RF amplifier and MRI device

Abstract

To compensate gain linearity relative to a plurality of input signals having different frequencies.SOLUTION: An RF amplifier includes an FB circuit, acquisition means and changing means. The FB circuit compensates gain linearity relative to an input RF signal. The acquisition means acquires information indicating a frequency of the RF signal. The changing means changes a control range of the FB circuit on the basis of the information indicating the frequency.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The embodiments disclosed in the present specification and drawings relate to an RF amplifier and an MRI apparatus. [Background technology]

[0002] Conventionally, there is a magnetic resonance imaging (MRI) device that excites the nuclear spins of biological tissue placed in a strong static magnetic field with a radio frequency signal having the Larmor frequency, and reconstructs image data based on the magnetic resonance (MR) signals generated from within the subject in response to this excitation. In an MRI device, a radio frequency (RF) coil receives an RF signal amplified by an RF amplifier and generates a radio frequency magnetic field, which is then irradiated onto the subject placed in the static magnetic field.

[0003] RF amplifiers are equipped with a feedback circuit that feeds back the output in order to maintain constant gain linearity, but the gain control range is sometimes limited by the dynamic range of the Log amplifier in the feedback circuit and the variable range of the voltage-variable ATT (attenuator).For example, RF amplifiers are generally designed with a level diagram of the signal that is fed back from the output and input to the feedback circuit so that the input signal to the Log amplifier is within the input range in accordance with the fundamental frequency.

[0004] As described above, RF amplifiers are not designed to handle input signals with different frequencies, such as signals from multiple nuclides, and when signals with frequencies other than the fundamental frequency are input, there is a problem in that they cannot provide gain linearity compensation for signals with frequencies other than the fundamental frequency. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-081161 Summary of the Invention [Problem to be solved by the invention]

[0006] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to compensate for gain linearity for a plurality of input signals with different frequencies. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the configurations shown in the embodiments described below can also be considered as other problems. [Means for solving the problem]

[0007] An RF amplifier according to an embodiment includes a feedback circuit, an acquisition unit, and a change unit. The feedback circuit compensates for gain linearity for an input RF signal. The acquisition unit acquires information indicating a frequency of the RF signal. The change unit changes a control range of the feedback circuit based on the information indicating the frequency. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a magnetic resonance imaging (MRI) apparatus according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of an RF (Radio Frequency) amplifier according to the embodiment. [Figure 3] FIG. 3 is a diagram showing an example of a lookup table showing the correspondence between information indicating a frequency and a control voltage of a voltage-variable ATT (attenuator) according to the embodiment. [Figure 4] FIG. 4 is a flowchart showing an example of the flow of an amplification process executed in the RF amplifier according to the embodiment. [Figure 5] FIG. 5 is a diagram for explaining limitations on the input range of the Log amplifier according to the embodiment. [Figure 6] FIG. 6 is a diagram for explaining the gain linearity in an RF amplifier that does not include a feedback control range reference variable circuit, unlike the RF amplifier according to the embodiment. [Figure 7] FIG. 7 is a diagram for explaining the gain linearity in the RF amplifier according to the embodiment. [Figure 8] FIG. 8 is a diagram showing another example of a lookup table showing the correspondence between information indicating a frequency and a control voltage of a voltage-variable ATT according to the embodiment. [Figure 9] FIG. 9 is a diagram illustrating another example of the configuration of the RF amplifier according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, RF (Radio Frequency) amplifiers and magnetic resonance imaging (MRI) according to each embodiment will be described with reference to the drawings. In the following description, components having the same or substantially the same functions as those described above with reference to the previous drawings will be given the same reference numerals and will be described only when necessary. Furthermore, even when the same parts are shown, the dimensions and proportions may differ depending on the drawing.

[0010] (First embodiment) FIG. 1 is a diagram showing an example of the configuration of an MRI apparatus 10 according to an embodiment. The MRI apparatus 10 is an apparatus that reconstructs an image based on magnetic resonance signals acquired by imaging in which a subject P placed in a static magnetic field is irradiated with a radio frequency magnetic field. As shown in FIG. 1, the MRI apparatus 10 includes a magnet gantry 111 and a bed 121. The magnet gantry 111 includes a static magnetic field magnet 112, a gradient magnetic field coil unit 115, and an RF coil 116. Note that FIG. 1 illustrates the internal configuration of the magnet gantry 111 in a longitudinal cross section. Note that the MRI apparatus 10 does not include a subject P (e.g., a human body). Also, the configuration shown in FIG. 1 is an example, and, for example, a sequence control circuit 135 and a console 141 may be partially or entirely configured as an integrated unit, or may be separated as appropriate. For example, the MRI apparatus 10 is installed in an MR imaging room.

[0011] The gradient magnetic field coil unit 115 includes a main coil 113 and a shield coil 114. The MRI apparatus 10 also includes a gradient magnetic field power supply 131, a transmission circuit 132, a reception circuit 133, a bed control circuit 134, a sequence control circuit 135, and a console 141.

