Magnetic resonance imaging device and method

Abstract

To improve sensitivity of a high frequency coil when magnetic field intensity of a static magnetic field changes spatially.SOLUTION: A magnetic resonance imaging device includes a static magnetic field magnet, a plurality of transmission / reception coils, and a control unit. The static magnetic field magnet generates a static magnetic field whose magnetic field intensity changes spatially. The plurality of transmission / reception coils transmits a high frequency pulse to a subject placed in the static magnetic field whose magnetic field intensity changes spatially, and receives a nuclear magnetic-resonance signal generated from the subject by the influence of the high frequency pulse. The control unit controls the plurality of transmission / reception coils so as to transmit the high frequency pulse by each of the plurality of frequencies adjusted at least according to a distribution of the static magnetic field, and receive the nuclear magnetic-resonance signal by each of the plurality of frequencies.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE The embodiments disclosed herein and in the drawings relate to magnetic resonance imaging apparatus and methods. [Background technology]

[0002] Conventionally, a magnetic resonance imaging (MRI) device transmits radio frequency (RF) pulses to a subject placed in a static magnetic field and receives nuclear magnetic resonance (NMR) signals generated from the subject under the influence of the RF pulses to generate an image. The MRI device includes an RF coil tuned to a predetermined resonance frequency in order to transmit RF pulses and receive NMR signals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-354589 A [Patent Document 2] Special Publication No. 2017-533811 Summary of the Invention [Problem to be solved by the invention]

[0004] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to improve the sensitivity of an RF coil when the magnetic field strength of a static magnetic field varies spatially. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0005] The MRI apparatus according to the embodiment includes a static magnetic field magnet, a plurality of transmit / receive coils, and a controller. The static magnetic field magnet generates a static magnetic field whose magnetic field strength varies spatially. The plurality of transmit / receive coils transmit RF pulses to a subject placed in the static magnetic field whose magnetic field strength varies spatially, and receive NMR signals generated from the subject under the influence of the RF pulses. The controller controls the plurality of transmit / receive coils to transmit the RF pulses at each of a plurality of frequencies adjusted according to at least the distribution of the static magnetic field, and to receive the NMR signals at each of the plurality of frequencies. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an MRI apparatus according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing a static magnetic field generated by the static magnetic field magnet according to the first embodiment. [Diagram 3] FIG. 3 is a diagram for explaining a decrease in sensitivity of the RF coil related to the first embodiment. [Figure 4] FIG. 4 is a diagram showing an example of an RF coil included in the MRI apparatus according to the first embodiment. [Diagram 5] FIG. 5 is a diagram showing an example of an RF coil included in the MRI apparatus according to the first embodiment. [Figure 6] FIG. 6 is a diagram showing an example of an RF coil included in the MRI apparatus according to the first embodiment. [Figure 7] FIG. 7 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus according to the first embodiment. [Figure 8] FIG. 8 is a diagram showing an example of imaging performed by the imaging control function according to the first embodiment. [Figure 9] FIG. 9 is a diagram showing an example of an RF coil included in the MRI apparatus according to the second embodiment. [Figure 10] FIG. 10 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus according to the second embodiment. [Figure 11]FIG. 11 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus according to the third embodiment. [Figure 12] FIG. 12 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus according to the fourth embodiment. [Figure 13] FIG. 13 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus according to the fifth embodiment. [Figure 14] FIG. 14 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus according to the sixth embodiment. [Figure 15] FIG. 15 is a diagram showing an example of the configuration of a transmission and reception system included in the MRI apparatus according to the seventh embodiment. [Figure 16] FIG. 16 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus according to the eighth embodiment. [Figure 17] FIG. 17 is a diagram showing an example of the configuration of a transmission / reception system included in an MRI apparatus according to the ninth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, embodiments of an MRI apparatus and method according to the present application will be described in detail with reference to the drawings.

[0008] (First embodiment) FIG. 1 is a diagram showing an example of the configuration of an MRI apparatus according to the first embodiment.

[0009] For example, as shown in FIG. 1, an MRI apparatus 100 includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a gradient magnetic field power supply 3, a whole-body RF coil 4, a local RF coil 5, a transmission circuit 6, a reception circuit 7, an RF shield 8, a gantry 9, a bed 10, an input interface 11, a display 12, a memory circuit 13, and processing circuits 14 to 17.

[0010] The static magnetic field magnet 1 generates a static magnetic field in an imaging space in which a subject S is placed. Specifically, the static magnetic field magnet 1 is formed in a hollow, approximately cylindrical shape (including a shape in which the cross section perpendicular to the central axis is elliptical), and generates a static magnetic field in an imaging space formed on its inner periphery. For example, the static magnetic field magnet 1 is a superconducting magnet or a permanent magnet. The superconducting magnet referred to here is composed of, for example, a container filled with a coolant such as liquid helium, and a superconducting coil immersed in the container.

[0011] The gradient coil 2 is disposed inside the static magnetic field magnet 1, and generates a gradient magnetic field in an imaging space in which the subject S is disposed. Specifically, the gradient coil 2 is formed in a hollow, substantially cylindrical shape (including a shape in which the cross section perpendicular to the central axis is elliptical), and has an X coil, a Y coil, and a Z coil corresponding to the X axis, the Y axis, and the Z axis, which are perpendicular to each other. The X coil, the Y coil, and the Z coil generate a gradient magnetic field in the imaging space that changes linearly along each axis direction based on a current supplied from the gradient magnetic field power supply 3. Here, the Z axis is set to be along the magnetic flux of the static magnetic field generated by the static magnetic field magnet 1. In addition, the X axis is set to be along the horizontal direction perpendicular to the Z axis, and the Y axis is set to be along the vertical direction perpendicular to the Z axis. Here, the X axis, the Y axis, and the Z axis constitute an apparatus coordinate system unique to the MRI apparatus 100.

[0012] The gradient magnetic field power supply 3 generates a gradient magnetic field in the imaging space by supplying a current to the gradient magnetic field coil 2. Specifically, the gradient magnetic field power supply 3 generates a gradient magnetic field in the imaging space that changes linearly along the mutually orthogonal readout direction, phase encoding direction, and slice direction, respectively, by supplying currents individually to the X coil, Y coil, and Z coil of the gradient magnetic field coil 2. Here, the axis along the readout direction, the axis along the phase encoding direction, and the axis along the slice direction form a logical coordinate system for defining a slice region or a volume region to be imaged.

[0013] Specifically, the gradient magnetic fields along the readout direction, phase encoding direction, and slice direction are superimposed on the static magnetic field generated by the static magnetic field magnet 1 to provide spatial position information to the NMR signal generated from the subject S. Specifically, the gradient magnetic field in the readout direction changes the frequency of the NMR signal according to the position in the readout direction, thereby providing the NMR signal with position information in the readout direction. The gradient magnetic field in the phase encoding direction changes the phase of the NMR signal according to the position in the phase encoding direction, thereby providing the NMR signal with position information in the phase encoding direction. The gradient magnetic field in the slice direction provides the NMR signal with position information in the slice direction. For example, when the imaging region is a slice region (2D imaging), the gradient magnetic field in the slice direction is used to determine the direction, thickness, and number of slice regions, and when the imaging region is a volume region (3D imaging), it is used to change the phase of the NMR signal according to the position in the slice direction.

[0014] The whole-body RF coil 4 is disposed on the inner circumference side of the gradient magnetic field coil 2, transmits an RF pulse to the subject S disposed in the imaging space, and receives an NMR signal generated from the subject S due to the influence of the RF pulse. Specifically, the whole-body RF coil 4 is formed in a hollow, substantially cylindrical shape (including a shape in which the cross section perpendicular to the central axis is elliptical), and applies an RF magnetic field to the subject S disposed in the imaging space located on the inner circumference side thereof based on an RF pulse supplied from the transmission circuit 6. The whole-body RF coil 4 receives an NMR signal generated from the subject S due to the influence of the RF magnetic field, and outputs the received NMR signal to the reception circuit 7. For example, the whole-body RF coil 4 is a birdcage coil or a TEM (Transverse Electromagnetic) coil. Note that the whole-body RF coil 4 does not necessarily have both a transmission function and a reception function, and may have only a transmission function.

