JPH0489033A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To drive two electric characteristic changing means correctly and synchronously and miniaturize a signal coil section by connecting one of two electric characteristic changing means to one protruded section of a motor rotary shaft, and connecting the other to the other protruded section. CONSTITUTION:When a receiving coil 2 is to be turned, the motor 5a of a turning circuit 3 is operated, protruded sections 6a, 6b of the rotary shaft of the motor 5a are rotated in the arrow direction, and variable capacitors 4a, 4b integrally connected to the protruded sections 6a, 6b are rotated correctly and synchronously. No drift is generated between rotating positions of the variable capacitors 4a, 4b, rotating angles of them coincide invariably and completely, and the receiving coil 2 can be tuned with high precision. The MR signal is detected by the receiving coil 2 with high precision, the S/N ratio of the signal is improved, and the quality of the displayed image can be improved.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention provides an MR signal that is received by an MR multiplied signal signal coil generated from an MR signal source such as a subject, and is based on the MR signal. It relates to a magnetic resonance imaging device (MRI device) that constructs and displays a tomographic image of a predetermined cross section of a source, and in particular has a tuning circuit in which components such as two variable capacitors with variable electrical characteristics are driven in synchronization. The present invention relates to a magnetic resonance imaging apparatus provided with a signal coil section.

(Prior Art) A magnetic resonance imaging apparatus, for example, as shown in FIG. 5, has a bed 1 on which a subject P as an MR signal source is placed.
01, and a pedestal 102 having an imaging hole 102A in the center. When photographing a subject, a head receiving coil part 10 having a cylindrical shape and an annular cross section is used as a signal coil part for detecting an MR multiplied signal generated from the subject P.
3, it is placed on the head of the subject P by the operator. Here, the signal coil section is limited to a receiving coil section, a transmitting coil section for applying a high frequency magnetic field to the subject P,
There is a transmitting/receiving coil section that has both functions, and there is also a signal coil section that corresponds to each part of the subject, not just the head.

When photographing the subject, the top of the bed] 01] 01A is the arrow a.
The subject P is moved in the direction and inserted into the imaging hole 102A, and the subject P is placed in the imaging hole 102A, and is covered by a magnet and a gradient magnetic field coil (not shown) provided in the pedestal 102 that generates a uniform magnetic field. A uniform static magnetic field and a gradient magnetic field are applied to the specimen P.

At the same time, a high-frequency magnetic field is applied to the subject P from a transmission coil unit (not shown) to cause a magnetic resonance phenomenon (MR phenomenon) only in a specific slice portion of the subject P, and after the high-frequency magnetic field is released, the subject P is removed from the subject P. The generated MR multiplied signal is received and detected by the receiving coil section 103.

This MR multiplied signal is sent to an information processing section (not shown), and the information processing section reconstructs an image of the subject P based on the data obtained by performing processing such as Fourier transformation on this signal.
An image signal containing this reconstructed image is sent to a display such as a CRT, and a tomographic image of a predetermined cross section of the subject P is displayed on the screen of the display. In addition, when photographing a part other than the head of the subject P, the operator should
Replace 03 with a receiving coil part appropriate for the part to be imaged.

As shown in FIG. 6, the receiving coil unit 103 includes a receiving coil 1]0 and a receiving coil 110 for adjusting the magnetic characteristics of the receiving coil 110 to make the receiving state of the receiving coil 110 the best (this operation is called tuning). A tuning circuit 111 is provided. In addition, a plurality of variable capacitors 112a to 112C with variable capacitances are connected to the tuned circuit 111 as an electric characteristic changing means for changing the characteristics of the tuned circuit 111 by changing the electric characteristics. It is provided. These variable capacitors 11
By rotating 2a to 112C by a predetermined angle, the capacitance thereof can be changed.

Two variable capacitors 11 of the above variable capacitors
2a and 112b need to be rotated synchronously to minimize electric field loss. To explain this rotational drive mechanism, as shown in FIG.
Ultrasonic motor 113 for rotationally driving a and 102b
A variable capacitor 102a is connected to a rotating shaft 114 of
A variable capacitor 102b is connected to a rotating shaft 116 fixed to a pulley 115. A pulley 117 is fixed to the rotating shaft 114 of the motor, and a pulley 115.11
A belt 118 is wound around 7.