[0012] The static magnetic field magnet 112 has a roughly cylindrical shape and generates a static magnetic field within a bore (the space inside the cylinder of the static magnetic field magnet 112) that includes an imaging region of the subject P. The static magnetic field magnet 112 may be a superconducting magnet or a permanent magnet.

[0013] The gradient magnetic field coil unit 115 has a roughly cylindrical shape and is held by a support structure such as vibration-proof rubber inside the static magnetic field magnet 112. The gradient magnetic field coil unit 115 has a main coil 113 that applies (generates) gradient magnetic fields in mutually orthogonal directions by current supplied from a gradient magnetic field power supply 131, and a shield coil 114 that cancels the leakage magnetic field of the main coil 113.

[0014] The bed 121 includes a top plate 122 on which the subject P is placed, and under the control of a bed control circuit 134, the top plate 122 is inserted into a cavity (imaging port) of the gradient magnetic field coil unit 115 with the subject P placed thereon. Under the control of a console 141, the bed control circuit 134 drives the bed 121 to move the top plate 122 in the longitudinal direction and the up-down direction.

[0015] The RF coil 116 is disposed inside the gradient magnetic field coil unit 115, and generates a high-frequency magnetic field upon receiving RF pulses from the transmission circuit 132. The RF coil 116 also receives magnetic resonance signals emitted from the subject P due to the influence of the high-frequency magnetic field, and outputs the received magnetic resonance signals to the reception circuit 133. The RF coil 116 may be configured as a separate transmission coil and reception coil.

[0016] The transmission circuitry 132 supplies radio frequency pulses modulated to the Larmor frequency (also referred to as magnetic resonance frequency) to the RF coil 116 under the control of the sequence control circuitry 135. In this embodiment, the radio frequency pulses modulated to the Larmor frequency (also referred to as magnetic resonance frequency) may be referred to as RF pulses or RF signals. The magnetic resonance frequency is set in advance according to the gyromagnetic ratio of the atoms of the magnetic resonance target and the magnetic flux density of the static magnetic field. In other words, the frequency of the RF signal differs depending on the nuclide of the measurement target in the measurement based on the RF signal. When the magnetic flux density of the static magnetic field is 1.5 T, the magnetic resonance frequency is approximately 64 MHz. When the magnetic flux density of the static magnetic field is 3 T, the magnetic resonance frequency is approximately 128 MHz. For example, the transmission circuitry 132 includes an oscillator, a phase selector, a frequency converter, an amplitude modulator, an RF (Radio Frequency) amplifier 50, and the like.

[0017] The oscillator generates an RF pulse with a resonance frequency specific to the target atomic nucleus in the static magnetic field. The oscillator corresponds to a crystal oscillator that uses an oscillation circuit using a crystal oscillator and a frequency multiplier. That is, the crystal oscillator is configured with a source of oscillation (system clock) that is an integer multiple of the oscillation frequency of the crystal oscillator using the frequency multiplier. Note that the oscillator circuit is not limited to using a crystal oscillator, and other oscillators may also be used. Furthermore, the oscillator may be provided in the processing circuit 142 or may be mounted on the console 141. In this case, the oscillator serves as a source of oscillation for the overall control of the MRI apparatus 10.

[0018] The phase selection section selects the phase of the RF pulse generated by the oscillation section.

[0019] The frequency conversion unit converts the frequency of the RF pulse output from the phase selection unit.

[0020] The amplitude modulation section modulates the amplitude of the RF pulse output from the frequency conversion section in accordance with, for example, a sinc function.

[0021] The RF amplifier 50 amplifies the RF pulse having the magnetic resonance frequency output from the amplitude modulation unit and supplies it to the RF coil 116 via a duplexer (not shown). For example, the RF amplifier 50 amplifies the RF pulse to several tens of kW to several tens of kW. Here, the RF pulse, which is a high-frequency pulse supplied from the transmission circuit 132 to the RF coil 116, is an example of an RF signal.

[0022] The receiving circuit 133 detects the magnetic resonance signal output from the RF coil 116 and generates magnetic resonance data based on the detected magnetic resonance signal. Specifically, the receiving circuit 133 generates the magnetic resonance data by digitally converting the magnetic resonance signal received by the RF coil 116. The receiving circuit 133 also transmits the generated magnetic resonance data to the sequence control circuit 135.

[0023] The sequence control circuit 135 executes a pulse sequence by driving the gradient magnetic field power supply 131, the transmission circuitry 132, and the reception circuitry 133 based on sequence information transmitted from the console 141, thereby imaging the subject P. Here, the sequence information is information that defines a procedure for performing imaging. The sequence information defines, as a pulse sequence, the strength of the current that the gradient magnetic field power supply 131 supplies to the main coil 113 and the timing of supplying the current, the strength of the RF pulse that the transmission circuitry 132 supplies to the RF coil 116 and the timing of applying the RF pulse, the timing at which the reception circuitry 133 detects a magnetic resonance signal, and the like. For example, the sequence control circuit 135 is realized by a processor.

[0024] The sequence information may include the nuclide to be measured and the frequency of the RF pulse (input signal) to be supplied to the RF coil 116.

