JPH08289880A - Method for generating high-frequency signal for mri and high-frequency amplifier for mri - Google Patents

Abstract

PURPOSE: To generate the high-frequency signals for MRI of large electric power at a low cost by separating phase control signals and amplitude control signals from envelope signals, generating phase modulation frequency signals by integrating the phase control signals and high-frequency reference signals, amplifying them and attenuating them by a prescribed attenuation rate. CONSTITUTION: A high-frequency pulse generation surface 1 for generating high-frequency envelope signals and the high-frequency reference signals for which a Larmor frequency matches is provided and the phase control signals and the amplitude control signals for controlling the phase and amplitude of the high-frequency reference signals are respectively separated and generated from the high-frequency envelope signals in a phase/amplitude separation circuit 2. Then, the high-frequency reference signals of the Larmor frequency and the phase control signals are integrated in an integration circuit 3 and phase modulation high-frequency signals are generated. The obtained phase modulation high-frequency signals are power-amplified 4 by switching, then the phase modulation high-frequency signals are attenuated correspondingly to the amplitude control signals in a variable attenuator 5 and the high-frequency pulses for the MRI of a desired waveform are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an M in a magnetic resonance imaging (MRI) apparatus.
High frequency signal generation method for RI and M for generating high frequency signal
The present invention relates to a high frequency amplifier for RI.

[0002]

2. Description of the Related Art An MRI apparatus measures the density distribution, relaxation time distribution, etc. of nuclear spins at a desired examination site in a subject by utilizing the nuclear magnetic resonance phenomenon, and the cross section of the subject is determined from the measured data. The image is displayed.

MRI for generating uniform and strong static magnetic field
The nuclear spins of the subject placed in the apparatus perform precession around the direction of the static magnetic field at a frequency (Larmor frequency) determined by the strength of the static magnetic field. Therefore, when a high frequency pulse having a frequency equal to this Larmor frequency is irradiated from the outside, spins are excited and transition to a high energy state. This is called a nuclear magnetic resonance phenomenon. When the irradiation of the high frequency pulse is stopped, the spin returns to the original low energy state with a time constant corresponding to each state, and at this time, the electromagnetic wave is radiated to the outside. This is detected by a high frequency receiving coil (high frequency coil) tuned to the frequency. At this time, a triaxial gradient magnetic field is applied to the static magnetic field space for the purpose of adding position information to the space. As a result, position information in the space can be captured as frequency information.

In such an MRI apparatus, a high frequency signal is supplied to a high frequency coil in order to apply a high frequency pulse to a subject. This high-frequency signal has a precisely controlled phase and amplitude, and its peak power reaches several kW to several tens of kW.

[0005]

In order to generate such a high-power high-frequency pulse, it is necessary to linearly amplify the phase and amplitude while keeping them accurate. Therefore, the output stage of the amplifier has a class A single, or class AB or class B push-pull configuration.

Further, depending on the Larmor frequency and its power, it is difficult to form the output stage of the amplifier from a semiconductor, and a vacuum tube is sometimes used. Further, when the output stage of the amplifier is composed of class A or class AB, the efficiency is poor and most of the power source is consumed as heat. For example, in the case of class AB, the efficiency is about 40%, and about 60% is consumed as heat. Since this is the efficiency in the case of the peak power, the efficiency is further reduced when the output is small.

By the way, generally, in the amplifying elements handling the same electric power, the elements used in the linear amplifier for class A or class AB amplification are often more expensive than the elements used in the class C or lower. Further, in the above-mentioned AB class, about 60% is consumed as heat, so that a large heat dissipation plate having a large heat dissipation capacity is required.

The present invention has been made in view of the above points, and an object thereof is to realize a high-frequency signal generation method for MRI which can inexpensively generate a high-power high-frequency signal.

Another object of the present invention is to realize an MRI high-frequency amplifier which can inexpensively generate a high-power high-frequency signal.

[0010]

Means for Solving the Problems The inventors of the present application have made earnest studies to improve the problems relating to the configuration and cost of high power amplification in the conventional MRI high frequency signal generation method and MRI high frequency amplifier. The present invention has been completed by newly finding a method for inexpensively amplifying large power while satisfying the phase characteristic and the amplitude characteristic.

