High-frequency amplification device and magnetic resonance imaging apparatus

Abstract

To provide a high-frequency amplification device and a magnetic resonance imaging apparatus capable of accurately monitoring the power of an RF pulse applied to a subject.SOLUTION: A high-frequency amplification device according to one embodiment includes a high-frequency amplifier, a directional coupler, and a processing circuit. The directional coupler includes: a first port that outputs a progressive wave heading from the high-frequency amplifier toward a load as a progressive wave monitor signal at a predetermined coupling level; and a second port that outputs a reflected wave from the load as a reflected wave monitor signal at a predetermined coupling level. The processing circuit performs at least one of vector operation and calculation using the cosine theorem on the basis of the power of the progressive wave monitor signal, the power of the reflected wave monitor signal, and a phase difference between the progressive wave monitor signal and the reflected wave monitor signal, to correct the progressive wave monitor signal affected by the reflected wave, and to calculate the true progressive wave power unaffected by the reflected wave.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to a radio frequency amplifier and a magnetic resonance imaging apparatus. [Background technology]

[0002] In magnetic resonance imaging (MRI) devices, in order to suppress the effects of high-frequency radio frequency (RF) pulses on the subject, such as an increase in temperature, the specific absorption rate (SAR, the amount of RF absorbed per unit mass) must be kept below a threshold value, as stipulated by the International Electrotechnical Commission (IEC).

[0003] In order to satisfy the safety standard for SAR, it is important to accurately monitor the power of the RF pulse applied to the subject. The power of the RF pulse is monitored, for example, by extracting a part of the RF pulse using a directional coupler or the like just before the output terminal to the transmitting coil.

[0004] However, in an MRI device, the distance between the subject and the transmitting coil is short, and the load impedance of the RF pulse changes depending on the subject's physique, etc. This causes impedance mismatch at the output end of the RF pulse, making it difficult to monitor the accurate power of the RF pulse. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-141575 A Summary of the Invention [Problem to be solved by the invention]

[0006] The problem that the embodiments disclosed in this specification and the drawings attempt to solve is to more accurately monitor the power of an RF pulse applied to a subject. [Means for solving the problem]

[0007] A high-frequency amplification device according to one embodiment includes a high-frequency amplifier, a directional coupler, and a processing circuit. The directional coupler has a first port that outputs a traveling wave from the high-frequency amplifier toward a load as a traveling-wave monitor signal with a predetermined degree of coupling, and a second port that outputs a reflected wave from the load as a reflected-wave monitor signal with a predetermined degree of coupling. The processing circuit performs at least one of vector calculations or calculations using the cosine theorem based on the power of the traveling-wave monitor signal, the power of the reflected-wave monitor signal, and the phase difference between the traveling-wave monitor signal and the reflected-wave monitor signal, to correct the traveling-wave monitor signal affected by the reflected wave and calculate a true traveling-wave power that is not affected by the reflected wave. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing an example of the configuration of an MRI apparatus including a high-frequency amplifier according to an embodiment. [Diagram 2] FIG. 1 is a block diagram showing a configuration example of a high-frequency amplifier device of a comparative example. [Diagram 3] 1 is a block diagram showing an example of the configuration of a high-frequency amplifier device according to a first embodiment. [Figure 4] 3A and 3B are diagrams for explaining a phase difference in the high-frequency amplifying device according to the first embodiment. [Diagram 5] 4 is a flowchart showing an example of the operation of the high-frequency amplifying device according to the first embodiment. [Figure 6] 3A and 3B are diagrams for explaining vector operations or operations using the cosine theorem used in the high-frequency amplifying device according to the first embodiment. [Figure 7] FIG. 11 is a block diagram showing an example of the configuration of a high-frequency amplifier device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of a radio frequency amplifier and a magnetic resonance imaging apparatus will be described in detail with reference to the drawings.

[0010] (Overall configuration of magnetic resonance imaging device) A magnetic resonance imaging (MRI) device 1 according to an embodiment can utilize magnetic resonance imaging technology. Fig. 1 is a block diagram showing an example of the configuration of an MRI device including a high-frequency amplifier device 600 according to an embodiment. The MRI device 1 includes a magnet gantry 100, a control cabinet 300, an image processing device 400 such as a console, and a bed 500.