[0015] The local RF coil 5 is disposed near the subject S during imaging, transmits an RF pulse to the subject S disposed in the imaging space, and receives an NMR signal generated from the subject S due to the influence of the RF pulse. Specifically, the local RF coil 5 is prepared for each part of the subject S, disposed near the part to be imaged when imaging the subject S, and applies an RF magnetic field to the subject S based on an RF pulse supplied from the transmission circuit 6. The local RF coil 5 receives an NMR signal generated from the subject S due to the influence of the RF magnetic field, and outputs the received NMR signal to the reception circuit 7. For example, the local RF coil 5 is a surface coil or a phased array coil configured by combining a plurality of surface coils as coil elements. Note that the local RF coil 5 does not necessarily have both a transmission function and a reception function, and may have only a reception function.

[0016] The transmission circuit 6 outputs to the whole-body RF coil 4 or the local RF coil 5 an RF pulse corresponding to a resonance frequency (Larmor frequency) specific to the target atomic nucleus placed in the static magnetic field.

[0017] The receiving circuitry 7 generates NMR data based on the NMR signal output from the whole-body RF coil 4 or the local RF coil 5, and outputs the generated NMR data to the processing circuitry 15.

[0018] The RF shield 8 is disposed between the gradient magnetic field coil 2 and the whole-body RF coil 4, and shields the gradient magnetic field coil 2 from the RF magnetic field generated by the whole-body RF coil 4. Specifically, the RF shield 8 is formed in a hollow, approximately cylindrical shape (including a cylinder whose cross section perpendicular to the central axis is elliptical), and is disposed in the space on the inner periphery side of the gradient magnetic field coil 2 so as to cover the outer periphery of the whole-body RF coil 4.

[0019] The gantry 9 has a hollow bore 9a formed in a substantially cylindrical shape (including one in which the cross section perpendicular to the central axis has an elliptical shape), and houses the static magnetic field magnet 1, the gradient magnetic field coil 2, the whole-body RF coil 4, and the RF shield 8. Specifically, the gantry 9 houses each of the following in a state in which the whole-body RF coil 4 is disposed on the outer periphery of the bore 9a, the RF shield 8 is disposed on the outer periphery of the whole-body RF coil 4, the gradient magnetic field coil 2 is disposed on the outer periphery of the RF shield 8, and the static magnetic field magnet 1 is disposed on the outer periphery of the gradient magnetic field coil 2. Here, the space within the bore 9a of the gantry 9 becomes an imaging space in which the subject S is disposed during imaging.

[0020] The bed 10 includes a top plate 10a on which the subject S is placed, and when imaging the subject S, the top plate 10a on which the subject S is placed is moved to an imaging space. For example, the bed 10 is installed so that the longitudinal direction of the top plate 10a is parallel to the central axis of the static magnetic field magnet 1.

[0021] The input interface 11 accepts input operations of various instructions and various information from an operator. Specifically, the input interface 11 is connected to the processing circuit 17, converts the input operation received from the operator into an electrical signal, and outputs the electrical signal to the processing circuit 17. For example, the input interface 11 is realized by a trackball for setting imaging conditions and a region of interest (ROI), a switch button, a mouse, a keyboard, a touchpad for performing an input operation by touching the operation surface, a touch screen in which a display screen and a touchpad are integrated, a non-contact input circuit using an optical sensor, and a voice input circuit. Note that in this specification, the input interface 11 is not limited to only those 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 a control circuit is also included as an example of the input interface 11.

[0022] The display 12 displays various information. Specifically, the display 12 is connected to the processing circuit 17, and converts various information data sent from the processing circuit 17 into an electric signal for display and outputs it. For example, the display 12 is realized by a liquid crystal monitor, a CRT monitor, a touch panel, or the like.

[0023] The memory circuitry 13 stores various data. Specifically, the memory circuitry 13 is connected to the processing circuits 14 to 17, and stores various data input and output by each processing circuit. For example, the memory circuitry 13 is realized by a semiconductor memory element such as a RAM (Random Access Memory) or a flash memory, a hard disk, an optical disk, or the like.

[0024] The processing circuitry 14 has a bed control function 14a. The bed control function 14a controls the operation of the bed 10 by outputting a control electrical signal to the bed 10. For example, the bed control function 14a receives an instruction to move the top board 10a in the longitudinal direction, the up-down direction, or the left-right direction from the operator via the input interface 11, and operates a moving mechanism of the top board 10a of the bed 10 so as to move the top board 10a in accordance with the received instruction.

[0025] The processing circuitry 15 has an acquisition function 15a. The acquisition function 15a executes various pulse sequences to acquire k-space data. Specifically, the acquisition function 15a executes various pulse sequences by driving the gradient magnetic field power supply 3, the transmission circuitry 6, and the reception circuitry 7 according to sequence execution data output from the processing circuitry 17. Here, the sequence execution data is data representing a pulse sequence, and is information that specifies the timing and strength of the current that the gradient magnetic field power supply 3 supplies to the gradient magnetic field coil 2, the timing and strength of the RF pulse that the transmission circuitry 6 supplies to the whole-body RF coil 4, and the timing at which the reception circuitry 7 samples an NMR signal. Then, the acquisition function 15a receives the NMR data output from the reception circuitry 7 as a result of executing the pulse sequence, and stores it in the memory circuitry 13. At this time, the NMR data stored in the memory circuitry 13 is stored as k-space data representing a two-dimensional or three-dimensional k-space by adding position information along each of the readout direction, phase encoding direction, and slice direction by each of the gradient magnetic fields described above.

[0026] The processing circuitry 16 has a generating function 16a. The generating function 16a generates an image from the k-space data collected by the processing circuitry 15. Specifically, the generating function 16a reads out the k-space data collected by the processing circuitry 15 from the storage circuitry 13, and performs reconstruction processing such as Fourier transform on the read out k-space data to generate a two-dimensional or three-dimensional image. Then, the generating function 16a stores the generated image in the storage circuitry 13.

[0027] The processing circuitry 17 has an imaging control function 17a. The imaging control function 17a performs various imaging by controlling each component of the MRI device 100. Specifically, the imaging control function 17a displays a GUI (Graphical User Interface) for receiving input operations of various instructions and various information from an operator on the display 12, and controls each component of the MRI device 100 according to the input operation received via the input interface 11. For example, the imaging control function 17a generates sequence execution data based on imaging conditions input by the operator, and outputs the generated sequence execution data to the processing circuitry 15 to collect k-space data. Also, for example, the imaging control function 17a controls the processing circuitry 16 to reconstruct an image from the k-space data collected by the processing circuitry 15. Also, for example, the imaging control function 17a reads an image from the storage circuitry 13 in response to a request from the operator, and displays the read image on the display 12.

[0028] Here, the above-mentioned processing circuits 14 to 17 are realized by, for example, a processor. In this case, the processing functions of each processing circuit are stored in the storage circuit 13 in the form of, for example, a program executable by a computer. Then, each processing circuit realizes the processing function corresponding to each program by reading each program from the storage circuit 13 and executing it. In other words, each processing circuit in a state where each program is read has each function shown in each processing circuit in FIG. 1.

[0029] In this embodiment, each processing circuit is described as being realized by a single processor, but the embodiment is not limited to this, and each processing circuit may be configured by combining multiple independent processors, and each processor may execute a program to realize each processing function. Also, the processing functions of each processing circuit may be appropriately distributed or integrated into a single or multiple processing circuits. In the example shown in FIG. 1, a single storage circuit 13 is described as storing a program corresponding to each processing function, but multiple storage circuits may be distributed and arranged, and the processing circuits may read out corresponding programs from individual storage circuits.

