Magnetic resonance imaging apparatus 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] The embodiments disclosed in this specification and the drawings relate to magnetic resonance imaging apparatuses and methods.

Background Art

[0002] Conventionally, a magnetic resonance imaging (MRI) apparatus transmits a radio frequency (RF) pulse to a subject placed in a static magnetic field, and receives a nuclear magnetic resonance (NMR) signal generated from the subject due to the influence of the RF pulse to generate an image. The MRI apparatus includes an RF coil adjusted to a predetermined resonance frequency in order to transmit the RF pulse and receive the NMR signal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems 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 the RF coil when the magnetic field strength of the static magnetic field changes spatially. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. It is also possible to position the problems corresponding to the respective effects of each configuration shown in the embodiments described later as other problems.

Means for Solving the Problems

[0005] The MRI apparatus according to this embodiment comprises a static magnetic field magnet, a plurality of transmitting and receiving coils, and a control unit. The static magnetic field magnet generates a static magnetic field in which the magnetic field strength changes spatially. The plurality of transmitting and receiving coils transmit RF pulses to a subject placed in the static magnetic field in which the magnetic field strength changes spatially, and receive NMR signals generated from the subject as a result of the influence of the high-frequency pulses. The control unit controls the plurality of transmitting and receiving 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 explanation of the drawing]

[0006] [Figure 1] Figure 1 shows an example of the configuration of an MRI apparatus according to the first embodiment. [Figure 2] Figure 2 shows the static magnetic field generated by the static magnetic field magnet according to the first embodiment. [Figure 3] Figure 3 is a diagram illustrating the decrease in sensitivity of the RF coil related to the first embodiment. [Figure 4] Figure 4 shows an example of an RF coil included in an MRI device according to the first embodiment. [Figure 5] Figure 5 shows an example of an RF coil included in an MRI device according to the first embodiment. [Figure 6] Figure 6 shows an example of an RF coil included in an MRI device according to the first embodiment. [Figure 7] Figure 7 shows an example of the configuration of the transmission and reception system of an MRI device according to the first embodiment. [Figure 8] Figure 8 shows an example of imaging performed by the imaging control function according to the first embodiment. [Figure 9] Figure 9 shows an example of an RF coil included in an MRI device according to the second embodiment. [Figure 10] Figure 10 shows an example of the configuration of the transmission and reception system of an MRI device according to the second embodiment. [Figure 11]Figure 11 shows an example of the configuration of the transmission and reception system included in an MRI device according to the third embodiment. [Figure 12] Figure 12 shows an example of the configuration of the transmission and reception system of an MRI device according to the fourth embodiment. [Figure 13] Figure 13 shows an example of the configuration of the transmission and reception system included in the MRI device according to the fifth embodiment. [Figure 14] Figure 14 shows an example of the configuration of the transmission and reception system of an MRI device according to the sixth embodiment. [Figure 15] Figure 15 shows an example of the configuration of the transmission and reception system of an MRI device according to the seventh embodiment. [Figure 16] Figure 16 shows an example of the configuration of the transmission and reception system of an MRI device according to the eighth embodiment. [Figure 17] Figure 17 shows an example of the configuration of the transmission and reception system of an MRI device according to the ninth embodiment. [Modes for carrying out the invention]

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

[0008] (First embodiment) Figure 1 shows an example of the configuration of an MRI apparatus according to the first embodiment.

