JPH0647018A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To set the resonance frequency of each receiving coil to the same and to increase the composite value of outputs of the receiving coils by constituting a device so that a voltage is applied to a variable capacity connected to plural receiving coils, respectively in the respective independent states by varying its voltage value. CONSTITUTION:In the receiving system of the magnetic resonance imaging device, a high-frequency coil 20b for detecting an NMR signal from an examinee is provided, and it is constituted of a receiving coil 1a, a series connected body of an impedance matching capacity 2a and a resonance frequency adjusting capacity 3a connected in parallel to this receiving coil 1a and a variable capacity 5a connected in parallel to the adjusting capacity 3a. Also, the high-frequency coil 20c of the same constitution as a high-frequency coil 20b arranged orthogonally with the high-frequency coil 20b is provided. In such a state, the outputs of respective receiving coil 1a, 1b are detected successively by a CPU, a voltage value at the time when the maximum output signal is obtained is detected and in a state that the voltage value at the time when the maximum output signal is obtained is applied, respective receiving coils 1a, 1b are driven.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus, and more particularly to improvement of its receiving system.

[0002]

2. Description of the Related Art A magnetic resonance imaging apparatus is designed to cause nuclear magnetic resonance in atomic nuclei constituting a living tissue and receive a magnetic resonance signal generated by the magnetic resonance signal in a receiving coil section. Then, a so-called Fourier transform is performed on the received magnetic resonance signal to reconstruct an image,
It is widely used to obtain a tomographic image of any part of the human body. The reception of the magnetic resonance signal in the receiving coil unit is performed by using tuning.
Therefore, it is necessary to tune the receiving coil in advance to a resonance frequency that causes a nuclear magnetic resonance that serves as a reference.

Therefore, from the above, the conventional receiving coil unit is constructed as shown in FIG. In the figure, first, there is a receiving coil 1a, and a series connection body of an impedance matching capacitance 2a and a resonance frequency adjusting capacitance 3a is connected in parallel with the receiving coil 1a. Then, the magnetic resonance signal is taken out from both ends of the resonance frequency adjusting capacitor 3a through a preamplifier (not shown). The impedance matching capacitance 2a is a capacitance for achieving impedance matching with the preamplifier. Further, both the impedance matching capacitance 2a and the resonance frequency adjusting capacitance 3a are variable, but they are adjusted in a state where the subject is not housed in the device and are incorporated in the device. Therefore, it cannot be adjusted from the outside while the subject is stored in the device.

Further, a variable capacitor 5a is connected in parallel with the resonance frequency adjusting capacitor 3a. This variable capacitance 5a
The capacitance can be arbitrarily changed by the voltage value applied to both ends thereof. The subject to be accommodated in the device is intended to adjust the displacement of the resonance point due to the difference in thickness or size of the body due to the individual difference, by the variable capacitance.

Further, a receiving coil 1b different from the receiving coil 1a is arranged orthogonal to the receiving coil 1a. The receiving coil 1b also has the same circuit configuration as the receiving coil 1a, and includes an impedance matching capacitance 2b, a resonance frequency adjusting capacitance 3b, and a variable capacitance 4.
b, a variable capacitor 5b. The two receiving coils 1a and 1b are provided in order to improve the sensitivity by amplifying the respective outputs with respective preamplifiers and then combining them.

[0006]

However, since the receiving coil section of the magnetic resonance imaging apparatus configured as described above has only one control system for adjusting the capacitances of the variable capacitance diodes 5a and 5b, The same voltage is applied to the capacitance diodes 5a and 5b.

For this reason, the variable capacitance diodes 5a, 5
The difference in the voltage-capacitance characteristic due to the individual difference in b, or the impedance matching capacitors 2a and 2b and the frequency adjustment capacitor 3a, which are connected in parallel with the variable capacitance diodes 5a and 5b
Due to the difference in capacity ratio with 3b, each receiving coil 1
However, the resonance frequencies of a and 1b cannot be made the same, which causes a problem that the image quality of the image cannot be improved.