When the motor 113 is operated to rotate the rotating shaft 114, the pulley 117 and variable capacitor 102a rotate, and the rotational force of the pulley 117 is transmitted to the pulley 115 via the belt 118, causing the rotating shaft 116 and variable capacitor 102b to rotate. do. That is, the receiving coil 110
During tuning, the motor 113 rotates the variable capacitors 102a and 102b in synchronization.

(Problem to be solved by the invention) However, in the case of the above-mentioned prior art, since there is generally always some deflection in the belt 118, it is necessary to rotate the two variable capacitors 1.02a and 102b in precise synchronization. It is difficult to
This results in a deviation in the rotational position of 02b. Therefore,
The tuning accuracy of the receiving coil 110 is poor, and the accuracy of detecting the MR multiplied signal by the receiving coil 110 is low, which hinders the improvement of the quality of the displayed image.

Furthermore, the variable capacitors 102a and 102b are not arranged on the same axis, and the pulleys 115 and 117 and the belt 118
Two rotating shafts 114, 1 connected and arranged in parallel by
16, so these variable capacitors 10
There is a tendency for the receiving coil section 103 in which 2a, 102b and the motor 113 are incorporated to become larger, and there is also a drawback that it is a heavy burden on the operator when carrying or replacing the receiving coil section.

The present invention has been made to solve the problems of the prior art described above, and its purpose is to accurately synchronize and drive the two electrical characteristic changing means of the tuning circuit of the signal coil section. An object of the present invention is to provide a magnetic resonance imaging apparatus that is capable of reducing the size of a signal coil section.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the present invention applies a high frequency magnetic field to an MR signal source or detects an MR multiplied signal generated from the MR signal source. A signal coil unit is provided, which has a signal coil for the signal and a tuning circuit for adjusting the magnetic characteristics of the signal coil, and the tuning circuit has variable electrical characteristics and changes the electrical characteristics. a plurality of electrical characteristic changing means for changing the characteristics of the tuned circuit; and a motor for driving the electric characteristic changing means to change the electrical characteristics; In a magnetic resonance imaging apparatus in which two of the electrical property changing means are driven synchronously by one motor, the rotating shaft of the motor protrudes from both ends of the motor, and the two electrical property changing means are driven synchronously by one motor. One of them is connected to one protrusion of the rotary shaft of the motor, and the other one is connected to the other protrusion of the rotary shaft.

The rotating shaft of one of the two electrical characteristic changing means is made to protrude from the electrical characteristic changing means on the opposite side of the motor, and the rotating shaft is connected to the protruding rotating shaft. A rotation angle detection means for detecting the rotation angle may be combined. Further, as the motor, an ultrasonic motor driven using a piezoelectric element is suitable.

(Function) In the signal coil section of the magnetic resonance imaging apparatus of the present invention having the above configuration, the two electrical characteristic changing means of the tuning circuit are connected to one rotating shaft of the motor. The electrical characteristic changing means are rotated integrally with the rotation of the rotating shaft of the motor. Therefore, 1
The two electric characteristic changing means can be driven in precise synchronization by two motors, increasing the tuning precision of the signal coil, and the signal coil can apply a high frequency magnetic field to the MR signal source or detect the MR multiplied signal. can be performed with high precision.

In addition, in this signal coil section, the two electrical characteristic changing means of the tuned circuit are connected to one rotating shaft of the motor and arranged on the same axis, so these electric characteristic changing means and the motor are incorporated. It becomes possible to downsize the signal coil section.

Furthermore, if the rotation angle detection means is coupled to the rotating shaft of one of the two electric characteristic change means as described above, the rotation angle detection means can detect these two electric characteristic change means.
It is possible to tune the signal coil with higher precision by detecting the rotation angles of the electrical characteristic changing means and controlling the driving of these electric characteristic changing means by the motor according to the detection results.

(Example) Below, an example of the present invention will be described based on the drawings. 1st
FIG. 2 is a perspective view showing the configuration of a part of a receiving coil section in a magnetic resonance imaging apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the electrical configuration of the apparatus according to the embodiment.

This embodiment apparatus is equipped with a mount and a bed (not shown) similar to those of the conventional example shown in FIG.
A receiving coil section 1 for the head is disposed on the head of the subject P as a signal source as a signal coil section having a shape similar to that of the conventional example. This receiving coil section 1 is equipped with the subject P during imaging.
a receiving coil 2 for detecting the MR multiplied signal generated from the receiving coil 2, a tuning circuit 3 for adjusting (tuning) the magnetic characteristics of the receiving coil 2, and a variable capacitor 4 provided in the tuning circuit 3 as means for changing electrical characteristics. An ultrasonic motor 5 for driving is incorporated.

