JP5122864B2 - RF coil drive circuit and MRI apparatus - Google Patents

Description

  The present invention relates to an RF (Radio Frequency) coil driving circuit and an MRI (Magnetic Resonance Imaging) apparatus. More specifically, the present invention relates to an RF coil (Coil) driving circuit capable of reducing power consumption of a power amplifier, and an MRI apparatus using the RF coil driving circuit.

  In cellular phones and wireless LANs (Local Area Networks), there is a limitation of battery driving, and thus low power consumption of RF analog circuits is strongly desired. In the RF analog circuit, if the power consumption of the power amplifier is particularly large and the power consumption can be reduced, it is effective for reducing the power consumption.

Therefore, paying attention to the fact that communication is possible even if the RF transmission signal is weak if the distance to the base station or the wireless LAN is short, the intensity of the RF transmission signal is adjusted according to the distance to the base station or the wireless LAN.
However, the power consumed by the power amplifier is determined by the power of the RF transmission signal transmitted from the RF coil, the power supply voltage of the power amplifier, and the DC bias (Bias) voltage. Further, the necessary power supply voltage and the DC bias voltage are different depending on the power of the RF transmission signal transmitted from the RF coil.
Therefore, the power or amplitude of the RF transmission signal output from the power amplifier is detected, and the power supply voltage and bias voltage supplied to the power amplifier are adjusted according to the power or amplitude (see, for example, Patent Document 1). .

In the MRI apparatus, since the power of the RF transmission signal transmitted from the RF coil is large, the power consumption of the power amplifier that amplifies the RF transmission signal is large. The MRI apparatus is not limited to battery drive, but it is important to reduce the power consumption of the power amplifier in the MRI apparatus as well as the mobile phone and the wireless LAN.
In the MRI apparatus, the RF transmission signal transmitted from the RF coil is also called an RF pulse (Pulse). Hereinafter, in the MRI apparatus, an RF transmission signal transmitted from the RF coil is referred to as an RF pulse.
US Pat. No. 6,148,220

  In the MRI apparatus, the intensity of the RF pulse necessary for imaging varies depending on the weight of the patient to be imaged, the size of the RF coil, the depth from the body surface of the affected area to be imaged, and the like. For example, the power of the RF pulse transmitted from the head coil or the wrist coil is smaller than the power of the RF pulse transmitted from the body coil. Therefore, it is desirable to adjust the power supply voltage and the bias voltage supplied to the power amplifier according to the power of the RF pulse necessary for imaging from the viewpoint of reducing the power consumption of the power amplifier.

  When the power of the RF pulse is small, the power supply voltage of the power amplifier may be small. However, if the power supply voltage and the DC bias voltage are the same as when the power of the RF pulse is the maximum, extra heat is generated. In order to cool this wasteful heat, the power amplifier needs to be cooled. From the viewpoint of suppressing heat generation of the power amplifier, it is desirable to adjust the power supply voltage and the bias voltage supplied to the power amplifier according to the power of the RF pulse necessary for imaging.

  However, the gain of the power amplifier changes as the power supply voltage changes. That is, the power amplifier decreases the amplitude of the amplified output signal when the power supply voltage decreases even if the amplitude of the input signal is the same. The gain of the power amplifier also changes due to the influence of the surrounding environment such as temperature.

  From the above, it is possible to adjust the power supply voltage and bias voltage supplied to the power amplifier according to the power of the RF pulse transmitted from the RF coil, and to compensate for changes in the gain of the power amplifier due to fluctuations in the power supply voltage etc. There is a demand for an RF coil driving circuit that can apply an RF pulse of power necessary for imaging to an RF coil, and an MRI apparatus using the RF coil driving circuit.

  The RF coil drive circuit according to the present invention includes a variable voltage power supply unit that can change the magnitude of the output power supply voltage, an RF transmission signal generation unit that generates an RF transmission signal, and power consumption when the supplied power supply voltage decreases. When the power supply voltage is decreased, the gain is changed. The amplification unit that amplifies the RF transmission signal with the changed gain and applies the RF transmission signal to the RF coil; and the power or amplitude of the RF transmission signal applied to the RF coil A detection unit that detects a power target value or an amplitude target value, and an amplitude adjustment unit that adjusts an amplitude of an RF transmission signal input to the amplification unit so that the detected power or amplitude matches. When the power supply voltage changes, the amplitude of the RF transmission signal input to the amplification unit is adjusted, and the power or amplitude of the RF transmission signal applied to the RF coil is the power target value or the amplitude target. Closer to.

