JP2019107230A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus capable of improving the stability of a directional coupler. A magnetic resonance imaging apparatus includes a first directional coupler 110, a second directional coupler 120, an acquisition unit, and a calculation unit. The first directional coupler and the second directional coupler are connected in series, and the phase of the output impedance of the first directional coupler and the phase of the output impedance of the second directional coupler are different. Thus, the transmission line between the output port of the first directional coupler and the input port of the second directional coupler is set. The acquisition unit acquires outputs from the first coupling port and the second coupling port from each of the first directional coupler and the second directional coupler. The calculation unit uses the output of the first coupling port and the output of the second coupling port to obtain information regarding the power of at least one of the traveling wave and the reflected wave. [Selection diagram] Figure 4

Description

  Embodiments of the present invention relate to a magnetic resonance imaging apparatus.

  The magnetic resonance imaging apparatus applies an RF (Radio Frequency) magnetic field to an object placed in a static magnetic field, and an object is detected based on a magnetic resonance (MR) signal generated from the object by the influence of the RF magnetic field. It is an apparatus for generating an image in a sample.

  In such a magnetic resonance imaging apparatus, for example, the magnitude of an RF magnetic field applied to an object using a directional coupler for the purpose of measurement of SAR (Specific Absorption Rate) which is an index value for safety, etc. Techniques to measure the are known.

Unexamined-Japanese-Patent No. 5-45387 JP, 2014-079573, A JP, 2014-204992, A

  The problem to be solved by the present invention is to improve the stability of the directional coupler.

  A magnetic resonance imaging apparatus according to an embodiment includes an input port for inputting a signal, a first coupling port for extracting a signal corresponding to power of a traveling wave, and a second coupling port for extracting a signal corresponding to power of a reflected wave. And a directional coupler having an output port for outputting a signal between the RF amplifier and the transmission coil, the magnetic resonance imaging apparatus including an acquisition unit and an operation unit. An acquisition unit acquires outputs from the first combined port and the second combined port. The calculation unit performs calculation using the information acquired by the acquisition unit. The magnetic resonance imaging apparatus has a first directional coupler and a second directional coupler as the directional couplers. The first directional coupler and the second directional coupler are connected in series, and a phase of an output impedance of the first directional coupler and an output impedance of the second directional coupler are A transmission line between the output port of the first directional coupler and the input port of the second directional coupler is set such that the phase is different. The acquisition unit acquires an output from the first coupling port and the second coupling port from each of the first directional coupler and the second directional coupler. The calculation unit obtains information on power of at least one of a traveling wave and a reflected wave using the output of the first coupling port and the output of the second coupling port.

FIG. 1 is a view showing a configuration example of a magnetic resonance imaging apparatus according to the first embodiment. FIG. 2 is a view showing a directional coupler according to a comparative example of the first embodiment. FIG. 3 is a diagram showing a change in the degree of coupling of the directional coupler according to the comparative example of the first embodiment. FIG. 4 is a view showing an example of a directional coupler included in the MRI apparatus according to the first embodiment. FIG. 5 is a Smith chart showing the relationship of the output impedance of the first directional coupler and the second directional coupler according to the present embodiment. FIG. 6 is a diagram showing a change in the degree of coupling of the first directional coupler and the second directional coupler according to the present embodiment. FIG. 7 is a diagram showing a change in the degree of coupling of the first directional coupler and the second directional coupler according to the present embodiment. FIG. 8 is a diagram showing an example of a signal processing system that processes traveling wave and reflected wave signals obtained by the first directional coupler and the second directional coupler according to the first embodiment. FIG. 9 is a view showing another example of a signal processing system that processes traveling wave and reflected wave signals obtained by the first directional coupler and the second directional coupler according to the first embodiment. is there. FIG. 10 is a view showing an example of a directional coupler included in the MRI apparatus according to the second embodiment.

  Hereinafter, embodiments of the magnetic resonance imaging apparatus will be described in detail with reference to the drawings.

First Embodiment
FIG. 1 is a view showing a configuration example of a magnetic resonance imaging apparatus according to the first embodiment.

  For example, as shown in FIG. 1, the magnetic resonance imaging (MRI) apparatus 100 according to the present embodiment includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a gradient magnetic field power supply 3, and a whole body (Whole Body: WB). The coil 4, the transmission circuit 5, the local coil 6, the reception circuit 7, the RF shield 8, the gantry 9, the bed 10, the interface 11, the display 12, the storage circuit 13, and the processing circuits 14 to 17.

  The static magnetic field magnet 1 generates a static magnetic field in an imaging space in which the subject S is disposed. Specifically, the static magnetic field magnet 1 is formed in a hollow, substantially cylindrical shape (including one in which the shape of the cross section orthogonal to the central axis of the cylinder is an elliptical shape), and a static magnetic field is generated in the space in the cylinder. generate. For example, the static magnetic field magnet 1 has a substantially cylindrical cooling container, and a magnet such as a superconducting magnet immersed in a coolant (for example, liquid helium or the like) filled in the cooling container. Here, for example, the static magnetic field magnet 1 may generate a static magnetic field using a permanent magnet.

  The gradient magnetic field coil 2 is disposed inside the static magnetic field magnet 1 and applies a gradient magnetic field to an imaging space in which the subject S is disposed. Specifically, the gradient magnetic field coil 2 is formed in a hollow, substantially cylindrical shape (including one in which the shape of the cross section orthogonal to the central axis of the cylinder is an elliptical shape), and the space in the cylinder is orthogonal to each other Gradient magnetic fields are generated along the X, Y, and Z axes. Here, the X-axis, the Y-axis, and the Z-axis constitute an apparatus coordinate system unique to the MRI apparatus 100. For example, the Z axis coincides with the axis of the cylinder of the gradient magnetic field coil 2 and is set along the magnetic flux of the static magnetic field generated by the static magnetic field magnet 1. Further, the X axis is set along the horizontal direction orthogonal to the Z axis, and the Y axis is set along the vertical direction orthogonal to the Z axis.

  The gradient magnetic field power supply 3 generates a gradient magnetic field along the X axis, the Y axis, and the Z axis in the space inside the gradient coil 2 by supplying current to the gradient coil 2. In this manner, the gradient magnetic field power supply 3 generates gradient magnetic fields along the readout direction, phase encoding direction, and slice direction by generating gradient magnetic fields along the X axis, Y axis, and Z axis, respectively. Can. The axes along the lead-out direction, the phase encoding direction, and the slice direction constitute a logical coordinate system for defining a slice area or volume area to be imaged. Hereinafter, the gradient magnetic field along the readout direction is referred to as a readout gradient magnetic field, the gradient magnetic field along the phase encoding direction is referred to as a phase encode gradient magnetic field, and the gradient magnetic field along the slice direction is referred to as a slice gradient magnetic field. .

