Magnetic Resonance Imaging System

Abstract

Precisely irradiating with broadband RF pulses as designed. [Solution] The waveform output unit outputs a control waveform of a broadband RF pulse. The adjustment unit adjusts the phase and / or amplitude of the control waveform. The signal generation unit generates a control signal for the adjusted control waveform. The selection unit has two or more frequency selection circuits corresponding to two or more passbands. The two or more frequency selection circuits output two or more frequency component signals corresponding to two or more passbands from the control signal. The coil unit has an RF coil group including two or more RF coils having two or more different resonant frequencies. The RF coil group receives two or more frequency component signals and irradiates a broadband RF pulse. The adjustment unit adjusts the phase and / or amplitude of the control waveform based on the first circuit characteristics of the RF coil group and the second circuit characteristics of the frequency selection circuit.

Description

TECHNICAL FIELD

[0001] Embodiments disclosed in the present specification and the drawings relate to a magnetic resonance imaging apparatus. BACKGROUND ART

[0002] A static magnetic field magnet is designed, for example, such that the radius of the FOV (Field Of View) is 50 cm. For this reason, the uniformity of the magnetic field is high inside the 50 cm radius, but the uniformity of the magnetic field sharply decreases outside the 50 cm radius. In order to include the area outside the 50 cm radius in the FOV, it is necessary to perform excitation with RF pulses even in a region with a non-uniform magnetic field. In order to excite a region with a non-uniform magnetic field, it is desirable to accurately apply an RF pulse capable of sweeping a wide range of frequencies as designed. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0003] PATENT DOCUMENT 1 Japanese Unexamined Patent Publication No. 2022-177552 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] One of the problems to be solved by the embodiments disclosed in the present specification and the drawings is to accurately apply a broadband RF pulse as designed. However, the problems to be solved by the embodiments disclosed in the present specification and the drawings are not limited to the above problem. Problems corresponding to the respective effects of the respective configurations shown in the embodiments described later can also be positioned as other problems. MEANS FOR SOLVING THE PROBLEMS

[0005] The magnetic resonance imaging apparatus according to the embodiment includes a waveform output unit, an adjustment unit, a signal generation unit, a selection unit, and a coil unit. The waveform output unit outputs a control waveform of a broadband RF pulse. The adjustment unit adjusts the phase and / or amplitude of the control waveform and outputs an adjusted control waveform. The signal generation unit generates a control signal for the adjusted control waveform. The selection unit is a selection unit having two or more frequency selection circuits corresponding to two or more passbands, and the two or more frequency selection circuits output two or more frequency component signals corresponding to the two or more passbands from the control signal. The coil unit is a coil unit having a single RF coil having two or more different resonant frequencies or a group of RF coils including two or more RF coils having two or more different resonant frequencies, and the single RF coil or the group of RF coils receives the two or more frequency component signals and irradiates the broadband RF pulse. The adjustment unit adjusts the phase and / or amplitude of the control waveform based on a first circuit characteristic of the single RF coil or the group of RF coils and a second circuit characteristic of the two or more frequency selection circuits. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 shows an example of the configuration of a magnetic resonance imaging apparatus according to this embodiment. [Figure 2] Figure 2 shows an example of the static magnetic field distribution in a bore. [Figure 3] Figure 3 shows an example of the frequency characteristics of an RF coil whose resonant frequency ω0 is tuned to a single frequency. [Figure 4] Figure 4 shows an example of the configuration of the RF pulse transmission system according to this embodiment. [Figure 5] Figure 5 shows a specific configuration example and processing example of the RF pulse transmission system according to this embodiment. [Figure 6] Figure 6 schematically illustrates the adjustment process for the control waveform. [Figure 7] Figure 7 shows an example of the first circuit characteristics of an RF coil. [Figure 8]Figure 8 shows an example of the second circuit characteristics of a high-pass filter and a low-pass filter. [Figure 9] Figure 9 shows an example of circuit characteristic determination and measurement processing using a sequence control circuit. [Figure 10] Figure 10 schematically shows the process for determining the circuit characteristics when there are two RF coils and two frequency filters. [Figure 11] Figure 11 schematically shows the process for determining the circuit characteristics when there are three RF coils and three frequency filters. [Modes for carrying out the invention]

[0007] The magnetic resonance imaging apparatus according to this embodiment will be described in detail below with reference to the drawings.

[0008] Figure 1 shows an example of the configuration of a magnetic resonance imaging apparatus 1 according to this embodiment. As shown in Figure 1, the magnetic resonance imaging apparatus 1 includes a frame 11, a bed 13, a gradient magnetic field power supply 21, a transmitting circuit 23, a receiving circuit 25, a bed drive device 27, a sequence control circuit 29, and a host computer 50.

[0009] The mounting base 11 includes a static magnetic field magnet 41 and a gradient magnetic field coil 43. The static magnetic field magnet 41 and the gradient magnetic field coil 43 are housed in a cylindrical mounting base housing. A cylindrical hollow space (hereinafter referred to as a bore) is formed in the mounting base housing. A transmitting coil 45 and a receiving coil 47 are arranged inside the bore of the mounting base 11.

[0010] The static magnetic field magnet 41 has a hollow, approximately cylindrical shape and generates a static magnetic field inside the approximately cylindrical interior. Here, the central axis of the static magnetic field magnet 41 is defined as the Z-axis, the axis perpendicular to the Z-axis is defined as the Y-axis, and the axis perpendicular to the Z-axis horizontally is defined as the X-axis. The X-axis, Y-axis, and Z-axis constitute an orthogonal three-dimensional coordinate system.

[0011] The gradient magnetic field coil 43 is mounted inside the static magnetic field magnet 41 and is a hollow, substantially cylindrical coil unit. The gradient magnetic field coil 43 generates a gradient magnetic field by receiving current from the gradient magnetic field power supply 21. More specifically, the gradient magnetic field coil 43 has three coils corresponding to the mutually orthogonal X, Y, and Z axes. These three coils form a gradient magnetic field in which the magnetic field strength changes along each of the X, Y, and Z axes. The gradient magnetic fields along each of the X, Y, and Z axes are combined to form mutually orthogonal slice-selective gradient magnetic field Gs, phase-encoded gradient magnetic field Gp, and frequency-encoded gradient magnetic field Gr in the desired direction. The slice-selective gradient magnetic field Gs is used to arbitrarily determine the imaging cross-section (slice). The phase-encoded gradient magnetic field Gp is ​​used to change the phase of the magnetic resonance signal (hereinafter referred to as the MR signal) according to the spatial position. The frequency-encoded gradient magnetic field Gr is used to change the frequency of the MR signal according to the spatial position. In the following explanation, the gradient direction of the slice selection gradient magnetic field Gs is assumed to be the Z-axis, the gradient direction of the phase encoding gradient magnetic field Gp is ​​assumed to be the Y-axis, and the gradient direction of the frequency encoding gradient magnetic field Gr is assumed to be the X-axis.