That is, the present invention, which is a means for solving the problems, is as described in (1) to (3) below. (1) A first means for solving the above problem is to separately generate a phase control signal for controlling the phase of a high frequency reference signal and an amplitude control signal for controlling the amplitude from a high frequency envelope signal for MRI. An amplitude of the separately generated amplitude control signal is generated by integrating the separately generated phase control signal and the high frequency reference signal to generate a phase modulated high frequency signal and amplifying the generated phase modulated high frequency signal by switching. Is a method for attenuating the amplified switching signal at an attenuation rate according to the absolute value of to generate an MRI high frequency signal.

(2) A second means for solving the above-mentioned problems is to provide a phase control signal for controlling the phase of the high frequency reference signal and an amplitude control signal for controlling the amplitude from the high frequency envelope signal for MRI. Phase / amplitude separation means for separating and generating, summing means for summing the phase control signal and high frequency reference signal separated by the phase / amplitude separating means to generate a phase modulated high frequency signal, and the summing means A switching amplification means for amplifying a phase-modulated high-frequency signal by switching, and a switching signal amplified by the switching amplification means at an attenuation rate according to the absolute value of the amplitude of the amplitude control signal generated by the phase / amplitude separation means. An attenuator for attenuating the high frequency amplifier for MRI.

(3) A third means for solving the above-mentioned problems is to provide a phase control signal for controlling the phase of the high frequency reference signal and an amplitude control signal for controlling the amplitude from the high frequency envelope signal for MRI. Phase / amplitude separation means for separating and generating, summing means for summing the phase control signal and high frequency reference signal separated by the phase / amplitude separating means to generate a phase modulated high frequency signal, and the summing means Switching amplification means for amplifying the phase-modulated high-frequency signal by switching; and power supply means for changing the power supply voltage supplied to the switching amplification means according to the absolute value of the amplitude of the amplitude control signal generated by the phase / amplitude separation means. , The attenuation factor according to the absolute value of the amplitude of the amplitude control signal generated by the phase / amplitude separating means, MR to the attenuating means for attenuating the amplified switching signal, characterized in that it has a Ri
It is a high frequency amplifier for I.

The present invention, which is means for solving the problems, includes the following means in addition to the above (1) to (3). (4) A fourth means for solving the above-mentioned problems is a control means for generating a high-frequency envelope signal and a high-frequency reference signal for MRI, and a variable voltage control signal for controlling a power supply voltage at the time of switching amplification, and a means for MRI. Phase / amplitude separating means for separately generating a phase control signal for controlling the phase of the high frequency reference signal and an amplitude control signal for controlling the amplitude from the high frequency envelope signal, and the phase separated by the phase / amplitude separating means An integrating means for integrating the control signal and the high-frequency reference signal to generate a phase-modulated high-frequency signal, a switching amplifying means for amplifying the phase-modulated high-frequency signal generated by the integrating means by switching, and a generating means for the control means. Power supply means for changing the power supply voltage supplied to the switching amplification means according to a voltage control signal; A high-frequency amplifier for MRI, comprising: an attenuator that attenuates the switching signal amplified by the switching amplifier at an attenuation rate according to the absolute value of the amplitude of the amplitude control signal generated by the width separator. Is.

[0015]

In the MRI high-frequency signal generating method which is the first means for solving the problem, the phase control signal for controlling the phase of the high-frequency reference signal and the amplitude control signal for controlling the amplitude are separated from the envelope signal. The phase-modulated high-frequency signal is generated by integrating the separately-generated phase control signal and the high-frequency reference signal, the generated phase-modulated high-frequency signal is amplified by switching, and the amplitude of the separately-generated amplitude control signal is calculated. The amplified switching signal is attenuated at the attenuation rate according to the absolute value to generate the MRI high frequency signal.

By thus performing switching amplification and attenuating the amplitude, a high-power MRI high-frequency signal can be inexpensively generated. In the high frequency amplifier for MRI which is the second means for solving the problem, a phase control signal for controlling the phase of the high frequency reference signal and an amplitude control signal for controlling the amplitude are phase-controlled from the high frequency envelope signal for MRI. It is generated by the amplitude separating means. Then, the separately generated phase control signal and the high frequency reference signal are integrated by the integrating means to separate and generate the phase modulated high frequency signal, and the generated phase modulated high frequency signal is amplified by switching by the switching amplification means. Further, the amplified switching signal is attenuated by the attenuator at an attenuation rate according to the absolute value of the amplitude of the separately generated amplitude control signal to generate the MRI high frequency signal.