[0030] The above describes an example of the configuration of the MRI apparatus 100 according to this embodiment. With this configuration, in this embodiment, the static magnetic field magnet 1 generates a static magnetic field whose magnetic field strength varies spatially in at least a part of the region inside the bore 9a, which is the imaging space.

[0031] FIG. 2 is a diagram showing the static magnetic field generated by the static magnetic field magnet 1 according to the first embodiment.

[0032] For example, as shown in FIG. 2, the static magnetic field generated by the cylindrically shaped static magnetic field magnet 1 has a uniform magnetic field strength in a region RC (hereinafter referred to as the uniform region) near the center of the bore 9a, but is not uniform in the surrounding region RP, and the magnetic field strength varies spatially.

[0033] In contrast, RF coils that receive NMR signals generally assume that the magnetic field strength of the static magnetic field is uniform, and are adjusted to a specific resonance frequency that corresponds to the magnetic field strength in the uniform region. Therefore, the sensitivity of the RF coil may decrease in regions where the magnetic field strength of the static magnetic field varies spatially.

[0034] FIG. 3 is a diagram for explaining a decrease in sensitivity of the RF coil related to the first embodiment.

[0035] Here, Figure 3 conceptually shows the region where the magnetic field strength of the static magnetic field varies spatially, with the distribution of the static magnetic field shown as a hatched pattern, with the darker the hatched pattern, the stronger the magnetic field strength of the static magnetic field.

[0036] For example, as shown in FIG. 3, when the magnetic field strength decreases as the distribution of the static magnetic field expands, the resonance frequency also decreases accordingly.

[0037] In contrast, the RF coil 20 generally has a sensitivity distribution in which the sensitivity is maximum at a specific resonance frequency and decreases as the frequency moves away from the resonance frequency, as shown by the curve SD in Fig. 3, and is adjusted to receive signals in a band Δf of a certain size centered on the resonance frequency. Therefore, as shown in Fig. 3, the region R in which the RF coil 20 can receive NMR signals is limited to the range in which the resonance frequency falls within the band Δf, and the sensitivity of the RF coil 20 decreases in positions where the resonance frequency falls outside the band Δf.

[0038] For this reason, the MRI apparatus 100 according to this embodiment is configured to be able to improve the sensitivity of the RF coil when the magnetic field strength of the static magnetic field varies spatially.

[0039] Specifically, the MRI apparatus 100 includes an RF coil that transmits RF pulses to a subject placed in a static magnetic field in which the magnetic field strength generated by a static magnetic field magnet 1 varies spatially, and receives an NMR signal generated from the subject by the effect of the RF pulse. Here, the RF coil may be a whole-body RF coil 4 or a local RF coil 5. Alternatively, the RF coil may be a combination of the transmitting function of the whole-body RF coil 4 and the receiving function of the local RF coil 5.

[0040] Then, the imaging control function 17a of the processing circuit 17 controls the RF coil so as to receive NMR signals at each of a plurality of frequencies adjusted according to the distribution of the static magnetic field generated by the static magnetic field magnet 1. Here, the imaging control function 17a is an example of a control unit.

[0041] In this embodiment, the MRI apparatus 100 includes a plurality of RF coils individually adjusted to a plurality of frequencies, and the imaging control function 17a controls each of the plurality of RF coils so as to receive an NMR signal at each of the plurality of frequencies.

[0042] 4 to 6 are diagrams showing an example of an RF coil included in the MRI apparatus 100 according to the first embodiment.

[0043] Here, similarly to FIG. 3, FIGS. 4 to 6 show an example in which the magnetic field strength decreases as the distribution of the static magnetic field expands.

[0044] 4, the MRI apparatus 100 includes a first RF coil 120a adjusted to a frequency A and a second RF coil 120b adjusted to a frequency B. Here, the frequency A of the first RF coil 120a is adjusted to a resonance frequency corresponding to the magnetic field strength of the static magnetic field in a first region Ra included in the range in which the static magnetic field is distributed. On the other hand, the frequency B of the second RF coil 120b is adjusted to a resonance frequency corresponding to the magnetic field strength of the static magnetic field in a second region Rb included in a range in which the magnetic field strength of the static magnetic field is lower than that of the first region Ra.

[0045] In this case, the first RF coil 120a is arranged at a position where it can receive an NMR signal generated in the first region Ra, and the second RF coil 120b is arranged at a position where it can receive an NMR signal generated in the second region Rb. For example, as shown in Fig. 4, the first RF coil 120a and the second RF coil 120b are arranged so that the detection surface of the first RF coil 120a is perpendicular to the direction in which the static magnetic field distribution spreads, and the detection surface of the second RF coil 120b is parallel to the direction in which the static magnetic field distribution spreads. Alternatively, for example, as shown in Fig. 5, the first RF coil 120a and the second RF coil 120b may be arranged in a stacked manner so that their detection surfaces are perpendicular to the direction in which the static magnetic field distribution spreads.

[0046] The imaging control function 17a then controls the first RF coil 120a to receive NMR signals at frequency A, and controls the second RF coil 120b to receive NMR signals at frequency B.

[0047] According to this configuration, by using two RF coils 120a and 120b, each of which is independently adjusted to two frequencies A and B in an electromagnetically coupled state, it becomes possible to receive NMR signals from two regions Ra and Rb along the direction in which the static magnetic field distribution spreads, for example, as shown in Fig. 6. This makes it possible to expand the range in which NMR signals can be received along the direction in which the static magnetic field distribution spreads, thereby improving the sensitivity of the RF coil.

[0048] Although an example of receiving NMR signals at two frequencies using two RF coils has been described here, the number of RF coils and frequencies is not limited to two, and may be three or more. This makes it possible to receive NMR signals from three or more regions along the direction in which the static magnetic field distribution spreads, and further expands the range in which NMR signals can be received.

[0049] For example, in this embodiment, the MRI apparatus 100 includes, as the above-mentioned RF coils, a plurality of transmitting coils for transmitting RF pulses and a plurality of receiving coils for receiving NMR signals.

[0050] FIG. 7 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus 100 according to the first embodiment.

[0051] For example, as shown in FIG. 7, the MRI apparatus 100 has a first transmitting coil 121a and a first receiving coil 122a tuned to a frequency A, and a second transmitting coil 121b and a second receiving coil 122b tuned to a frequency B.

[0052] The first transmitting coil 121a transmits an RF signal of frequency A to the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuit 17 via the processing circuit 15. The first receiving coil 122a receives an NMR signal of frequency A generated from the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuit 17 via the processing circuit 15. The second transmitting coil 121b transmits an RF signal of frequency B to the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuit 17 via the processing circuit 15. The second receiving coil 122b receives an NMR signal of frequency B generated from the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuit 17 via the processing circuit 15.

[0053] The MRI apparatus 100 also includes a pulse generator 161, a DAC (Digital to Analog Converter) 162, a changeover switch 163, a synthesizer 164, a first modulator 165a, a second modulator 165b, a first RF amplifier 166a, and a second RF amplifier 166b. For example, these devices are included in the transmission circuit 6 shown in FIG.

[0054] The pulse generator 161 generates a waveform of an RF pulse. The DAC 162 converts the waveform of the RF pulse generated by the pulse generator 161 from an analog signal to a digital signal and outputs the converted signal. The changeover switch 163 outputs the digital signal output from the DAC 162 to either the first modulator 165a or the second modulator 165b in response to a control signal transmitted from the imaging control function 17a of the processing circuit 17 via the processing circuit 15. The synthesizer 164 generates and outputs an RF signal. The first modulator 165a converts the frequency of the RF signal output from the synthesizer 164 to frequency A, and then modulates the RF signal with the waveform of the digital signal output from the changeover switch 163, thereby generating an RF pulse of frequency A. The second modulator 165b converts the frequency of the RF signal output from the synthesizer 164 to frequency B, and then modulates the RF signal with the waveform of the digital signal output from the changeover switch 163, thereby generating an RF pulse of frequency B. The first RF amplifier 166a amplifies the RF pulse of frequency A generated by the first modulator 165a and outputs it to the first transmission coil 121a. The second RF amplifier 166b amplifies the RF pulse of frequency B generated by the second modulator 165b and outputs it to the second transmission coil 121b.