[0012] The gradient power supply 21 supplies current to the gradient coil 43 according to the sequence control signal from the sequence control circuit 29. By supplying current to the gradient coil 43, the gradient power supply 21 generates gradient magnetic fields along the X, Y, and Z axes. These gradient magnetic fields are superimposed on the static magnetic field formed by the static magnetic field magnet 41 and applied to the subject P.

[0013] The transmitting coil 45 is, for example, positioned inside the gradient magnetic field coil 43 and receives current from the transmitting circuit 23 to generate high-frequency pulses (hereinafter referred to as RF pulses).

[0014] The transmission circuit 23 supplies a current to the transmission coil 45 in order to irradiate the subject P with RF pulses for exciting target protons present in the subject P via the transmission coil 45. The RF pulses oscillate at a resonance frequency specific to the target protons to excite the target protons. MR signals are generated from the excited target protons and detected by the reception coil 47. The transmission coil 45 is, for example, a whole-body coil (WB coil). The whole-body coil may be used as a transmit-receive coil.

[0015] The reception coil 47 receives MR signals emitted from target protons present in the subject P under the action of RF magnetic field pulses. The reception coil 47 has a plurality of reception coil elements capable of receiving MR signals. The received MR signals are supplied to the reception circuit 25 via wire or wirelessly. Although not illustrated in FIG. 1, the reception coil 47 has a plurality of reception channels mounted in parallel. Each reception channel includes a reception coil element that receives MR signals, an amplifier that amplifies the MR signals, and the like. MR signals are output for each reception channel. The total number of reception channels and the total number of reception coil elements may be the same, or the total number of reception channels may be larger or smaller than the total number of reception coil elements.

[0016] The reception circuit 25 receives MR signals generated from excited target protons via the reception coil 47. The reception circuit 25 performs signal processing on the received MR signals to generate digital MR signals. The digital MR signals can be represented in k-space defined by spatial frequencies. Therefore, hereinafter, the digital MR signals will be referred to as k-space data. The k-space data is a type of raw data used for image reconstruction. The k-space data is supplied to the host computer 50 via wire or wirelessly.

[0017] Note that the above-described transmission coil 45 and reception coil 47 are merely examples. Instead of the transmission coil 45 and the reception coil 47, a transmit-receive coil having both a transmission function and a reception function may be used. Further, the transmission coil 45, the reception coil 47, and the transmit-receive coil may be used in combination.

[0018] A couch 13 is installed adjacent to the gantry 11. The couch 13 has a top plate 131 and a base 133. A subject P is placed on the top plate 131. The base 133 supports the top plate 131 so as to be slidable along each of the X-axis, Y-axis, and Z-axis. A couch driving device 27 is housed in the base 133. The couch driving device 27 moves the top plate 131 under the control from a sequence control circuit 29. The couch driving device 27 may include any motor such as a servo motor or a stepping motor, for example.

[0019] The sequence control circuit 29 has, as hardware resources, a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The sequence control circuit 29 synchronously controls a gradient magnetic field power supply 21, a transmission circuit 23, and a reception circuit 25 based on the imaging conditions set by a processing circuit 51, executes MR imaging on the subject P in accordance with a pulse sequence corresponding to the imaging conditions, and collects k-space data related to the subject P.

[0020] As shown in FIG. 1, the host computer 50 is a computer having a processing circuit 51, a memory 52, a display 53, an input interface 54, and a communication interface 55.

[0021] The processing circuit 51 has a processor such as a CPU as a hardware resource. The processing circuit 51 functions as the core of the magnetic resonance imaging apparatus 1. For example, the processing circuit 51 automatically or manually sets imaging conditions. Further, the processing circuit 51 reconstructs an MR image related to the subject P based on the k-space data collected via the reception circuit 25. The processing circuit 51 can also perform various processes such as rendering processing, image recognition, and image analysis on the MR image.

[0022] Memory 52 is a storage device such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or integrated circuit storage device that stores various types of information. Alternatively, memory 52 may be a drive device that reads and writes various types of information to and from portable storage media such as a CD-ROM drive, DVD drive, or flash memory. For example, memory 52 stores imaging conditions, k-space data, MR images, control programs, and the like.

[0023] The display 53 displays various information. For example, the display 53 displays MR images, imaging condition setting screens, etc. As the display 53, for example, a CRT display, liquid crystal display, organic EL display, LED display, plasma display, or any other display known in the art can be used as appropriate.

[0024] The input interface 54 includes an input device that receives various commands from the operator. Possible input devices include keyboards, mice, various switches, touchscreens, and touchpads. However, the input device is not limited to those with physical operating components such as mice and keyboards. For example, an electrical signal processing circuit that receives electrical signals corresponding to input operations from an external input device separate from the magnetic resonance imaging apparatus 1 and outputs the received electrical signals to various circuits is also an example of the input interface 54. Furthermore, the input interface 54 may also be a voice recognition device that converts audio signals collected by a microphone into instruction signals.

[0025] The communication interface 55 is an interface that connects the magnetic resonance imaging apparatus 1 to workstations, PACS (Picture Archiving and Communication System), HIS (Hospital Information System), RIS (Radiology Information System), etc., via a LAN (Local Area Network) or the like. The network interface transmits and receives various types of information between the connected workstation, PACS, HIS, and RIS.

[0026] The above configuration is merely an example and is not limited thereto. For example, the sequence control circuit 29 may be incorporated into the host computer 50. The sequence control circuit 29 and the processing circuit 51 may be mounted on the same board.

[0027] Here, we will explain the non-uniformity of the static magnetic field assumed in this embodiment.

[0028] Figure 2 shows an example of the static magnetic field distribution of a bore. In Figure 2, the horizontal axis is defined as the radial distance [cm] from the central axis (Z axis) of the bore, and the vertical axis is defined as the relative magnetic field strength [ppm], specifically representing the relative magnetic field strength when the magnetic field strength at the central axis of the bore is set to 0. Note that the static magnetic field distribution shown in Figure 2 is a cross-section that includes an arbitrary point on the central axis, but the position of this arbitrary point is not particularly limited. In a cylindrical space R1 with a diameter of 50 (-25 to +25) cm, the magnetic field strength is spatially approximately uniform. In a cylindrical region R2 located 10 cm (-25 to -35 and +25 to +35) cm outside region R1, the magnetic field strength is spatially non-uniform. This embodiment attempts to utilize region R2, which was conventionally considered unsuitable as an imaging region (hereinafter referred to as FOV) due to its non-uniform magnetic field strength, as an FOV. That is, the FOV in this embodiment is assumed to be the sum of the cylindrical region R1 and the cylindrical region R2, known as region R0.