By thus switching-amplifying and attenuating the amplitude, it is possible to inexpensively generate a high-power MRI high-frequency signal. In the high frequency amplifier for MRI which is the third means for solving the problem, a phase control signal for controlling the phase of the high frequency reference signal and an amplitude control signal for controlling the amplitude are phase-controlled from the high frequency envelope signal for MRI. It is generated by the amplitude separating means. Then, the separately generated phase control signal and the high frequency reference signal are integrated by the integrating means to generate a phase modulated high frequency signal. The phase-modulated high-frequency signal generated in this way is amplified by switching by the switching amplification means to which the power supply voltage according to the absolute value of the amplitude of the amplitude control signal is supplied. Further, the amplified switching signal is attenuated by the attenuator at an attenuation rate according to the absolute value of the amplitude of the separately generated amplitude control signal to generate the MRI high frequency signal.

By thus switching-amplifying and attenuating the amplitude, it is possible to inexpensively generate a high-power MRI high-frequency signal. Then, by changing the power supply voltage for switching amplification, heat generation in the attenuator can be suppressed.

In the high frequency amplifier for MRI which is the fourth means for solving the problems, a phase control signal for controlling the phase of the high frequency reference signal from the high frequency envelope signal for MRI and an amplitude control signal for controlling the amplitude are provided. Is generated by the phase / amplitude separation means. Then, the separately generated phase control signal and the high frequency reference signal are integrated by the integrating means to generate a phase modulated high frequency signal. The phase-modulated high-frequency signal generated in this way is amplified by switching by the switching amplification means to which the power supply voltage according to the variable voltage control signal is supplied. Further, the amplified switching signal is attenuated by the attenuator at an attenuation rate according to the absolute value of the amplitude of the separately generated amplitude control signal to generate the MRI high frequency signal.

By thus switching-amplifying and attenuating the amplitude, a high-power MRI high-frequency signal can be inexpensively generated. Then, by changing the power supply voltage for switching amplification, heat generation in the attenuator can be suppressed.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. <Structure (1) of MRI High Frequency Amplifier> First, the structure of the MRI high frequency amplifier will be described with reference to FIG. FIG. 2 is a block diagram showing the configuration of the first embodiment of the high frequency amplifier for MRI of the present invention.

In FIG. 2, the high frequency pulse generator 1
Generates a high frequency reference signal (carrier) matching the Larmor frequency and a high frequency envelope signal having a waveform corresponding to a desired pulse sequence.

The phase / amplitude separation circuit 2 separates and generates a phase control signal for controlling the phase of the high frequency reference signal and an amplitude control signal for controlling the amplitude from the high frequency envelope signal.

The integrating circuit 3 integrates the high frequency reference signal of the Larmor frequency and the phase control signal to generate a phase modulated high frequency signal, and is composed of a balanced modulation circuit and the like.
The switching amplifier 4 is a switching amplification means for amplifying the power of the phase-modulated high frequency signal by switching,
Switching amplification generally called class D or class E is performed.

The variable attenuator 5 is an attenuating means for attenuating the amplified phase-modulated high frequency signal according to the amplitude control signal. The variable attenuator 5 may be a combination of a plurality of stages of attenuators and switching means, or FE.
It can be composed of T or the like.

<High Frequency Signal Generation Procedure (1)> Here,
The operation of the MRI high-frequency amplifier and the MRI high-frequency signal generation method will be described using an example of the high-frequency signal generation procedure in FIG. Further, the waveform chart of FIG. 3 is referred to as necessary.

The high frequency pulse generator 1 generates a high frequency envelope signal having a waveform corresponding to the pulse sequence required in the MRI apparatus and a high frequency reference signal matching the Larmor frequency (step 1 in FIG. 1). An example of this high frequency reference signal is shown in FIG. 3 (a), and an example of this high frequency envelope signal is shown in FIG. 3 (b).

Then, the phase / amplitude separation circuit 2 which receives the high frequency envelope signal from the high frequency pulse generator 1 separates the phase control signal for controlling the phase of the high frequency reference signal and the amplitude control signal for controlling the amplitude. Generate (Figure 1
Step 2).