[0055] The MRI apparatus 100 also includes a first preamplifier 171a, a second preamplifier 171b, a first detector 172a, a second detector 172b, a first ADC (Analog to Digital Converter) 173a, and a second ADC 173b. For example, these devices are included in the receiving circuit 7 shown in FIG.

[0056] The first preamplifier 171a amplifies and outputs the NMR signal of frequency A received by the first receiving coil 122a. The second preamplifier 171b amplifies and outputs the NMR signal of frequency B received by the second receiving coil 122b. The first detector 172a converts the frequency of the RF signal output from the synthesizer 164 to frequency A, and then detects the NMR signal output from the first preamplifier 171a using the RF signal and outputs it to the first ADC 173a. The second detector 172b converts the frequency of the RF signal output from the synthesizer 164 to frequency B, and then detects the NMR signal output from the second preamplifier 171b using the RF signal and outputs it to the second ADC 173b. The first ADC 173a generates NMR data by converting the NMR signal output from the first detector 172a from an analog signal to a digital signal, and outputs the generated NMR data to the processing circuit 15. The second ADC 173 b converts the NMR signal output from the second detector 172 b from an analog signal to a digital signal to generate NMR data, and outputs the generated NMR data to the processing circuit 15 .

[0057] Then, the imaging control function 17a controls the first transmitting coil 121a to transmit RF pulses at frequency A, and controls the first receiving coil 122a to receive NMR signals at frequency A. The imaging control function 17a also controls the second transmitting coil 121b to transmit RF pulses at frequency B, and controls the second receiving coil 122b to receive NMR signals at frequency B.

[0058] At this time, when one of the first transmitting coil 121a and the second transmitting coil 121b transmits an RF pulse, the imaging control function 17a controls the other transmitting coil to be in a decoupled state. Also, at this time, the imaging control function 17a controls both the first receiving coil 122a and the second receiving coil 122b to be in a decoupled state.

[0059] In addition, when the first receiving coil 122a and the second receiving coil 122b receive an NMR signal, the imaging control function 17a controls the first receiving coil 122a and the second receiving coil 122b so that they are simultaneously in a receiving state. In addition, at this time, the imaging control function 17a controls the first transmitting coil 121a and the second transmitting coil 121b so that they are both in a decoupled state.

[0060] For example, the imaging control function 17a controls each RF coil to transmit or receive at a desired frequency by controlling an element such as a PIN diode provided in each RF coil. Also, for example, the imaging control function 17a controls each RF coil to be in a decoupled state by controlling an element such as a PIN diode provided in each RF coil to shift the adjusted frequency from the desired frequency.

[0061] With this configuration, the imaging control function 17a controls each of the multiple RF coils so as to receive NMR signals at each of the multiple frequencies, thereby performing various types of imaging.

[0062] In this case, the imaging control function 17a controls the RF coil so as to switch the frequency at which the NMR signal is received, based on the frequency at which the RF pulse is transmitted.

[0063] Specifically, the imaging control function 17a controls the RF coil so as to switch the frequency for receiving the NMR signal, based on the position of the imaging slice.

[0064] For example, the imaging control function 17a controls the RF coil so as to sequentially transmit RF pulses at each of a plurality of frequencies and sequentially receive NMR signals at each of a plurality of frequencies.

[0065] FIG. 8 is a diagram showing an example of imaging performed by the imaging control function 17a according to the first embodiment.

[0066] For example, as shown in (a) of Fig. 8, when imaging a plurality of imaging slices A to C, it is assumed that the magnetic field strength of the static magnetic field generated by the static magnetic field magnet 1 varies along the slice direction. In this case, the imaging control function 17a controls each transmitting coil and each receiving coil to transmit RF pulses and receive NMR at different frequencies for each imaging slice.

[0067] For example, as shown in (b) of Fig. 8, the imaging control function 17a controls an RF coil (transmitting coil) to transmit an RF pulse (90° pulse) at a resonance frequency corresponding to the magnetic field strength of the static magnetic field at the position of each imaging slice at an interval of TR (Repetition Time) for each imaging slice. Then, the imaging control function 17a controls an RF coil (receiving coil) to receive an NMR signal at the same frequency as the RF pulse while changing the magnetic field strength of the gradient magnetic field in the phase encoding direction for each TR.

[0068] At this time, for example, when the change in the magnetic field strength of the static magnetic field along the slice direction has a sufficient gradient, the gradient magnetic field in the slice direction may not be used. Or, the gradient magnetic field in the slice direction may be used supplementarily to correct the linearity of the change in the magnetic field strength of the static magnetic field. In this case, the imaging control function 17a controls the RF coil to transmit and receive at each of a plurality of frequencies adjusted according to the distribution of the static magnetic field and the gradient magnetic field.

[0069] As described above, in the first embodiment, the static magnetic field magnet 1 generates a static magnetic field whose magnetic field strength varies spatially. Also, the RF coil transmits RF pulses to a subject placed in the static magnetic field whose magnetic field strength varies spatially, generated by the static magnetic field magnet 1, and receives an NMR signal generated from the subject by the influence of the RF pulse. Then, the imaging control function 17a controls the RF coil so as to receive an NMR signal at each of a plurality of frequencies adjusted according to at least the distribution of the static magnetic field.

[0070] Specifically, in the first embodiment, the MRI apparatus 100 includes a plurality of RF coils individually adjusted to a plurality of frequencies, and the imaging control function 17a controls each of the plurality of RF coils so as to receive an NMR signal at each of the plurality of frequencies.

[0071] According to such a configuration, when the magnetic field strength of the static magnetic field varies spatially, the range in which NMR signals can be received can be expanded by using a plurality of frequencies, and the sensitivity of the RF coil can be improved.

[0072] Although the first embodiment has been described above, the embodiment of the MRI apparatus 100 according to the present application is not limited to this. Therefore, other embodiments of the MRI apparatus 100 according to the present application will be described below. Note that in the following embodiments, differences from the first embodiment will be mainly described, and descriptions of contents common to the first embodiment will be omitted.

[0073] Second embodiment For example, in the above-mentioned first embodiment, the MRI apparatus 100 is described as having a plurality of RF coils individually adjusted to a plurality of frequencies, but the embodiment is not limited to this. For example, the MRI apparatus 100 may be provided with an RF coil configured to be adjustable to a plurality of frequencies. In the following, such an example will be described as a second embodiment.

[0074] In this embodiment, the MRI apparatus 100 includes an RF coil that is adjustable to a plurality of frequencies, and the imaging control function 17a switches the frequency of the RF coil so as to receive NMR signals at each of the plurality of frequencies.

[0075] For example, the RF coil configured to be adjustable to a plurality of frequencies is a dual-tuned coil, etc. For example, the imaging control function 17a switches the frequency of the RF coil by controlling an element such as a PIN diode provided in the RF coil to change the pattern of the coil elements included in the RF coil. Alternatively, for example, the imaging control function 17a switches the frequency of the RF coil by changing the capacitance of a trimmer capacitor provided in the RF coil to shift the adjusted frequency.

[0076] FIG. 9 is a diagram showing an example of an RF coil included in the MRI apparatus 100 according to the second embodiment.

[0077] Similarly to FIG. 3, FIG. 9 shows an example in which the magnetic field strength decreases as the distribution of the static magnetic field expands.