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

[0010] The static magnetic field magnet 1 generates a static magnetic field in the imaging space where the subject S is placed. Specifically, the static magnetic field magnet 1 is formed in a hollow substantially cylindrical shape (including those with an elliptical cross-sectional shape orthogonal to the central axis), and generates a static magnetic field in the imaging space formed on the inner peripheral side thereof. For example, the static magnetic field magnet 1 is a superconducting magnet, a permanent magnet, or the like. The superconducting magnet mentioned 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 magnetic field coil 2 is disposed inside the static magnetic field magnet 1 and generates a gradient magnetic field in the imaging space where the subject S is placed. Specifically, the gradient magnetic field coil 2 is formed in a hollow substantially cylindrical shape (including those with an elliptical cross-sectional shape orthogonal to the central axis), and has an X coil, a Y coil, and a Z coil corresponding to the X axis, the Y axis, and the Z axis orthogonal to each other, respectively. The X coil, the Y coil, and the Z coil generate a gradient magnetic field that linearly changes along each axial direction in the imaging space based on the 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. Also, the X axis is set to be along the horizontal direction orthogonal to the Z axis, and the Y axis is set to be along the vertical direction orthogonal to the Z axis. Here, the X axis, the Y axis, and the Z axis constitute a device 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 current to the gradient magnetic field coil 2. Specifically, the gradient magnetic field power supply 3 supplies current to the X coil, the Y coil, and the Z coil of the gradient magnetic field coil 2 individually, thereby generating a gradient magnetic field that linearly changes along the readout direction, the phase encoding direction, and the slice direction orthogonal to each other in the imaging space. Here, the axis along the readout direction, the axis along the phase encoding direction, and the axis along the slice direction constitute a logical coordinate system for defining the slice region or volume region to be imaged.

[0013] Specifically, the gradient magnetic fields along the readout direction, the phase encoding direction, and the slice direction are superimposed on the static magnetic field generated by the static magnetic field magnet 1, thereby imparting spatial position information to the NMR signal generated from the subject S. Specifically, the gradient magnetic field in the readout direction imparts the position information in the readout direction to the NMR signal by changing the frequency of the NMR signal according to the position in the readout direction. Further, the gradient magnetic field in the phase encoding direction imparts the position information in the phase encoding direction to the NMR signal by changing the phase of the NMR signal according to the position in the phase encoding direction. Also, the gradient magnetic field in the slice direction imparts the position information in the slice direction to the NMR signal. 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 slices of the slice region, 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 peripheral side of the gradient magnetic field coil 2, transmits an RF pulse to the subject S disposed in the imaging space, and receives the 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 those having an elliptical shape in the cross-section orthogonal to the central axis), and based on the RF pulse supplied from the transmission circuit 6, applies an RF magnetic field to the subject S disposed in the imaging space located on its inner peripheral side. Then, the whole-body RF coil 4 receives the 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-type 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 positioned near the subject S during imaging and transmits RF pulses to the subject S positioned in the imaging space, and receives the NMR signal generated from the subject S due to the influence of the RF pulses. Specifically, a local RF coil 5 is prepared for each part of the subject S and is positioned near the part to be imaged when imaging of the subject S is performed, and applies an RF magnetic field to the subject S based on the RF pulses supplied from the transmission circuit 6. The local RF coil 5 then receives the NMR signal generated from the subject S due to the influence of the RF magnetic field and outputs the received NMR signal to the receiving circuit 7. For example, the local RF coil 5 is a surface coil or a phased array coil composed of multiple surface coils combined 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 transmitting circuit 6 outputs an RF pulse corresponding to the resonance frequency (Larmor frequency) unique to the target atomic nucleus placed in the static magnetic field to the whole-body RF coil 4 or the local RF coil 5.

[0017] The receiving circuit 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 circuit 15.

[0018] The RF shield 8 is positioned between the gradient magnetic field coil 2 and the whole-body RF coil 4, shielding 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, substantially cylindrical shape (including those with an elliptical cross-sectional shape perpendicular to the central axis of the cylinder), and is positioned in the space on the inner circumference side of the gradient magnetic field coil 2 so as to cover the outer surface of the whole-body RF coil 4.

[0019] The rig 9 has a hollow bore 9a formed in a substantially cylindrical shape (including those with an elliptical cross-sectional shape perpendicular to the central axis), and houses a static magnetic field magnet 1, a gradient magnetic field coil 2, a whole-body RF coil 4, and an RF shield 8. Specifically, the rig 9 houses the whole-body RF coil 4 on the outer circumference of the bore 9a, the RF shield 8 on the outer circumference of the whole-body RF coil 4, the gradient magnetic field coil 2 on the outer circumference of the RF shield 8, and the static magnetic field magnet 1 on the outer circumference of the gradient magnetic field coil 2. Here, the space within the bore 9a of the rig 9 becomes the imaging space where the subject S is placed during imaging.