  These gradient magnetic fields are superimposed on the static magnetic field generated by the static magnetic field magnet 1 and are used to give spatial position information to the MR signal. Specifically, the read-out gradient magnetic field gives positional information in the read-out direction to the MR signal by changing the frequency of the MR signal according to the position in the read-out direction. In addition, the phase encoding gradient magnetic field gives positional information in the phase encoding direction to the MR signal by changing the phase of the MR signal along the phase encoding direction. The slice gradient magnetic field is used to determine the direction, thickness, and number of slice areas when the imaging area is a slice area, and according to the position in the slice direction when the imaging area is a volume area. By changing the phase of the MR signal, position information along the slice direction is given to the MR signal.

  The WB coil 4 is disposed inside the gradient magnetic field coil 2, applies an RF magnetic field to an imaging space in which the subject S is disposed, and receives an MR signal generated from the subject S under the influence of the RF magnetic field. It is an RF coil. Specifically, the WB coil 4 is formed in a hollow, substantially cylindrical shape (including one in which the shape of the cross section orthogonal to the central axis of the cylinder is an elliptical shape), and the RF pulse supplied from the transmission circuit 5 is An RF magnetic field is applied to the space in the cylinder based on the signal. Further, the WB coil 4 receives an MR signal generated from the subject S under the influence of the RF magnetic field, and outputs the received MR signal to the receiving circuit 7. The WB coil 4 is an example of a means for realizing the transmission coil.

  The transmitter circuit 5 outputs an RF wave signal corresponding to the Larmor frequency to the WB coil 4. Specifically, the transmission circuit 5 includes an oscillator, a phase selector, a frequency converter, an amplitude modulator, and an RF amplifier. The oscillator generates an RF wave (high frequency) signal at a resonance frequency (Larmor frequency) specific to a target nucleus placed in a static magnetic field. The phase selector selects the phase of the RF wave signal. The frequency converter converts the frequency of the RF wave signal output from the phase selector. The amplitude modulator generates an RF pulse signal by modulating the amplitude of the RF wave signal output from the frequency converter with, for example, a sinc function waveform. The RF amplifier amplifies the power of the RF pulse signal output from the amplitude modulator and outputs it to the WB coil 4.

  The local coil 6 is an RF coil that receives an MR signal generated from the subject S. Specifically, the local coil 6 is mounted on the subject S disposed inside the WB coil 4 and receives an MR signal generated from the subject S under the influence of the RF magnetic field applied by the WB coil 4, The received MR signal is output to the receiving circuit 7. For example, the local coil 6 is a receiving coil prepared for each part to be imaged, and is a receiving coil for the head, a receiving coil for the neck, a receiving coil for the shoulder, a receiving coil for the chest, and for the abdomen It is a receiving coil, a receiving coil for the lower limbs, a receiving coil for the spine, and the like. The local coil 6 may further have a transmitting function of applying an RF magnetic field. In that case, the local coil 6 is connected to the transmission circuit 5 and applies an RF magnetic field to the subject S based on the RF pulse signal supplied from the transmission circuit 5.

  The receiving circuit 7 generates MR signal data based on the MR signal output from the WB coil 4 or the local coil 6, and outputs the generated MR signal data to the processing circuit 15. For example, the receiving circuit 7 includes a selector, a pre-amplifier, a phase detector, and an A / D (Analog / Digital) converter. The selector selectively inputs the MR signal output from the WB coil 4 or the local coil 6. The pre-amplifier amplifies the power of the MR signal output from the selector. The phase detector detects the phase of the MR signal output from the pre-stage amplifier. The A / D converter generates MR signal data by converting an analog signal output from the phase detector into a digital signal, and outputs the generated MR signal data to the processing circuit 15.

  The RF shield 8 is disposed between the gradient coil 2 and the WB coil 4 and shields the gradient coil 2 from the RF magnetic field generated by the WB coil 4. Specifically, the RF shield 8 is formed in a hollow, substantially cylindrical shape (including one in which the shape of the cross section orthogonal to the central axis of the cylinder is elliptical), and the RF shield 8 is formed on the inner peripheral side of the gradient magnetic field coil 2. In the space, it is arranged to cover the outer peripheral surface of the WB coil 4.

  The gantry 9 accommodates the static magnetic field magnet 1, the gradient magnetic field coil 2, the WB coil 4, and the RF shield 8. Specifically, the gantry 9 has a cylindrically formed hollow bore B, and the static magnetic field magnet 1, the gradient magnetic field coil 2, the WB coil 4 and the RF shield 8 are disposed so as to surround the bore B. In each condition, it accommodates each one. Here, a space inside the bore B of the gantry 9 is an imaging space in which the subject S is disposed when imaging of the subject S is performed.

  Here, an example will be described in which the MRI apparatus 100 has a so-called tunnel type configuration in which the static magnetic field magnet 1, the gradient magnetic field coil 2, and the WB coil 4 are each formed in a substantially cylindrical shape. Is not limited to this. For example, the MRI apparatus 100 has a so-called open configuration in which a pair of static magnetic field magnets, a pair of gradient magnetic field coils, and a pair of RF coils are disposed to face each other across the imaging space in which the subject S is disposed. It may be done.

  The bed 10 includes a top 10 a on which the subject S is placed, and inserts the top 10 a inside the bore B of the gantry 9 when imaging of the subject S is performed. For example, the bed 10 is installed so that the longitudinal direction is parallel to the central axis of the static magnetic field magnet 1.

  The interface 11 receives input operations of various instructions and various information from the operator. Specifically, the interface 11 is connected to the processing circuit 17, converts the input operation received from the operator into an electrical signal, and outputs the signal to the processing circuit 17. For example, the interface 11 includes a trackball for setting imaging conditions and a region of interest (ROI), a switch button, a mouse, a keyboard, a touch pad for performing an input operation by touching an operation surface, and a display screen. And a touch pad integrated with each other, a non-contact input circuit using an optical sensor, an audio input circuit, and the like. In the present specification, the interface 11 is not limited to one having physical operation parts such as a mouse and a keyboard. For example, an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the device and outputs the electrical signal to the control circuit is also included in the example of the interface 11.