[0078] 9, the MRI apparatus 100 includes an RF coil 220 that is adjustable to two frequencies A and B. The imaging control function 17a switches the frequency of the RF coil 220 so as to receive NMR signals at the frequencies A and B, respectively.

[0079] Here, in this embodiment, frequency A is set to a resonance frequency corresponding to the magnetic field strength of the static magnetic field in a first region Ra included in the range in which the static magnetic field is distributed, and frequency B is set to a resonance frequency corresponding to the magnetic field strength of the static magnetic field in a second region Rb included in a range in which the magnetic field strength of the static magnetic field is lower than that of the first region Ra.

[0080] According to this configuration, by using the RF coil 220 that can be adjusted to two frequencies A and B, it becomes possible to receive NMR signals from two regions Ra and Rb along the direction in which the static magnetic field distribution spreads, as in the first embodiment. This makes it possible to widen the range in which NMR signals can be received along the direction in which the static magnetic field distribution spreads, and improve the sensitivity of the RF coil.

[0081] Although an example of receiving NMR signals at each frequency using an RF coil that can be adjusted to two frequencies has been described here, the number of frequencies is not limited to two and may be three or more. This makes it possible to receive NMR signals from three or more regions along the direction in which the static magnetic field distribution spreads, thereby further expanding the range in which NMR signals can be received.

[0082] For example, in this embodiment, the MRI apparatus 100 includes, as the above-mentioned RF coils, one transmitting coil configured to be adjustable to a plurality of frequencies and one receiving coil configured to be adjustable to a plurality of frequencies.

[0083] FIG. 10 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus 100 according to the second embodiment.

[0084] For example, as shown in FIG. 10, the MRI apparatus 100 includes a transmission coil 221 configured to be adjustable to frequencies A and B, and a reception coil 222 tuned to frequency B.

[0085] The transmitting coil 221 transmits an RF signal of frequency A or B to the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuitry 17 via the processing circuitry 15. The receiving coil 222 receives an NMR signal of frequency A or B generated from the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuitry 17 via the processing circuitry 15.

[0086] The MRI apparatus 100 also includes a pulse generator 161, a DAC 162, a changeover switch 163, a synthesizer 164, a first modulator 165a, a second modulator 165b, a first RF amplifier 266a, and a second RF amplifier 266b. For example, these devices are included in the transmission circuit 6 shown in FIG.

[0087] The pulse generator 161, the DAC 162, the changeover switch 163, the synthesizer 164, the first modulator 165a, and the second modulator 165b are the same as those in the first embodiment. The first RF amplifier 266a amplifies the RF pulse of frequency A generated by the first modulator 165a and outputs it to the transmission coil 221. The second RF amplifier 266b amplifies the RF pulse of frequency B generated by the second modulator 165b and outputs it to the transmission coil 221.

[0088] The MRI apparatus 100 also includes a first preamplifier 271a, a second preamplifier 271b, a first detector 172a, a second detector 172b, a first ADC 173a, and a second ADC 173b. For example, these devices are included in the receiving circuit 7 shown in FIG.

[0089] The first preamplifier 271a amplifies and outputs the NMR signal of frequency A received by the receiving coil 222. The second preamplifier 271b amplifies and outputs the NMR signal of frequency B received by the receiving coil 222. The first detector 172a, the second detector 172b, the first ADC 173a, and the second ADC 173b are the same as those in the first embodiment.

[0090] Then, the imaging control function 17a controls the transmitting coil 221 to transmit an RF pulse at a frequency A, and controls the receiving coil 222 to receive an NMR signal at the frequency A. The imaging control function 17a also controls the transmitting coil 221 to transmit an RF pulse at a frequency B, and controls the receiving coil 222 to receive an NMR signal at the frequency B.

[0091] With this configuration, the imaging control function 17a switches the frequency of the RF coil so as to receive NMR signals at each of a plurality of frequencies, and performs various imaging operations.

[0092] In this case, the imaging control function 17a controls the RF coil so as to switch the frequency for receiving the NMR signal based on the frequency for transmitting the RF pulse, as in the first embodiment.

[0093] Specifically, the imaging control function 17a controls the RF coil so as to switch the frequency for receiving the NMR signal, based on the position of the imaging slice, in the same manner as in the first embodiment.

[0094] For example, the imaging control function 17a controls the RF coil so as to sequentially transmit RF pulses at each of a plurality of frequencies and sequentially receive NMR signals at each of a plurality of frequencies, similarly to the first embodiment.

[0095] As described above, in the second embodiment, the MRI apparatus 100 includes an RF coil that is adjustable to multiple frequencies, and the imaging control function 17a switches the frequency of the RF coil so as to receive NMR signals at each of the multiple frequencies.

[0096] According to this configuration, as in the first embodiment, when the magnetic field strength of the static magnetic field varies spatially, the range in which NMR signals can be received can be expanded by using multiple frequencies, thereby improving the sensitivity of the RF coil.

[0097] (Third embodiment) In the above-mentioned first embodiment, the imaging control function 17a controls the RF coil to transmit RF pulses at a plurality of frequencies in sequence and receive NMR signals at a plurality of frequencies in sequence, but the embodiment is not limited to this. For example, the imaging control function 17a may transmit RF pulses in a wide band including a plurality of frequencies. In the following, such an example will be described as a third embodiment.

[0098] In this embodiment, the imaging control function 17a transmits RF pulses in a band including a plurality of frequencies, and controls the RF coil so as to simultaneously receive NMR signals at each of the plurality of frequencies.

[0099] For example, in this embodiment, the MRI apparatus 100 includes, as the above-mentioned RF coils, one transmission coil for transmitting RF pulses and a plurality of reception coils for receiving NMR signals.

[0100] FIG. 11 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus 100 according to the third embodiment.

[0101] For example, as shown in FIG. 11, the MRI apparatus 100 has a transmit coil 321 tuned to a band including frequencies A and B, a first receive coil 122a tuned to frequency A, and a second receive coil 122b tuned to frequency B.

[0102] The transmitting coil 321 transmits an RF signal in a band including frequencies A and B to the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuitry 17 via the processing circuitry 15. The first receiving coil 122a and the second transmitting coil 121b are the same as those in the first embodiment.

[0103] The MRI apparatus 100 also includes a pulse generator 161, a DAC 162, a modulator 365, and an RF amplifier 366. For example, these devices are included in the transmission circuit 6 shown in FIG.

[0104] Pulse generator 161, DAC 162, and synthesizer 164 are the same as those in the first embodiment. Modulator 365 converts the frequency of the RF signal output from synthesizer 164 to frequency A, and then modulates the RF signal with the waveform of the digital signal output from DAC 162 to generate an RF pulse in a band including frequencies A and B. RF amplifier 366 amplifies the RF pulse in a band including frequencies A and B generated by modulator 365a, and outputs the amplified RF pulse to transmission coil 321.

[0105] The MRI apparatus 100 also includes a first preamplifier 171a, a second preamplifier 171b, a first detector 172a, a second detector 172b, a first ADC 173a, and a second ADC 173b. For example, these devices are included in the receiving circuit 7 shown in FIG.

[0106] The first preamplifier 171a, the second preamplifier 171b, the first wave detector 172a, the second wave detector 172b, the first ADC 173a, and the second ADC 173b are similar to those in the first embodiment.

[0107] Then, the imaging control function 17a controls the transmitting coil 321 to transmit RF pulses in a band including frequencies A and B. The imaging control function 17a also controls the first receiving coil 122a to receive NMR signals at frequency A, and controls the second receiving coil 122b to receive NMR signals at frequency B.

[0108] At this time, the imaging control function 17a controls so that both the first receiving coil 122a and the second receiving coil 122b are in a decoupled state when the transmitting coil 321 transmits an RF pulse.