  Preferably, in the RF coil driving circuit of the present invention, the variable voltage power supply unit outputs a DC constant voltage source that outputs a DC constant voltage, and a DC-DC that converts the DC constant voltage to a DC voltage lower than the DC constant voltage. Includes converter.

  Preferably, in the RF coil drive circuit of the present invention, the variable voltage power supply unit supplies the DC constant voltage to the DC-DC converter, and supplies the DC-DC converter with a DC voltage lower than the DC constant voltage. A selection unit configured to select whether to output as a voltage or to stop the DC-DC converter and output the DC constant voltage as the power supply voltage;

  Preferably, the RF coil driving circuit of the present invention is a power amplifier in which power consumption is reduced when the amplifying unit lowers a DC bias voltage.

  Preferably, the RF coil driving circuit of the present invention includes a bias voltage adjusting unit that adjusts the DC bias voltage to a voltage corresponding to the power supply voltage.

  The MRI apparatus of the present invention includes an RF coil that transmits an RF pulse, and an RF coil drive circuit that applies the RF pulse to the RF coil, and the RF coil drive circuit outputs a power supply voltage that is output from the RF coil. A variable voltage power supply unit that can change the length, an RF pulse generation unit that generates an RF pulse, and when the supplied power supply voltage decreases, power consumption decreases, and when the power supply voltage changes, a gain changes and the change An amplification unit that amplifies the RF pulse with a gain and applies it to the RF coil, a detection unit that detects power or amplitude of the RF pulse applied to the RF coil, a power target value or an amplitude target value, and the detected An amplitude adjustment unit that adjusts the amplitude of the RF pulse input to the amplification unit so that the power or the amplitude matches, and when the power supply voltage changes, the input to the amplification unit The amplitude of the RF pulse is to adjust the power or amplitude of the RF pulses applied to the RF coil approaches the power target value or amplitude target value.

  Preferably, in the MRI apparatus of the present invention, the variable voltage power supply unit includes a DC constant voltage source that outputs a DC constant voltage, and a DC-DC converter that converts the DC constant voltage to a DC voltage lower than the DC constant voltage. Including.

  Preferably, in the MRI apparatus of the present invention, the variable voltage power supply unit supplies the DC constant voltage to the DC-DC converter, and the DC-DC converter uses a DC voltage lower than the DC constant voltage as the power supply voltage. And a selection unit that selects whether to output the DC constant voltage as the power supply voltage by stopping the DC-DC converter.

  Preferably, the MRI apparatus of the present invention is a power amplifier in which power consumption is reduced when the amplifying unit lowers a DC bias voltage.

  Preferably, the MRI apparatus of the present invention includes a bias voltage adjustment unit that adjusts the DC bias voltage to a voltage corresponding to the power supply voltage.

  As described above, according to the present invention, the power supply voltage and the bias voltage supplied to the power amplifier can be adjusted according to the power of the RF pulse transmitted from the RF coil, and the power amplifier due to fluctuations in the power supply voltage or the like Thus, an RF pulse having a power necessary for imaging while compensating for a change in gain can be applied to the RF coil.

  FIG. 1 is a diagram showing an MRI apparatus. As shown in FIG. 1, the MRI apparatus 10 includes a magnet system 11, a cradle 12, a gradient magnetic field drive circuit 13, an RF coil drive circuit 14, a data collection circuit 15, a control unit 16, an operator console ( (Operator Console) 17.

  As shown in FIG. 1, the magnet system 11 has a generally cylindrical inner space (Bore) 111, and a cradle 12 on which the subject 20 is placed via a cushion is placed in the bore 111. It is carried in by a transport unit (not shown).

  In the magnet system 11, as shown in FIG. 1, a static magnetic field generation unit 112, a gradient magnetic field coil unit 113, and an RF coil unit 114 are arranged around a magnet center (Magnet Center, center position for scanning) in the bore 111. Is arranged.

  The static magnetic field generator 112 generates a static magnetic field in the bore 111. The direction of the static magnetic field is, for example, parallel to the body axis direction of the subject 20. However, the direction of the static magnetic field may be perpendicular to the body axis direction of the subject 20.