Here, the phase control signal is for switching and controlling the phase of the high frequency reference signal, and is a signal in which +/- is switched depending on whether the value of the high frequency envelope signal is positive or negative (FIG. 3 (c)). ). The amplitude control signal is a signal for controlling the amplitude of the switching-amplified high frequency signal, and is a signal obtained by converting the high frequency envelope signal into an absolute value.

Next, the integrating circuit 3 integrates the high frequency reference signal of the Larmor frequency and the phase control signal to generate a phase modulated high frequency signal (step 3 in FIG. 1). For example, this integration is performed using a balanced modulation circuit or the like.
The phase-modulated high-frequency signal generated by this integration processing is
The phase is inverted (0 ° by the sign (+/-) of the phase control signal.
/ 180 °), and the signal has a constant amplitude as shown in FIG.

Power is amplified by switching the phase-modulated high frequency signal by the switching amplifier 4 (step 4 in FIG. 1). In this case, the phase-modulated high-frequency signal that is the input is a signal that has a constant amplitude and changes only in phase, and is therefore suitable for switching amplification called class D or class E. And this switching amplification has the advantage that the power conversion efficiency is extremely high.

The phase-modulated high-frequency signal thus switching-amplified is supplied to the variable attenuator 5.
The variable attenuator 5 attenuates the phase-modulated high-frequency signal amplified by switching in accordance with the amplitude control signal (step 5 in FIG. 1). By such processing, FIG.
A high-frequency pulse for MRI having a desired waveform as shown in (f) is obtained.

Various configurations are conceivable as the variable attenuator 5, and the following may be considered, for example. Connect multiple attenuators in cascade, and attach a diode switch, etc. to each attenuator.
Then, obtain the required attenuation rate according to the amplitude control signal,
The on / off of the diode switch is controlled so as to realize the attenuation rate. In this case, the resolution is determined by the number of attenuator stages.

Using a FET or the like as a switching element, a phase modulation high frequency signal is applied to the source or drain and an amplitude control signal is applied to the gate. As a result, the FET does not work as an amplifying element but as a variable resistance element. Since it is used as a simple variable resistance element as described above, it can be used regardless of the frequency characteristics of the element (the frequency range where a constant amplification factor can be obtained), and an inexpensive element can also be used.

<Effects Obtained by Configuration (1) and Generation Procedure (1)>: Since the power amplification by switching is performed using the switching amplifier 4, the efficiency is extremely high. If the conventional one is class AB amplification, the efficiency is about 40%, but if it is class D or class E amplification, a power conversion efficiency of 90% or more can be obtained. Therefore, the heat radiation means of the switching amplifier 4 can be downsized, and the cost can be reduced.

Since the variable attenuator 5 changes the amplitude with a variable attenuation factor, it is possible to use a variable resistance element, a plurality of stages of attenuators and switches, and it can be constructed at low cost.

For the above reasons, the conventional A
It can be constructed at a lower cost than a class amplifier. <Configuration of MRI High Frequency Amplifier (2)> Next, the configuration of the MRI high frequency amplifier will be described with reference to FIG. FIG. 4 is a block diagram showing the configuration of the second embodiment of the high frequency amplifier for MRI of the present invention.

In FIG. 4, the high frequency pulse generator 1
Generates a high frequency reference signal (carrier) matching the Larmor frequency and a high frequency envelope signal having a waveform corresponding to a desired pulse sequence.

The phase / amplitude separation circuit 2 separates and generates a phase control signal for controlling the phase of the high frequency reference signal and an amplitude control signal for controlling the amplitude from the high frequency envelope signal.

The integrating circuit 3 integrates the high frequency reference signal of the Larmor frequency and the phase control signal to generate a phase modulated high frequency signal, and is composed of a balanced modulation circuit and the like.
The switching amplifier 4 is a switching amplification means for amplifying the power of the phase-modulated high frequency signal by switching,
Amplification generally called D-class or E-class is performed.

The variable attenuator 5 is an attenuator for attenuating the amplified phase-modulated high frequency signal according to the amplitude control signal. The variable attenuator 5 may be a combination of a plurality of stages of attenuators and switching means, or FE.
It can be composed of T or the like.

The variable voltage power supply 6 generates a variable voltage according to the amplitude control signal. The variable voltage in this case is ideally a linear voltage that changes according to the absolute value of the amplitude of the amplitude control signal, but it may be a voltage that changes in two steps.