[0109] In addition, when the first receiving coil 122a and the second receiving coil 122b receive an NMR signal, the imaging control function 17a controls the first receiving coil 122a and the second receiving coil 122b so that they are simultaneously in a receiving state. In addition, at this time, the imaging control function 17a controls the first transmitting coil 121a and the second transmitting coil 121b so that they are both in a decoupled state.

[0110] With this configuration, the imaging control function 17a transmits RF pulses in a band including a plurality of frequencies, and controls the RF coil to simultaneously receive NMR signals at each of the plurality of frequencies, thereby performing various types of imaging.

[0111] For example, the imaging control function 17a performs parallel imaging using a plurality of receiving coils tuned to different frequencies, where the plurality of receiving coils are, for example, a plurality of coil elements included in a phased array coil.

[0112] In this case, the frequency of each receiving coil is adjusted to a resonance frequency corresponding to the magnetic field strength of the static magnetic field at the position of each coil. Then, the imaging control function 17a controls the transmitting coil to transmit RF pulses in a band including the frequency of each receiving coil, and controls the multiple receiving coils to simultaneously receive NMR signals at each of the multiple frequencies.

[0113] In parallel imaging, NMR signals received by multiple receiving coils are synthesized to generate an image, and then the image is expanded to generate an image with aliasing removed. In general, the signal-to-noise ratio (SNR) when using parallel imaging is parallel is expressed by the following formula:

[0114]

number

[0115] Here, SNR is the SNR without parallel imaging, g is the g-factor, and R is the speed ratio. Among these parameters, the g-factor is a factor that affects the image quality, and the higher the independence of the sensitivity distribution of each receiving coil, the smaller the g-factor value becomes, and the higher the image quality of the generated image becomes.

[0116] In this embodiment, by receiving NMR signals at each of a plurality of frequencies, a frequency-dependent sensitivity distribution is generated in addition to the normal sensitivity distribution of a receiving coil, and the sensitivity distribution of each receiving coil becomes more independent. As a result, the g-factor value is reduced, and the image quality of the image generated by parallel imaging can be improved.

[0117] As described above, in the third embodiment, the imaging control function 17a transmits RF pulses in a band including a plurality of frequencies, and controls the RF coil to simultaneously receive NMR signals at each of the plurality of frequencies.

[0118] According to this configuration, as in the first embodiment, when the magnetic field strength of the static magnetic field varies spatially, the range in which NMR signals can be received can be expanded by using multiple frequencies, thereby improving the sensitivity of the RF coil.

[0119] Moreover, in the third embodiment, the quality of the image generated by parallel imaging can be improved.

[0120] (Fourth embodiment) In the above-mentioned second embodiment, an example in which a plurality of modulators and a plurality of detectors are used has been described, but the embodiment is not limited to this. For example, in the configuration of the transmission and reception system shown in Fig. 10, the modulator and detector may be shared by using a modulator and a detector that can be switched to a plurality of frequencies. In the following, such an example will be described as a fourth embodiment.

[0121] FIG. 12 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus 100 according to the fourth embodiment.

[0122] For example, as shown in FIG. 12, the MRI apparatus 100 includes a transmission coil 221 configured to be adjustable to frequencies A and B, and a reception coil 222 tuned to frequency B.

[0123] The transmitting coil 221 and the receiving coil 222 are similar to those in the second embodiment.

[0124] The MRI apparatus 100 also includes a pulse generator 161, a DAC 162, a synthesizer 164, a modulator 465, a changeover switch 467, a first RF amplifier 266a, and a second RF amplifier 266b. For example, these devices are included in the transmission circuit 6 shown in FIG.

[0125] The pulse generator 161, the DAC 162, and the synthesizer 164 are the same as those in the first embodiment. The modulator 465 converts the frequency of the RF signal output from the synthesizer 164 into frequencies A and B, respectively, and then modulates the RF signal with the waveform of the digital signal output from the DAC 162 to generate an RF pulse of frequency A and an RF pulse of frequency B. The changeover switch 467 outputs the RF pulse of frequency A generated by the modulator 456 to the first RF amplifier 266a, or outputs the RF pulse of frequency B generated by the modulator 456 to the second RF amplifier 266b, in response to a control signal transmitted from the imaging control function 17a of the processing circuit 17 via the processing circuit 15. The first RF amplifier 266a and the second RF amplifier 266b are the same as those in the second embodiment.

[0126] 1. The MRI apparatus 100 also includes a first preamplifier 271a, a second preamplifier 271b, a changeover switch 474, a detector 472, and an ADC 473. For example, these devices are included in the receiving circuit 7 shown in FIG.

[0127] The first preamplifier 271a and the second preamplifier 271b are the same as those in the second embodiment. The changeover switch 474 outputs the NMR signal of frequency A output from the first preamplifier 271a or the NMR signal of frequency B output from the second preamplifier 271b to the detector 472 in response to a control signal transmitted from the imaging control function 17a of the processing circuit 17 via the processing circuit 15. The detector 472 converts the frequency of the RF signal output from the synthesizer 164 to frequencies A and B, respectively, and then detects and outputs the NMR signal output from the changeover switch 474 using the RF signal. The ADC 473 generates NMR data by converting the NMR signal output from the detector 472 from an analog signal to a digital signal, and outputs the generated NMR data to the processing circuit 15.

[0128] Then, the imaging control function 17a controls the transmitting coil 221 and the receiving coil 222 in the same manner as in the second embodiment.

[0129] Fifth embodiment In the above-mentioned first embodiment, an example in which a plurality of modulators and a plurality of detectors are used as in the second embodiment has been described, but the embodiment is not limited to this. For example, in the configuration of the transmission and reception system shown in Fig. 7, a modulator and a detector that can be switched to a plurality of frequencies as in the fourth embodiment may be used to make the modulator and the detector common to each other. In the following, such an example will be described as the fifth embodiment.

[0130] FIG. 13 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus 100 according to the fifth embodiment.

[0131] For example, as shown in FIG. 13, the MRI apparatus 100 has a first transmitting coil 121a and a first receiving coil 122a tuned to frequency A, and a second transmitting coil 121b and a second receiving coil 122b tuned to frequency B.

[0132] The first transmitting coil 121a, the first receiving coil 122a, the second transmitting coil 121b, and the second receiving coil 122b are similar to those in the first embodiment.

[0133] The MRI apparatus 100 also includes a pulse generator 161, a DAC 162, a synthesizer 164, a modulator 465, a changeover switch 467, a first RF amplifier 166a, and a second RF amplifier 166b. For example, these devices are included in the transmission circuit 6 shown in FIG.

[0134] The pulse generator 161, the DAC 162, the synthesizer 164, the first RF amplifier 166a, and the second RF amplifier 166b are the same as those in the first embodiment. The modulator 465 and the changeover switch 467 are the same as those in the fourth embodiment.

[0135] 1. The MRI apparatus 100 also includes a first preamplifier 171a, a second preamplifier 171b, a changeover switch 474, a detector 472, and an ADC 473. For example, these devices are included in the receiving circuit 7 shown in FIG.

[0136] The first preamplifier 171a and the second preamplifier 171b are the same as those in the first embodiment. The changeover switch 474, the wave detector 472, and the ADC 473 are the same as those in the fourth embodiment.

[0137] Then, the imaging control function 17a controls the first transmitting coil 121a, the second transmitting coil 121b, the first receiving coil 122a, and the second receiving coil 122b, in the same manner as in the first embodiment.

[0138] Sixth embodiment In the above-mentioned first embodiment, an example of using a plurality of transmitting coils and a plurality of receiving coils is described, but the embodiment is not limited thereto. For example, in the configuration of the transmitting and receiving system shown in FIG. 7, a plurality of transmitting and receiving coils may be used instead of a plurality of transmitting coils and a plurality of receiving coils. In the following, such an example will be described as a sixth embodiment.

[0139] FIG. 14 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus 100 according to the sixth embodiment.