  The gradient magnetic field coil unit 113 generates a gradient magnetic field that gives a gradient to the strength of the static magnetic field formed by the static magnetic field generation unit 112 so that the magnetic resonance signal received by the RF coil unit 114 has three-dimensional position information. . There are three types of gradient magnetic fields generated by the gradient magnetic field coil unit 113: a slice selection gradient magnetic field, a frequency encoding (Encode) gradient magnetic field, and a phase encoding gradient magnetic field. The coil unit 113 has three types of gradient magnetic field coils.

  The RF coil unit 114 transmits an RF pulse, and generates a magnetic resonance signal by exciting protons (Spin) in the body of the subject 20 in the static magnetic field space formed by the static magnetic field generation unit 112. . Further, the RF coil unit 114 receives a magnetic resonance signal emitted from the subject 20. The RF coil unit 114 may have a structure in which a transmission RF coil and a reception RF coil are separately provided, or may have a structure in which transmission of an RF pulse and reception of a magnetic resonance signal are performed by the same RF coil. good.

  The gradient magnetic field drive circuit 13 gives a drive signal DR to the gradient magnetic field coil unit 113 based on an instruction from the control unit 16 to generate a gradient magnetic field. The gradient magnetic field drive circuit 13 has three drive circuits (not shown) corresponding to the three gradient magnetic field coils of the gradient coil unit 113.

  The RF coil drive circuit 14 includes an RF pulse generation circuit and a power amplifier, which will be described later. The RF pulse generation circuit generates an RF pulse, and the power amplifier amplifies the RF pulse in accordance with a transmission condition specified from the operator console 17. The transmission condition is, for example, the target value of the power voltage of the power amplifier and the power of the RF pulse applied to the RF coil unit 114. The amplified RF pulse is applied to the RF coil unit 114.

  The data (Data) collection circuit 15 takes in the magnetic resonance signal received by the RF coil unit 114, converts it into a digital signal, and outputs it to the data processing unit 171 of the operator console 17.

  The control unit 16 controls the gradient magnetic field drive circuit 13 and the RF coil drive circuit 14 according to a predetermined pulse sequence (Pulse Sequence), and generates a drive signal DR and an RF pulse. Further, the control unit 16 controls the data collection circuit 15.

As shown in FIG. 1, the operator console 17 includes a data processing unit 171, an image database (Data Base) 172, an operation unit 173, and a display unit 174.
The data processing unit 171 performs overall control of the MRI apparatus 10, image reconstruction processing, and the like. A control unit 16 is connected to the data processing unit 171, and the data processing unit 171 controls the control unit 16.
In addition, an image database 172, an operation unit 173, and a display unit 174 are connected to the data processing unit 171. The image database 172 includes, for example, a hard disk (Hard Disk) device that can be recorded and reproduced, and records the reconstructed reconstructed image data and the like. The operation unit 173 includes a keyboard, a mouse, and the like, and the display unit 174 includes a graphic display.

FIG. 2 is a block diagram illustrating an example of an RF coil driving circuit according to an embodiment of the present invention.
The RF coil drive circuit 14A includes a variable voltage power supply circuit 31A, an RF pulse generation circuit 32, a power amplifier 33, a bias voltage adjustment unit 34, an amplitude adjustment unit 35, and a detection circuit 36. The RF coil drive circuit 14A is an example of the RF coil drive circuit 14 of FIG.

The variable voltage power supply circuit 31 </ b> A includes a DC constant voltage source 311 and a DC-DC converter (Direct-Current-to-Direct-Current Converter) 312.
When the voltage value of the power supply voltage is specified from the operator console 17 via the control unit 16, the variable voltage power supply circuit 31 </ b> A generates a power supply voltage of the specified voltage value and supplies it to the power amplifier 33. The DC constant voltage source 311 supplies a DC constant voltage to the DC-DC converter 312. The DC-DC converter 312 converts the supplied DC constant voltage into a lower DC voltage. The converted DC voltage is supplied to the power amplifier 33 as a power supply voltage. By reducing the power supply voltage, the power consumption of the power amplifier 33 can be reduced.