[0011] The magnet gantry 100 and the bed 500 are arranged, for example, in a shielded room called an examination room. On the other hand, the control cabinet 300 is arranged, for example, in a machine room, and the image processing device 400 is arranged, for example, in an operation room. Note that the image processing device 400 may be connected to the MRI apparatus 1 via a network and installed in a remote location away from the operation room.

[0012] The magnet gantry 100 includes a static magnetic field magnet 10, a gradient magnetic field coil 11, a WB (Whole Body) coil 12, and the like. The static magnetic field magnet 10 of the magnet gantry 100 is broadly classified into a cylindrical type in which the magnet has a cylindrical magnetic structure, and an open type in which a pair of magnets are arranged above and below with an imaging space in between. Below, an MRI device 1 with a cylindrical magnet gantry 100 will be described, but an open type MRI device may also be used. Note that the open type MRI device has the same configuration as the cylindrical type MRI device 1, except that the static magnetic field magnet, gradient magnetic field coil, and WB coil that constitute the magnet gantry are parallel plate-shaped.

[0013] The static magnetic field magnet 10 has a roughly cylindrical shape and generates a static magnetic field in a bore into which the subject P is transported. The bore is the space inside the cylinder of the magnet gantry 100. The static magnetic field magnet 10 is composed of, for example, a housing for holding liquid helium, a refrigerator for cooling the liquid helium to an extremely low temperature, and a superconducting coil inside the housing. The static magnetic field magnet 10 may be composed of a permanent magnet. Below, a case where the static magnetic field magnet 10 has a superconducting coil will be described.

[0014] The static magnetic field magnet 10 has a built-in superconducting coil, which is cooled to an extremely low temperature by liquid helium. In the excitation mode, the static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power supply to the superconducting coil. After that, when the mode is switched to the persistent current mode, the static magnetic field power supply is disconnected. Once in the persistent current mode, the static magnetic field magnet 10 continues to generate a static magnetic field for a long time, for example, for more than one year.

[0015] The gradient magnetic field coil 11 has a roughly cylindrical shape like the static magnetic field magnet 10, and is placed inside the static magnetic field magnet 10. The gradient magnetic field coil 11 is composed of three gradient magnetic field coils for the X-axis, Y-axis, and Z-axis. Each gradient magnetic field coil is supplied with a gradient magnetic field current (power) from a gradient magnetic field power supply 31 (31x for the X-axis, 31y for the Y-axis, and 31z for the Z-axis), thereby generating gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions and applying them to the subject P. Here, the Z-axis direction is the direction along the static magnetic field, the Y-axis direction is the vertical direction, and the X-axis direction is the direction perpendicular to the Z-axis and Y-axis, respectively.

[0016] The WB coil 12 is also called a whole-body coil, and is disposed inside the gradient magnetic field coil 11 in a generally cylindrical shape so as to surround the subject P. The WB coil 12 functions as a transmitting coil. That is, the WB coil 12 transmits RF pulses to the subject P in accordance with a radio frequency (RF) signal transmitted from the RF transmitter 32. Meanwhile, the WB coil 12 may also function as a receiving coil in addition to the function as a transmitting coil that transmits RF pulses. In that case, the WB coil 12 serves as a receiving coil to receive MR signals emitted from the subject P due to excitation of atomic nuclei. The WB coil 12 is an example of an RF coil that applies RF pulses to the subject.

[0017] The MRI apparatus 1 includes a local coil 20 in addition to the WB coil 12. The local coil 20 is a coil placed close to the body surface of the subject. The local coil 20 may include a plurality of coil elements. There are various types of local coils 20, such as a head coil, a chest coil as shown in FIG. 1, an abdominal coil, a spine coil, and a knee coil. The local coil 20 is dedicated to reception or transmission, or performs both transmission and reception. The local coil 20 is an example of an RF coil that applies an RF pulse to the subject. The local coil 20 is configured to be detachable from the tabletop 51 via a cable, for example.

[0018] The bed 500 includes a bed body 50 and a tabletop 51. The bed body 50 can move the tabletop 51 in the vertical and horizontal directions, and moves the subject P placed on the tabletop 51 to a predetermined height before imaging. Thereafter, during imaging, the tabletop 51 is moved horizontally to move the subject P into the bore.

[0019] The control cabinet 300 includes gradient magnetic field power supplies 31 (for the X-axis 31x, for the Y-axis 31y, and for the Z-axis 31z), an RF transmitter 32, an RF receiver 33, and a sequence controller .