[0025] Furthermore, when the sequence control circuit 135 drives the gradient magnetic field power supply 131, the transmission circuit 132, and the reception circuit 133 to image the subject P, and receives magnetic resonance data from the reception circuit 133, it transfers the received magnetic resonance data to the console 141.

[0026] Similarly, the transmitting circuit 132, the receiving circuit 133, the bed control circuit 134, etc. are also configured by electronic circuits such as the above-mentioned processor.

[0027] The console 141 is a computer that controls the MRI apparatus 10. The console 141 performs overall control of the MRI apparatus 10 and generates images. The console 141 includes a processing circuitry 142, a memory circuitry 143, an input interface 144, a display 145, and a communication circuitry 146.

[0028] The processing circuitry 142 includes, as hardware resources, a processor such as a CPU and memories such as a ROM and a RAM. The processing circuitry 142 executes each function of the MRI apparatus 10 using a processor that executes a program loaded in the memory. The processing circuitry 142 performs overall control of the MRI apparatus 10, controlling imaging, image generation, image display, and the like. For example, the processing circuitry 142 accepts input of imaging conditions (imaging parameters, etc.) via a GUI and generates sequence information according to the accepted imaging conditions. The processing circuitry 142 also transmits the generated sequence information to the sequence control circuitry 135. The processing circuitry 142 also receives magnetic resonance data from the sequence control circuitry 135 and stores the received magnetic resonance data in the storage circuitry 143. The processing circuitry 142 also reads k-space data from the storage circuitry 143 and generates an image by performing reconstruction processing such as a Fourier transform on the read k-space data. That is, the processing circuitry 142 reconstructs an image based on magnetic resonance signals acquired by imaging in which a radio frequency magnetic field is irradiated onto a subject P placed in a static magnetic field.

[0029] The memory circuitry 143 stores various types of information used by the processing circuitry 142. Specifically, the memory circuitry 143 stores magnetic resonance data received by the processing circuitry 142, k-space data arranged in k-space by the processing circuitry 142, image data generated by the processing circuitry 142, etc. The memory circuitry 143 also stores various programs executed by the processing circuitry 142 and various types of setting information. Specifically, the memory circuitry 143 stores a program that supports positioning of the imaging range, a program related to signal processing of magnetic resonance data, etc. For example, the memory circuitry 143 is realized by a semiconductor memory element such as a RAM, a ROM, or a flash memory, a hard disk, an optical disk, etc.

[0030] The input interface 144 accepts various input operations from the operator, converts the accepted input operations into electrical signals, and outputs the electrical signals to the processing circuitry 142. For example, the input interface 144 is a selection device such as a pointing device, such as a mouse or a trackball, or an input device, such as a keyboard. Another example of the input interface 144 is an electrical signal processing circuit that receives electrical signals corresponding to input operations from an external input device provided separately from the console 141 and outputs the electrical signals to the processing circuitry 142.

[0031] The display 145, under the control of the processing circuitry 142, displays a GUI (Graphical User Interface) for receiving input related to setting and adjusting imaging conditions, images generated by the processing circuitry 142, etc. Any of a variety of displays can be used as appropriate as the display 145. For example, a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic electroluminescence display (OLED), or a plasma display can be used as the display 145.

[0032] The display 145 may be provided in any location. For example, the display 145 may be provided in an imaging room, an operation room, or the like. The display 145 may also be provided on the magnetic stand 111. The display 145 may be a desktop type, or may be configured as a tablet terminal or the like capable of wireless communication with the main body of the console 141. The display 145 may also be one or more projectors.

[0033] The communication circuit 146 communicates with external devices such as the information processing device 30 via a network. The communication circuit 146 is, for example, a communication interface such as a network card, a network adapter, or a NIC (Network Interface Controller).

[0034] Fig. 2 is a diagram showing an example of the configuration of an RF (Radio Frequency) amplifier 50 according to the embodiment. In Fig. 2, elements other than the RF amplifier 50 in the MRI apparatus 10 are shown as an MRI system 30. Fig. 2 illustrates a first RF amplifier 50a as the RF amplifier 50.

[0035] As shown in FIG. 2, the first RF amplifier 50a includes a distribution circuit 51, a first voltage variable ATT (attenuator) 52, an amplifier circuit 53, a directional coupler 54, an FB (feedback) control range reference variable circuit 55, and an FB circuit 56.

[0036] An input terminal of the distribution circuit 51 is electrically connected to an output terminal of the amplitude modulation unit of the transmission circuit 132. An output terminal of the distribution circuit 51 is electrically connected to each input terminal of the first voltage variable ATT 52 and the third voltage variable ATT 553. The distribution circuit 51 distributes and outputs an RF pulse having a magnetic resonance frequency from the amplitude modulation unit of the transmission circuit 132 to each input terminal of the first voltage variable ATT 52 and the third voltage variable ATT 553. Hereinafter, the signal distributed and output from the distribution circuit 51 to the input terminal of the third voltage variable ATT 553 will be referred to as a reference signal.