[0020] The examination bed 10 is equipped with a top plate 10a on which the subject S is placed, and when imaging of the subject S is performed, the top plate 10a on which the subject S is placed is moved into the imaging space. For example, the examination 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 receives various instructions and information input operations from the operator. Specifically, the input interface 11 is connected to the processing circuit 17 and converts the input operations received from the operator into electrical signals and outputs them to the processing circuit 17. For example, the input interface 11 can be implemented by a trackball for setting imaging conditions and regions of interest (ROI), a switch button, a mouse, a keyboard, a touchpad for input operations by touching the operating surface, a touchscreen that integrates a display screen and a touchpad, a non-contact input circuit using an optical sensor, and an audio input circuit. In this specification, the input interface 11 is not limited to those equipped with physical operating components such as a mouse or keyboard. For example, an electrical signal processing circuit that receives electrical signals corresponding to input operations from an external input device provided separately from the device and outputs these electrical signals to a control circuit is also included as an example of the input interface 11.

[0022] The display 12 displays various types of information. Specifically, the display 12 is connected to the processing circuit 17 and converts the data of various types of information sent from the processing circuit 17 into electrical signals for display and outputs them. For example, the display 12 can be implemented as an LCD monitor, a CRT monitor, a touch panel, or the like.

[0023] The memory circuit 13 stores various types of data. Specifically, the memory circuit 13 is connected to processing circuits 14-17 and stores various types of data input and output by each processing circuit. For example, the memory circuit 13 can be implemented using semiconductor memory elements such as RAM (Random Access Memory) or flash memory, or a hard disk or optical disc.

[0024] The processing circuit 14 has a bed control function 14a. The bed control function 14a controls the operation of the bed 10 by outputting control electrical signals to the bed 10. For example, the bed control function 14a receives instructions from the operator via the input interface 11 to move the top plate 10a in the longitudinal direction, vertical direction, or horizontal direction, and operates the bed 10's top plate 10a movement mechanism to move the top plate 10a according to the received instructions.

[0025] The processing circuit 15 has an acquisition function 15a. The acquisition function 15a acquires k-space data by executing various pulse sequences. Specifically, the acquisition function 15a executes various pulse sequences by driving the gradient power supply 3, the transmitting circuit 6, and the receiving circuit 7 according to the sequence execution data output from the processing circuit 17. Here, the sequence execution data is data representing the pulse sequence, and is information that defines the timing and strength of the current supplied by the gradient power supply 3 to the gradient coil 2, the timing and strength of the RF pulse supplied by the transmitting circuit 6 to the whole-body RF coil 4, and the timing of the NMR signal sampling by the receiving circuit 7. The acquisition function 15a then receives the NMR data output from the receiving circuit 7 as a result of executing the pulse sequence and stores it in the memory circuit 13. At this time, the NMR data stored in the memory circuit 13 is stored as k-space data representing two-dimensional or three-dimensional k-space, with position information along the readout direction, phase encoding direction, and slice direction assigned by each of the aforementioned gradient magnetic fields.

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

[0027] The processing circuit 17 has an imaging control function 17a. The imaging control function 17a performs various types of imaging by controlling each component of the MRI device 100. Specifically, the imaging control function 17a displays a GUI (Graphical User Interface) on the display 12 to receive various instructions and input operations of various information from the operator, and controls each component of the MRI device 100 in accordance with the input operations 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 circuit 15 to collect k-space data. Also, for example, the imaging control function 17a controls the processing circuit 16 to reconstruct an image from the k-space data collected by the processing circuit 15. Also, for example, the imaging control function 17a reads an image from the memory circuit 13 in response to a request from the operator and displays the read image on the display 12.