[0020] The gradient magnetic field power supply 31 includes gradient magnetic field power supplies 31x, 31y, and 31z for each channel that drive coils that generate gradient magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. The gradient magnetic field power supplies 31x, 31y, and 31z output required currents independently for each channel in response to a command from a sequence controller 34.

[0021] The RF transmitter 32 is configured to include a high-frequency oscillator, a modulator, and a high-frequency amplifier device 600. The RF transmitter 32 generates an RF pulse based on an instruction from a sequence controller 34. The generated RF pulse is transmitted to an RF coil (i.e., the local coil 20 and the WB coil 12) and applied to the subject. Application of the RF pulse generates an MR signal from the subject. The RF coil receives this MR signal.

[0022] The high frequency amplifier 600 amplifies the RF signal of the Larmor frequency outputted from the modulator to be irradiated to the subject, and supplies the amplified RF signal to a load including at least an RF coil and the subject. The high frequency amplifier 600 will be described in detail later.

[0023] The MR signal received by the RF coil is transmitted to the RF receiver 33. The RF receiver 33 converts the MR signal from the RF coil into an analog-to-digital (AD) signal and outputs the signal to a sequence controller 34. The digitally converted MR signal is sometimes called raw data.

[0024] The sequence controller 34, under the control of the image processing device 400, drives the gradient magnetic field power supply 31, the RF transmitter 32, and the RF receiver 33 to image the subject P. When raw data is received from the RF receiver 33 by imaging, the sequence controller 34 transmits the raw data to the image processing device 400.

[0025] The sequence controller 34 includes a processing circuit (not shown). The processing circuit is configured with hardware such as a processor that executes a predetermined program, a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC).

[0026] The image processing device 400 includes a processing circuit 40 , a memory circuit 41 , a display 42 , and an input interface 43 .

[0027] The storage circuit 41 is configured with a storage medium including, for example, a semiconductor memory element such as a random access memory (RAM) or a flash memory, a hard disk, an optical disk, or other external storage device. The storage circuit 41 may be a portable medium such as a universal serial bus (USB) memory or a digital video disk (DVD). The storage circuit 41 stores various information and data, and also stores various programs executed by a processor included in the processing circuit 40.

[0028] The display 42 is configured by a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display. The display 42 displays various information under the control of the processing circuit 40. The display 42 is a display device, and may also be a GUI (Graphical User Interface) capable of receiving various operations from a user, such as a touch panel.

[0029] The input interface 43 includes an input device that can be operated by a user, and an input circuit that inputs a signal from the input device. The input device can be realized by a trackball, a switch, a mouse, a keyboard, a touchpad, a touchscreen, a non-contact input device using an optical sensor, a voice input device, etc. When the input device is operated by a user, the input circuit generates a signal according to the operation and outputs it to the processing circuit 40.

[0030] The processing circuit 40 is a circuit including, for example, a CPU or a dedicated or general-purpose processor. The processor realizes various functions by software processing by executing various programs stored in the storage circuit 41 or directly built into the processing circuit 40. The processing circuit 40 realizes the function of controlling the operation of the sequence controller 34 and performing imaging according to a pulse sequence to generate an MR image. The processing circuit 40 may be configured with hardware such as an FPGA or an ASIC. Various functions described later can also be realized by such hardware. Moreover, the processing circuit 40 may realize various functions by combining software processing and hardware processing.

[0031] Next, the configuration and operation of the high frequency amplifier 600 will be described.

[0032] 2 is a block diagram showing an example of the configuration of a radio frequency amplifier of a comparative example. In the radio frequency amplifier of the comparative example, an RF pulse input from a modulator to an RF pulse input end 61 is amplified by a radio frequency amplifier 63. In addition, the radio frequency amplifier of the comparative example separates at least a part of the forward wave power of the amplified RF pulse (hereinafter referred to as the power of the forward wave monitor signal) and at least a part of the reflected wave power (hereinafter referred to as the power of the reflected wave monitor signal) by a directional coupler 64 before an RF pulse output end 65 to an RF coil, and outputs them from a forward wave power monitor output end 66 (hereinafter referred to as the first port) and a reflected wave power monitor output end 67 (hereinafter referred to as the second port), respectively.

[0033] In the high frequency amplifier of the comparative example, the power of the RF pulse output from RF pulse output end 65 is monitored based on the power of the traveling wave monitor signal output from this first port 66 .