[0037] An output terminal of the first voltage variable ATT 52 is electrically connected to an input terminal of the amplifier circuit 53. A control terminal of the first voltage variable ATT 52 is electrically connected to an output terminal of the amplifier 563 of the FB circuit 56. The first voltage variable ATT 52 attenuates the RF signal from the distribution circuit 51 by an attenuation amount according to the control voltage from the amplifier 563. More specifically, the first voltage variable ATT 52 varies the FWD signal, the output of which is monitored and input to the input terminal of the second voltage variable ATT 552 via the directional coupler 54, to a level corresponding to the frequency.

[0038] The output terminal of the amplifier circuit 53 is electrically connected to the input terminal (input port) of the directional coupler 54. The amplifier circuit 53 amplifies the RF signal from the first voltage variable ATT 52 with a predetermined gain (amplification factor) and supplies the amplified RF signal to the directional coupler 54.

[0039] An output end (output port) of the directional coupler 54 is electrically connected to an input end of the RF coil 116. An output end (coupling port) of the directional coupler 54 is electrically connected to an input end of the second voltage variable ATT 552. The directional coupler 54 supplies an RF signal amplified by the amplifier circuit 53 at a predetermined amplification factor to the input end of the RF coil 116. The directional coupler 54 also extracts a traveling wave FWD signal from a signal transmitted in the forward direction through the transmission line and supplies the signal to the input end of the second voltage variable ATT 552.

[0040] The feedback control range reference variable circuit 55 is a circuit configured to change the voltage control range of the feedback circuit 56 based on information indicating the frequency of the RF signal input to the RF amplifier 50. As shown in FIG. 2 , the feedback control range reference variable circuit 55 has a frequency vs. gain voltage conversion circuit 551, a second voltage variable ATT 552, and a third voltage variable ATT 553.

[0041] An input terminal of the frequency vs. GAIN voltage conversion circuit 551 is connected to, for example, the sequence control circuit 135 or the console 141 of the MRI system 30. An output terminal of the frequency vs. GAIN voltage conversion circuit 551 is electrically connected to each control terminal of the second voltage variable ATT 552 and the third voltage variable ATT 553. Here, the frequency vs. GAIN voltage conversion circuit 551 is an example of a voltage conversion circuit. The frequency vs. GAIN voltage conversion circuit 551 according to this embodiment includes a processor and a memory.

[0042] The frequency vs. GAIN voltage conversion circuit 551 acquires information indicating the frequency of the RF signal input to the RF amplifier 50 from the MRI system 30. The information indicating the frequency of the RF signal may be the frequency value of the RF signal or information indicating the nuclide to be measured. Here, the FB control range reference variable circuit 55, which acquires the information indicating the frequency of the RF signal input to the RF amplifier 50, is an example of an acquisition means.

[0043] As an example, the frequency vs. GAIN voltage conversion circuit 551 acquires information indicating the frequency of the RF signal input to the RF amplifier 50 from the MRI system 30 by the processor executing a control program loaded in the memory.

[0044] As another example, the frequency vs. GAIN voltage conversion circuit 551 has a circuit configuration configured to acquire information indicating the frequency of the RF signal input to the RF amplifier 50 from the MRI system 30.

[0045] The frequency vs. GAIN voltage conversion circuit 551 may acquire information indicating the frequency of the RF signal actively, such as by sending a push to request the information, or passively, such as by receiving information from the MRI system 30.

[0046] The frequency vs. GAIN voltage conversion circuit 551 determines a control voltage according to the frequency of the RF signal (input signal) input to the RF amplifier 50, and supplies it to each control terminal of the second voltage variable ATT 552 and the third voltage variable ATT 553.

[0047] As an example, the frequency vs. GAIN voltage conversion circuit 551 determines a control voltage according to the frequency of the input RF signal by having a processor execute a control program expanded in memory and referencing a lookup table in which the relationship between frequency and control voltage stored in memory is pre-registered.

[0048] As another example, the frequency vs. GAIN voltage conversion circuit 551 has a circuit configuration configured to output a control voltage according to an input frequency, similar to the correspondence between the frequency and the control voltage shown in the above lookup table.

[0049] The correspondence between frequency and control voltage can be found, for example, from the characteristic data of "frequency vs. gain" of the RF amplifier 50. The characteristic data of "frequency vs. gain" of the RF amplifier 50 can be measured in advance using, for example, a network analyzer.

[0050] 3 is a diagram showing an example of a lookup table showing correspondence between information indicating frequency and control voltage according to the embodiment. As shown in FIG. 3, the lookup table shows correspondence between the frequency of the input signal, the gain of the input signal by the amplifier circuit 53, the gain difference of the input signal with respect to the reference frequency of the input signal, and the control voltage.

[0051] The frequencies have different values, for example, frequencies for each nuclide that can be used for imaging in the MRI apparatus 10. As an example, f1 to f4 are frequencies corresponding to the nuclides H, F19, P31, and C13, respectively. Note that these nuclides are only examples, and f1 to f4 may be frequencies corresponding to other nuclides.

[0052] The number of frequencies registered in the lookup table may be a plurality of numbers, such as three or less, or five or more.

[0053] The items registered in the lookup table of FIG. 3 need only include at least the items of the frequency of the input signal and the control voltage, and do not necessarily include the items of the gain and gain difference.