[0028] Here, the processing circuits 14 to 17 described above are implemented, for example, by a processor. In this case, the processing functions of each processing circuit are stored in the memory circuit 13 in the form of a program that can be executed by a computer, for example. Then, each processing circuit implements the processing function corresponding to each program by reading and executing each program from the memory circuit 13. In other words, each processing circuit, in the state where each program has been read, will have the functions shown in each processing circuit of Figure 1.

[0029] Here, we describe the implementation of each processing circuit as being realized by a single processor, but the embodiments are not limited to this. Multiple independent processors may be combined to constitute each processing circuit, and each processor may execute a program to realize each processing function. Furthermore, the processing functions of each processing circuit may be appropriately distributed or integrated across one or more processing circuits. In addition, although the example shown in Figure 1 describes a single memory circuit 13 that stores the programs corresponding to each processing function, multiple memory circuits may be distributed and arranged so that the processing circuit reads the corresponding program from each individual memory circuit.

[0030] The configuration example of the MRI apparatus 100 according to this embodiment has been described above. With this configuration, in this embodiment, the static magnetic field magnet 1 generates a static magnetic field in which the magnetic field strength changes spatially in at least a part of the region within the bore 9a which is the imaging space.

[0031] Figure 2 shows the static magnetic field generated by the static magnetic field magnet 1 according to the first embodiment.

[0032] For example, as shown in Figure 2, the static magnetic field generated by the cylindrically formed static magnetic field magnet 1 has a uniform magnetic field strength in the central region RC (hereinafter referred to as the uniform region) within the bore 9a, but it is not uniform in the surrounding region RP, and the magnetic field strength changes spatially.

[0033] In contrast, RF coils that receive NMR signals are generally designed assuming a uniform magnetic field strength in the static magnetic field, and are tuned to a specific resonance frequency corresponding to the magnetic field strength in the uniform region. Therefore, in regions where the magnetic field strength of the static magnetic field changes spatially, the sensitivity of the RF coil may decrease.

[0034] Figure 3 is a diagram illustrating the 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 changes spatially. The distribution of the static magnetic field is shown by a shaded pattern, and the darker the shade, the stronger the magnetic field strength of the static magnetic field.

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

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

[0038] For these reasons, the MRI apparatus 100 according to this embodiment is configured to improve the sensitivity of the RF coil when the magnetic field strength of the static magnetic field changes spatially.

[0039] Specifically, the MRI apparatus 100 includes an RF coil that transmits RF pulses to a subject placed in a static magnetic field where the magnetic field strength generated by the static magnetic field magnet 1 changes spatially, and receives NMR signals generated from the subject as a result of the RF pulses. 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 to receive the NMR signal at each of several 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 is equipped with multiple RF coils, each individually tuned for a different frequency. The imaging control function 17a controls each of the multiple RF coils to receive NMR signals at each of the different frequencies.

[0042] Figures 4-6 show examples of RF coils included in the MRI apparatus 100 according to the first embodiment.

[0043] Here, Figures 4-6 show examples, similar to Figure 3, where the magnetic field strength decreases as the distribution of the static magnetic field expands.

[0044] For example, as shown in Figure 4, the MRI apparatus 100 includes a first RF coil 120a tuned to frequency A and a second RF coil 120b tuned to frequency B. Here, frequency A of the first RF coil 120a is tuned to a resonance frequency corresponding to the magnetic field strength of the static magnetic field in a first region Ra, which is included in the range where the static magnetic field is distributed. On the other hand, frequency B of the second RF coil 120b is tuned to a resonance frequency corresponding to the magnetic field strength of the static magnetic field in a second region Rb, which is included in the range where 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 positioned to receive the NMR signal generated in the first region Ra, and the second RF coil 120b is positioned to receive the NMR signal generated in the second region Rb. For example, as shown in Figure 4, the first RF coil 120a and the second RF coil 120b are arranged such that the detection surface of the first RF coil 120a is perpendicular to the direction in which the static magnetic field distribution expands, and the detection surface of the second RF coil 120b is parallel to the direction in which the static magnetic field distribution expands. Alternatively, for example, as shown in Figure 5, the first RF coil 120a and the second RF coil 120b may be stacked and arranged such that their respective detection surfaces are perpendicular to the direction in which the static magnetic field distribution expands.