[0029] For magnetic resonance imaging, the nuclear spins of target nuclei within the field of view (FOV) must be spatially uniformly excited by RF pulses emitted from an RF coil in the transmitting coil 45. The RF coil is tuned to a specific single frequency and emits RF pulses with a center frequency at that frequency. This frequency-dependent property of the RF coil is called its frequency response.

[0030] Since the resonance frequency of a nuclear spin depends on the magnetic field strength at the location of the nuclear spin, if the static magnetic field within the field of view (FOV) is non-uniform, the resonance frequency of the nuclear spin will vary significantly depending on the location. To excite regions with non-uniform magnetic fields, it is desirable to precisely irradiate them with RF pulses capable of sweeping a wide range of frequencies as designed. Therefore, an RF coil with good frequency characteristics over a wide range of frequencies is desirable.

[0031] Figure 3 shows an example of the frequency characteristics of an RF coil whose resonant frequency ω0 is tuned to a single frequency. In Figure 3, the vertical axis is defined by the S11 parameter, which is the reflection coefficient, and the horizontal axis is defined by the frequency ω. The reflection coefficient is an example of an indicator that represents the frequency characteristics of an RF coil, and a larger absolute value in the negative direction indicates higher transmission sensitivity of the RF coil. Hereinafter, a large absolute value of the negative reflection coefficient is defined as a small reflection coefficient, and a small absolute value of the negative reflection coefficient is defined as a large reflection coefficient. In this embodiment, it is assumed that a reflection coefficient of -1 dB or less is a condition for use as an RF coil.

[0032] As described above, the resonant frequency ω0 of the RF coil is tuned to a single frequency. At the resonant frequency ω0, the reflection coefficient takes a minimum value, but as the frequency moves away from the resonant frequency ω0, the reflection coefficient increases. A predetermined width centered around the resonant frequency ω0 is set as the bandwidth BW (ω-~ω+) of the RF pulse. It is desirable for the reflection coefficient within the bandwidth BW to be -1dB or less, but as shown in Figure 3, the reflection coefficient is greater than -1dB near the boundaries of the bandwidth BW, such as ω- and ω+.

[0033] Thus, while RF coils exhibit good frequency characteristics near their resonant frequency, they do not possess the intended frequency characteristics at frequency ranges a certain distance from the resonant frequency. Therefore, in RF coils whose resonant frequency is tuned to a single frequency, uniform excitation is difficult within a non-uniform field of view (FOV), resulting in poor transmission efficiency and poor excitation efficiency of nuclear spins.

[0034] The magnetic resonance imaging apparatus according to this embodiment efficiently transmits RF pulses using a single RF coil having two or more resonant frequencies, or a group of RF coils including two or more RF coils having two or more resonant frequencies.

[0035] Figure 4 shows an example of the configuration of an RF pulse transmission system according to this embodiment. As shown in Figure 4, the transmission system is configured with a sequence control circuit 29, a transmission circuit 23, and a transmission coil 45. The sequence control circuit 29 performs a design function 61, an adjustment function 62, and a measurement function 64. The sequence control circuit 29 also has a memory 63.

[0036] By realizing the design function 61, the sequence control circuit 29 outputs a control waveform of a broadband RF pulse. In this embodiment, "broadband" means that the excitation frequency band is wider than the excitation frequency band of an RF pulse irradiated by an RF coil tuned to a single resonant frequency. The control waveform is assumed to be digital data. The design function 61 is an example of a waveform output unit.

[0037] With the implementation of the adjustment function 62, the sequence control circuit 29 adjusts the phase and / or amplitude of the control waveform output by the design function 61 and outputs an adjusted control waveform. More specifically, the sequence control circuit 29 adjusts the phase and / or amplitude of the control waveform based on the first circuit characteristics of a single RF coil or group of RF coils included in the coil section 68 and the second circuit characteristics of multiple frequency selection circuits included in the frequency selection section 67. The adjusted control waveform is assumed to be digital data. The adjustment function 62 is an example of an adjustment section.

[0038] When adjusting the amplitude of the control waveform, the sequence control circuit 29 estimates the attenuation of the control waveform in a single RF coil or group of RF coils and two or more frequency selection circuits based on the first circuit characteristics and the second circuit characteristics. Then, based on the estimated attenuation, the sequence control circuit 29 adjusts the amplitude of the control waveform so that the waveform of the broadband RF pulse irradiated from the coil section 68 resembles the control waveform output from the design function 61. When adjusting the phase of the control waveform, the sequence control circuit 29 estimates the amount of phase change of the control waveform in a single RF coil or group of RF coils and two or more frequency selection circuits based on the first circuit characteristics and the second circuit characteristics. Then, based on the estimated amount of phase change, the sequence control circuit 29 adjusts the phase of the control waveform so that the phase of the waveform of the broadband RF pulse irradiated from the coil section 68 matches the phase of the control waveform output from the design function 61.

[0039] Memory 63 stores data for the first circuit characteristics of a single RF coil or group of RF coils included in the coil section 68, and data for the second circuit characteristics of two or more frequency selection circuits included in the frequency selection section 67. The data for the first and second circuit characteristics are used to adjust the control waveform by the adjustment function 62. Memory 63 is an example of a storage unit.

[0040] By implementing the measurement function 64, the sequence control circuit 29 measures the first circuit characteristics of a single RF coil or group of RF coils included in the coil section 68, and the second circuit characteristics of multiple frequency selection circuits included in the frequency selection section 67. The measured data of the first and second circuit characteristics are stored in the memory 63. The timing of the circuit characteristic measurement by the measurement function 64 is not particularly limited; it may be measured during installation, after adjustment of circuit constants, or at any other arbitrary timing. The measurement function 64 is an example of a measurement unit.

[0041] As shown in Figure 4, the transmitting circuit 23 includes a control signal generation circuit 65, an amplifier 66, and a frequency selection unit 67. The control signal generation circuit 65 generates a control signal of the adjusted control waveform output by the adjustment function 62. The control signal is assumed to be an analog electrical signal. The control signal generation circuit 65 is an example of a signal generation unit.

[0042] Amplifier 66 amplifies the power of the control signal output from the control signal generation circuit 65 and outputs an amplified control signal. For example, a power amplifier (PA) can be used as amplifier 66. Amplifier 66 is an example of an amplification section.