  The display 12 displays various information and various images. Specifically, the display 12 is connected to the processing circuit 17, and converts data of various information and various images sent from the processing circuit 17 into an electrical signal for display and outputs it. For example, the display 12 is realized by a liquid crystal monitor, a CRT (Cathode Ray Tube) monitor, a touch panel, or the like.

  The storage circuit 13 stores various data. Specifically, the storage circuit 13 stores MR signal data and image data. For example, the storage circuit 13 is realized by a semiconductor memory device such as a random access memory (RAM), a flash memory, a hard disk, an optical disk, or the like.

  The processing circuit 14 has a bed control function 14a. The bed control function 14 a is connected to the bed 10 and outputs an electric signal for control to the bed 10 to control the operation of the bed 10. For example, the bed control function 14a receives an instruction to move the table 10a in the longitudinal direction, the vertical direction, or the lateral direction from the operator via the interface 11, and moves the table 10a according to the received instruction. The drive mechanism of the top 10 a of 10 is operated.

  The processing circuit 15 has an execution function 15a. The execution function 15a executes various pulse sequences by driving the gradient magnetic field power supply 3, the transmission circuit 5, and the reception circuit 7 based on the sequence execution data output from the processing circuit 17. For example, the execution function 15 a drives the gradient magnetic field power supply 3, the transmission circuit 5, and the reception circuit 7 by transmitting an input signal to each of the gradient magnetic field power supply 3, the transmission circuit 5, and the reception circuit 7.

  Here, the sequence execution data is information defining a pulse sequence indicating a procedure for acquiring MR signal data. Specifically, the sequence execution data includes the timing at which the gradient power supply 3 supplies a current to the gradient coil 2 and the strength of the supplied current, the strength and the supply of the RF pulse signal that the transmission circuit 5 supplies to the WB coil 4 It is information defining timing, detection timing at which the receiving circuit 7 detects an MR signal, and the like.

  Then, the execution function 15a receives MR signal data from the receiving circuit 7 as a result of executing various pulse sequences, and stores the received MR signal data in the storage circuit 13. The set of MR signal data received by the executive function 15a is two-dimensionally or three-dimensionally arranged according to the positional information provided by the readout gradient magnetic field, the phase encoding gradient magnetic field, and the slice gradient magnetic field described above. Thus, the data is stored in the storage circuit 13 as data constituting the k space.

  The processing circuit 16 has an image generation function 16a. The image generation function 16 a generates an image based on the MR signal data stored in the storage circuit 13. Specifically, the image generation function 16a reads the MR signal data stored in the storage circuit 13 by the execution function 15a, and performs post-processing, that is, reconstruction processing such as Fourier transform on the read MR signal data. Generate an image. Further, the image generation function 16 a stores the image data of the generated image in the storage circuit 13.

  The processing circuit 17 has a main control function 17a, an acquisition function 17b, and an arithmetic function 17c. The main control function 17 a performs overall control of the MRI apparatus 100 by controlling each component of the MRI apparatus 100. For example, the main control function 17 a receives an input of imaging conditions from the operator via the interface 11. Then, the main control function 17a generates sequence execution data based on the received imaging condition, and transmits the sequence execution data to the processing circuit 15, thereby executing various pulse sequences. Also, for example, the main control function 17 a reads out image data from the storage circuit 13 and outputs it to the display 12 in response to a request from the operator. The acquisition function 17 b and the calculation function 17 c will be described in detail later.

  Here, the processing functions of the processing circuits 14 to 17 are stored in the storage circuit 13 in the form of a program that can be executed by a computer. Here, each processing circuit is a processor that realizes a function corresponding to each program by reading out each program from the storage circuit 13 and executing it. In other words, each processing circuit in a state where each program is read out has each function shown in each processing circuit of FIG. In the example shown in FIG. 1, although each processing function is realized by a plurality of processors, a single processor constitutes a processing circuit, and the processor executes a program to realize the function. It does not matter as a thing. In addition, the processing function of each processing circuit may be realized by being appropriately distributed or integrated into a single or a plurality of processing circuits. In the example shown in FIG. 1, the single memory circuit 13 is described as storing the program corresponding to each processing function, but a plurality of memory circuits are distributed and arranged, and the processing circuit is an individual memory The configuration may be such that the corresponding program is read out from the circuit.

  The entire configuration of the MRI apparatus 100 according to the present embodiment has been described above. With such a configuration, in the MRI apparatus 100 according to the present embodiment, the RF amplifier of the transmission circuit 5 has a plurality of amplifier modules, and the WB coil 4 has a plurality of substantially independent coil channels. The RF pulse signal can be separately supplied to each coil channel via a plurality of transmission channels provided between the RF amplifier and the WB coil 4. According to such a configuration, for example, when the RF magnetic field is applied to the subject S by controlling the amplitude and phase of the RF pulse signal individually for each coil channel, the influence of the dielectric constant or the like in the subject S Inhomogeneous distribution of the RF magnetic field caused by Such techniques are also referred to as multi-channel transmission or parallel transmission.

  Then, the MRI apparatus 100 according to the present embodiment is for measuring the magnitude of the RF magnetic field applied to the subject S in the transmission circuit 5 for the purpose of measurement of the SAR which is an index value for safety, etc. It has a directional coupler.

  Specifically, the directional coupler is provided between the RF amplifier included in the transmission circuit 5 and the WB coil 4, and an input port for inputting a signal, and a first for extracting a signal corresponding to the power of the traveling wave. And a second coupling port for extracting a signal corresponding to the power of the reflected wave, and an output port for outputting the signal.

  Here, as a comparative example of the present embodiment, an example in which one directional coupler is disposed in each of a plurality of transmission channels included in the MRI apparatus 100 will be temporarily described.

  FIG. 2 is a view showing a directional coupler according to a comparative example of the first embodiment. Moreover, FIG. 3 is a figure which shows the change of the coupling degree of the directional coupler based on the comparative example of 1st Embodiment. Note that FIG. 2 shows the first transmission channel ch1 that is one of the plurality of transmission channels that the MRI apparatus 100 has. Further, the RF amplifier 5a shown in FIG. 2 shows an amplifier module corresponding to the first transmission channel ch1, and the WB coil 4 shown in FIG. 2 has one coil channel corresponding to the first transmission channel ch1. It shows.