FIG. 3 is a block diagram illustrating an example of an RF pulse generation circuit.
The RF pulse generation circuit 32 includes a direct digital synthesizer (hereinafter referred to as DDS) 41, an envelope signal generator 42, a digital mixer (Digital Mixer) 43, and a digital / analog converter (Digital-to-digital converter). -Analog Converter (hereinafter referred to as D / A converter) 44 and a low-pass filter (hereinafter referred to as LPF) 45.

The DDS 41 includes a phase storage unit 411, a phase accumulation unit 412, and a waveform table (Table) 413.
The phase storage unit 411 stores a phase increase amount. The phase accumulation unit 412 calculates an accumulation phase by adding a phase increase amount for each clock period. Here, the clock cycle is the reciprocal of the sampling frequency of the D / A converter 44. The accumulated phase is input to the waveform table 413.
The waveform table 413 is composed of, for example, a ROM (Read Only Memory), and stores a digital value of a carrier wave signal corresponding to the accumulated phase. The accumulated phase is input to the address (Address) of the ROM, and the digital value of the carrier wave signal stored at the address is output from the ROM.
The envelope signal generator 42 generates an envelope signal. The digital mixer 43 modulates the carrier wave signal with the envelope signal, and generates an RF pulse signal having a predetermined bandwidth.
The RF pulse signal is converted into an analog RF pulse by the D / A converter 44. Since the RF pulse output from the D / A converter 44 includes harmonics, the LPF 45 removes the harmonic components.

The power amplifier 33 amplifies the RF pulse output from the RF pulse generation circuit 32. The RF pulse amplified by the power amplifier 33 is applied to the RF coil. In the MRI apparatus 10, it is important that the RF pulse waveform is maintained before and after being amplified by the power amplifier 33. When the waveform of the RF pulse is distorted, problems such as artifacts appear in the reconstructed image.
On the other hand, the class A amplifier (Amplifier) operates linearly in a wide input / output range, so that the problem of waveform distortion does not occur. For this reason, a class A amplifier is often used as the power amplifier 33 of the MRI apparatus 10.

The power consumption of the class A amplifier decreases even if the DC bias voltage is lowered in addition to the power supply voltage.
In the class A amplifier, it is desirable to change the DC bias voltage from the viewpoint of widening the input / output range that can be amplified when the power supply voltage changes. For example, when the power amplifier 33 is made of an emitter-grounded bipolar transistor (Bipolar transistor), it is desirable to set the DC bias voltage applied to the base (Base) to an optimum operating point. That is, when the power supply voltage becomes low, it is desirable to reduce the DC bias voltage applied to the base accordingly.
Similarly, when the power amplifier 33 is made of a source-grounded field effect transistor, it is desirable to set the DC bias voltage applied to the gate (Gate) to an optimum operating point. That is, when the power supply voltage becomes low, it is desirable to reduce the DC bias voltage applied to the gate accordingly.

  The bias voltage adjustment unit 34 calculates an optimum DC bias voltage based on the power supply voltage supplied from the variable voltage power supply circuit 31 </ b> A to the power amplifier 33, and sets the DC bias voltage in the power amplifier 33. For example, the bias voltage adjustment unit 34 calculates a voltage that maximizes the input / output range that can be amplified as the DC bias voltage.

  However, the gain of the class A amplifier changes when the power supply voltage changes. In the class A amplifier, even when the amplitude of the input signal is the same, the amplitude of the amplified output signal decreases when the power supply voltage decreases. The gain of the class A amplifier also changes due to the influence of the surrounding environment such as temperature.

  The detection circuit 36 detects the power of the RF pulse amplified by the power amplifier 33. The detection circuit 36 is made of, for example, a capacitor (Condenser) connected to a wiring for applying the amplified RF pulse to the RF coil, and a resistor having a very high resistance value connected between the capacitor and the ground potential. be able to. The power of the RF pulse is determined by measuring the voltage generated across the resistor. The RF pulse amplified by the power amplifier 33 is applied to the RF coil via the detection circuit 36.