[0043] The frequency selection unit 67 has two or more frequency selection circuits corresponding to two or more passbands. The two or more frequency selection circuits output two or more frequency component signals corresponding to two or more passbands from the amplification control signal output from the amplifier 66. That is, one frequency selection circuit corresponds to one passband, and the signal (frequency component signal) corresponding to that passband from the amplification control signal is output from that one frequency selection circuit. In other words, the frequency component signal is a signal with the frequency corresponding to the passband as its center frequency. A frequency filter that extracts or removes a specific frequency component is used as the frequency selection circuit. The two or more frequency selection circuits are, for example, resonant circuits including a coil and a capacitor, and are preferably formed as high-voltage analog circuits. The frequency selection unit 67 is an example of a selection unit.

[0044] As shown in Figure 4, the transmitting coil 45 has a coil section 68. The coil section 68 has a single RF coil having two or more different resonant frequencies, or a group of RF coils including two or more RF coils having two or more different resonant frequencies. The single RF coil or group of RF coils receives two or more frequency component signals and irradiates a broadband RF pulse. The waveform of the superposition of the two or more RF pulses is similar to the control waveform of the broadband RF pulse output by the design function 61. The circuit parameters of the single RF coil or group of RF coils are adjusted so that the reflection coefficient of the single RF coil or group of RF coils is -1 dB or less in the bandwidth of the broadband RF pulse based on the reference frequency. For example, a whole-body coil is used as the RF coil.

[0045] The structure and operation of the RF pulse transmission system according to this embodiment will be described in detail below. In the following embodiment, the coil section 68 is assumed to be an RF coil group including two RF coils having two different resonant frequencies. In this case, the frequency selection section 67 has two frequency selection circuits corresponding to the two RF coils.

[0046] Figure 5 shows a specific configuration example and processing example of the RF pulse transmission system according to this embodiment. As shown in Figure 5, the design function 61 of the sequence control circuit 29 outputs a control waveform of a wideband RF pulse, the adjustment function 62 of the sequence control circuit 29 adjusts the control waveform, the control signal generation circuit 65 generates a control signal of the adjusted control waveform, and the amplifier 66 (PA) amplifies the power of the control signal. The amplified control signal is distributed to a high-pass filter 671 (HP) and a low-pass filter 672 (LP). The high-pass filter 671 extracts the high-frequency component signal from the amplified control signal, and the low-pass filter 672 extracts the low-frequency component signal from the amplified control signal. The high-frequency component signal is supplied to the first RF coil 681, and the first RF pulse corresponding to the high-frequency component signal is generated from the first RF coil 681. The low-frequency component signal is supplied to the second RF coil 682, and the second RF pulse corresponding to the low-frequency component signal is generated from the second RF coil 682. The waveform obtained by superimposing the first RF pulse and the second RF pulse is similar to the control waveform designed by the design function 61.

[0047] The following is a detailed explanation. First, the sequence control circuit 29 uses the design function 61 to design a control waveform for a broadband RF pulse expected to be irradiated from the coil section 68. Here, the sequence control circuit 29 calculates the bandwidth of the resonance frequency based on the maximum and minimum magnetic field strengths in the distribution of the magnetic field applied to the imaging area, and sets the calculated bandwidth of the resonance frequency to the bandwidth of the broadband RF pulse. Specifically, a bandwidth of a predetermined width centered on the resonance frequency is set to the bandwidth of the broadband RF pulse. As the distribution of the magnetic field applied to the imaging area, the distribution of the static magnetic field applied by the static magnetic field magnet 41 may be used, or the distribution of the superimposed magnetic field of the static magnetic field applied by the static magnetic field magnet 41 and the gradient magnetic field applied by the gradient magnetic field coil 43 may be used. The magnetic field distribution may be measured, or it may be calculated based on imaging conditions such as the strength of the static magnetic field and the pulse sequence.

[0048] The control waveform generated by design function 61 may be designed for each combination of static magnetic field strength, gradient magnetic field strength, and transmit magnetic field strength. The broadband RF pulse is used as an excitation pulse or refocusing pulse in the pulse sequence. The broadband RF pulse may be, for example, a pulse intended for broadband excitation such as CHIRP or WURST. Another example is a broadband RF pulse that is a simultaneous multi-slice excitation pulse such as Simultaneous Multi-Slice.

[0049] The adjustment function 62 causes the sequence control circuit 29 to adjust the phase and / or amplitude of the control waveform output by the design function 61 based on the first circuit characteristics of the RF coils 681 and 682 included in the coil section 68 and the second circuit characteristics of the high-pass filter 671 and low-pass filter 672 included in the frequency selection section 67.

[0050] When adjusting the amplitude, the adjustment function 62 estimates the attenuation of the control waveform in the RF coils 681 and 682 included in the coil section 68 and the high-pass filter 671 and low-pass filter 672 included in the frequency selection section 67, based on the first and second circuit characteristics. The sequence control circuit 29 then adjusts the amplitude of the control waveform based on the estimated attenuation so that the waveform of the broadband RF pulse irradiated from the RF coils 681 and 682 resembles the control waveform output from the design function 61.

[0051] When adjusting the phase, the adjustment function 62 estimates the amount of phase change of the control waveform in the RF coils 681 and 682 included in the coil section 68 and the high-pass filter 671 and low-pass filter 672 included in the frequency selection section 67, based on the first and second circuit characteristics. The sequence control circuit 29 then adjusts the phase of the control waveform based on the estimated amount of phase change so that the phase of the waveform of the broadband RF pulses irradiated from the RF coils 681 and 682 matches the phase of the control waveform output from the design function 61.

[0052] Figure 6 is a schematic diagram illustrating the adjustment process of the control waveform. As shown in Figure 6, the first circuit characteristics of the RF coils 681 and 682 and the second circuit characteristics of the high-pass filter 671 and low-pass filter 672 are acquired. As an example, the sequence control circuit 29 reads out the data of the first circuit characteristics and the data of the second circuit characteristics that have been measured in advance by the measurement function 64 and stored in the memory 63, and adjusts the phase and / or amplitude of the control waveform based on the read-out data of the first and second circuit characteristics. As another example, the sequence control circuit 29 may measure the first circuit characteristics of the RF coils 681 and 682 and the second circuit characteristics of the high-pass filter 671 and low-pass filter 672 for each adjustment process, and adjust the phase and / or amplitude of the control waveform based on the measured first and second circuit characteristics.

[0053] Figure 7 shows an example of the first circuit characteristics of RF coils 681 and 682. The vertical axis of Figure 7 is defined by the reflection coefficient (S11 parameter), and the horizontal axis is defined by frequency. Curve C1 represents the frequency change of the reflection coefficient for RF coil 681, and curve C2 represents the frequency change of the reflection coefficient for RF coil 682. The frequency change of the reflection coefficient is an example of circuit characteristics. Curve C1 shows that the reflection coefficient takes a minimum value at the center frequency ω1, and the reflection coefficient increases as it moves away from the center frequency ω1. The shape of curve C1 is unique to RF coil 681. When a control signal flows through RF coil 681, the amplitude and / or phase of the control signal are disturbed according to the circuit characteristics corresponding to curve C1. The same applies to curve C2. The sum of curves C1 and C2 represents the circuit characteristics of the coil section 68, including RF coils 681 and 682. The amplitude and / or phase of the control signal are disturbed according to the circuit characteristics of the coil section 68.