  For example, as shown in FIG. 2, the directional coupler 90 receives, via the input port 91, an RF pulse signal output from the RF amplifier 5a (amplifier module) corresponding to the first transmission channel ch1, An RF pulse signal is output to the WB coil 4 (coil channel) corresponding to the first transmission channel ch1 via the output port 92. In addition, the directional coupler 90 extracts a traveling wave signal (FWD) from the signal transmitted in the forward direction through the transmission line and outputs the signal from the first coupling port 93 and transmits the signal in the reverse direction through the transmission line. Signal (RFL) of the reflected wave is output from the second coupled port 94.

  In such a configuration, it is assumed that in the directional coupler 90, the coupling degree [dB] changes according to the change in the phase [degree] of the impedance of the WB coil 4, as shown in FIG. 3, for example. Such a change in the degree of coupling in the directional coupler 90 is considered to be affected by the antinodes and nodes of the standing wave generated by the reflected wave. The degree of coupling is generally determined from the power [dB] of the signal transmitted through the transmission line when the voltage standing wave ratio (VSWR) = 1 and the coupling port of the directional coupler. It is defined as the ratio to the power [dB] of the output signal, but here, the same ratio at VSWRVS1 is also defined as the degree of coupling.

  Here, in general, it is known that the WB coil changes in impedance in various ways as the subject S enters therein, and accordingly, the degree of coupling in the directional coupler also changes in various ways. It is thought that. When the degree of coupling of the directional coupler changes in this manner, the magnitude of the signal output from the coupling port of the directional coupler becomes unstable, and the error in the measurement by the directional coupler is considered to be large.

  On the other hand, for example, in the case of a configuration called a so-called 90 ° hybrid in which RF pulse signals transmitted by one transmission channel are distributed and supplied to a plurality of coil channels of the WB coil 4, reflection is generally Because the wave is configured not to return to the directional coupler, the error in the measurement by the directional coupler is considered to be small.

  However, as in the MRI apparatus 100 according to the present embodiment, in the case of transmitting an RF pulse signal through a plurality of transmission channels, the 90 ° hybrid is not necessary, so that the reflected wave returns to the RF amplifier. become. Here, although the RF amplifier generally has a circulator, the influence of the reflected wave is small, but the directional coupler can not be protected by the circulator because it measures the reflected wave, and therefore the influence of the reflected wave is inevitable. Do not get. On the other hand, there is also a method of using a directional coupler with less measurement error, but such directional couplers are generally expensive and tend to be large in size, and thus are difficult to adopt.

  As such, the MRI apparatus 100 according to the present embodiment is configured to be able to improve the stability of the directional coupler.

  Specifically, the MRI apparatus 100 according to the present embodiment has a first directional coupler and a second directional coupler as directional couplers. Here, the first directional coupler and the second directional coupler are connected in series, and the phase of the output impedance of the first directional coupler and the output impedance of the second directional coupler The transmission line between the output port of the first directional coupler and the input port of the second directional coupler is set so that the phase of. Here, the output impedance is the impedance of the WB coil 4 as viewed from the directional coupler.

  FIG. 4 is a view showing an example of a directional coupler included in the MRI apparatus 100 according to the first embodiment. Note that FIG. 4 illustrates the first transmission channel ch1 which is one of the plurality of transmission channels that the MRI apparatus 100 has. Also, the RF amplifier 5a shown in FIG. 4 shows an amplifier module corresponding to the first transmission channel ch1, and the WB coil 4 shown in FIG. 4 has one coil channel corresponding to the first transmission channel ch1. It shows.

  For example, as shown in FIG. 4, the MRI apparatus 100 according to the present embodiment includes a first directional coupler 110 and a second directional coupler 120. Here, the first directional coupler 110 and the second directional coupler 120 are connected in series and provided between the RF amplifier 5 a included in the transmission circuit 5 and the WB coil 4. Here, although the first transmission channel ch1 will be described as an example, other transmission channels may be similarly divided into the first directional coupler 110 and the second directional coupler for each transmission channel. 120 are provided.

  The first directional coupler 110 receives an RF pulse signal output from the RF amplifier 5a (amplifier module) corresponding to the first transmission channel ch1 via the input port 111, and via the output port 112. , And outputs an RF pulse signal to the second directional coupler 120. In addition, the first directional coupler 110 extracts a traveling wave signal (FWD) from the signal transmitted in the forward direction by the transmission line, outputs the signal from the first coupling port 113, and transmits the signal in the reverse direction by the transmission line. Signal (RFL) is extracted from the signal to be output from the second combined port 114.

  The second directional coupler 120 receives the RF pulse signal output from the first directional coupler 110 through the input port 121, and transmits the RF pulse signal to the first transmission channel ch1 through the output port 122. An RF pulse signal is output to the corresponding WB coil 4 (coil channel). In addition, the second directional coupler 120 extracts a traveling wave signal (FWD) from the signal transmitted in the forward direction through the transmission line, outputs the signal from the first coupling port 123, and transmits the signal in the reverse direction through the transmission line. Signal (RFL) is extracted from the signal to be output from the second coupled port 124.

  Then, for example, the transmission line between the output port 112 of the first directional coupler 110 and the input port 121 of the second directional coupler 120 is transmitted between the RF amplifier 5 a and the WB coil 4. And the phase of the output impedance of the first directional coupler 110 and the phase of the output impedance of the second directional coupler 120 (where λ is the wavelength of the RF wave signal and N is an integer of 2 or more) It is set to shift by a size corresponding to the interval of λ / 2) / N.

  For example, in the example shown in FIG. 4, the phase of the output impedance of the first directional coupler 110 and the phase of the output impedance of the second directional coupler 120 are λ / 4 in the RF wave signal, where N = 2. The transmission line between the output port 112 of the first directional coupler 110 and the input port 121 of the second directional coupler 120 is set so as to be shifted by a size corresponding to the interval of.

  As a specific example, for example, when the center frequency of the MRI is 63.7 MHz, the distance between the output port 112 of the first directional coupler 110 and the input port 121 of the second directional coupler 120 is By connecting with a cable of about 1 m, the phase of the output impedance of the first directional coupler 110 and the phase of the output impedance of the second directional coupler 120 have a size corresponding to the distance of λ / 4. Make it shift.

  FIG. 5 is a Smith chart showing the relationship of the output impedance of the first directional coupler 110 and the second directional coupler 120 according to the present embodiment. 6 and 7 are diagrams showing changes in the degree of coupling of the first directional coupler 110 and the second directional coupler 120 according to the present embodiment. In FIG. 6, changes in the degree of coupling of the traveling waves of the first directional coupler 110 are indicated by solid lines, and changes in the degree of coupling of the traveling waves of the second directional coupler 120 are indicated by broken lines.