Here, the ultrasonic motor 5 includes a piezoelectric element (not shown), an elastic body, and a rotating body, and the piezoelectric element vibrates the surface of the elastic body, and the resulting elastic waves rotate the rotating body and drive the rotating shaft. It is something to do.

When tuning the receiving coil 2, the motor 5 rotates the variable capacitor 4, thereby changing the capacitance of the variable capacitor 4, changing the characteristics of the tuning circuit 3, and adjusting the receiving state of the receiving coil 2. I can do it.

A plurality of variable capacitors 4 are provided in the tuning circuit 3, or two variable capacitors 4a and 4b are connected to the rotating shaft of one motor 5a, as shown in FIG. As shown in FIG. 3, this motor 5a is
The rotating shaft protrudes from both ends of the motor 5a, and two of the rotating shafts
It has two protruding parts 6a and 6b. variable capacitor 4a,
4b, the shafts 7a and 7b supporting each are connected to a shaft joint 8.
A different protrusion 6 of the rotation axis of the motor 5a is connected via a8b.
a, 6b.

Further, in the vicinity of the subject P, a transmitting coil section 9 is provided separately from the receiving coil section 1, and this transmitting coil section 9
A transmitting coil 10 for applying a high-frequency magnetic field to the subject P during imaging, a tuning circuit 11 for tuning the transmitting coil 10, and an ultrasonic motor 13 for driving a variable capacitor 12 provided in the tuning circuit 11. and has.

When photographing the subject P, first place the subject P in the photographing hole of a gantry (not shown) in the same manner as in the conventional example, and place the subject P in a uniform position using a magnet that generates a uniform magnetic field within the gantry. After applying a similar static magnetic field, according to a predetermined pulse sequence,
A gradient magnetic field generated from a gradient magnetic field coil in the mount and a high-frequency magnetic field generated from the transmitting coil 10 are applied to the subject P. Then, after the high-frequency magnetic field is released, the receiver coil]
The MR multiplied signal generated from the MR signal is received and sent to the signal processing unit 14, and the signal processing unit 14 performs processing such as Fourier transformation on this signal to determine at least one of the hydrogen atom density in the specimen P and its relaxation time constant. The reflected information is obtained and the image is reconstructed based on this information. An image signal containing this reconstructed image is sent from the signal processing section 14 to a display 15 such as a CRT display, and a tomographic image (CT image) of a predetermined cross section of the subject P is displayed on the display 15.

When tuning the receiving coil 2 and the transmitting coil 10, as described above, the characteristics of the tuning circuits 3, 11 are adjusted by rotating the variable capacitor 4.12 by a predetermined angle by the motors 5, 13 and changing its capacitance. is adjusted so that the receiving and transmitting conditions of the receiving coil 2 and the transmitting coil 10 are optimal. Reference numeral 16 in FIG.
A variable capacitor adjustment signal is sent to motor drive section 17.
A controller 18 controls the drive of the motors 5 and 13 and sends control signals to each part of the device, and an RF controller 18 sends RF pulses to the transmitting coil 10 via the tuning circuit 11 in accordance with an RF control signal sent from the controller 16. It's an amplifier.

In this embodiment, when the receiving coil 2 is tuned, when the motor 5a is operated in the tuning circuit 3, the protrusion 5a of the rotating shaft of the motor.

6b rotates in the direction of the arrow shown in FIG. 1, and the variable capacitors 4a and 4b integrally connected to the protrusions 6a and 6b rotate in precise synchronization, so that the rotational position of the variable capacitors 4a and 4b is The rotation angles of the two always match perfectly without any deviation, and the receiving coil 2 can be tuned with high precision. Therefore, since the receiving coil 2 can detect the MR multiplied signal with high precision, the S/N ratio of the signal can be improved and the quality of the displayed image can be improved.

In this embodiment, since an ultrasonic motor is used as the motor 5 that drives the variable capacitor 4, it does not affect the magnetic field during imaging of the subject P, and the magnetic field does not interfere with the function of the motor. Since the ultrasonic motor is small and lightweight, the receiving coil section 1 can be made smaller and lighter. Moreover, since the variable capacitors 4a and 4b are connected to one rotating shaft of the motor 5a and arranged on the same axis, the receiving coil section 1 in which these variable capacitors 4 and the motor 5 are incorporated can be miniaturized. It becomes possible to do so. Therefore, the burden on the operator when carrying and replacing the receiving coil section 1 can be reduced.