[0034] However, the impedance of the load side seen from the directional coupler 64, i.e., the impedance of the load side connected to the RF pulse output end 65, changes depending on the physique of the subject and the position and movement of the subject in the RF coil, and the magnitude of the reflected wave also changes accordingly. On the other hand, it is also known that the traveling wave monitor signal of the directional coupler 64 changes depending on the magnitude of the reflected wave due to leakage of the reflected wave into the traveling wave monitor signal. Therefore, when impedance mismatch occurs due to the physique of the subject, the magnitude of the traveling wave monitor signal of the RF pulse output end 65 changes, which affects the accuracy of the monitor power of the RF pulse. In particular, when the VSWR value is large (i.e., when the degree of impedance mismatch is large), the error tends to be large.

[0035] Errors in the monitor power of the RF pulse affect the calculation of the SAR. For example, for safety reasons, the upper limit of the SAR may be set to a value lower than the SAR threshold (for example, the threshold based on the IEC regulations). In this case, however, the power of the RF pulse must be set to a value lower than the originally possible output, which may result in longer imaging times.

[0036] Therefore, the high-frequency amplifier device 600 according to the embodiment reduces the error in the monitored power of the RF pulse even when there is a mismatch in the load impedance, and improves the accuracy of the monitored power of the RF pulse.

[0037] (High frequency amplifier according to the first embodiment) 3 is a block diagram showing an example of the configuration of a high-frequency amplifier 600 according to the first embodiment. The high-frequency amplifier 600 according to the first embodiment is configured to remove the influence of a reflected wave from a traveling wave monitor signal of the directional coupler 64 and output a true traveling wave monitor signal as an analog signal. In addition, the high-frequency amplifier 600 is also configured to remove the influence of a traveling wave from a reflected wave monitor signal of the directional coupler 64 and output a true reflected wave monitor signal as an analog signal.

[0038] As shown in FIG. 3, the high-frequency amplifying device 600 according to the first embodiment includes an input monitor coupler 62, a high-frequency amplifier 63, a directional coupler 64, a processing circuit 610, a first adjuster 631, and a second adjuster 632.

[0039] An RF pulse input from the modulator to an RF pulse input end 61 is input to a processing circuit 610 via a coupler 62, and is also input to a high-frequency amplifier 63 where it is amplified. The amplified RF pulse is input to an input end 64A of a directional coupler 64 as a traveling wave, and is output from an output end 64B of the directional coupler 64 to an RF pulse output end 65 via the directional coupler 64. The RF pulse output from the directional coupler 64 is input to an RF coil and applied to the subject. A part of the traveling wave is reflected from the RF coil due to mismatching of the load impedance seen from the directional coupler 64.

[0040] The directional coupler 64 has a first port 66 that outputs a traveling wave proceeding from the high frequency amplifier 63 to the load as a traveling wave monitor signal at a predetermined degree of coupling, and a second port 67 that outputs a reflected wave from the load as a reflected wave monitor signal at a predetermined degree of coupling. The first port 66 extracts and outputs at least a part of the traveling wave of the RF pulse amplified by the high frequency amplifier 63. The traveling wave monitor signal output from the first port 66 is a traveling wave monitor signal output from a main line (the main line of the traveling wave from the input end 64A of the directional coupler 64 to the output end 64B of the directional coupler 64 in FIG. 4) at a predetermined degree of coupling, such as a coupling degree of 30 dB (1 / 1000).

[0041] The second port 67 extracts and outputs at least a part of the reflected wave from the RF coil, which is input from the output end 64B of the directional coupler 64. The reflected wave monitor signal output from the second port 67 is a monitor signal of the reflected wave output from the main line with a predetermined degree of coupling. Note that the power of the traveling wave monitor signal and the power of the reflected wave monitor signal may be extracted by one directional coupler 64 as shown in Fig. 3, or each may be extracted by a different directional coupler.

[0042] Here, the phase difference in the high-frequency amplifier 600 will be described with reference to Fig. 4. As shown in Fig. 4, a traveling wave input to an input end 64A of a directional coupler 64 is output to a first port 66 as a traveling-wave monitor signal with a predetermined degree of coupling. In addition, a traveling wave output from an output end 64B of the directional coupler 64 is reflected due to mismatching of the load impedance, and the reflected wave from the load is output to a second port 67 as a reflected-wave monitor signal with a predetermined degree of coupling.