  For example, as shown in FIG. 5, the phase of the output impedance of the first directional coupler 110 and the phase of the output impedance of the second directional coupler 120 correspond to the interval of λ / 4 in the RF wave signal. In the case where they are shifted by a certain size, the equal VSWRs shown on the Smith chart (VSWR1 and VSWR2 shown in FIG. 5) have a relationship shifted by 180 °.

  In such a configuration, for example, as shown in FIG. 6, the degree of coupling [dB] of the traveling wave of the first directional coupler 110 and the coupling of the traveling wave of the second directional coupler 120 The degree [dB] changes in such a way that the positive and negative become opposite according to the change in the phase [degree] of the impedance of the WB coil 4. Therefore, the traveling wave signal output from the first coupling port 113 of the first directional coupler 110 and the traveling wave signal output from the first coupling port 123 of the second directional coupler 120. By combining or averaging, for example, as shown in FIG. 7, it is possible to generate a traveling wave signal with small fluctuation. The same applies to the reflected wave signals output from the second coupling port 114 of the first directional coupler 110 and the second coupling port 124 of the second directional coupler 120.

  And according to such a configuration, averaging or combining the signal output from the coupling port of the first directional coupler 110 and the signal output from the coupling port of the second directional coupler 120 Thus, stable traveling wave and reflected wave signals with small fluctuation can be obtained. Therefore, according to the present embodiment, the stability of the directional coupler can be improved.

  Here, the phase of the output impedance of the first directional coupler 110 and the phase of the output impedance of the second directional coupler 120 have a size corresponding to an interval of λ / 4 in the RF wave signal. Although the case of shifting (that is, shifting the phase by 180 °) has been described, the amount of shifting the phase is not limited thereto, and may be larger than zero. That is, if the phase of the output impedance of the first directional coupler 110 and the phase of the output impedance of the second directional coupler 120 are even slightly deviated, the signals output from the respective ones are averaged or synthesized. By this, it is possible to obtain traveling wave and reflected wave signals with less fluctuation as compared with the case of using one directional coupler as in the comparative example shown in FIG.

  Also, although an example in which two directional couplers are arranged in one transmission channel connecting between the RF amplifier and the WB coil 4 has been described here, directional coupling arranged in one transmission channel is described. The number of vessels is not limited to two. That is, three or more directional couplers may be connected in series to one transmission channel. In that case, for example, assuming that the number of directional couplers arranged in one transmission channel is N, the phase of the output impedance is equivalent to the interval of (λ / 2) / N between the directional couplers. Transmission lines between the directional couplers are set so as to be displaced by the magnitude.

  Furthermore, although an example in which directional couplers are provided for each of the plurality of transmission channels included in the MRI apparatus 100 has been described here, the embodiment is not limited thereto, and directional couplers may be used for only some of the transmission channels. May be provided.

  Moreover, although the example in case the MRI apparatus 100 has a several transmission channel was demonstrated here, embodiment is not restricted to this. For example, even when the MRI apparatus 100 has only one transmission channel, similar effects can be obtained by providing at least two directional couplers in the transmission channel as in the above-described example. Thereby, for example, even in a configuration where the WB coil 4 has a single coil channel and the RF pulse signal is transmitted to the coil channel by a single transmission channel, the directional coupler It will be possible to improve the stability.

  Then, in the present embodiment, the MRI apparatus 100 travels using the signals of stable traveling waves and reflected waves with small fluctuations obtained by the first directional coupler 110 and the second directional coupler 120 described above. It further has a configuration for obtaining information on waves and reflected waves.

  First, the MRI apparatus 100 detects a plurality of analog signals obtained by detecting traveling wave signals output from the first coupling port of each of the first directional coupler 110 and the second directional coupler 120. After combining, the combined analog signal is converted to a digital signal. Further, the MRI apparatus 100 detects a plurality of analog signals obtained by detecting the reflected wave signals output from the second coupling port of each of the first directional coupler 110 and the second directional coupler 120. After combining, the combined analog signal is converted to a digital signal.

  FIG. 8 is a view showing an example of a signal processing system that processes signals of traveling waves and reflected waves obtained by the first directional coupler 110 and the second directional coupler 120 according to the first embodiment. is there.

  For example, as shown in FIG. 8, the MRI apparatus 100 according to the present embodiment includes a first detector 131, a second detector 132, a first signal processing circuit 141, and a first A / D. And a converter 151. The MRI apparatus 100 further includes a third detector 133, a fourth detector 134, a second signal processing circuit 142, and a second A / D converter 152.

  The first detector 131 detects an analog signal from the signal of the traveling wave output from the first coupling port 113 of the first directional coupler 110. The second detector 132 detects an analog signal from the traveling wave signal output from the first coupling port 123 of the second directional coupler 120. The first signal processing circuit 141 combines the analog signal output from the first detector 131 and the analog signal output from the second detector 132. The first A / D converter 151 converts an analog signal output from the first signal processing circuit 141 into a digital signal.

  The third detector 133 detects the analog signal of the reflected wave from the signal output from the second coupling port 114 of the first directional coupler 110. The fourth detector 134 detects the analog signal of the reflected wave from the signal output from the second coupling port 124 of the second directional coupler 120. The second signal processing circuit 142 combines the analog signal output from the third detector 133 and the analog signal output from the fourth detector 134. The second A / D converter 152 converts an analog signal output from the second signal processing circuit 142 into a digital signal.

  According to such a configuration, for each of the traveling wave signal and the reflected wave signal, after combining the plurality of signals output from the first directional coupler 110 and the second directional coupler 120, A / A Since D conversion is performed, the number of A / D converters can be reduced as compared with the case where the signals output from each directional coupler are individually A / D converted and then averaged.

  Here, although the example in the case of performing A / D conversion after combining a signal about each of a signal of a traveling wave and a signal of a reflected wave was explained, the order of processing of a signal is not restricted to this. For example, for each of the traveling wave signal and the reflected wave signal, the signals may be averaged after performing A / D conversion.

  FIG. 9 shows another example of a signal processing system that processes traveling wave and reflected wave signals obtained by the first directional coupler 110 and the second directional coupler 120 according to the first embodiment. FIG.