In the above embodiment, as shown in FIG. 4, one of the variable capacitors 4a and 4b has a
The side opposite to the motor 5a with respect to the variable capacitor 4b (
In other words, a rotating shaft 20 protruding from the opposite side of the shaft 7b may be provided, and a rotary encoder 21 serving as a rotation angle detection means for detecting the rotation angle of this rotating shaft 20 may be coupled to the rotating shaft 20. In this case, the rotary encoder 21
The rotation angle of the rotating shaft 20, that is, the variable capacitor 4a,
4b is detected, and the control section 16 controls the motor drive section 17 according to the detection result to control the drive of the variable capacitors 4a, 4b by the motor 5a, thereby increasing the rotational position accuracy of the variable capacitors 4a, 4b. The receiving coil 2 can be tuned with higher accuracy.

In the above embodiment, the head receiving coil section 1 is used as an example of the signal coil section, but the present invention is not limited to this, and for example, the transmitting coil section or the transmitting/receiving coil section may also be used. It is also applicable to signal coil sections corresponding to various parts of the subject other than the head.

Further, in the above embodiments, a variable capacitor was used as an example of the electric characteristic changing means, but the present invention is not limited thereto, and for example, a variable resistor, a variable inductor, etc. can also be applied.

[Effects of the Invention] The magnetic resonance imaging apparatus of the present invention has the above-described configuration and function, and drives the two electric characteristic changing means of the tuning circuit in the signal coil section in accurate synchronization, thereby achieving high precision. You can tune the signal coil.

Therefore, application of a high frequency magnetic field to the MR signal source by the signal coil or detection of the MR multiplied signal can be performed with high precision, thereby improving the S/N ratio of the signal and improving the quality of the displayed image. Furthermore, it is possible to reduce the size of the signal coil section and reduce the burden on the operator when carrying and replacing the signal coil section.

Furthermore, by providing a rotation angle detection means on the rotating shaft of one of the two electric characteristic changing means, the rotation angle of these two electric characteristic changing means is detected, It is possible to tune the signal coil with higher precision.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a partial configuration of a receiving coil section in a magnetic resonance imaging apparatus according to an embodiment of the present invention;
The figure is a block diagram showing the electrical configuration of the device according to the third embodiment.
The figure is a perspective view showing the motor of the receiving coil section in the same embodiment, FIG. 4 is a perspective view showing an example in which a rotary encoder is provided in the receiving coil section, and FIG. 5 is a pedestal and bed of a conventional magnetic resonance imaging apparatus A vertical sectional view schematically showing the sixth
FIG. 7 is a circuit diagram showing the electrical configuration of a part of the receiving coil section in the conventional example, and FIG. 7 is a perspective view showing the structure of a part of the receiving coil section. 1... Receiving coil section (signal coil section) 2... Receiving coil (signal coil) 3... Tuning circuit 4.4a, 4b... Variable capacitor (electrical characteristic changing means) 5.5a. ...Motor 6a, 6b...Protruding portion 20 of the motor's rotating shaft...Protruding rotating shaft 21 of the variable capacitor (electrical characteristic changing means)...Rotary encoder (rotation angle detecting means) P.
...Object (MR signal source)

Claims (3)

[Claims] (1) A signal coil having a signal coil for applying a high frequency magnetic field to an MR signal source or detecting an MR signal generated from the MR signal source, and a tuning circuit for adjusting the magnetic characteristics of the signal coil. and the tuned circuit includes:
A plurality of electrical property changing means whose electrical properties are variable and for changing the properties of the tuned circuit by changing the electrical properties, and driving the electrical property changing means to change the electrical properties. a magnetic resonance imaging apparatus, wherein two of the electric characteristic changing means are driven synchronously by one motor, wherein the rotation axis of the motor is The electric characteristic changing means protrudes from both ends, one of the two electric characteristic changing means is connected to one protrusion of the rotating shaft of the motor, and the other one is connected to the other protruding part of the rotating shaft. A magnetic resonance imaging device characterized by: (2) The rotating shaft of one of the two electrical characteristic changing means driven synchronously by one motor is on the opposite side of the electric characteristic changing means from the motor. 2. The magnetic resonance imaging apparatus according to claim 1, further comprising a protruding rotating shaft, and a rotation angle detecting means for detecting a rotation angle of the rotating shaft is coupled to the protruding rotating shaft. (3) The magnetic resonance imaging apparatus according to claim 1, wherein the motor is an ultrasonic motor driven using a piezoelectric element.