[0140] For example, as shown in FIG. 14, the MRI apparatus 100 has a first transmit / receive coil 623a tuned to a frequency A and a second transmit / receive coil 623b tuned to a frequency B.

[0141] The first transmit / receive coil 623a transmits an RF signal of frequency A to the subject and receives an NMR signal of frequency A generated from the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuitry 17 via the processing circuitry 15. The second transmit / receive coil 623b transmits an RF signal of frequency B to the subject and receives an NMR signal of frequency B generated from the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuitry 17 via the processing circuitry 15.

[0142] The MRI apparatus 100 also includes a pulse generator 161, a DAC 162, a changeover switch 163, a synthesizer 164, a first modulator 165a, a second modulator 165b, a first RF amplifier 666a, and a second RF amplifier 666b. For example, these devices are included in the transmission circuit 6 shown in FIG.

[0143] The pulse generator 161, DAC 162, changeover switch 163, synthesizer 164, first modulator 165a, and second modulator 165b are the same as those in the first embodiment. The first RF amplifier 666a amplifies the RF pulse of frequency A generated by the first modulator 165a and outputs it to the first transmission / reception coil 623a. The second RF amplifier 666b amplifies the RF pulse of frequency B generated by the second modulator 165b and outputs it to the second transmission / reception coil 623b.

[0144] The MRI apparatus 100 also includes a first preamplifier 671a, a second preamplifier 671b, a first detector 172a, a second detector 172b, a first ADC 173a, and a second ADC 173b. For example, these devices are included in the receiving circuit 7 shown in FIG.

[0145] The first preamplifier 671a amplifies and outputs the NMR signal of frequency A received by the first transmission / reception coil 623a. The second preamplifier 671b amplifies and outputs the NMR signal of frequency B received by the second transmission / reception coil 623b. The first detector 172a, the second detector 172b, the first ADC 173a, and the second ADC 173b are the same as those in the first embodiment.

[0146] The imaging control function 17a then controls the first transmitting / receiving coil 623a to transmit RF pulses at frequency A, and controls the first transmitting / receiving coil 623a to receive NMR signals at frequency A. The imaging control function 17a also controls the second transmitting / receiving coil 623b to transmit RF pulses at frequency B, and controls the second transmitting / receiving coil 623b to receive NMR signals at frequency B.

[0147] At this time, the imaging control function 17a controls one of the first transmission / reception coil 623a and the second transmission / reception coil 623b so that when the other transmission / reception coil transmits an RF pulse, the other transmission / reception coil is in a decoupled state.

[0148] Furthermore, when the first transmission / reception coil 623a and the second transmission / reception coil 623b receive an NMR signal, the imaging control function 17a controls the first transmission / reception coil 623a and the second transmission / reception coil 623b so that the first transmission / reception coil 623a and the second transmission / reception coil 623b are in a state in which they can simultaneously receive signals.

[0149] Seventh embodiment In the sixth embodiment described above, an example in which multiple modulators and multiple detectors are used as in the first embodiment has been described, but the embodiment is not limited to this. For example, in the configuration of the transmission and reception system shown in Fig. 15, the modulator and detector may be shared by using a modulator and detector that can be switched to multiple frequencies as in the fourth embodiment. In the following, such an example will be described as the seventh embodiment.

[0150] FIG. 15 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus 100 according to the seventh embodiment.

[0151] For example, as shown in FIG. 15, the MRI apparatus 100 has a first transmit / receive coil 623a tuned to a frequency A and a second transmit / receive coil 623b tuned to a frequency B.

[0152] The first transmission / reception coil 623a and the second transmission / reception coil 623b are similar to those in the sixth embodiment.

[0153] The MRI apparatus 100 also includes a pulse generator 161, a DAC 162, a synthesizer 164, a modulator 465, a changeover switch 467, a first RF amplifier 666a, and a second RF amplifier 666b. For example, these devices are included in the transmission circuit 6 shown in FIG.

[0154] The pulse generator 161, the DAC 162, and the synthesizer 164 are the same as those in the first embodiment. The modulator 465 and the changeover switch 467 are the same as those in the fourth embodiment. The first RF amplifier 666a and the second RF amplifier 666b are the same as those in the sixth embodiment.

[0155] 1. The MRI apparatus 100 also includes a first preamplifier 671a, a second preamplifier 671b, a changeover switch 474, a detector 472, and an ADC 473. For example, these devices are included in the receiving circuit 7 shown in FIG.

[0156] The first preamplifier 671a and the second preamplifier 671b are the same as those in the sixth embodiment. The changeover switch 474, the wave detector 472, and the ADC 473 are the same as those in the fourth embodiment.

[0157] Then, the imaging control function 17a controls the first transmission / reception coil 623a and the second transmission / reception coil 623b in the same manner as in the sixth embodiment.

[0158] Eighth embodiment In the above-mentioned second embodiment, an example is described in which one transmitting coil configured to be adjustable to a plurality of frequencies and one receiving coil configured to be adjustable to a plurality of frequencies are used, but the embodiment is not limited thereto. For example, in the configuration of the transmitting and receiving system shown in FIG. 10, one transmitting and receiving coil configured to be adjustable to a plurality of frequencies may be used instead of one transmitting coil and one receiving coil. In the following, such an example is described as the eighth embodiment.

[0159] FIG. 16 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus 100 according to the eighth embodiment.

[0160] For example, as shown in FIG. 16, the MRI apparatus 100 has a transmit / receive coil 823 that is adjustable to frequencies A and B.

[0161] The transmission / reception coil 823 transmits an RF signal of frequency A or B to the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuitry 17 via the processing circuitry 15. The transmission / reception coil 823 also receives an NMR signal of frequency A or B generated from the subject in response to a control signal transmitted from the imaging control function 17a of the processing circuitry 17 via the processing circuitry 15.

[0162] The MRI apparatus 100 also includes a pulse generator 161, a DAC 162, a changeover switch 163, a synthesizer 164, a first modulator 165a, a second modulator 165b, a first RF amplifier 866a, and a second RF amplifier 866b. For example, these devices are included in the transmission circuit 6 shown in FIG.

[0163] The pulse generator 161, DAC 162, changeover switch 163, synthesizer 164, first modulator 165a, and second modulator 165b are the same as those in the first embodiment. The first RF amplifier 866a amplifies the RF pulse of frequency A generated by the first modulator 165a and outputs it to the transmitting / receiving coil 823. The second RF amplifier 866b amplifies the RF pulse of frequency B generated by the second modulator 165b and outputs it to the transmitting / receiving coil 823.

[0164] The MRI apparatus 100 also includes a first preamplifier 871a, a second preamplifier 871b, a first detector 172a, a second detector 172b, a first ADC 173a, and a second ADC 173b. For example, these devices are included in the receiving circuit 7 shown in FIG.

[0165] The first preamplifier 871a amplifies and outputs the NMR signal of frequency A received by the transmission and reception coil 823. The second preamplifier 871b amplifies and outputs the NMR signal of frequency B received by the transmission and reception coil 823. The first detector 172a, the second detector 172b, the first ADC 173a, and the second ADC 173b are the same as those in the first embodiment.

[0166] Then, the imaging control function 17a controls the transmission / reception coil 823 to transmit RF pulses at frequency A, and controls the transmission / reception coil 823 to receive NMR signals at frequency A. The imaging control function 17a also controls the transmission / reception coil 823 to transmit RF pulses at frequency B, and controls the transmission / reception coil 823 to receive NMR signals at frequency B.

[0167] Ninth embodiment In the above-mentioned eighth embodiment, an example in which a plurality of modulators and a plurality of detectors are used as in the first embodiment has been described, but the embodiment is not limited to this. For example, in the configuration of the transmission and reception system shown in Fig. 16, a modulator and a detector that can be switched to a plurality of frequencies as in the fourth embodiment may be used to make the modulator and the detector common to each other. In the following, such an example will be described as the ninth embodiment.