The amplitude adjustment unit 35 adjusts the amplitude of the RF pulse input to the power amplifier 33. When the voltage value of the power supply voltage designated from the operator console 17 is changed, the power supply voltage supplied from the variable voltage power supply circuit 31A to the power amplifier 33 is changed. When the power supply voltage changes, the gain of the power amplifier 33 changes. For this reason, if the amplitude of the RF pulse input to the power amplifier 33 is constant, the amplitude of the RF pulse output from the power amplifier 33 changes before and after the power supply voltage changes.
A target value of power of the RF pulse applied to the RF coil from the operator console 17 via the control unit 16 (hereinafter referred to as a power target value) is designated. The amplitude adjusting unit 35 calculates an initial value of the amplitude of the RF pulse based on the power target value. At this time, the calculation may be performed in consideration of the power supply voltage designated from the operator console 17.
The amplitude of the RF pulse generated by the RF pulse generation circuit 32 is first amplified (or attenuated) to the initial value of the amplitude and input to the power amplifier 33. The detection circuit 36 detects the power of the RF pulse amplified by the power amplifier 33 (hereinafter referred to as a power detection value). The amplitude adjustment unit 35 compares the power detection value with the power target value, changes the amplitude of the RF pulse input to the power amplifier 33 until the difference between them falls within a predetermined range, and repeats the amplification of the RF pulse. Thereby, the power of the RF pulse applied to the RF coil approaches the power target value.

  Note that the bias voltage adjustment unit 34 and the amplitude adjustment unit 35 may all be realized by hardware (hardware), or some of those functions may be implemented as software (software) executed by a computer (computer). It may be realized.

FIG. 4 is a diagram showing processing of the RF coil driving circuit according to the embodiment of the present invention.
First, the power supply voltage of the power amplifier 33 generated by the variable voltage power supply circuit 31A and the power target value of the RF pulse amplified by the power amplifier 33 are designated from the operator console 17 via the control unit 16 (step ST1). .
The power amplifier 33 operates linearly in a wide input / output range, but the output waveform is crushed when the output power becomes too large or too small, and the waveform of the amplified RF pulse is distorted. When the waveform of the RF pulse is distorted, artifacts or the like occur in the reconstructed image, and the image quality deteriorates. As a result of the visual check (Check) of the reconstructed image, if the image quality is poor, the power supply voltage is set lower than the power target value, and the waveform of the amplified RF pulse may be distorted.
Therefore, in the present embodiment, when the image quality of the reconstructed image is poor, a higher power supply voltage is specified and the processing shown in FIG. 4 is executed again to enable re-imaging. The power target value is specified. However, the power supply voltage may be specified based on the power target value at the time of the first imaging, and the power supply voltage and the power target value may be designated when the image quality is poor as a result of visually checking the reconstructed image.

Next, the bias voltage adjustment unit 34 calculates an optimum DC bias voltage based on the power supply voltage generated by the variable voltage power supply circuit 31A and sets it in the power amplifier 33 (step ST2).
Further, the amplitude adjustment unit calculates the initial value of the amplitude of the RF pulse input to the power amplifier 33 based on the power target value (step ST3).
Then, the RF pulse amplitude generated by the RF pulse generation circuit 32 is amplified (or attenuated) to the initial value of the amplitude and input to the power amplifier 33. The power of the RF pulse amplified by the power amplifier 33 is detected by the detection circuit 36 (step ST4).

The amplitude adjustment unit 35 determines whether or not the difference between the power detection value and the power target value is within a predetermined range (step ST5).
When the difference between the detected power value and the target power value is within a predetermined range, the amplitude adjustment unit 35 outputs an imaging permission to the operator console 17 via the control unit 16 (step ST6). Imaging is performed under the control of the data processing unit 171 (step ST7).
When the difference between the power detection value and the power target value is outside the predetermined range, the amplitude adjustment unit 35 determines whether or not a predetermined number of retries has been exceeded (step ST8).
When the predetermined number of retries has been exceeded, the amplitude adjustment unit 35 outputs an error (Error) to the operator console 17 via the control unit 16 and ends (step ST9). For example, since the power supply voltage is extremely lower than the power target value, sufficient power cannot be obtained, and step ST9 is executed when the power detection value cannot reach the power target value.
When it is within the predetermined number of retries, the amplitude adjuster 35 changes the amplitude of the RF pulse input to the power amplifier 33 (step ST10), and returns to the power detection process of step ST4 again.

  The variable voltage power supply circuit 31A is an example of the variable voltage power supply unit of the present invention, the RF pulse generation circuit 32 is an example of the RF transmission signal generation unit and the RF pulse generation unit of the present invention, and the power amplifier 33 is the present invention. The bias voltage adjustment unit 34 is an example of the bias voltage adjustment unit of the present invention, the amplitude adjustment unit 35 is an example of the amplitude adjustment unit of the present invention, and the detection circuit 36 is the present example. It is an example of the detection part of the invention, the DC constant voltage source 311 is an example of the DC constant voltage source of the present invention, and the DC-DC converter 312 is an example of the DC-DC converter of the present invention.