[0054] Figure 8 shows an example of the second circuit characteristics of the high-pass filter 671 and the low-pass filter 672. In Figure 8, the vertical axis is defined by gain and the horizontal axis is defined by frequency. Line F1 represents the frequency change of gain for the high-pass filter 671, and line F2 represents the frequency change of gain for the low-pass filter 672. As shown by line F1, for the high-pass filter 671, the passband is set to a frequency band ω1 or higher, which is higher than the cutoff frequency ω0. As shown by line F2, for the low-pass filter 672, the passband is set to a frequency band ω2 or lower, which is lower than the cutoff frequency ω0. When the control signal flows through the high-pass filter 671, the amplitude and / or phase of the control signal are disturbed according to the circuit characteristics corresponding to line F1. The sum of lines F1 and S2 represents the circuit characteristics related to the amplitude of the frequency selection unit 67, which includes the high-pass filter 671 and the low-pass filter 672. The amplitude and / or phase of the control signal are disturbed according to the circuit characteristics of the frequency selection unit 67.

[0055] As shown in Figure 6, the sequence control circuit 29 estimates the attenuation and phase change of the control signal based on the first and second circuit characteristics. The attenuation refers to the degree of attenuation of the signal strength of the control signal at each frequency when the control signal flows through the frequency selection unit 67 and the coil unit 68. The attenuation is estimated based on the first and second circuit characteristics, which represent the frequency change of the reflection coefficient, such as the S11 parameter. The phase change refers to the degree of phase shift of the control signal at each frequency when the control signal flows through the frequency selection unit 67 and the coil unit 68. The phase change is estimated based on the first and second circuit characteristics, which represent the frequency change of the phase change.

[0056] Once the attenuation and phase change amounts are estimated, the sequence control circuit 29 applies the attenuation and phase change amounts to the control waveform (input control waveform) output from the design function 61 to generate an output control waveform. The output control waveform represents the control waveform after the output waveform from the design function 61 has undergone attenuation and phase change by the frequency selection unit 67 and the coil unit 68.

[0057] Next, the sequence control circuit 29 calculates the difference between the output control waveform and the ideal control waveform. The calculated difference represents the difference between the control waveform after attenuation and phase shift by the frequency selection unit 67 and the coil unit 68, and the ideal control waveform. The ideal control waveform is the waveform that the RF pulse irradiated from the coil unit 68 is expected to have, and is set to, for example, the control waveform designed by the design function 61. The sequence control circuit 29 generates an adjusted control waveform by applying the calculated difference to the control waveform. In the case of adjustment by attenuation, the sequence control circuit 29 increases the signal strength of the control waveform by an amount (difference) that cancels out the estimated attenuation. For example, if the attenuation is -10dB at 40MHz, the signal strength of the control waveform at 40MHz is increased tenfold. In the case of adjustment by phase shift, the sequence control circuit 29 changes the phase of the control waveform by an amount (difference) that cancels out the estimated phase shift. For example, if the attenuation is -10φ at 40MHz, the phase of the control waveform at 40MHz is advanced by +10φ. By adjusting the control waveform according to the difference in this way, an adjusted control waveform is generated. It is expected that the adjusted control waveform will change into an ideal control waveform as it undergoes attenuation and phase change by the frequency selection unit 67 and the coil unit 68.

[0058] Subsequently, as shown in Figure 5, the control signal generation circuit 65 generates a control signal with an adjusted control waveform, the amplifier 66 (PA) amplifies the power of the control signal, and the amplified control signal is distributed to the high-pass filter 671 (HP) and the low-pass filter 672 (LP). The amplified control signal passes through the high-pass filter 671 and the low-pass filter 672, and the high-frequency component signal and the low-frequency component signal are extracted. By placing the frequency filters 671 and 672 before the RF coils 681 and 682, it is possible to change the frequency characteristics of the control signal supplied to the RF coils 681 and 682 to the optimal frequency characteristics for the RF coils 681 and 682 to which it is supplied.

[0059] The waveform of the high-frequency component signal undergoes amplitude attenuation and phase shift according to the circuit characteristics of the high-pass filter 671, and the waveform of the low-frequency component signal undergoes amplitude attenuation and phase shift according to the circuit characteristics of the low-pass filter 672. The high-frequency component signal is supplied to the first RF coil 681, and a first RF pulse corresponding to the high-frequency component signal is generated from the first RF coil 681. The waveform of the first RF pulse undergoes amplitude attenuation and phase shift according to the circuit characteristics of the first RF coil 681, and the waveform of the second RF pulse undergoes amplitude attenuation and phase shift according to the circuit characteristics of the second RF coil 682. The waveform of the pulse obtained by superimposing the first RF pulse and the second RF pulse is similar to the control waveform designed by the design function 61.

[0060] As shown in Figure 5, only one amplifier 66 is provided before the high-pass filter 671 and the low-pass filter 672. This configuration reduces the number of amplifiers 66 and thus the cost of introducing the amplifiers 66, compared to the case where an amplifier 66 is provided after each of the high-pass filter 671 and the low-pass filter 672.

[0061] Next, we will explain how to determine and measure circuit characteristics.

[0062] One or more cutoff frequencies of two or more frequency selector circuits (frequency filters) are adjusted to the frequency of one or more intersection points of two or more frequency distribution waveforms of the reflection coefficient of a single RF coil or group of RF coils. The two or more frequency selector circuits in Processing Example 1 below have two frequency selector circuits: a first frequency selector circuit and a second frequency selector circuit. The first frequency selector circuit is a high-pass filter with a passband of frequencies higher than one cutoff frequency, and the second frequency selector circuit is a low-pass filter with a passband of frequencies lower than one cutoff frequency. The two or more frequency selector circuits in Processing Example 2 below have a first frequency selector circuit, a second frequency selector circuit and a third frequency selector circuit. The first frequency selector is a high-pass filter with a passband frequency band higher than the highest of the two or more cutoff frequencies; the second frequency selector is a low-pass filter with a passband frequency band lower than the lowest of the two or more cutoff frequencies; and the third frequency selector is a band-pass filter with a passband frequency band between the highest and lowest of the two or more cutoff frequencies. The number of band-pass filters can be one or two or more.

[0063] <Processing Example 1> This section describes how to determine and measure the circuit characteristics when there are two RF coils and two frequency filters.