That is, as shown in FIG. 6, when the voltage applied to the variable capacitance diodes 5a and 5b is plotted on the horizontal axis and the frequency is plotted on the vertical axis, the inclinations of the graphs differ depending on the respective receiving coils 1a and 1b. For example, in order to tune the receiving coils 1a and 1b to the same frequency, it is necessary to give the voltage difference V to the voltage applied to the receiving coils 1a and 1b side.

The present invention has been made in view of the above circumstances, and its object is to make the resonance frequency of each receiving coil the same with the voltage applied to each receiving coil being an appropriate value. Another object of the present invention is to provide a magnetic resonance imaging apparatus capable of achieving the above.

[0010]

In order to achieve such an object, the present invention basically provides a plurality of receiving coils and a plurality of receiving coils which are respectively connected to the respective receiving coils and respond to the voltage value by voltage application. In a magnetic resonance imaging apparatus comprising a variable capacitance whose capacitance is changed to improve the output sensitivity by combining the respective outputs of the respective receiving coils, by changing the voltage value independently of each of the variable capacitances. Means for applying, a means for detecting the voltage value when the maximum output signal is obtained from each receiving coil for a voltage value changing in each variable capacitance, and a detecting means for detecting the voltage value in each variable capacitance. And a means for driving each receiving coil by applying a different voltage value.

[0011]

According to the magnetic resonance imaging apparatus configured as described above, first, a voltage is applied to the variable capacitors respectively connected to the plurality of receiving coils by changing their voltage values independently of each other. Is. As a result, the voltage value applied to the variable capacitor at the maximum value of the output of each receiving coil when the frequency of each receiving coil changes and becomes the magnetic resonance frequency can be known. Therefore, the resonance frequency of each receiving coil can be made the same by applying the voltage of the voltage value to the variable capacitance in each receiving coil, and by driving each receiving coil, The maximum value of the combined output of the receiving coils can be obtained.

[0012]

1 is a block diagram showing the overall construction of a magnetic resonance imaging apparatus according to the present invention. This magnetic resonance imaging apparatus is roughly classified into a central processing unit (CPU) 11, a sequencer 12, and a transmission system 13.
A static magnetic field generating magnet 14, a receiving system 15, and a signal processing system 16.

The central processing unit (CPU) 11 includes a sequencer 12 and a transmission system 1 according to a predetermined program.
3, each of the receiving system 15 and the signal processing system 16 is controlled. The sequencer 12 operates based on a control command from the central processing unit 11 and transmits various commands necessary for collecting data of a tomographic image of the subject 6 to the transmission system 13 and the magnetic field gradient generation system 21 of the static magnetic field generation magnet 14. It is sent to the receiving system 15.

The transmission system 13 has a high-frequency oscillator 17, a modulator 18, and a high-frequency coil 20a. The high-frequency pulse from the high-frequency oscillator 17 is amplitude-modulated by the modulator 18 according to a command from the sequencer 12, and the amplitude is modulated. The high frequency pulse is amplified by the high frequency amplifier 19 and is amplified by the high frequency coil 20a.
Is supplied to the subject 6 so that the subject 6 is irradiated with a predetermined pulsed electromagnetic wave.

The static magnetic field generating magnet 14 is for generating a uniform static magnetic field around the subject 6 in an arbitrary direction. Inside the static magnetic field generating magnet 14, in addition to the high frequency coil 20a, a gradient magnetic field coil 2 for generating a gradient magnetic field is provided.
1 and a high frequency coil 20 which is a receiving coil of the receiving system 15.
b and 20c are installed. The gradient magnetic field generation system 14 has Cartesian coordinate axis directions orthogonal to each other, that is, the X-axis direction,
A gradient magnetic field coil 21 having a configuration capable of independently applying a gradient magnetic field in the Y-axis direction and a Z-axis direction, a gradient magnetic field power source 22 supplying a current to the gradient magnetic field coil, and a sequencer 12 controlling the gradient magnetic field power source 22. To do.