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

[0047] With this configuration, by using two RF coils 120a and 120b, each independently or electromagnetically coupled, tuned 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 expands, as shown in Figure 6, for example. This expands the range over which NMR signals can be received along the direction in which the static magnetic field distribution expands, thereby improving the sensitivity of the RF coils.

[0048] In this example, we have described the case where NMR signals are received at two frequencies using two RF coils. However, the number of RF coils and frequencies is not limited to two; there may be three or more. This allows for the reception of NMR signals from three or more regions along the direction in which the static magnetic field distribution expands, further broadening the range over which NMR signals can be received.

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

[0050] Figure 7 shows an example of the configuration of the transmission and reception system of the MRI apparatus 100 according to the first embodiment.

[0051] For example, as shown in Figure 7, 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.

[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] Furthermore, the MRI apparatus 100 includes a pulse generator 161, a DAC (Digital to Analog Converter) 162, a selector 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 Figure 1.

[0054] The pulse generator 161 generates an RF pulse waveform. The DAC 162 converts the RF pulse waveform generated by the pulse generator 161 from an analog signal to a digital signal and outputs it. The toggle switch 163 outputs the digital signal output from the DAC 162 to either the first modulator 165a or the second modulator 165b in accordance with the 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 generates an RF pulse of frequency A by converting the frequency of the RF signal output from the synthesizer 164 to frequency A, and then modulating the RF signal with the waveform of the digital signal output from the toggle switch 163. The second modulator 165b generates an RF pulse of frequency B by converting the frequency of the RF signal output from the synthesizer 164 to frequency B, and then modulating the RF signal with the waveform of the digital signal output from the toggle switch 163. The first RF amplifier 166a amplifies the RF pulse of frequency A generated by the first modulator 165a and outputs it to the first transmitting 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 transmitting coil 121b.

[0055] Furthermore, the MRI apparatus 100 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 components are included in the receiving circuit 7 shown in Figure 1.

[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, then uses this RF signal to detect the NMR signal output from the first preamplifier 171a 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, then uses this RF signal to detect the NMR signal output from the second preamplifier 171b 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 173b generates NMR data by converting the NMR signal output from the second detector 172b from an analog signal to a digital signal, and outputs the generated NMR data to the processing circuit 15.

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

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

[0059] Furthermore, when the first receiving coil 122a and the second receiving coil 122b receive an NMR signal, the imaging control function 17a controls them so that each receiving coil is in a state where it can receive signals simultaneously. At the same time, the imaging control function 17a controls both 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 elements such as PIN diodes provided on each RF coil. Alternatively, for example, the imaging control function 17a controls each RF coil to decouple by shifting the adjusted frequency from the desired frequency by controlling elements such as PIN diodes provided on each RF coil.

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

[0062] In that case, the imaging control function 17a controls the RF coil to switch the frequency for receiving the NMR signal, based on the frequency for transmitting the RF pulse.

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

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

[0065] Figure 8 shows an example of imaging performed by the imaging control function 17a according to the first embodiment.

[0066] For example, as shown in Figure 8(a), when imaging multiple imaging slices A to C, the magnetic field strength of the static magnetic field generated by the static magnetic field magnet 1 changes 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 Figure 8(b), the imaging control function 17a controls the RF coil (transmitting coil) to transmit RF pulses (90° pulses) sequentially at intervals of TR (Repetition Time) for each imaging slice, at a resonance frequency corresponding to the magnetic field strength of the static magnetic field at the position of each imaging slice. Then, the imaging control function 17a controls the RF coil (receiving coil) to receive the NMR signal sequentially 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] In this case, for example, if the change in 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. Alternatively, the gradient magnetic field in the slice direction may be used auxiliaryly to correct the linearity of the change in 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 changes spatially. The RF coil transmits RF pulses to a subject placed in the static magnetic field whose magnetic field strength changes spatially, and receives an NMR signal generated from the subject as a result of the RF pulses. The imaging control function 17a then controls the RF coil to receive the NMR signal at each of a plurality of frequencies adjusted according to the distribution of the static magnetic field.

