside of the RF antenna coil. Is an exploded perspective view, FIGS. 4A and 4B are schematic perspective views showing examples of use, and FIG. 5 is a schematic perspective view of a conventional example. 1 ... RF antenna coil (this invention), 11 ... upper half-cylindrical portion, 12 ... lower half-cylindrical portion, 13 ... window, 14 ... protruding piece, 15 ... joint part, 2 ... outer element 3 ...
… Inner element, 4 …… Spacer, 5 …… RF antenna coil (conventional).

Claims (1)

[Scope of utility model registration request] 1. An outer conductor part and an inner conductor part, which are formed in a cylindrical shape and are concentrically arranged on both ends of the cylinder with a dielectric spacer interposed therebetween and do not form a closed loop. At least two first linear conductor portions extending from the arc-shaped outer conductor portion arranged at one end of the both ends to the other end side, and a first short-circuiting tip end of these first linear conductor portions Short-circuited portion, a first tuning variable capacitance element inserted between the first short-circuited portion and the arcuate outer conductor portion on the other end side, and an arcuate shape arranged at one of the both ends. The first of the inner conductor portion
At least two second linear conductor portions extending from the opposite side to the other end side of the linear portion by 180 degrees, and a second short-circuit portion that short-circuits the tips of these second linear conductor portions. , The second
And a second tuning variable capacitance element inserted between the short-circuited portion and the arc-shaped inner conductor portion on the other end side, and the first two straight lines parallel to the central axis of the cylinder. In a plane that passes between the conductor portions and between the second linear conductor portions, the arc-shaped outer conductor portions, inner conductor portions, and dielectric spacers at both ends and the first and second short-circuit portions are divided into two. And the two divided parts are mechanically and detachably joined by six joining jigs, and the arc-shaped outer conductor portion and inner conductor at both ends are formed by each of these six joining jigs. Division and first and second
An RF antenna coil for an MRI apparatus, which is configured such that the six divided portions of the short-circuited portion are electrically detachably coupled.