The receiving system 15 has a high-frequency coil 20b, an operational amplifier 23a connected to the high-frequency coil 20b, a quadrature phase detector 24 and an A / D converter 25.
When the high frequency coil 20b detects the NMR signal from the signal, the signal is detected by the operational amplifier 23a, the quadrature detector 24,
The digital amount is converted through the D converter 25, and at the timing according to a command from the sequencer 12, converted into two series of collected data sampled by the quadrature phase detector 24 and sent to the central processing unit 11.
A voltage is applied to the high frequency coil 20b via an amplifier 29a, and this voltage is applied to a variable capacitance diode (not shown) incorporated in the high frequency coil 20b. .

Further, there is a high frequency coil 20c arranged orthogonal to the high frequency coil 20b. Further, it has an operational amplifier 23b connected to the high-frequency coil 20c, a quadrature phase detector 24 and an A / D converter 25, and when the high-frequency coil 20c detects an NMR signal from the subject 6, the signal is detected by the operational amplifier 23b, Quadrature detector 24, A / D
The data is converted into a digital amount through the converter 25, and converted into two series of collected data sampled by the quadrature phase detector 24 at a timing according to a command from the sequencer 12 and sent to the central processing unit 11. A voltage is applied to the high frequency coil 20c through an amplifier 29b, and this voltage is applied to a variable capacitance diode (not shown) incorporated in the high frequency coil 20c. .

Here, detailed configurations of the high frequency coil 20b and the high frequency coil 20c will be described with reference to FIG.
In the figure, first, there is a receiving coil 1a, and a series connection body of an impedance matching capacitance 2a and a resonance frequency adjusting capacitance 3a is connected in parallel with the receiving coil 1a.
Then, the magnetic resonance signal is taken out from both ends of the resonance frequency adjusting capacitor 3a through a preamplifier (not shown). The impedance matching capacitance 2a is a capacitance for achieving impedance matching with the preamplifier. Further, both the impedance matching capacitance 2a and the resonance frequency adjusting capacitance 3a are variable, but they are adjusted in a state where the subject is not housed in the device and are incorporated in the device. Therefore, it cannot be adjusted from the outside while the subject is stored in the device.

Further, a variable capacitor 5a is connected in parallel with the resonance frequency adjusting capacitor 3a. This variable capacitance 5a
The capacitance can be arbitrarily changed by the voltage value applied to both ends thereof. The subject to be accommodated in the device is intended to adjust the displacement of the resonance point due to the difference in thickness or size of the body due to the individual difference, by the variable capacitance.

Further, a receiving coil 1b different from the receiving coil 1a is arranged orthogonal to the receiving coil 1a. The receiving coil 1b also has the same circuit configuration as the receiving coil 1a, and includes an impedance matching capacitance 2b, a resonance frequency adjusting capacitance 3b, and a variable capacitance 4.
b, a variable capacitor 5b.

From the central processing unit 11, the voltage is applied to the variable capacitance diodes 4a and 5a through the amplifier 29a by changing the voltage value. And
The central processing unit 11 sequentially detects the output from the receiving coil 1a at this time and also detects the voltage value when the maximum output signal is obtained. After that, the central processing unit 11 drives the receiving coil 1a in a state where the voltage value at the time when the receiving coil 1a obtains the maximum output signal is applied. The operation of the central processing unit 11 as described above is performed by the high frequency coil 20c.
The same is done on the side.

That is, such operation in the central processing unit 11 is as shown in the flowchart of FIG. In the figure,

Step 1. A supply voltage (for example, 0 V at the beginning) is added by ΔV and applied to the high frequency coil 20b.

Step 2. The output signal detected by the high frequency coil 20b is detected by the voltage applied in step 1.