[0054] The FB control range reference variable circuit 55 may acquire the gain of the input RF signal or the gain difference between the input RF signal and an RF signal of a reference frequency as information indicating the frequency of the RF signal input to the RF amplifier 50. That is, the FB control range reference variable circuit 55 may be configured to supply a control voltage corresponding to the gain or the gain difference to each control terminal of the second voltage variable ATT 552 and the third voltage variable ATT 553. In this case, the look-up table may be configured to pre-register at least the correspondence between the gain or the gain difference and the control voltage. Alternatively, the frequency vs. GAIN voltage conversion circuit 551 may have a circuit configuration configured to output a control voltage corresponding to an input of the gain or the gain difference.

[0055] The second voltage variable ATT 552 attenuates the FWD signal from the directional coupler 54 by an amount of attenuation according to the control voltage from the frequency vs. GAIN voltage conversion circuit 551. In other words, the second voltage variable ATT 552 changes the level of the FWD signal from the directional coupler 54 to a level according to the frequency of the input signal.

[0056] The third voltage variable ATT 553 attenuates the reference signal from the distribution circuit 51 by an amount of attenuation according to the control voltage from the frequency vs. GAIN voltage conversion circuit 551. In other words, the third voltage variable ATT 553 changes the level of the reference signal from the distribution circuit 51 to a level according to the frequency of the input signal.

[0057] As described above, in the FB control range reference variable circuit 55, the frequency vs. GAIN voltage conversion circuit 551 determines the control voltages of the second voltage-variable ATT 552 and the third voltage-variable ATT 553 based on information indicating the frequency from the MRI system 30. Furthermore, the second voltage-variable ATT 552 and the third voltage-variable ATT 553 vary the reference signal and FWD signal input to the FB circuit 56 to levels corresponding to the frequency of the input signal, according to the control voltage from the frequency vs. GAIN voltage conversion circuit 551.

[0058] Here, the reference signal and FWD signal input to the FB circuit 56 are signals that change the control range of the FB circuit 56 by changing the control range reference of the FB circuit 56. In other words, the FB control range reference variable circuit 55 changes the control range of the FB circuit 56 based on information indicating the frequency. Here, the FB control range reference variable circuit 55, which changes the control range of the FB circuit 56 based on information indicating the frequency, is an example of a changing means.

[0059] The FB circuit 56 feeds back the output of the RF amplifier 50 to compensate for gain linearity. Specifically, the FB circuit 56 is configured to supply a control voltage to the control end of the first voltage-variable ATT 52 based on the control range standard corresponding to each frequency for each nuclide, which is changed by the FB control range standard variable circuit 55. As shown in FIG. 2 , the FB circuit 56 includes a first Log amplifier 561, a second Log amplifier 562, and an amplifier 563.

[0060] The input terminal of the first Log amplifier 561 is electrically connected to the output terminal of the second voltage variable ATT 552. The first Log amplifier 561 outputs the logarithmic value of the FWD signal from the second voltage variable ATT 552.

[0061] The input terminal of the second Log amplifier 562 is electrically connected to the output terminal of the third voltage variable ATT 553. The second Log amplifier 562 outputs the logarithmic value of the reference signal from the third voltage variable ATT 553.

[0062] A pair of input terminals of the amplifier 563 are electrically connected to the output terminals of the first Log amplifier 561 and the second Log amplifier 562, respectively. The output terminal of the amplifier 563 is electrically connected to the control terminal of the first voltage variable ATT 52. The amplifier 563 is configured to output a control voltage corresponding to the difference between the logarithmic values ​​of the FWD signal and the reference signal. In other words, the amplifier 563 supplies the control voltage, determined based on the signal before and after amplification by the RF amplifier 50, to the control terminal of the first voltage variable ATT 52.

[0063] Here, a processing flow according to the embodiment will be described. FIG. 4 is a flowchart showing an example of the flow of the amplification processing executed in the first RF amplifier 50a according to the embodiment. The flow of FIG. 4 is performed at least prior to the main scan. The flow of FIG. 4 may also be performed in a pre-scan. The flow of FIG. 4 is performed in a state where sequence information is obtained, that is, a state where an imaging protocol has been determined, or a state where the nuclide to be used for the scan has been determined.

[0064] First, the FB control range reference variable circuit 55 receives information indicating the frequency from the MRI system 30 (S101). Note that the FB control range reference variable circuit 55 may acquire, as the information indicating the frequency, not only the frequency value itself but also information indicating the nuclide used for the scan or information indicating the imaging protocol.

[0065] The FB control range reference variable circuit 55 determines the frequency based on information indicating the frequency from the MRI system 30 (S102). Note that if the frequency value itself is received in the process of S101, the process of this step is not necessary.

[0066] The FB control range reference variable circuit 55 determines the control voltages of the second voltage variable ATT 552 and the third voltage variable ATT 553 based on the relationship between the frequency and the control voltage (S103).

[0067] The FB control range reference variable circuit 55 determines the attenuation amounts of the second voltage variable ATT 552 and the third voltage variable ATT 553 using a control voltage according to the frequency (S104).