[0168] FIG. 17 is a diagram showing an example of the configuration of a transmission / reception system included in the MRI apparatus 100 according to the ninth embodiment.

[0169] For example, as shown in FIG. 17, the MRI apparatus 100 includes a transmit / receive coil 823 that is adjustable to frequencies A and B.

[0170] The transmission and reception coil 823 is the same as that in the eighth embodiment.

[0171] The MRI apparatus 100 also includes a pulse generator 161, a DAC 162, a synthesizer 164, a modulator 465, a changeover switch 467, a first RF amplifier 866a, and a second RF amplifier 866b. For example, these devices are included in the transmission circuit 6 shown in FIG.

[0172] The pulse generator 161, the DAC 162, and the synthesizer 164 are the same as those in the first embodiment. The modulator 465 and the changeover switch 467 are the same as those in the fourth embodiment. The first RF amplifier 866a and the second RF amplifier 866b are the same as those in the eighth embodiment.

[0173] 1. The MRI apparatus 100 also includes a first preamplifier 871a, a second preamplifier 871b, a changeover switch 474, a detector 472, and an ADC 473. For example, these devices are included in the receiving circuit 7 shown in FIG.

[0174] The first preamplifier 871a and the second preamplifier 871b are the same as those in the eighth embodiment. The changeover switch 474, the wave detector 472, and the ADC 473 are the same as those in the fourth embodiment.

[0175] Then, the imaging control function 17a controls the transmission and reception coil 823 in the same manner as in the eighth embodiment.

[0176] (Other embodiments) In the above-mentioned embodiment, the MRI apparatus 100 having a so-called tunnel-type structure in which the static magnetic field magnet 1, the gradient magnetic field coil 2, and the whole-body RF coil 4 are each formed in a substantially cylindrical shape has been described, but the embodiment is not limited thereto. For example, the technology disclosed in the present application can be similarly applied to an MRI apparatus having a so-called open-type structure in which a pair of static magnetic field magnets, a pair of gradient magnetic field coils, and a pair of RF coils are arranged to face each other across the imaging space in which the subject S is placed. In other words, the technology disclosed in the present application can be applied to various MRI apparatuses as long as the MRI apparatus has a static magnetic field magnet that generates a static magnetic field whose magnetic field strength varies spatially in at least a part of the region in the imaging space in which the subject is placed.

[0177] In addition, in each of the above-mentioned embodiments, an example has been described in which the control unit in this specification is realized by the imaging control function 17a of the processing circuit 17, but the embodiment is not limited to this. For example, the control unit in this specification may be realized by only hardware, only software, or a combination of hardware and software, in addition to being realized by the imaging control function 17a described in the embodiments.

[0178] In the above description, the "processor" reads out and executes a program corresponding to each processing function from a storage circuit, but the embodiment is not limited to this. The term "processor" refers to a circuit such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an Application Specific Integrated Circuit (ASIC), a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)). When the processor is a CPU, for example, the processor reads out and executes a program stored in a storage circuit to realize each processing function. On the other hand, when the processor is an ASIC, instead of storing a program in a storage circuit, the processing function is directly incorporated as a logic circuit in the circuit of the processor. Note that each processor in this embodiment is not limited to being configured as a single circuit for each processor, but may be configured as a single processor by combining multiple independent circuits to realize its processing function. Furthermore, multiple components in FIG. 1 may be integrated into one processor to realize the processing functions.

[0179] Here, the program executed by the processor is provided by being pre-installed in a ROM (Read Only Memory), a storage circuit, or the like. The program may be provided by being recorded in a computer-readable storage medium such as a CD (Compact Disk)-ROM, a FD (Flexible Disk), a CD-R (Recordable), or a DVD (Digital Versatile Disk) in a format that can be installed in these devices or in a format that can be executed. The program may also be provided or distributed by being stored on a computer connected to a network such as the Internet and downloaded via the network. For example, the program is composed of modules including each of the above-mentioned functional units. As actual hardware, a CPU reads out the program from a storage medium such as a ROM and executes it, so that each module is loaded onto a main storage device and generated on the main storage device.

[0180] According to at least one of the embodiments described above, it is possible to improve the sensitivity of the RF coil when the magnetic field strength of the static magnetic field varies spatially.

[0181] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0182] 100 MRI machine 1 Static magnetic field magnet 4 Whole-body RF coil 5 Local RF coil 17 Processing circuit 17a Imaging control function

Claims

1. a static magnetic field magnet that generates a static magnetic field whose magnetic field strength varies spatially; a plurality of transmit / receive coils for transmitting radio frequency pulses to a subject placed in a static magnetic field whose magnetic field strength varies spatially and receiving nuclear magnetic resonance signals generated from the subject by the effect of the radio frequency pulses; a control unit that controls the plurality of transmission / reception coils so as to transmit the radio frequency pulse at each of a plurality of frequencies adjusted in accordance with at least the distribution of the static magnetic field and to receive the nuclear magnetic resonance signal at each of the plurality of frequencies; A magnetic resonance imaging apparatus comprising:

2. The control unit controls the plurality of transmission / reception coils so as to switch a frequency for receiving the nuclear magnetic resonance signal based on a frequency for transmitting the radio frequency pulse.

2. A magnetic resonance imaging apparatus according to claim 1.

3. the control unit controls the plurality of transmission / reception coils so as to switch a frequency for receiving the nuclear magnetic resonance signal based on a position of an imaging slice.

3. A magnetic resonance imaging apparatus according to claim 1 or 2.

4. the control unit controls the plurality of transmission / reception coils to sequentially transmit the radio frequency pulses at each of the plurality of frequencies and sequentially receive the nuclear magnetic resonance signals at each of the plurality of frequencies.

4. The magnetic resonance imaging apparatus according to claim 1,

5. the control unit controls the plurality of transmission / reception coils to transmit the radio frequency pulse in a band including the plurality of frequencies and to simultaneously receive the nuclear magnetic resonance signal at each of the plurality of frequencies.

4. The magnetic resonance imaging apparatus according to claim 1,

6. the frequency of each of the plurality of transmitting / receiving coils is adjusted to a resonance frequency corresponding to a magnetic field strength of a static magnetic field at the position of each transmitting / receiving coil; The control unit performs parallel imaging using the plurality of transmit / receive coils.

6. A magnetic resonance imaging apparatus according to claim 5.

7. A receiving coil configured to be tunable to the plurality of frequencies, The control unit switches the frequency of the receiving coil so as to receive the nuclear magnetic resonance signal at each of the plurality of frequencies.

5. A magnetic resonance imaging apparatus according to claim 1.

8. The control unit controls the other transmission / reception coils to be in a decoupled state when one transmission / reception coil of the plurality of transmission / reception coils transmits the radio frequency pulse.

8. A magnetic resonance imaging apparatus according to claim 7.

9. The control unit controls the plurality of transmission / reception coils to be in a state in which they can simultaneously receive the nuclear magnetic resonance signal when the plurality of transmission / reception coils receive the nuclear magnetic resonance signal.

9. A magnetic resonance imaging apparatus according to claim 8.

10. A static magnetic field magnet generates a static magnetic field whose field strength varies spatially, a plurality of transmit / receive coils transmit radio frequency pulses to a subject placed in a static magnetic field whose magnetic field strength varies spatially, and receive nuclear magnetic resonance signals generated from the subject by the effect of the radio frequency pulses; a receiving coil receives a nuclear magnetic resonance signal generated from the subject by the effect of the radio frequency pulse; A control unit controls the plurality of transmission / reception coils so as to transmit the radio frequency pulse at each of a plurality of frequencies adjusted according to at least the distribution of the static magnetic field and to receive the nuclear magnetic resonance signal at each of the plurality of frequencies. A magnetic resonance imaging method comprising:

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