<High Frequency Signal Generation Procedure (2)> Here,
The operation of the MRI high-frequency amplifier and the MRI high-frequency signal generation method will be described using an example of the high-frequency signal generation procedure in FIG. Further, the waveform chart of FIG. 3 and the waveform chart of FIG. 5 are referred to as necessary.

The high frequency pulse generator 1 generates a high frequency envelope signal having a waveform corresponding to a pulse sequence required in the MRI apparatus and a high frequency reference signal matching the Larmor frequency. This high frequency reference signal is shown in FIG.
It is the same as that shown in FIG. 3A, and the high frequency envelope signal is the same as that shown in FIG.

Then, the phase / amplitude separation circuit 2 receiving the high frequency envelope signal from the high frequency pulse generator 1 separates the phase control signal for controlling the phase of the high frequency reference signal and the amplitude control signal for controlling the amplitude. To generate.

Here, the phase control signal is for switching control of the phase of the high frequency reference signal, and is a signal in which +/- is switched depending on whether the value of the high frequency envelope signal is positive or negative (FIG. 3 (c)). ).

Next, the integrating circuit 3 integrates the high frequency reference signal of the Larmor frequency and the phase control signal to generate a phase modulated high frequency signal. For example, this integration is performed using a balanced modulation circuit or the like. The phase-modulated high-frequency signal generated by this integration processing has its phase inverted (0 ° / 180 °) depending on the sign (+/−) of the phase control signal, and is constant as shown in FIG. It is a signal of amplitude.

The phase-modulated high frequency signal is switched by the switching amplifier 4 to perform power amplification. In this case, the phase-modulated high-frequency signal that is the input is a signal that has a constant amplitude and changes only in phase, and is therefore suitable for switching amplification called class D or class E. And this switching amplification has the advantage that the power conversion efficiency is extremely high.

At this time, the variable voltage power supply 6 controls the power supply voltage to be supplied to the switching amplifier 4 so as to have a different voltage according to the amplitude of the amplitude control signal. FIG. 5C shows a case where the voltage is controlled in two stages (V1, V2).

The variable voltage generated by the variable voltage power source 6 may be switched based on the amplitude control signal. However, when a time problem such as delay occurs in voltage generation, a high frequency pulse is generated. Part 1 and phase / amplitude separation circuit 2
Signal with advanced timing (variable voltage control signal)
Should be supplied.

If the voltage is controlled in two steps, a relatively good result can be obtained by setting V2 to the maximum voltage and V1 to a voltage range of relatively high frequency. The phase-modulated high frequency signal thus switching-amplified is supplied to the variable attenuator 5. The variable attenuator 5 attenuates the switching-amplified phase-modulated high-frequency signal in accordance with the amplitude control signal (FIG. 5B).

By such processing, a high-frequency pulse for MRI having a desired waveform as shown in FIG. 5D can be obtained.
In FIG. 5D, the high frequency pulse for MRI and the power supply voltage are shown in an overlapping manner. Therefore, there is an advantage that the electric power attenuated by the variable attenuator 5 (hatched portion in FIG. 5D) can be reduced as compared with the conventional case.

<Effects Obtained by Configuration (2) and Generation Procedure (2)>: Since the power amplification by switching is performed using the switching amplifier 4, the efficiency is extremely high. If the conventional one is class AB amplification, the efficiency is about 40%, but if it is class D or class E amplification, a power conversion efficiency of 90% or more can be obtained. Therefore, the heat radiation means in the switching amplifier 4 portion can be downsized, and the cost can be reduced.

Since the variable attenuator 5 changes the amplitude with a variable attenuation rate, it is possible to use a variable resistance element, a plurality of stages of attenuators and switches, and it can be constructed at low cost.

For the above reasons, the overall structure can be inexpensive. : Since the voltage supplied to the switching amplifier 4 is changed, high efficiency can be obtained even at a small output.

[0056]

As described in detail above, the M of the present invention
In the high frequency signal generation method for RI, a phase control signal for controlling the phase of the high frequency reference signal and an amplitude control signal for controlling the amplitude are separately generated from the envelope signal, and the phase control signal and the high frequency reference signal are integrated. Then, a phase-modulated high-frequency signal is generated, the phase-modulated high-frequency signal is amplified by switching, and the amplified switching signal is attenuated at an attenuation rate according to the absolute value of the amplitude of the amplitude control signal to generate a MRI high-frequency signal. Therefore, it is possible to inexpensively generate a high-power MRI high-frequency signal.