[0043] 4 illustrates an example in which the phase of the reflected wave monitor signal is θ1 [°] and the phase of the reflected wave monitor signal is θ2 [°] when the phase of the traveling wave monitor signal is θ0 [°]. Depending on the mismatch of the load impedance, the phase difference between the traveling wave monitor signal and the reflected wave monitor signal changes to (θ1-θ0) [°] and (θ2-θ0) [°], respectively. The phase θ0 of the traveling wave monitor signal may be, for example, 0 (no phase). In addition, a phase difference α based on the propagation path length also occurs between the first port 66 and the second port 67.

[0044] Furthermore, the traveling wave monitor signal output to the first port 66 is affected by the leakage power of the reflected wave from the main line of the directional coupler 64. Also, the reflected wave monitor signal output to the second port 67 is affected by the leakage power of the traveling wave from the main line of the directional coupler 64. The leakage power of the reflected wave is output to the first port 66, and the leakage power of the traveling wave is output to the second port 67.

[0045] The details of the processing circuit 610 of the high frequency amplifier 600 will be described later, but the influence of the leakage power of the reflected wave from the main line of the directional coupler 64 and the influence of the leakage power of the forward wave are removed by the first adjuster 631 and the second adjuster 632. The first adjuster 631 and the second adjuster 632 are adjusters for increasing or decreasing the power of the RF pulse monitor signal, such as a variable attenuator (ATT). As shown in Fig. 3, the high frequency amplifier 600 according to the first embodiment outputs the power of the true forward wave monitor signal and the power of the true reflected wave monitor signal as analog signals.

[0046] The first adjuster 631 adjusts the calculated monitor signal of the true forward wave power so as to output it as a true forward wave monitor signal. Then, the true forward wave monitor signal is output from the variable attenuator serving as the first adjuster 631.

[0047] The second adjuster 632 adjusts the monitor signal of the calculated true reflected wave power so as to output it as a true reflected wave monitor signal. Then, the true reflected wave monitor signal is output from the variable attenuator functioning as the second adjuster 632.

[0048] The processing circuit 610 is composed of, for example, a processor that executes a predetermined program, or hardware such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). The processing circuit 610 is a processor that can execute a process of calculating the power of a true traveling wave monitor signal, or the power of a true traveling wave monitor signal and the power of a true reflected wave monitor signal, by reading and executing a program stored in the storage circuit 620, in order to more accurately monitor the power of an RF pulse applied to a subject.

[0049] The storage circuit 620 is configured with a storage medium including, for example, a semiconductor memory element such as a random access memory (RAM) or a flash memory, a hard disk, an optical disk, or other external storage device. The storage circuit 41 may be a portable medium such as a universal serial bus (USB) memory or a digital video disk (DVD). The storage circuit 620 stores various information and data, as well as various programs executed by a processor included in the processing circuit 610.

[0050] The processor of the processing circuit 610 realizes a coupler detection function 611, a FWD detection function 612, an RFL detection function 613, a phase detection function 614, and a correction function 615. Each of these functions is stored in the form of a program in the storage circuit 620. The configuration and operation of each function realized by the processing circuit 610 will be described with reference to the flowchart of FIG.

[0051] In the high-frequency amplifier 600, the leakage power of the traveling wave when the load impedance is matched (for example, 50Ω) is measured in advance as the leakage power of the traveling wave used in step ST40 described later. The value of the leakage power of the traveling wave when the load impedance is matched is stored in the memory circuit 620, for example.

[0052] In step ST10, an RF pulse is input to the RF pulse input terminal 61. The coupler detection function 611 detects the amplitude of the RF pulse via the coupler 62 that monitors the RF pulse input to the RF pulse input terminal 61. Based on the amplitude of the RF pulse input to the coupler 62, it is preferable to determine the timing for detecting the power of the traveling wave monitor signal output by the directional coupler 64, the power of the reflected wave monitor signal, and the phase difference between the traveling wave monitor signal and the reflected wave monitor signal. During the on-period of the RF pulse output from the coupler 62, the power of the traveling wave monitor signal output by the directional coupler 64, the power of the reflected wave monitor signal, and the phase difference between the traveling wave monitor signal and the reflected wave monitor signal may be detected.

[0053] In step ST20, the power of the traveling wave monitor signal, the power of the reflected wave monitor signal, and the phase difference between the traveling wave monitor signal and the reflected wave monitor signal are detected. The FWD detection function 612 detects the power of the traveling wave monitor signal (or the amplitude of the traveling wave monitor signal) output from the first port 66 of the directional coupler 64. The RFL detection function 613 detects the power of the reflected wave monitor signal (or the amplitude of the reflected wave monitor signal) output from the second port 67 of the directional coupler 64. The phase detection function 614 detects the phase difference between the traveling wave monitor signal and the reflected wave monitor signal. As described above, a part of the input traveling wave is reflected depending on the mismatch of the load impedance seen from the directional coupler 64.