[0064] Figure 9 shows an example of the circuit characteristic determination and measurement process by the sequence control circuit 29. Figure 10 schematically shows the circuit characteristic determination process when there are two RF coils and two frequency filters. The left side of Figure 10 shows the reference frequency ωstd on the frequency axis, the center side of Figure 10 shows the frequency characteristic waveform C1 for RF coil 681 and the frequency characteristic waveform C2 for RF coil 682, and the right side of Figure 10 shows the frequency characteristic waveform F1 for high-pass filter 671 and the frequency characteristic waveform F2 for low-pass filter 672.

[0065] As shown in Figures 9 and 10, the sequence control circuit 29 determines a single reference frequency ωstd (step S1). The reference frequency ωstd corresponds to the frequency of the center of the k-space or MR image. For example, the sequence control circuit 29 may identify the maximum and minimum magnetic field strengths in the distribution of the magnetic field applied to the imaging region, calculate the magnetic field strength approximately at the center of the identified maximum and minimum magnetic field strengths, and set the frequency corresponding to the calculated magnetic field strength as the reference frequency ωstd. As the distribution of the magnetic field applied to the imaging region, the distribution of the static magnetic field applied by the static magnetic field magnet 41 may be used, or the distribution of the superimposed magnetic field of the static magnetic field applied by the static magnetic field magnet 41 and the gradient magnetic field applied by the gradient magnetic field coil 43 may be used. The sequence control circuit 29 may refer to the magnetic field distribution displayed on the display 53 or the like by the operator and set the frequency corresponding to the magnetic field specified via the input interface 54 or the frequency specified via the input interface 54 as the reference frequency ωstd.

[0066] When step S1 is performed, the sequence control circuit 29 adjusts the resonant frequencies of the RF coils 681 and 682 (step S2). Specifically, the sequence control circuit 29 reads first circuit characteristic data for the RF coils 681 and 682 from the memory 63. The first circuit characteristic data is assumed to have been measured at a predetermined time, such as during installation.

[0067] The circuit parameters of RF coils 681 and 682, such as capacitors, capacitances, and reactances, are adjusted according to the operator's instructions so that the reflection coefficients of RF coils 681 and 682 satisfy the following conditions: Condition 1: The sum of waveforms C1 and C2 is -1 dB or less across the entire bandwidth BW of the broadband RF pulse. It is more preferable if it is -3 dB or less. Condition 2: The resonant frequency (center frequency) ω1 of RF coil 681 is greater than the reference frequency ωstd, and the resonant frequency (center frequency) ω2 of RF coil 682 is less than the reference frequency ωstd. By satisfying conditions 1 and 2, it is possible to design an RF pulse capable of sweeping a broadband.

[0068] When step S2 is performed, the sequence control circuit 29 determines the cutoff frequencies ωco of the frequency filters 671 and 672 (step S3). Specifically, as shown in the right diagram of Figure 10, the sequence control circuit 29 sets the reference frequency ωstd, which is the frequency corresponding to the intersection of the waveform C1 of the RF coil 681 and the waveform C2 of the RF coil 682, to the cutoff frequencies ωco of the high-pass filter 671 and the low-pass filter 672. The sequence control circuit 29 then sets the passband of the high-pass filter 671 to a frequency band higher than the cutoff frequency ωco. The lower limit of the passband of the high-pass filter 671 may be set to, for example, the resonant frequency ω1 of the RF coil 681. The sequence control circuit 29 then sets the passband of the low-pass filter 672 to a frequency band lower than the cutoff frequency ωco. The upper limit of the passband of the low-pass filter 672 may be set to, for example, the resonant frequency ω2 of the RF coil 682.

[0069] When step S4 is performed, the sequence control circuit 29 measures the circuit characteristics of the RF coils 681 and 682 and the frequency filters 671 and 672 using the measurement function 64 (step S4). As an example, the reflection coefficients, such as the S11 parameters of the RF coils 681 and 682 and the frequency filters 671 and 672 are measured for each frequency using a measuring instrument such as a network analyzer. The sequence control circuit 29 generates first circuit characteristic data representing the frequency change of the reflection coefficient by plotting the measurement results of the RF coils 681 and 682 on a graph defined by frequency and reflection coefficient, and generates second circuit characteristic data representing the frequency change of the reflection coefficient by plotting the measurement results of the frequency filters 671 and 672. Similarly, the phase change of the signal intensity of the RF coils 681 and 682 and the frequency filters 671 and 672 is measured for each frequency using a measuring instrument such as a network analyzer. The sequence control circuit 29 generates first circuit characteristic data representing the frequency change of the phase change by plotting the measurement results of RF coils 681 and 682 on a graph defined by frequency and phase, and generates second circuit characteristic data representing the frequency change of the phase change by plotting the measurement results of frequency filters 671 and 672.

[0070] When step S4 is performed, the sequence control circuit 29 stores the circuit characteristic data measured in step S4 in the memory 63 (step S5). The circuit characteristics of the RF coils 681 and 682 are stored as first circuit characteristic data, and the circuit characteristics of the frequency filters 671 and 672 are stored as second circuit characteristic data. In this case, the first and second circuit characteristic data may be stored in association with the measurement date and time of each circuit characteristic.

[0071] When step S5 is performed, the processing related to processing example 1 is completed.

[0072] <Processing Example 2> Next, the determination and measurement of circuit characteristics in the case of three RF coils and three frequency filters will be explained with reference to Figures 9 and 11. The procedure for determining and measuring circuit characteristics in the case of three RF coils and three frequency filters is the same as in Figure 9. Figure 11 is a schematic diagram showing the process of determining circuit characteristics in the case of three RF coils and three frequency filters. The left side of Figure 11 represents the reference frequency ωstd on the frequency axis, the center side of Figure 11 represents the frequency characteristic waveform C1 for RF coil 681, the frequency characteristic waveform C2 for RF coil 682, and the frequency characteristic waveform C3 for RF coil 683, and the right side of Figure 11 represents the frequency characteristic waveform F1 for high-pass filter 671, the frequency characteristic waveform F2 for low-pass filter 672, and the frequency characteristic waveform F3 for band-pass filter 673.

[0073] As shown in Figures 9 and 11, the sequence control circuit 29 determines two reference frequencies ωstd1 and ωstd2 (step S1). As an example, the sequence control circuit 29 sets a reference frequency ωstd corresponding to the frequency of the center of the k-space or MR image, sets a reference frequency ωstd1 that is a predetermined amount greater than the reference frequency ωstd, and sets a reference frequency ωstd2 that is a predetermined amount smaller than the reference frequency ωstd. The method for setting the reference frequency ωstd is the same as in processing example 1.

[0074] When step S1 is performed, the sequence control circuit 29 adjusts the resonant frequencies of the RF coils 681, 682, and 683 (step S2). Specifically, the sequence control circuit 29 reads first circuit characteristic data for the RF coils 681, 682, and 683 from the memory 63. The first circuit characteristic data is assumed to have been measured at a predetermined time, such as during installation.