Further, in the high frequency amplifier for MRI of the present invention, the phase control signal for controlling the phase of the high frequency reference signal and the amplitude control signal for controlling the amplitude are separated from the high frequency envelope signal by the phase / amplitude separating means. The phase-modulated high-frequency signal is generated by integrating the phase control signal and the high-frequency reference signal by the integrating means, the phase-modulated high-frequency signal is amplified by the switching amplification means, and the amplified switching signal is converted into the amplitude control signal. By attenuating the attenuator at an attenuation rate according to the absolute value of the amplitude to generate the MRI high-frequency signal, it is possible to inexpensively generate a high-power MRI high-frequency signal.

Further, in the high frequency amplifier for MRI of the present invention, the phase control signal for controlling the phase of the high frequency reference signal and the amplitude control signal for controlling the amplitude are separated from the high frequency envelope signal by the phase / amplitude separating means. The phase control signal and the high frequency reference signal are integrated by the integrating means to generate a phase modulated high frequency signal, and the power supply voltage corresponding to the absolute value of the amplitude of the amplitude control signal is supplied to the phase modulation by the switching amplifying means. The high frequency signal is amplified by switching, and the amplified switching signal is attenuated by the attenuator at an attenuation rate according to the absolute value of the amplitude of the amplitude control signal to generate the high frequency signal for MRI. A high frequency signal for use can be generated. And
Efficiency is improved by changing the power supply voltage for switching amplification.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of an MRI high-frequency signal generation method of the present invention.

FIG. 2 is a configuration diagram showing a configuration example of an MRI high-frequency amplifier according to a first embodiment of the present invention.

FIG. 3 is a waveform diagram showing a signal waveform generated in the operating state of the first embodiment of the present invention.

FIG. 4 is a configuration diagram showing a configuration example of an MRI high-frequency amplifier according to a second embodiment of the present invention.

FIG. 5 is a waveform diagram showing signal waveforms generated in the operating state of the second embodiment of the present invention.

[Explanation of symbols]

 1 High-frequency pulse generator 2 Phase / amplitude separation circuit 3 Integration circuit 4 Switching amplifier 5 Variable attenuator

Claims (3)

[Claims] 1. A phase control signal for controlling a phase of a high frequency reference signal and an amplitude control signal for controlling an amplitude are separately generated from a high frequency envelope signal for MRI, and the phase control signal thus generated is separated from the phase control signal. A high-frequency reference signal is integrated to generate a phase-modulated high-frequency signal, the generated phase-modulated high-frequency signal is amplified by switching, and an attenuation factor according to the absolute value of the amplitude of the separately-generated amplitude control signal is obtained. An M high-frequency signal is generated by attenuating the amplified switching signal.
A high frequency signal generation method for RI. 2. A phase / amplitude separating means for separately generating a phase control signal for controlling a phase of a high frequency reference signal and an amplitude control signal for controlling an amplitude from a high frequency envelope signal for MRI, and the phase / amplitude separating means. Integrating means for integrating the phase control signal and the high frequency reference signal separated by the amplitude separating means to generate a phase modulated high frequency signal, and switching amplifying means for amplifying the phase modulated high frequency signal generated by the integrating means by switching. Attenuating means for attenuating the switching signal amplified by the switching amplifying means at an attenuation rate according to the absolute value of the amplitude of the amplitude control signal generated by the phase / amplitude separating means. High frequency amplifier for MRI. 3. A phase / amplitude separating means for separately generating a phase control signal for controlling the phase of the high frequency reference signal and an amplitude control signal for controlling the amplitude from the high frequency envelope signal for MRI, and the phase / amplitude separating means. Integrating means for integrating the phase control signal and the high frequency reference signal separated by the amplitude separating means to generate a phase modulated high frequency signal, and switching amplifying means for amplifying the phase modulated high frequency signal generated by the integrating means by switching. A power supply means for changing a power supply voltage supplied to the switching amplification means according to an absolute value of the amplitude of an amplitude control signal generated by the phase / amplitude separation means; and an amplitude control generated by the phase / amplitude separation means. Attenuating the switching signal amplified by the switching amplification means with an attenuation rate according to the absolute value of the signal amplitude. MRI high-frequency amplifier, characterized in that it comprises a damping means, a to.