  For example, as shown in FIG. 9, in this example, the MRI apparatus 100 includes a first detector 231, a second detector 232, a first A / D converter 251, and a second A / D. A D converter 252 and a first signal processing circuit 241 are provided. In addition, the MRI apparatus 100 includes a third detector 233, a fourth detector 234, a third A / D converter 253, a fourth A / D converter 254, and a second signal processing. And a circuit 242.

  The first detector 231 detects an analog signal from the traveling wave signal output from the first coupling port 113 of the first directional coupler 110. The second detector 232 detects an analog signal from the traveling wave signal output from the first coupling port 123 of the second directional coupler 120. The first A / D converter 251 converts an analog signal output from the first detector 231 into a digital signal. The second A / D converter 252 converts the analog signal output from the second detector 232 into a digital signal. The first signal processing circuit 241 calculates an average value of the digital signal output from the first A / D converter 251 and the digital signal output from the second A / D converter 252.

  The third detector 233 detects an analog signal from the traveling wave signal output from the second coupling port 114 of the first directional coupler 110. The fourth detector 234 detects an analog signal from the traveling wave signal output from the second coupling port 124 of the second directional coupler 120. The third A / D converter 253 converts an analog signal output from the third detector 233 into a digital signal. The fourth A / D converter 254 converts the analog signal output from the fourth detector 234 into a digital signal. The second signal processing circuit 242 calculates an average value of the digital signal output from the third A / D converter 253 and the digital signal output from the fourth A / D converter 254.

  In the present embodiment, the acquisition function 17b of the processing circuit 17 shown in FIG. 1 corresponds to the first coupling port and the second coupling port of the first directional coupler 110 and the second directional coupler 120, respectively. Get the output from the bonded port. Further, the arithmetic function 17 c of the processing circuit 17 shown in FIG. 1 performs the arithmetic operation using the information acquired by the acquisition function 17 b. The acquisition function 17 b is an example of realization means of the acquisition unit, and the arithmetic function 17 c is an example of realization means of the arithmetic unit.

  Specifically, the acquisition function 17 b outputs the first coupling of the second directional coupler 120 to the output from the first coupling port 113 and the second coupling port 114 of the first directional coupler 110. The output from the port 123 and the second combined port 124 is obtained.

  For example, the acquiring function 17b acquires respective signals of the traveling wave and the reflected wave after being converted into digital signals by the signal processing system shown in FIG. Specifically, the acquisition function 17 b outputs the signal of the traveling wave output from the first A / D converter 151 shown in FIG. 8 and the reflected wave output from the second A / D converter 152. Get the signal of

  Alternatively, for example, the acquisition function 17b acquires respective signals of the traveling wave and the reflected wave after being averaged by the signal processing system illustrated in FIG. Specifically, the acquisition function 17b acquires the traveling wave signal output from the first signal processing circuit 241 shown in FIG. 9 and the reflected wave signal output from the second signal processing circuit 242. Do.

  The arithmetic function 17 c then outputs the outputs from the first coupling port 113 and the second coupling port 114 of the first directional coupler 110 acquired by the acquiring function 17 b and the second directional coupler 120. Information on the power of at least one of the traveling wave and the reflected wave is obtained using the first coupled port 123 and the output from the second coupled port 124.

  Specifically, the arithmetic function 17 c obtains information on power of at least one of the traveling wave and the reflected wave using the signals of the traveling wave and the reflected wave acquired by the acquiring function 17 b.

  First, the computing function 17 c outputs the first coupling port 113 and the second coupling port 114 of the first directional coupler 110, the first coupling port 123 of the second directional coupler 120, and the like. The output of the second coupled port 124 is used to measure the SAR.

  Specifically, the arithmetic function 17 c measures the SAR by a known measurement method using the traveling wave signal and the reflected wave signal acquired by the acquisition function 17 b.

  According to such a configuration, by using the stable traveling wave and reflected wave signals with small fluctuation obtained by the first directional coupler 110 and the second directional coupler 120, the SAR can be made with high accuracy. It will be able to measure.

  Here, the SAR measured by the calculation function 17 c is used, for example, as an index value at the time of determining whether or not the imaging of the subject S can be performed by the main control function 17 a for safety. For example, the main control function 17a compares the SAR measured by the arithmetic function 17c with a predetermined reference value before imaging is started, and performs imaging when the SAR is below the reference value. Is determined to be possible.

  In such a case, generally, the reference value used in the determination is set in anticipation of an error in measurement by the directional coupler since the impedance of the WB coil 4 changes variously as described above. It is often set lower by the margin. On the other hand, in the present embodiment, since the SAR is measured with high accuracy, the margin can be reduced to increase the reference value, and the output performance of the WB coil 4 can be more effectively utilized.

  Also, the computing function 17 c outputs the first coupling port 113 and the second coupling port 114 of the first directional coupler 110, the first coupling port 123 of the second directional coupler 120, and the like. The phase from the impedance of the WB coil 4 is measured using the output from the second coupling port 124.

  Specifically, the arithmetic function 17 c measures the phase of the impedance of the WB coil 4 using the traveling wave signal and the reflected wave signal acquired by the acquisition function 17 b.

  In this case, for example, a table is prepared by measuring in advance the relationship between the phase value of the impedance of the WB coil 4 and the degree of coupling of each directional coupler, and storage is performed when operation of the MRI apparatus 100 is started. It is stored in the circuit 13. Then, the arithmetic function 17 c refers to the table stored in the storage circuit 13, and the phase value corresponding to the degree of coupling obtained from the signal of the traveling wave acquired by the acquiring function 17 b and the degree of coupling obtained from the signal of the reflected wave The phase of the impedance of the WB coil 4 is measured.

  For example, as shown in FIG. 6, when the number of directional couplers arranged in one transmission channel is two, the degree of coupling may be the same, and in such a case, The phase value will not be determined uniquely. For example, in the example shown in FIG. 6, the degrees of coupling of the two directional couplers are the same at phases of 20 ° and 200 °. In such a case, by setting the number of directional couplers arranged in one transmission channel to three or more as described above, there is no case where the coupling degrees of all directional couplers match. It becomes possible to uniquely determine the phase value.

  Here, the phase of the impedance of the WB coil 4 measured by the calculation function 17 c is used, for example, to control the transmission efficiency of the WB coil 4 by the main control function 17 a. For example, the main control function 17a is an RF pulse signal supplied to the WB coil 4 at the time of imaging so that the transmission efficiency of the WB coil 4 can be enhanced based on the phase of the impedance of the WB coil 4 measured by the arithmetic function 17c. Control the size of the

  According to such a configuration, transmission of the WB coil 4 can be performed by using the stable traveling wave and reflected wave signals with small fluctuation obtained by the first directional coupler 110 and the second directional coupler 120. You will be able to better control the efficiency.