[0075] The circuit parameters of RF coils 681, 682, and 683, such as capacitors, capacitances, and reactances, are adjusted according to the operator's instructions so that the reflection coefficients of RF coils 681, 682, and 683 satisfy the following conditions: Condition 1: The sum of waveforms C1, C2, and C3 is -1 dB or less across the entire bandwidth BW of the broadband RF pulse. It is more preferable if it is -3 dB or less. Condition 2: The resonant frequency (center frequency) ω1 of RF coil 681 is greater than the reference frequency ωstd, and the resonant frequency (center frequency) ω2 of RF coil 682 is less than the reference frequency ωstd. The resonant frequency (center frequency) ω3 of RF coil 683 should be set between the resonant frequencies ω1 and ω2. By satisfying conditions 1 and 2, it is possible to design an RF pulse capable of sweeping a broadband.

[0076] When step S2 is performed, the sequence control circuit 29 determines the cutoff frequencies ωco1 and ωco2 of the frequency filters 671, 672, and 673 (step S3). Specifically, as shown in the right figure of Figure 11, the sequence control circuit 29 sets the reference frequency ωstd1, which is the frequency corresponding to the intersection of the waveform C1 of RF coil 681 and the waveform C3 of RF coil 683, as the cutoff frequency ωco1 for the high-pass filter 671 and the band-pass filter 673, and sets the reference frequency ωstd2, which is the frequency corresponding to the intersection of the waveform C2 of RF coil 682 and the waveform C3 of RF coil 683, as the cutoff frequency ωco2 for the low-pass filter 672 and the band-pass filter 673.

[0077] Next, the sequence control circuit 29 sets the passband of the high-pass filter 671 to a frequency band higher than the cutoff frequency ωco1. The lower limit of the passband of the high-pass filter 671 may be set to, for example, the resonant frequency ω1 of the RF coil 681. The sequence control circuit 29 sets the passband of the band-pass filter 673 to a frequency band between the cutoff frequency ωco1 and the cutoff frequency ωco2. The sequence control circuit 29 sets the passband of the low-pass filter 672 to a frequency band lower than the cutoff frequency ωco2. The upper limit of the passband of the low-pass filter 672 may be set to, for example, the resonant frequency ω2 of the RF coil 682.

[0078] When step S4 is performed, the sequence control circuit 29 measures the circuit characteristics of the RF coils 681, 682, and 683 and the frequency filters 671, 672, and 673 using the measurement function 64 (step S4). When step S4 is performed, the sequence control circuit 29 stores the circuit characteristic data measured in step S4 in the memory 63 (step S5). The circuit characteristics of the RF coils 681, 682, and 683 are stored as first circuit characteristic data, and the circuit characteristics of the frequency filters 671, 672, and 673 are stored as second circuit characteristic data. In this case, the first and second circuit characteristic data may be stored in association with the measurement date and time of each circuit characteristic.

[0079] When step S5 is performed, the processing related to processing example 2 is completed.

[0080] According to some embodiments described above, the magnetic resonance imaging apparatus 1 includes a sequence control circuit 29, a transmission circuit 23, and a transmission coil 45. The sequence control circuit 29 includes a design function 61 that outputs a control waveform of a broadband RF pulse, and an adjustment function 62 that adjusts the phase and / or amplitude of the control waveform to output an adjusted control waveform. The transmission circuit 23 includes a control signal generation circuit 65 that generates a control signal of the adjusted control waveform, and a section having two or more frequency selection circuits corresponding to two or more passbands, wherein the two or more frequency selection circuits include a frequency selection section 67 that outputs two or more frequency component signals corresponding to two or more passbands from the control signal. The transmission coil 45 is a coil section having a single RF coil having two or more different resonant frequencies, or a group of RF coils including two or more RF coils having two or more different resonant frequencies, wherein the single RF coil or the group of RF coils includes a coil section 68 that receives two or more frequency component signals and irradiates a broadband RF pulse. The adjustment function 62 adjusts the phase and / or amplitude of the control waveform based on the first circuit characteristics of a single RF coil or group of RF coils and the second circuit characteristics of two or more frequency selection circuits.

[0081] According to the above configuration, a single or multiple RF coils with resonant frequencies tuned to two or more different frequencies are used to apply RF pulses capable of exciting over a wide bandwidth. Two or more frequency selection circuits are placed immediately before the single or multiple RF coils. By placing frequency selection circuits immediately before the RF coils, it becomes possible to irradiate RF pulses in the bandwidth around the resonant frequency of each RF coil. Furthermore, since the phase and / or amplitude of the control waveform are adjusted based on the circuit characteristics of the frequency selection circuits and RF coils through which the control signal passes, it becomes possible to accurately irradiate wideband RF pulses as designed. In addition, when using wideband RF pulses that take off-resonance into account in magnetic resonance imaging with non-uniform magnetic fields, it is possible to perform the intended excitation and improve the excitation characteristics.

[0082] The above embodiments are examples, and various elements can be added, deleted, and / or modified without departing from the spirit of the invention.

[0083] The magnetic resonance imaging apparatus 1 according to the above embodiment is a cylindrical magnetic resonance imaging apparatus having a frame 11 that houses a cylindrical static magnetic field magnet 41, a gradient magnetic field coil 43, and a transmitting coil 45 surrounding a hollow space having a cylindrical shape. However, this embodiment is not limited to this and can be applied to any type of magnetic resonance imaging apparatus capable of performing MR imaging in areas where the uniformity of the magnetic field is not high. For example, a planar open type magnetic resonance imaging apparatus equipped with a pair of upper and lower magnet housings having a flat plate shape may also be used. In this case, a planar static magnetic field magnet 41, a gradient magnetic field coil 43, and a transmitting coil 45 are housed in each magnet housing, and an imaging area including a region of non-uniform magnetic field is set in the planar open space sandwiched between the pair of magnet housings. As another example, a fully open type magnetic resonance imaging apparatus equipped with only one of the pair of magnet housings may also be used. In this case, a planar static magnetic field magnet 41, a gradient magnetic field coil 43, and a transmitting coil 45 are housed in the magnet housing, and an imaging area including a region of non-uniform magnetic field is set in the open space located below or above the magnet housing.

[0084] The magnetic resonance imaging apparatus 1 according to the above embodiment uses two or more RF coils having two or more different resonant frequencies, where the resonant frequencies of the two or more RF coils themselves are different from each other. However, this embodiment is not limited to this. For example, the magnetic resonance imaging apparatus 1 may have two or more ports having two or more resonant frequencies, and an RF coil may be connected to each port. The RF coil connected to one port and the RF coil connected to another port may have different or the same resonant frequencies.