FIG. 5 is a block diagram showing an example of an RF coil driving circuit according to another embodiment of the present invention.
The RF coil drive circuit 14B includes a variable voltage power supply circuit 31B, an RF pulse generation circuit 32, a power amplifier 33, a bias voltage adjustment unit 34, an amplitude adjustment unit 35, and a detection circuit 36. 2 and 5 indicate the same components.
The RF coil drive circuit 14B is an example of the RF coil drive circuit 14 of FIG. The RF coil drive circuit 14A and the RF coil drive circuit 14B differ only in the variable voltage power supply circuit 31A and the variable voltage power supply circuit 31B, and the other blocks are the same.

The variable voltage power supply circuit 31 </ b> B includes a DC constant voltage source 311, a DC-DC converter 312, and a selection switch (Switch) 313.
The selection switch 313 supplies the DC constant voltage output from the DC constant voltage source 311 to the DC-DC converter 312 and causes the DC-DC converter 312 to output a DC voltage lower than the DC constant voltage as a power supply voltage, or DC -Select whether to stop the DC converter 312 and output the DC constant voltage output from the DC constant voltage source 311 as the power supply voltage.
When the selection of the DC constant voltage source is specified from the operator console 17 via the control unit 16, the DC constant voltage source 311 and the power amplifier 33 are directly connected by the selection switch 313, and the DC-DC converter 312 is stopped. . When it is designated to select the DC constant voltage source, the amplitude adjusting unit 35 stops. That is, the amplitude adjustment unit 35 does not perform the processes of step ST5, step ST6, step ST8, step ST9, and step ST10 of FIG.

Depending on the type of image to be captured, noise (Noise) generated from the DC-DC converter 312 may degrade the image quality of the reconstructed image. In such a case, the power supply voltage is directly supplied from the DC constant voltage source 311 to the power amplifier 33, and the DC-DC converter 312 is stopped. Thereby, it is possible to prevent noise from being generated from the DC-DC converter 312.
Further, when the power of the RF pulse transmitted from the RF coil is large and there is no effect of reducing the power consumption by using the DC-DC converter 312, it is specified that the DC constant voltage source is selected from the operator console 17, and the DC -The DC converter 312 may be stopped. The DC-DC converter 312 is also slightly consuming power. This has the effect of reducing power.

  The variable voltage power supply circuit 31B is an example of the variable voltage power supply unit of the present invention, and the selection switch 313 is an example of the selection unit of the present invention.

  In the above embodiment, the detection circuit 36 detects the power of the amplified RF pulse, and the amplitude adjustment unit 35 determines whether or not the difference between the power detection value and the power target value is within a predetermined range. The detection circuit 36 may detect the amplitude of the amplified RF pulse, and the amplitude adjustment unit 35 may determine whether or not the difference between the amplitude detection value and the amplitude target value is within a predetermined range. In this case, an amplitude target value is designated from the operator console 17. When the difference between the amplitude detection value and the amplitude target value is within a predetermined range, the amplitude adjustment unit 35 outputs an imaging permission. On the other hand, when the difference between the amplitude detection value and the amplitude target value is outside the predetermined range, the amplitude adjustment unit 35 amplifies the RF pulse by changing the amplitude of the RF pulse input to the power amplifier 33, and performs amplitude detection processing again. I do.

  Thus, according to the RF coil drive circuit of the present invention, the power supply voltage and the bias voltage supplied to the power amplifier can be adjusted according to the power of the RF pulse transmitted from the RF coil. It is possible to apply an RF pulse of electric power necessary to compensate for a change in the gain of the power amplifier due to fluctuations and capture an image to the RF coil. For this reason, the power consumption of the power amplifier can be reduced. Further, the cost for cooling the power amplifier can be reduced.

  Although the embodiments of the present invention have been described above, various modifications and combinations necessary for design reasons and other factors are described in the inventions described in the claims and the specific embodiments described in the embodiments of the invention. It should be understood that it falls within the scope of the invention corresponding to the examples.