[0070] Specifically, in the first embodiment, the MRI apparatus 100 includes multiple RF coils, each individually tuned to a different frequency. The imaging control function 17a controls each of the multiple RF coils to receive NMR signals at each of the multiple frequencies.

[0071] With this configuration, when the magnetic field strength of the static magnetic field changes spatially, the range over which NMR signals can be received can be broadened by using multiple frequencies, thereby improving the sensitivity of the RF coil.

[0072] The first embodiment has been described above, but the embodiments of the MRI apparatus 100 according to the present application are not limited to this. Therefore, other embodiments of the MRI apparatus 100 according to the present application will be described below. In the following embodiments, the focus will be on the differences from the first embodiment, and the explanation of content common to the first embodiment will be omitted.

[0073] (Second embodiment) For example, in the first embodiment described above, an example was described in which the MRI apparatus 100 is equipped with multiple RF coils individually tuned to each of multiple frequencies, but the embodiments are not limited to this. For example, the MRI apparatus 100 may be equipped with RF coils configured to be adjustable to each of multiple frequencies. Such an example will be described below as the second embodiment.

[0074] In this embodiment, the MRI apparatus 100 includes an RF coil configured to be adjustable to multiple frequencies. The imaging control function 17a switches the frequency of the RF coil to receive NMR signals at each of the multiple frequencies.

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

[0076] Figure 9 shows an example of an RF coil included in the MRI apparatus 100 according to the second embodiment.

[0077] Figure 9, like Figure 3, shows an example where the magnetic field strength decreases as the distribution of the static magnetic field expands.

[0078] For example, as shown in Figure 9, the MRI apparatus 100 includes an RF coil 220 configured to be adjustable to two frequencies, A and B. The imaging control function 17a then switches the frequency of the RF coil 220 to receive NMR signals at frequencies A and B, respectively.

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

[0080] With this configuration, by using an 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 expands, similar to the first embodiment. This expands the range in which NMR signals can be received along the direction in which the static magnetic field distribution expands, thereby improving the sensitivity of the RF coil.

[0081] In this example, we have described the case of receiving NMR signals at two frequencies using an RF coil adjustable to two frequencies. However, the number of frequencies is not limited to two; there may be three or more. This allows for the reception of NMR signals from three or more regions along the direction in which the static magnetic field distribution expands, further broadening the range over which NMR signals can be received.

[0082] For example, in this embodiment, the MRI apparatus 100 includes, as the RF coil described above, one transmitting coil configured to be adjustable to multiple frequencies and one receiving coil configured to be adjustable to multiple frequencies.

[0083] Figure 10 shows an example of the configuration of the transmission and reception system of the MRI apparatus 100 according to the second embodiment.

[0084] For example, as shown in Figure 10, the MRI apparatus 100 has a transmitting coil 221 configured to be adjustable to frequencies A and B, and a receiving coil 222 adjusted 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 circuit 17 via the processing circuit 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 circuit 17 via the processing circuit 15.

[0086] Furthermore, the MRI apparatus 100 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 Figure 1.

[0087] The pulse generator 161, DAC 162, changeover switch 163, synthesizer 164, first modulator 165a, and second modulator 165b are the same as 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 transmitting 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 transmitting coil 221.

[0088] Furthermore, the MRI apparatus 100 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 components are included in the receiving circuit 7 shown in Figure 1.

[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 in the first embodiment.

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

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

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

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

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

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

[0096] With this configuration, similar to the first embodiment, when the magnetic field strength of the static magnetic field changes spatially, the range over which NMR signals can be received can be broadened by using multiple frequencies, thereby improving the sensitivity of the RF coil.

[0097] (Third embodiment) Furthermore, in the first embodiment described above, an example was described in which the imaging control function 17a controls the RF coil to sequentially transmit RF pulses at multiple frequencies and sequentially receive NMR signals at multiple frequencies, but the embodiments are not limited to this. For example, the imaging control function 17a may transmit RF pulses in a wide bandwidth that includes multiple frequencies. Such an example will be described below as a third embodiment.