[0068] After the control range reference of the FB circuit 56 is changed in accordance with the frequency of the input signal in the processes of S101 to S104, the RF signal is input to the RF amplifier 50 (S105).

[0069] In the RF amplifier 50, the input RF signal is amplified by the amplifier circuit 53, and the FB circuit 56 performs FB control, i.e., gain linearity compensation, based on the reference signal from the distribution circuit 51 that is attenuated to a level corresponding to the frequency and that corresponds to the input, and the FWD signal that monitors the output (S106).The RF signal amplified under FB control is then output from the RF amplifier 50 (S107).

[0070] Here, the RF amplifier 50 is provided with an FB circuit 56 that feeds back the output in order to maintain constant gain linearity, but the gain control range may be limited by the dynamic range of the Log amplifiers 561 and 562 and the variable range of the first voltage variable ATT 52.

[0071] Fig. 5 is a diagram illustrating limitations on the input range of the Log amplifiers 561 and 562 according to the embodiment. In the graph of Fig. 5, the vertical and horizontal axes respectively represent the output [V] of the Log amplifiers 561 and 562 and the magnitude [dBm] of the input RF signal.

[0072] As shown on the left side of FIG. 5, the RF amplifier 50 is generally designed with a level diagram of the reference signal and the FWD signal so that the input signals to the Log amplifiers 561 and 562 are within the input range in accordance with the fundamental frequency f1.

[0073] In such a situation, a signal of a frequency f2 other than frequency f1 may be input, for example, when the nuclide used for scanning is changed or multiple nuclides are used. However, when a signal of a frequency f2 other than frequency f1 is input, the variable range widens as shown in region R1, as shown on the right side of Figure 5, and the gain of amplifier circuit 53 decreases, so that the FWD signal input to Log amplifiers 561 and 562 may fall outside the input range as shown in region R2. Furthermore, amplifier circuit 53 and directional coupler 54 of RF amplifier 50 have frequency characteristics, and the gain changes depending on the frequency of the input signal.

[0074] Fig. 6 is a diagram illustrating the gain linearity of an RF amplifier that does not include a feedback control range reference variable circuit 55, unlike the RF amplifier 50 according to the embodiment. In the graph of Fig. 6, the vertical and horizontal axes respectively represent the gain [dB] of the amplifier circuit 53 and the magnitude [dBm] of the input RF signal. The left side of Fig. 6 schematically illustrates the gain linearity of the amplifier circuit with respect to input signals of frequencies f1, f2, and f3 when no feedback control is performed. The right side of Fig. 6 schematically illustrates the gain linearity with respect to input signals of frequencies f1, f2, and f3 by an RF amplifier that does not include a feedback control range reference variable circuit 55.

[0075] The feedback circuit 56 generally has a control range of only about ±500 kHz for the frequency used (frequency f1 in FIG. 6). For this reason, in an RF amplifier that does not incorporate a feedback control range reference variable circuit 55, there is a problem in that it is not possible to maintain constant linearity for signals at a frequency f2 other than frequency f1, as shown on the right side of FIG. 6. In other words, conventional RF amplifiers have not been designed to handle input signals with different frequencies, such as those of multiple nuclides, and have therefore been unable to provide gain linearity compensation for multiple input signals with different frequencies.

[0076] In this regard, the RF amplifier 50 according to the present embodiment is equipped with a feedback control range reference variable circuit 55. FIG. 7 is a diagram illustrating the gain linearity in the RF amplifier 50 according to the embodiment. In the graph of FIG. 7, the vertical and horizontal axes respectively represent the gain [dB] by the amplifier circuit 53 and the magnitude [dBm] of the input RF signal. The left side of FIG. 7 schematically illustrates the gain linearity of the amplifier circuit with respect to input signals of frequencies f1, f2, and f3 when feedback control is not performed. The right side of FIG. 7 schematically illustrates the gain linearity with respect to input signals of frequencies f1, f2, and f3 by the RF amplifier 50 according to the embodiment equipped with the feedback control range reference variable circuit 55.

[0077] As described above, the feedback control range reference variable circuit 55 is configured to vary the gain control range reference of the feedback circuit 56 based on information indicating the frequency of the input RF signal. Therefore, the RF amplifier 50 according to the embodiment can provide gain linearity compensation corresponding to the frequencies of other nuclides, as shown in FIG.

[0078] That is, the RF amplifier 50 according to the embodiment varies the control range of the FB circuit 56 according to the frequency of the input signal, thereby achieving the effect of maintaining constant gain linearity for input signals with a wider band than conventional ones. As a result, even when a scan using multiple nuclides is performed in the MRI apparatus 10, the gain linearity of the RF amplifier 50 can be appropriately compensated. In other words, the RF amplifier 50 according to the embodiment can perform gain linearity compensation for a plurality of input signals with different frequencies.

[0079] (Second embodiment) In the RF amplifier 50 according to the above embodiment, the control voltage of the voltage-variable ATT may be determined from information indicating the frequency using an arithmetic expression. In this case, the memory of the frequency vs. GAIN voltage conversion circuit 551 stores an approximation expression that approximates the following gain curve, which is predetermined from the characteristic data of "frequency vs. gain" of the RF amplifier 50.