[0054] In step ST30, the correction function 615 obtains the phase difference α based on the propagation path length between the first port 66 and the second port 67.

[0055] In step ST40, the correction function 615 calculates the true reflected wave power that is not influenced by the leakage power of the forward wave from the difference between the power of the reflected wave monitor signal and the leakage power of the forward wave.

[0056] The power of the reflected wave monitor signal output to the second port 67 of the directional coupler 64 is affected by the leakage power of the forward wave. That is, the power of the reflected wave monitor signal is the true reflected wave power plus the leakage power of the forward wave, and is output to the second port 67. Here, the leakage power of the forward wave output to the second port 67 is constant regardless of the load impedance as long as the power of the forward wave is constant. As described above, the leakage power of the forward wave can be obtained by measuring in advance the power of the forward wave output from the second port 67 in a state where no reflected wave exists, that is, when the load impedance is matched (for example, when a load of 50Ω is connected). Therefore, as shown in formula (1), the influence of the leakage power of the forward wave can be eliminated by subtracting the leakage power of the forward wave measured in advance from the power of the detected reflected wave monitor signal, and the power of the true reflected wave monitor signal can be obtained.

[0057] True power of reflected wave monitor signal = power of reflected wave monitor signal output to the second port 67 - leakage power of forward wave Equation (1)

[0058] In step ST50, the correction function 615 calculates the true power of the traveling wave monitor signal that is not affected by the leakage power of the reflected wave, based on the power of the traveling wave monitor signal and the leakage power of the reflected wave. The correction function 615 can also calculate the true traveling wave power using the power of the true traveling wave monitor signal and the coupling degree of the directional coupler 64.

[0059] The power of the traveling wave monitor signal at the first port 66 of the directional coupler 64 is affected by the leakage power of the reflected wave. In addition, the amplitude and phase of the reflected wave from the load change depending on the matching state of the load. In other words, the amplitude and phase of the reflected wave (or the amplitude and phase of the reflected wave monitor signal) change depending on the load impedance. For this reason, the power of the traveling wave monitor signal (or the amplitude of the traveling wave monitor signal) is output to the first port 66 in a state in which the true traveling wave monitor signal is affected by the reflected wave monitor signal, the amplitude and phase of which change depending on the load impedance.

[0060] Here, the calculation of the true forward wave power in step ST50 will be described in detail with reference to Fig. 6. Fig. 6 is a diagram for explaining the vector calculation or the calculation using the cosine theorem used in the high frequency amplifying device 600 according to the first embodiment. As shown in Fig. 6(A), the forward wave monitor signal output from the first port 66 of the directional coupler 64 can be expressed as a vector diagram affected by the leakage power of the reflected wave.

[0061] Here, the leakage power of the reflected wave that affects the traveling wave monitor signal can be considered to be the same power as the true reflected wave monitor signal. Also, as shown in Fig. 6(B), the phase difference θ between the traveling wave monitor signal and the true reflected wave monitor signal can be considered to be the sum of the phase difference between the traveling wave monitor signal and the reflected wave monitor signal (for example, θ1-θ0, θ2-θ0 in Fig. 4) and the phase difference α based on the propagation path length between the first port 66 and the second port 67.

[0062] Therefore, as shown in FIG. 6(A) and equation (2), by performing at least one of vector operations or operations using the cosine theorem using the power of the forward wave monitor signal detected in step ST20 and the leakage power of the reflected wave (i.e., the power of the true reflected wave monitor signal calculated in step ST40), the influence of the leakage power of the reflected wave can be eliminated and the power of the true forward wave monitor signal can be obtained.

[0063] C 2 =A 2 +B 2 -2A*B*COS(θ)...Equation (2) Here, C is the voltage of the true traveling wave monitor signal not affected by the reflected wave, A is the voltage of the traveling wave monitor signal affected by the reflected wave (i.e., the voltage of the traveling wave monitor signal output from the first port 66), and B is the leakage voltage of the reflected wave that affects the traveling wave monitor signal (i.e., the voltage of the true reflected wave monitor signal calculated by equation (1)). Also, θ is the phase difference obtained by adding the phase difference α based on the propagation path length between the first port 66 and the second port 67 to the phase difference (θ1-θ0) between the traveling wave monitor signal and the reflected wave monitor signal, as shown in Fig. 6(B).