  Further, although the RF coil driving circuit included in the MRI apparatus has been described as an example, the present invention can be similarly applied to a circuit for driving a power amplifier included in an RF analog circuit of a mobile phone or a wireless LAN.

It is a figure which shows an MRI apparatus. It is a block diagram which shows the example of the RF coil drive circuit which concerns on one Embodiment of this invention. It is a block diagram which shows an example of RF pulse generation circuit. It is a figure which shows the process of the RF coil drive circuit which concerns on one Embodiment of this invention. It is a block diagram which shows the example of the RF coil drive circuit which concerns on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... MRI apparatus, 31A, 31B ... Variable voltage power supply circuit, 32 ... RF pulse generation circuit, 33 ... Power amplifier, 34 ... Bias voltage adjustment part, 35 ... Amplitude adjustment part, 36 ... Detection circuit, 311 ... DC constant voltage source , 312 ... DC-DC converter, 313 ... selection switch

Claims (8)

A variable voltage power supply that can change the magnitude of the output power supply voltage;
An RF transmission signal generator for generating an RF transmission signal;
When the power supply voltage to be supplied decreases, power consumption decreases, and when the power supply voltage changes, the gain changes, and the amplification unit that amplifies the RF transmission signal with the changed gain and applies it to the RF coil;
A detection unit for detecting power or amplitude of an RF transmission signal applied to the RF coil;
An amplitude adjustment unit that adjusts the amplitude of the RF transmission signal input to the amplification unit so that the power target value or the amplitude target value matches the detected power or amplitude, and
When the power supply voltage changes, the amplitude of the RF transmission signal input to the amplifying unit is adjusted, and the RF transmission signal applied to the RF coil approaches the power target value or the amplitude target value. A circuit,
The variable voltage power supply unit is
DC constant voltage source that outputs DC constant voltage;
A DC-DC converter that converts the DC constant voltage to a DC voltage lower than the DC constant voltage;
An RF coil driving circuit including: The variable voltage power supply unit is
The DC constant voltage is supplied to the DC-DC converter to cause the DC-DC converter to output a DC voltage lower than the DC constant voltage as the power supply voltage, or the DC-DC converter is stopped to stop the DC constant voltage. The RF coil drive circuit according to claim 1, further comprising a selection unit that selects whether to output a voltage as the power supply voltage. The RF coil driving circuit according to claim 1, wherein the amplifying unit is a power amplifier whose power consumption is reduced when the DC bias voltage is lowered. The RF coil drive circuit according to claim 3, further comprising a bias voltage adjustment unit that adjusts the DC bias voltage to a voltage corresponding to the power supply voltage. An RF coil for transmitting RF pulses;
An RF coil driving circuit for applying the RF pulse to the RF coil,
The RF coil drive circuit is
A variable voltage power supply that can change the magnitude of the output power supply voltage;
An RF pulse generator for generating an RF pulse;
When the power supply voltage to be supplied decreases, power consumption decreases, and when the power supply voltage changes, a gain changes, and an amplification unit that amplifies the RF pulse with the changed gain and applies it to the RF coil;
A detection unit for detecting power or amplitude of an RF pulse applied to the RF coil;
An amplitude adjustment unit that adjusts the amplitude of the RF pulse input to the amplification unit so that the power target value or amplitude target value matches the detected power or amplitude, and
When the power supply voltage changes, the amplitude of the RF pulse input to the amplification unit is adjusted, and the power or amplitude of the RF pulse applied to the RF coil approaches an electric power target value or an amplitude target value. ,
The variable voltage power supply unit is
DC constant voltage source that outputs DC constant voltage;
A DC-DC converter that converts the DC constant voltage to a DC voltage lower than the DC constant voltage. The variable voltage power supply unit is
The DC constant voltage is supplied to the DC-DC converter to cause the DC-DC converter to output a DC voltage lower than the DC constant voltage as the power supply voltage, or the DC-DC converter is stopped to stop the DC constant voltage. The MRI apparatus according to claim 5, further comprising a selection unit that selects whether to output a voltage as the power supply voltage. The MRI apparatus according to claim 5, wherein the amplification unit is a power amplifier that reduces power consumption when a DC bias voltage is reduced. The MRI apparatus according to claim 7, further comprising a bias voltage adjustment unit that adjusts the DC bias voltage to a voltage corresponding to the power supply voltage.

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