Second Embodiment
In the first embodiment described above, an example in which the phase of the output impedance is shifted between two directional couplers arranged in one transmission channel has been described, but the embodiment is not limited to this. . For example, the output impedance may be out of phase between directional couplers arranged in different transmission channels. Hereinafter, an example of such a case will be described as a second embodiment. In the second embodiment, differences from the first embodiment will be mainly described, and components having the same roles as the components described in the first embodiment are denoted by the same reference numerals. As a detailed explanation is omitted.

  Specifically, in the present embodiment, the first directional coupler is arranged in the first transmission channel of the plurality of transmission channels, and the second directional coupler is arranged in the plurality of transmission channels. And a second transmission channel different from the first transmission channel. And in this embodiment, the output port of the first directional coupler and the transmission are transmitted so that the phase of the output impedance of the first directional coupler and the phase of the output impedance of the second directional coupler are different. A transmission line between the coil and the transmission line between the output port of the second directional coupler and the transmission coil is set.

  FIG. 10 is a diagram showing an example of a directional coupler included in the MRI apparatus 100 according to the second embodiment. Note that FIG. 10 shows two transmission channels ch1 and ch2 among the plurality of transmission channels that the MRI apparatus 100 has. Further, two RF amplifiers 5a shown in FIG. 10 respectively indicate amplifier modules corresponding to one transmission channel, and two WB coils 4 shown in FIG. 10 respectively correspond to one transmission channel. Shows two coil channels.

  For example, as shown in FIG. 10, the MRI apparatus 100 according to the present embodiment has a first directional coupler 210 and a second directional coupler 220. Here, the first directional coupler 210 is disposed in the first transmission channel ch1 of the plurality of transmission channels, and the second directional coupler 220 is configured in the first of the plurality of transmission channels. It is arranged in a second transmission channel ch2 different from the transmission channel ch1. Although two transmission channels ch1 and ch2 will be described as an example here, directional couplers are similarly provided for the other transmission channels.

  The first directional coupler 210 receives an RF pulse signal output from the RF amplifier 5 a (amplifier module) corresponding to the first transmission channel ch 1 via the input port 211, and via the output port 212. The RF pulse signal is output to the WB coil 4 (coil channel) corresponding to the first transmission channel ch1. In addition, the first directional coupler 210 extracts a traveling wave signal (FWD) from the signal transmitted in the forward direction by the transmission line and outputs the signal from the first coupling port 213 and transmits the signal in the reverse direction by the transmission line. Signal (RFL) is extracted from the signal to be output from the second coupled port 214.

  The second directional coupler 220 receives an RF pulse signal output from the RF amplifier 5a (amplifier module) corresponding to the second transmission channel ch2 via the input port 221, and via the output port 222. The RF pulse signal is output to the WB coil 4 (coil channel) corresponding to the second transmission channel ch2. In addition, the second directional coupler 220 extracts the traveling wave signal (FWD) from the signal transmitted in the forward direction by the transmission line and outputs it from the first coupling port 223, and transmits the signal in the reverse direction by the transmission line. Signal (RFL) is extracted from the signal to be output from the second coupled port 224.

  Then, for example, a transmission line between the output port 212 of the first directional coupler 210 and the WB coil 4 (coil channel) corresponding to the first transmission channel ch1, and the second directional coupler 220. The transmission line between the output port 222 and the WB coil 4 (coil channel) corresponding to the second transmission channel ch2 has the wavelength of the RF wave signal transmitted between the RF amplifier 5a and the WB coil 4 as λ. The phase of the output impedance of the first directional coupler 210 and the phase of the output impedance of the second directional coupler 220 are (λ / 2) / N, where N is an integer of 2 or more. It is set to shift by the size corresponding to.

  For example, in the example shown in FIG. 10, assuming that N = 2, the phase of the output impedance of the first directional coupler 210 and the phase of the output impedance of the second directional coupler 220 are λ / 4 in the RF wave signal. And a transmission line between the output port 212 of the first directional coupler 210 and the WB coil 4 (coil channel) corresponding to the first transmission channel ch1, and A transmission line between the output port 222 of the second directional coupler 220 and the WB coil 4 (coil channel) corresponding to the second transmission channel ch2 is set.

  For example, if the length of the transmission line between the output port 212 of the first directional coupler 210 and the WB coil 4 (coil channel) corresponding to the first transmission channel ch1 is l, the second The length of the transmission line between the output port 222 of the directional coupler 220 and the WB coil 4 (coil channel) corresponding to the second transmission channel ch2 is set to be l + λ / 4.

  According to such a configuration, as in the first embodiment, the signal output from the coupling port of the first directional coupler 210 and the signal output from the coupling port of the second directional coupler 220 By combining or averaging, it becomes possible to obtain stable traveling wave and reflected wave signals with less fluctuation. Therefore, the stability of the directional coupler can be improved also in this embodiment.

  Here, although the example in the case of shifting the phase of the output impedance between two directional couplers arranged in the first transmission channel ch1 and the second transmission channel ch2 has been described, the embodiment is not limited thereto. The output impedance may be shifted between two or more directional couplers without limitation. In that case, for example, let N be the number of directional couplers targeted for shifting the phase of the output impedance, and the phase of the output impedance is equivalent to the interval of (λ / 2) / N between each directional coupler. The transmission line between each directional coupler and the WB coil 4 (coil channel) is set so as to be shifted by the desired size.

  Furthermore, although an example in which directional couplers are provided for each of the plurality of transmission channels included in the MRI apparatus 100 has been described here, the embodiment is not limited thereto, and directional couplers may be used for only some of the transmission channels. May be provided.

  Also in the present embodiment, as in the first embodiment, the first directional coupler is obtained by the signal processing system shown in FIG. 8 or 9 and the acquisition function 17 b and the arithmetic function 17 c of the processing circuit 17. It is possible to determine the information on the traveling wave and the reflected wave using the small traveling stable wave and the reflected wave signal obtained by the 210 and the second directional coupler 220.

  In each of the above-described embodiments, an example in which the directional coupler is provided in the transmission circuit 5 has been described, but the embodiment is not limited thereto. For example, the directional coupler may be disposed outside the transmission circuit 5 as long as it is between the RF amplifier and the WB coil 4.