[0064] In this way, the correction function 615 performs at least one of vector calculations or calculations using the cosine law based on the power of the forward wave monitor signal, the power of the reflected wave monitor signal, and the phase difference between the forward wave monitor signal and the reflected wave monitor signal, to correct the forward wave monitor signal affected by the reflected wave and calculate the true forward wave power that is not affected by the reflected wave.

[0065] In step ST60, the first adjuster 631 adjusts the power of the traveling wave monitor signal output from the first port 66 so that it becomes the power of the calculated true traveling wave monitor signal, and outputs it to a subsequent stage (for example, to a SAR calculation circuit). Also, the second adjuster 632 adjusts the power of the reflected wave monitor signal output from the second port 67 so that it becomes the power of the calculated true reflected wave monitor signal, and outputs it to a subsequent stage.

[0066] In step ST70, the adjusted true reflected power monitor signal and true forward power monitor signal are displayed.

[0067] According to the high frequency amplifier 600 of the first embodiment, at least one of vector calculations or calculations using the cosine law is performed based on the power of the traveling wave monitor signal output from the first port 66 of the directional coupler 64, the power of the reflected wave monitor signal output from the second port 67, and the phase difference between the traveling wave monitor signal and the reflected wave monitor signal. This makes it possible to calculate and correct the true traveling wave power excluding the influence of the reflected wave, and to more accurately monitor the power of the RF pulse applied to the subject even when there is a load mismatch. Furthermore, by more accurately monitoring the power of the RF pulse, it becomes possible to accurately grasp the power of the RF pulse irradiated to the subject on the MRI apparatus 1 side, and the power of the RF pulse defined by SAR can be output from the high frequency amplifier 600 with high accuracy.

[0068] (High frequency amplifier according to the second embodiment) 7 is a block diagram showing an example of the configuration of a high-frequency amplifier 600 according to the second embodiment. The high-frequency amplifier 600 according to the first embodiment transmits the power of the true traveling wave monitor signal and the power of the true reflected wave monitor signal in an analog manner. In contrast, the high-frequency amplifier 600 according to the second embodiment differs in that the power of the true traveling wave monitor signal and the power of the true reflected wave monitor signal are transmitted in a digital manner. Other configurations and operations that are substantially the same as those of the high-frequency amplifier 600 according to the first embodiment are denoted by the same reference numerals, and duplicated explanations will be omitted.

[0069] 5, in the high-frequency amplifying device 600 according to the first embodiment, the first adjuster 631 and the second adjuster 632 are used for adjustment so as to output the calculated monitor signal of the true forward wave power and the monitor signal of the true reflected wave power as a true forward wave monitor signal and a true reflected wave monitor signal by analog transmission. In contrast, the high-frequency amplifying device 600 according to the second embodiment does not perform adjustment by the first adjuster 631 and the second adjuster 632.

[0070] In the high-frequency amplifier 600 according to the second embodiment, the correction function 615 outputs, as a digital signal, the calculated true forward power that is not influenced by the reflected wave in step ST40 of the flowchart in Fig. 5. Also, the correction function 615 outputs, as a digital signal, the calculated true reflected power that is not influenced by the leakage power of the forward wave in step ST50 of the flowchart in Fig. 5.

[0071] In this case, by digitally transmitting the true monitor power, it is possible to omit AD conversion processing performed at a later stage for the calculation of SAR, etc.

[0072] The high-frequency amplifying device 600 according to the second embodiment provides the same effects as the high-frequency amplifying device 600 according to the first embodiment.

[0073] According to at least one of the embodiments described above, the power of an RF pulse applied to a subject can be monitored more accurately.

[0074] In the above embodiment, the term "processor" refers to a circuit such as a dedicated or general-purpose CPU (Central Processing Unit), GPU (Graphics Processing Unit), or an Application Specific Integrated Circuit (ASIC), a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and an FPGA), etc. The processor realizes various functions by reading and executing a program stored in a storage medium.

[0075] In addition, the functions of the processing circuitry 40 and the functions of the processing circuitry 610 may be realized by a single processor, such as the processor of the processing circuitry 40 of the image processing device 400.