[0080] The calculation formula for gain G with respect to frequency f of the input signal is expressed as follows, using constants A, B, C, and D determined by the RF amplifier 50 and a constant fc defined from the “frequency vs. gain” characteristic data of the RF amplifier 50:

[0081] f <fcのとき、 G=A*f+B When f ≥ fc, G=C*f+D

[0082] The calculation formula for the difference ΔG between the gain G1 of the fundamental frequency f1 and the gain G for the frequency f of the input signal is expressed as follows:

[0083] ΔG=G-G1

[0084] The frequency vs. GAIN voltage conversion circuit 551 uses the above-mentioned equation to calculate the gain for the frequency of the input signal and the difference between the gain and the gain of the fundamental frequency. The frequency vs. GAIN voltage conversion circuit 551 also determines a control voltage according to the gain difference calculated by the equation.

[0085] As an example, the frequency vs. GAIN voltage conversion circuit 551 determines a control voltage according to the frequency of the input RF signal by having a processor execute a control program expanded in memory and referencing a lookup table in which the relationship between the gain difference and the control voltage stored in memory is pre-registered.

[0086] 8 is a diagram showing another example of a lookup table showing the correspondence between information indicating frequency and the control voltage of a voltage-variable ATT according to the embodiment. As shown in FIG. 8, the lookup table shows the correspondence between the frequency of an input signal, the gain difference of the input signal with respect to the reference frequency of the input signal, and the control voltage.

[0087] It should be noted that the items registered in the lookup table of FIG. 8 need only include at least the items of gain difference and control voltage, and do not necessarily include the item of frequency.

[0088] As another example, the frequency vs. GAIN voltage conversion circuit 551 has a circuit configuration configured to output a control voltage according to an input of a gain difference, similar to the correspondence between the gain difference and the control voltage indicated in the lookup table above.

[0089] As described above, in the RF amplifier 50 according to this embodiment, the feedback control range reference variable circuit 55 is configured to calculate the gain and gain difference using an arithmetic expression from the frequency of the input signal from the MRI system 30, and to determine a control voltage according to the gain difference. Even with this configuration, the feedback control range reference variable circuit 55 can vary the control range of the feedback circuit 56 according to the frequency of the input signal based on information indicating the frequency, and therefore, the same effects as those of the above-described embodiments can be obtained.

[0090] (Third embodiment) In the above-described embodiments, the RF amplifier 50 according to the embodiment has been described using the first RF amplifier 50a that acquires information indicating the frequency from the MRI system 30 as an example. However, the RF amplifier 50 is not limited to this. The RF amplifier 50 may be configured to be able to detect the frequency of an input signal.

[0091] Fig. 9 is a diagram showing another example of the configuration of the RF amplifier 50 according to the embodiment. Fig. 9 illustrates a second RF amplifier 50b as the RF amplifier 50. Unlike Fig. 2, Fig. 9 does not illustrate the MRI system 30.

[0092] 2 except that the second RF amplifier 50b further includes a frequency detection circuit 57. Specifically, the frequency detection circuit 57 is provided in the upstream stage of the distribution circuit 51. Specifically, the frequency detection circuit 57 is inserted between the output terminal of the amplitude modulation unit of the transmission circuit 132 and the input terminal of the distribution circuit 51. The output terminal of the detection frequency of the frequency detection circuit 57 is electrically connected to the input terminal of the frequency vs. GAIN voltage conversion circuit 551.

[0093] The amplification process executed in the second RF amplifier 50b will now be described, focusing mainly on the differences from the flow of the amplification process executed in the first RF amplifier 50a in FIG.

[0094] In the process of S101 of the amplification process according to this embodiment, an RF signal is input to the second RF amplifier 50b instead of acquiring information indicating the frequency of the input signal from the MRI system 30. Furthermore, the frequency detection circuit 57 detects the frequency from the input RF signal and supplies the detected frequency to the frequency vs. GAIN voltage conversion circuit 551. The frequency vs. GAIN voltage conversion circuit 551 acquires the detected frequency from the frequency detection circuit 57 as information indicating the frequency of the input signal.

[0095] In the amplification process according to this embodiment, the process of S101 above and processes similar to S102 to S104 of the amplification process according to the first embodiment are performed as a frequency detection mode.

[0096] In the amplification process according to this embodiment, after the frequency detection mode, a normal sequence (S105 to S107) is executed.

[0097] As described above, the RF amplifier 50 according to this embodiment further includes a frequency detection circuit 57 that detects the frequency of the input RF signal. With this configuration, information indicating the frequency of the input signal can be obtained based on the input RF signal, eliminating the need to obtain this information from the MRI system 30. Therefore, even in an environment where sequence information cannot be obtained from the MRI system 30, the FB control range reference variable circuit 55 can vary the control range of the FB circuit 56 according to the frequency of the input signal, thereby achieving the same effects as those of the above-described embodiments.

[0098] In the RF amplifier 50 according to each of the above-described embodiments, the frequency vs. GAIN voltage conversion circuit 551 may be realized by the sequence control circuit 135 or the processing circuit 142 of the console 141.