[0085] According to at least one embodiment described above, a broadband RF pulse can be precisely irradiated as designed.

[0086] In the above description, the term "processor" refers to circuits such as CPUs, GPUs, or Application Specific Integrated Circuits (ASICs), programmable logic devices (e.g., Simple Programmable Logic Devices (SPLDs), Complex Programmable Logic Devices (CPLDs), and Field Programmable Gate Arrays (FPGAs)). A processor functions by reading and executing a program stored in a memory circuit. Alternatively, instead of storing the program in a memory circuit, the program may be directly incorporated into the processor's circuitry. In this case, the processor functions by reading and executing the program incorporated into the circuitry. On the other hand, if the processor is an ASIC, for example, the program is not stored in a memory circuit, but the function is directly incorporated into the processor's circuitry as a logic circuit. In this embodiment, each processor is not limited to being configured as a single circuit; multiple independent circuits may be combined to form a single processor and realize its functions. Furthermore, the multiple components shown in Figures 1 and 3 may be integrated into a single processor to realize its functions.

[0087] While several embodiments have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in a variety of other forms, and various omissions, substitutions, modifications, and combinations of embodiments are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0088] 1. Magnetic Resonance Imaging System 11. Stand 13 berths 21 Gradient magnetic field power supply 23 Transmitter Circuit 25 Receiving Circuit 27 Bed drive mechanism 29 Sequence control circuit 41 Static magnetic field magnet 43. Gradient field coil 45 Transmitter coil 47 Receiving coil 50 Host Computers 51 Processing Circuit 52 memory 53 displays 54 Input Interfaces 55 Communication Interfaces 61 Design functions 62 Adjustment function 63 memory 64 Measurement Functions 65 Control signal generation circuit 66 Amplifier 67 Frequency Selection Section 68 Coil section 131 Top plate 133 Base 671 High-pass filter 672 Low-pass filter 681 First RF coil 682 Second RF coil

Claims

1. A waveform output section that outputs a control waveform of a wideband RF pulse, An adjustment unit that adjusts the phase and / or amplitude of the control waveform and outputs an adjusted control waveform, A signal generation unit that generates a control signal for the adjusted control waveform, A selection unit having two or more frequency selection circuits corresponding to two or more passbands, wherein the two or more frequency selection circuits output two or more frequency component signals corresponding to the two or more passbands from the control signal, A coil section comprising a single RF coil having two or more different resonant frequencies, or a group of RF coils including two or more RF coils having two or more different resonant frequencies, wherein the single RF coil or the group of RF coils receives the two or more frequency component signals and irradiates the broadband RF pulse, The adjustment unit adjusts the phase and / or amplitude of the control waveform based on the first circuit characteristics of the single RF coil or the group of RF coils and the second circuit characteristics of the two or more frequency selection circuits. Magnetic resonance imaging device.

2. The magnetic resonance imaging apparatus according to claim 1, wherein the circuit parameters of the single RF coil or the group of RF coils are adjusted such that the reflection coefficient of the single RF coil or the group of RF coils is -1 dB or less in the bandwidth of the broadband RF pulse based on a reference frequency.

3. The magnetic resonance imaging apparatus according to claim 1, wherein one or more cutoff frequencies of the two or more frequency selection circuits are adjusted to the frequency of one or more intersection points of two or more frequency distribution waveforms of the reflection coefficient of the single RF coil or the group of RF coils.

4. The two or more frequency selection circuits mentioned above have two frequency selection circuits: a first frequency selection circuit and a second frequency selection circuit. The first frequency selection circuit is a high-pass filter having a passband with a frequency band higher than one cutoff frequency. The second frequency selection circuit is a low-pass filter having a passband with a frequency band lower than the one cutoff frequency, The magnetic resonance imaging apparatus according to claim 3.

5. The two or more frequency selection circuits include a first frequency selection circuit, a second frequency selection circuit, and a third frequency selection circuit. The first frequency selection circuit is a high-pass filter having a passband with a frequency band higher than the highest of two or more cutoff frequencies. The second frequency selection circuit is a low-pass filter having a passband with a frequency band lower than the lowest cutoff frequency among the two or more cutoff frequencies. The third frequency selection circuit is a band-pass filter having a passband with a frequency band between the highest and lowest cutoff frequencies among the two or more cutoff frequencies. The magnetic resonance imaging apparatus according to claim 3.

6. The magnetic resonance imaging apparatus according to claim 1, wherein the waveform output unit calculates the bandwidth of the resonance frequency based on the maximum and minimum magnetic field strengths in the distribution of the magnetic field applied to the imaging region, and sets the calculated bandwidth to the bandwidth of the broadband RF pulse.

7. The system further includes a storage unit that stores the data of the first circuit characteristics and the data of the second circuit characteristics measured at the time of installation. The adjustment unit adjusts the phase and / or amplitude of the control waveform based on the data of the first circuit characteristics and the data of the second circuit characteristics. The magnetic resonance imaging apparatus according to claim 1.

8. The adjustment unit is, The first circuit characteristics and the second circuit characteristics are measured. The phase and / or amplitude of the control waveform are adjusted based on the measured first circuit characteristics and the second circuit characteristics. The magnetic resonance imaging apparatus according to claim 1.

9. The adjustment unit is, Based on the first circuit characteristics and the second circuit characteristics, the attenuation of the control waveform in the single RF coil or the group of RF coils and the two or more frequency selection circuits is estimated. Based on the estimated attenuation amount, the amplitude of the control waveform is adjusted so that the waveform of the broadband RF pulse irradiated from the coil section resembles the control waveform output from the waveform output section. The magnetic resonance imaging apparatus according to claim 1.

10. The adjustment unit is, Based on the first circuit characteristics and the second circuit characteristics, the amount of phase change of the control waveform in the single RF coil or the group of RF coils and the two or more frequency selection circuits is estimated. Based on the estimated amount of phase change, the phase of the control waveform is adjusted so that the phase of the waveform of the broadband RF pulse irradiated from the coil unit matches the phase of the control waveform output from the waveform output unit. The magnetic resonance imaging apparatus according to claim 1.

11. The magnetic resonance imaging apparatus according to claim 1, wherein the single RF coil or the group of RF coils receives the two or more frequency component signals and irradiates two or more RF pulses, and the waveform of the superposition of the two or more RF pulses is similar to the control waveform.

12. The system further comprises an amplification unit that amplifies the power of the aforementioned control signal and outputs an amplified control signal, The two or more frequency selection circuits extract the two or more frequency component signals from the amplification control signal. The magnetic resonance imaging apparatus according to claim 1.

13. The magnetic resonance imaging apparatus according to claim 12, wherein the amplification unit is one.

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