[0098] In this embodiment, the imaging control function 17a transmits RF pulses in a bandwidth that includes multiple frequencies and controls the RF coil to receive NMR signals simultaneously at each of the multiple frequencies.

[0099] For example, in this embodiment, the MRI apparatus 100 includes, as described above, one transmitting coil that transmits RF pulses and a plurality of receiving coils that receive NMR signals.

[0100] Figure 11 shows an example of the configuration of the transmitting and receiving system of the MRI apparatus 100 according to the third embodiment.

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

[0102] The transmitting coil 321 transmits an RF signal to the subject in a bandwidth including frequencies A and B, 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 and the second transmitting coil 121b are the same as in the first embodiment.

[0103] Furthermore, the MRI device 100 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 Figure 1.

[0104] The pulse generator 161, DAC 162, and synthesizer 164 are the same as in the first embodiment. The modulator 365 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 DAC 162 to generate an RF pulse in a band including frequencies A and B. The RF amplifier 366 amplifies the RF pulse in a band including frequencies A and B generated by the modulator 365a and outputs it to the transmitting coil 321.

[0105] Furthermore, the MRI apparatus 100 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 components are included in the receiving circuit 7 shown in Figure 1.

[0106] The first preamplifier 171a, the second preamplifier 171b, the first detector 172a, the second detector 172b, the first ADC 173a, and the second ADC 173b are the same as in the first embodiment.

[0107] 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 the NMR signal at frequency A and the second receiving coil 122b to receive the NMR signal at frequency B.

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

[0109] Furthermore, when the first receiving coil 122a and the second receiving coil 122b receive an NMR signal, the imaging control function 17a controls them so that each receiving coil is in a state where it can receive signals simultaneously. At the same time, the imaging control function 17a controls both 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 bandwidth containing multiple frequencies and controls the RF coil to simultaneously receive NMR signals at each of the multiple frequencies, thereby performing various types of imaging.

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

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

[0113] In parallel imaging, an image is generated by combining NMR signals received by multiple receiving coils, and by unfolding this image, an image with aliasing removed is generated. Generally, the SNR (Signal-to-Noise Ratio) when using parallel imaging is... parallel It can be 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 modulo. Of these parameters, the g-factor is an element that affects image quality; the higher the independence of the sensitivity distribution of each receiving coil, the smaller the value becomes, and consequently, the higher the image quality of the generated image.

[0116] In this embodiment, by receiving NMR signals at multiple frequencies, a frequency-dependent sensitivity distribution is generated in addition to the normal sensitivity distribution of the receiving coil, thus increasing the independence of the sensitivity distribution of each receiving coil. As a result, the g-factor value becomes smaller, 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 controls the RF coil to transmit RF pulses in a band containing multiple frequencies and to receive NMR signals simultaneously at each of the multiple frequencies.

[0118] With this configuration, similar to the first embodiment, when the magnetic field strength of the static magnetic field changes spatially, the range over which NMR signals can be received can be broadened by using multiple frequencies, thereby improving the sensitivity of the RF coil.

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

[0120] (Fourth embodiment) Furthermore, although the second embodiment described above illustrates an example using multiple modulators and multiple detectors, the embodiments are not limited to this. For example, in the transmitting and receiving system configuration shown in Figure 10, the modulator and detector may be made common by using a modulator and detector that can switch between multiple frequencies. Such an example will be described below as the fourth embodiment.

[0121] Figure 12 shows an example of the configuration of the transmission and reception system of the MRI apparatus 100 according to the fourth embodiment.

[0122] For example, as shown in Figure 12, the MRI apparatus 100 has a transmitting coil 221 configured to be adjustable to frequencies A and B, and a receiving coil 222 adjusted to frequency B.

[0123] The transmitting coil 221 and the receiving coil 222 are the same as in the second embodiment.

[0124] Furthermore, the MRI apparatus 100 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 Figure 1.