Step 3. The output value of the output signal detected in step 2 is stored in the memory.

Step 4. It is determined whether the supply voltage applied to the high frequency coil 20b has a predetermined voltage value. If it is not the predetermined voltage value, step 1. Then, the voltage supplied to the high frequency coil 20b is further increased by ΔV and the above steps are repeated. If it is a predetermined voltage value, proceed to the next step.

Step 5. The applied voltage corresponding to the maximum value is detected from the output signal value stored in the memory.

Step 6. The applied voltage detected in step 5 is applied to the high frequency coil 20b.

Step 7. The same operation (steps 1 to 6) is performed on the high frequency coil 20c.

Step 8. Start receiving.

Further, the signal processing system 16 has an external storage device such as a magnetic disk 26 and a magnetic tape 27, and a display 28 such as a CRT, and the data from the receiving system 15 is input to the central processing unit 11. Then, the central processing unit 11 executes processing such as signal processing and image reconstruction, displays a desired sectional image of the subject 6 as a result thereof on the display 28, and displays it on the magnetic disk 26 or the like of the external storage device. Remember.

According to the magnetic resonance imaging apparatus constructed as in the above-described embodiment, first, each receiving coil 1a,
Variable capacitance diodes 5a, 5 respectively connected to 1b
The voltage is applied to b independently of each other by changing its voltage value. As a result, the voltage value applied to the variable capacitance diodes 5a, 5b at the maximum value of the output of each receiving coil 1a, 1b due to the change of the frequency of each receiving coil 1a, 1b to the magnetic resonance frequency can be known. Become. Therefore, the variable capacitance diodes 5a in the respective receiving coils 1a and 1b,
By applying a voltage of the voltage value to 5b, the resonance frequencies of the receiving coils 1a and 1b can be made the same, and the receiving coils 1a and 1b can be made to have the same resonance frequency.
By driving the respective receiving coils 1a, 1
The maximum combined value of the outputs of b can be obtained.

FIG. 4 is a graph showing such a state. The high frequency coils 23a and 23b have different characteristics, and by applying voltage values V ₁ and V ₂ to the respective high frequency coils 23a and 23b, the respective high frequency coils 23a and 23b are tuned to the magnetic resonance frequency. It will be.

The above-described embodiment has been described with respect to the one having two receiving coils, but the present invention is not limited to this and can be applied to the one having more receiving coils.

[0035]

As is apparent from the above description,
According to the magnetic resonance imaging apparatus of the present invention, the resonance frequency of each receiving coil can be made the same by setting the voltage applied to each receiving coil to an appropriate value.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention, and is a configuration diagram particularly showing a receiving coil unit.

FIG. 2 is a schematic configuration diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention.

FIG. 3 is a flowchart showing an operation of a CPU incorporated in the magnetic resonance imaging apparatus according to the present invention.

FIG. 4 is an explanatory diagram showing an effect of the magnetic resonance imaging apparatus according to the present invention.

FIG. 5 is a configuration diagram showing an example of a receiving coil unit in a conventional magnetic resonance imaging apparatus.

FIG. 6 is an explanatory diagram showing a problem of a conventional magnetic resonance imaging apparatus.

[Explanation of symbols]

 1a receiving coil 1b receiving coil 5a variable capacitance diode 5b variable capacitance diode 23a operational amplifier 23b operational amplifier

Claims (1)

[Claims] 1. A plurality of receiving coils and a variable capacitor which is connected to each of these receiving coils and whose capacitance is changed according to the voltage value when a voltage is applied. The output of each receiving coil is synthesized. In a magnetic resonance imaging apparatus for improving sensitivity, means for applying a voltage independently to each of the variable capacitors by changing its voltage value,
Means for detecting the voltage value when the maximum output signal is obtained from each receiving coil for the voltage value changing in each variable capacitance, and applying the voltage value detected by the detection means to each variable capacitance And a means for driving each receiving coil.