  In each of the above-described embodiments, the acquisition unit in this specification is realized by the acquisition function 17b of the processing circuit 17, and the arithmetic unit is realized by the arithmetic function 17c of the processing circuit 17. Is not limited to this. For example, the acquiring unit and the arithmetic unit in the present specification may be realized by hardware alone or a combination of hardware and software, in addition to being realized by the acquiring function 17 b and the arithmetic function 17 c described in the embodiment, respectively. May be realized.

  Further, the term “processor” used in the above description refers to, for example, a central processing unit (CPU), a graphics processing unit (GPU), or an application specific integrated circuit (ASIC), a programmable logic device It means circuits such as (for example, Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (CPLD), and Field Programmable Gate Array (FPGA)). Note that instead of storing the program in the memory circuit, the program may be directly incorporated in the circuit of the processor. In this case, the processor implements the function by reading and executing a program embedded in the circuit. In addition, each processor of the present embodiment is not limited to the case where it is configured as a single circuit for each processor, and a plurality of independent circuits may be combined to be configured as one processor to realize its function. Good. Furthermore, a plurality of components in FIG. 1 may be integrated into one processor to realize its function.

  Here, the program executed by the processor is provided, for example, by being incorporated in advance in a ROM (Read Only Memory), a storage circuit, or the like. This program is a file in a form installable or executable in these devices, and a computer such as a CD (Compact Disk) -ROM, a FD (Flexible Disk), a CD-R (Recordable), a DVD (Digital Versatile Disk), etc. And may be provided by being recorded on a readable storage medium. In addition, this program may be stored on a computer connected to a network such as the Internet, and may be provided or distributed by being downloaded via the network. For example, this program is configured by a module including each of the functional units described above. As actual hardware, each module is loaded onto the main storage device and generated on the main storage device by the CPU reading and executing a program from a storage medium such as a ROM.

  According to at least one embodiment described above, the stability of the directional coupler can be improved.

  While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These embodiments can be implemented in other various forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and the equivalents thereof as well as included in the scope and the gist of the invention.

100 Magnetic Resonance Imaging (MRI) System 17 Processing Circuit 17b Acquisition Function 17c Arithmetic Function 110, 210 First Directional Coupler 120, 220 Second Directional Coupler

Claims (7)

An input port for inputting the signal, a first coupled port for extracting the signal corresponding to the power of the traveling wave, a second coupled port for extracting the signal corresponding to the power of the reflected wave, and an output port for outputting the signal What is claimed is: 1. A magnetic resonance imaging apparatus comprising a directional coupler provided between an RF amplifier and a transmitter coil, wherein
An acquisition unit for acquiring an output from the first combined port and the second combined port;
And an operation unit that performs operation using the information acquired by the acquisition unit.
The directional coupler includes a first directional coupler and a second directional coupler,
The first directional coupler and the second directional coupler are connected in series,
An output port of the first directional coupler and the second direction such that a phase of an output impedance of the first directional coupler and a phase of an output impedance of the second directional coupler are different. Transmission line to the input port of the
The acquisition unit acquires an output from the first coupling port and the second coupling port from each of the first directional coupler and the second directional coupler.
The operation unit obtains information on power of at least one of a traveling wave and a reflected wave using the output of the first coupling port and the output of the second coupling port.
Magnetic resonance imaging system. An input port for inputting the signal, a first coupled port for extracting the signal corresponding to the power of the traveling wave, a second coupled port for extracting the signal corresponding to the power of the reflected wave, and an output port for outputting the signal What is claimed is: 1. A magnetic resonance imaging apparatus comprising a directional coupler provided between an RF amplifier and a transmitter coil, wherein
An acquisition unit for acquiring an output from the first combined port and the second combined port;
And an operation unit that performs operation using the information acquired by the acquisition unit.
The directional coupler includes a first directional coupler and a second directional coupler,
A plurality of transmission channels are provided between the RF amplifier and the transmission coil,
The first directional coupler is disposed on a first transmission channel of the plurality of transmission channels, and the second directional coupler is configured to transmit the first transmission of the plurality of transmission channels. The second transmission channel different from the channel is
The output port of the first directional coupler and the transmission coil are connected so that the phase of the output impedance of the first directional coupler and the phase of the output impedance of the second directional coupler are different. And a transmission line between an output port of the second directional coupler and the transmission coil,
The acquisition unit acquires an output from the first coupling port and the second coupling port from each of the first directional coupler and the second directional coupler.
The operation unit obtains information on power of at least one of a traveling wave and a reflected wave using the output of the first coupling port and the output of the second coupling port.
Magnetic resonance imaging system. When the wavelength of the RF wave signal transmitted between the RF amplifier and the transmission coil is λ, and the integer of 2 or more is N, the transmission line has the output impedance of the first directional coupler. It is set such that the phase and the phase of the output impedance of the second directional coupler are deviated by a size corresponding to the interval of (λ / 2) / N,
The magnetic resonance imaging apparatus according to claim 1. Synthesized after synthesizing a plurality of analog signals obtained by detecting traveling wave signals output from the first coupling port of each of the first directional coupler and the second directional coupler Convert analog signals to digital signals,
Synthesized after synthesizing a plurality of analog signals obtained by detecting signals of reflected waves output from second coupling ports of the first directional coupler and the second directional coupler. Convert the signal to a digital signal,
The acquisition unit acquires respective signals of the traveling wave and the reflected wave after being converted into digital signals.
The magnetic resonance imaging apparatus according to any one of claims 1 to 3. Each analog signal obtained by detecting the traveling wave signal output from the first coupling port of each of the first directional coupler and the second directional coupler is converted into a digital signal, and then converted. Averaged multiple digital signals, and
Each analog signal obtained by detecting the signal of the reflected wave output from the second coupling port of each of the first directional coupler and the second directional coupler is converted into a digital signal, and then converted. Averaged multiple digital signals, and
The acquisition unit acquires respective signals of the traveling wave and the reflected wave after being averaged.
The magnetic resonance imaging apparatus according to any one of claims 1 to 3. The arithmetic unit measures SAR using the output of the first coupled port and the output of the second coupled port.
The magnetic resonance imaging apparatus according to any one of claims 1 to 5. The operation unit measures the phase of the impedance of the transmission coil using the output of the first coupling port and the output of the second coupling port.
The magnetic resonance imaging apparatus according to any one of claims 1 to 6.

Images