[0099] In the RF amplifier 50 according to each of the above-described embodiments, the control voltage of the voltage-variable ATT is determined from information indicating the frequency, but the present invention is not limited to this. The RF amplifier 50 according to each of the above-described embodiments can also be configured to switch the control voltage of the voltage-variable ATT to be used based on information indicating the frequency.

[0100] The term "processor" used in the above description refers to circuits such as a CPU, a GPU, an ASIC, and a programmable logic device (PLD). PLDs include simple programmable logic devices (SPLDs), complex programmable logic devices (CPLDs), and field programmable gate arrays (FPGAs). A processor realizes its functions by reading and executing a program stored in a memory circuit. The memory circuit storing the program is a computer-readable non-transitory recording medium. Note that instead of storing a program in a memory circuit, the program may be directly embedded in the processor circuit. In this case, the processor realizes its functions by reading and executing the program embedded in the circuit. Alternatively, the function corresponding to the program may be realized by combining logic circuits rather than executing a program. Note that each processor in this embodiment is not limited to being configured as a single circuit. It is also possible to configure multiple independent circuits as a single processor and realize its functions. Furthermore, multiple components in FIG. 1 may be integrated into a single processor to realize its functions.

[0101] According to at least one of the embodiments described above, it is possible to perform gain linearity compensation for a plurality of input signals with different frequencies.

[0102] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are intended to be included within the scope and spirit of the invention, as well as within the scope of the inventions and their equivalents as defined in the claims. [Explanation of symbols]

[0103] 10 MRI machine 132 Transmitting circuit 133 Receiving circuit 135 Sequence control circuit 141 Console 142 Processing Circuit 30 MRI systems 50 RF amplifier 51 Distribution circuit 52 First voltage variable ATT 53 Amplification circuit 54 Directional coupler 55 Feedback control range reference variable circuit 551 Frequency vs. GAIN voltage conversion circuit 552 Second voltage variable ATT 553 Third voltage variable ATT 56 FB circuit 561 First Log Amplifier 562 Second Log Amplifier 563 Amplifier 57 Frequency detection circuit

Claims

1. an FB circuit that compensates for gain linearity with respect to an input RF signal; an acquisition means for acquiring information indicating the frequency of the RF signal; a change unit that changes a control range standard of the FB circuit based on the information indicating the frequency, thereby changing the control range of the FB circuit; The change means is a second voltage-variable ATT that attenuates a traveling wave FWD signal extracted from the amplified RF signal transmitted in the forward direction through a transmission line and supplies the attenuated FWD signal to the FB circuit; a third voltage variable ATT that attenuates a reference signal distributed from the RF signal before amplification and supplies the attenuated reference signal to the FB circuit; a voltage conversion circuit that determines a control voltage that varies the amount of attenuation of the RF signal by the second voltage variable ATT and the third voltage variable ATT in accordance with the frequency of the RF signal. RF amplifier.

2. The RF amplifier according to claim 1 , wherein the acquiring means acquires the information indicating the frequency from an MRI system that outputs the RF signal to the RF amplifier.

3. 3. The RF amplifier according to claim 1, wherein the information indicating the frequency includes information indicating a frequency value of the RF signal or information indicating a nuclide to be measured in a measurement based on the RF signal.

4. Further comprising a frequency detection circuit for detecting the frequency of the input RF signal; the information indicating the frequency is the value of the frequency of the RF signal detected by the frequency detection circuit; The RF amplifier according to claim 1 .

5. 5. The RF amplifier according to claim 1, wherein a frequency of the RF signal varies depending on a nuclide to be measured.

6. the changing means determines a signal level to be supplied to the feedback circuit in accordance with the frequency of the RF signal; the FB circuit determines a control voltage for varying the amount of attenuation of the RF signal by a first voltage-variable ATT that attenuates the RF signal before amplification, in response to a signal supplied from the change means; The RF amplifier according to any one of claims 1 to 5.

7. 2. The RF amplifier according to claim 1, wherein the changing means refers to a table showing a correspondence between the frequency of the RF signal and the control voltages of the second voltage-variable ATT and the third voltage-variable ATT, and determines a control voltage that varies the amount of attenuation of the RF signal by the second voltage-variable ATT and the third voltage-variable ATT.

8. 2. The RF amplifier according to claim 1, wherein the changing means calculates a gain for the frequency of the RF signal from the frequency of the RF signal using an arithmetic expression, and refers to a table showing a correspondence between the gain for the frequency of the RF signal and the control voltages of the second voltage-variable ATT and the third voltage-variable ATT, and determines a control voltage that varies the amount of attenuation of the RF signal by the second voltage-variable ATT and the third voltage-variable ATT.

9. An RF amplifier according to any one of claims 1 to 8; an RF coil that receives the RF signal output from the RF amplifier and generates a high-frequency magnetic field; a processing circuit for reconstructing an image based on magnetic resonance signals acquired by imaging in which the subject placed in a static magnetic field is irradiated with the radio frequency magnetic field; An MRI apparatus comprising:

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