[0076] In the above embodiment, an example was shown in which a single processor of the processing circuit 610 realizes each of the functions 611-615, but a processing circuit may be configured by combining multiple independent processors, and each processor may realize each function. In addition, when multiple processors are provided, a storage medium for storing a program may be provided separately for each processor, or one storage medium may collectively store programs corresponding to the functions of all the processors.

[0077] 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 embodiments can be implemented 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 included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0078] 1...Magnetic resonance imaging (MRI) device 12...WB coil 20...Local coil 32...RF transmitter 33...RF receiver 600...High frequency amplifier 61...RF pulse input terminal 62...Coupler 63...High frequency amplifier 64...Directional coupler 65...RF pulse output terminal 66...Output terminal for forward wave power monitor (first port) 67...Output terminal for reflected wave power monitor (second port) 610...Processing circuit 611...Coupler detection function 612...FWD detection function 613...RFL detection function 614...Phase detection function 615...Correction function 631...First adjuster 632...Second adjuster

Claims

1. A high frequency amplifier; a directional coupler having a first port for outputting a traveling wave from the high frequency amplifier toward a load as a traveling wave monitor signal with a predetermined degree of coupling, and a second port for outputting a reflected wave from the load as a reflected wave monitor signal with a predetermined degree of coupling; a processing circuit that performs at least one of vector calculations and calculations using the cosine law based on the power of the traveling wave monitor signal, the power of the reflected wave monitor signal, and the phase difference between the traveling wave monitor signal and the reflected wave monitor signal, to correct the traveling wave monitor signal that is affected by the reflected wave, and calculates a true traveling wave power that is not affected by the reflected wave; A high frequency amplifier device comprising:

2. a first adjuster that adjusts the monitor signal of the calculated true forward wave power that is not affected by the reflected wave so as to output it as a true forward wave monitor signal; 2. The high frequency amplifier according to claim 1.

3. The processing circuitry includes: calculating a true reflected wave power that is not influenced by the leakage power of the forward wave based on a difference between the power of the reflected wave monitor signal and the leakage power of the forward wave; 2. The high frequency amplifier according to claim 1.

4. a second adjuster that adjusts the monitor signal of the true reflected wave power that is not affected by the calculated leakage power of the forward wave so as to output it as a true reflected wave monitor signal; 4. The high frequency amplifier according to claim 3.

5. The leakage power of the traveling wave is is the leakage power of the traveling wave monitor signal output from the second port in a 50 Ω load; 4. The high frequency amplifier according to claim 3.

6. The leakage power of the reflected wave affecting the forward wave monitor signal has the same power as the true reflected wave monitor signal; The phase difference between the forward wave monitor signal and the true reflected wave monitor signal is the sum of a phase difference between the traveling wave monitor signal and the reflected wave monitor signal and a phase difference based on a propagation path length between the first port and the second port.

5. The high frequency amplifier according to claim 4.

7. The processing circuitry includes: outputting the calculated true forward wave power that is not influenced by the reflected wave as a digital signal; 2. The high frequency amplifier according to claim 1.

8. The processing circuitry includes: outputting the calculated true reflected wave power that is not affected by the leakage power of the forward wave as a digital signal; 4. The high frequency amplifier according to claim 3.

9. a coupler for monitoring an RF pulse input to the high frequency amplifier; The processing circuitry includes: detecting a power of the traveling wave monitor signal output by the directional coupler, a power of the reflected wave monitor signal output by the directional coupler, and a phase difference between the traveling wave monitor signal and the reflected wave monitor signal during an on-period of the RF pulse output by the coupler; 2. The high frequency amplifier according to claim 1.

10. A magnetic resonance imaging apparatus comprising a radio frequency amplifier that amplifies an RF signal having a Larmor frequency to be irradiated to a subject and supplies the amplified RF signal to a load including at least an RF coil and the subject, The high frequency amplifier device comprises: A high frequency amplifier; a directional coupler having a first port for outputting a traveling wave from the high frequency amplifier toward a load as a traveling wave monitor signal with a predetermined degree of coupling, and a second port for outputting a reflected wave from the load as a reflected wave monitor signal with a predetermined degree of coupling; a processing circuit that performs at least one of a vector operation and an operation using the cosine law based on the power of the traveling wave monitor signal, the power of the reflected wave monitor signal, and the phase difference between the traveling wave monitor signal and the reflected wave monitor signal, to correct the traveling wave monitor signal that is affected by the reflected wave, and calculates a true traveling wave power that is not affected by the reflected wave. Magnetic resonance imaging device.

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