[0125] The pulse generator 161, DAC 162, and synthesizer 164 are the same as in the first embodiment. The modulator 465 converts the frequency of the RF signal output from the synthesizer 164 to 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 RF pulses of frequency A and RF pulses 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 in the second embodiment.

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

[0127] The first preamplifier 271a and the second preamplifier 271b are the same as in the second embodiment. The changeover switch 474 outputs either 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 uses the RF signal to detect and output the NMR signal output from the changeover switch 474. 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] The imaging control function 17a then controls the transmitting coil 221 and the receiving coil 222, similar to the second embodiment.

[0129] (Fifth embodiment) Furthermore, while the first embodiment described above illustrates an example using multiple modulators and multiple detectors, similar to the second embodiment, the embodiments are not limited to this. For example, in the transceiver configuration shown in Figure 7, the modulators and detectors may be made common by using modulators and detectors that can switch between multiple frequencies, similar to the fourth embodiment. Such an example will be described below as the fifth embodiment.

[0130] Figure 13 shows an example of the configuration of the transmitting and receiving system of the MRI apparatus 100 according to the fifth embodiment.

[0131] For example, as shown in Figure 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 the same as in the first embodiment.

[0133] Furthermore, the MRI apparatus 100 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 Figure 1.

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

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

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

[0137] 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, similar to the first embodiment.

[0138] (Sixth embodiment) Furthermore, while the first embodiment described above illustrates an example using multiple transmitting coils and multiple receiving coils, the embodiments are not limited to this. For example, in the transceiver configuration shown in Figure 7, multiple transmitting and receiving coils may be used instead of multiple transmitting and receiving coils. Such an example will be described below as the sixth embodiment.

[0139] Figure 14 shows an example of the configuration of the transmission and reception system of the MRI apparatus 100 according to the sixth embodiment.

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

[0141] The first transmitting / receiving 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 circuit 17 via the processing circuit 15. The second transmitting / receiving 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 circuit 17 via the processing circuit 15.

[0142] Furthermore, the MRI apparatus 100 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 Figure 1.

[0143] The pulse generator 161, DAC 162, changeover switch 163, synthesizer 164, first modulator 165a, and second modulator 165b are the same as 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 transmit / receive 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 transmit / receive coil 623b.

[0144] Furthermore, the MRI apparatus 100 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 components are included in the receiving circuit 7 shown in Figure 1.

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

[0146] The imaging control function 17a controls the first transmit / receive coil 623a to transmit an RF pulse at frequency A, and controls the first transmit / receive coil 623a to receive an NMR signal at frequency A. The imaging control function 17a also controls the second transmit / receive coil 623b to transmit an RF pulse at frequency B, and controls the second transmit / receive coil 623b to receive an NMR signal at frequency B.

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

[0148] Furthermore, the imaging control function 17a controls the first transmit / receive coil 623a and the second transmit / receive coil 623b to be in a state where they can receive NMR signals simultaneously.

[0149] (Seventh Embodiment) Furthermore, while the sixth embodiment described above illustrates an example using multiple modulators and multiple detectors, similar to the first embodiment, the embodiments are not limited to this. For example, in the transmitting and receiving system configuration shown in Figure 15, the modulators and detectors may be made common by using modulators and detectors that can be switched to multiple frequencies, similar to the fourth embodiment. Such an example will be described below as the seventh embodiment.

[0150] Figure 15 shows an example of the configuration of the transmitting and receiving system of the MRI apparatus 100 according to the seventh embodiment.

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

[0152] The first transmitting / receiving coil 623a and the second transmitting / receiving coil 623b are the same as in the sixth embodiment.

[0153] Furthermore, the MRI apparatus 100 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 Figure 1.

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

[0155] Furthermore, the MRI apparatus 100 includes a first preamplifier 671a, a second preamplifier 671b, a selector switch 474, a detector 472, and an ADC 473. For example, these components are included in the receiving circuit 7 shown in Figure 1.

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

[0157] Then, the imaging control function 17a controls the first transmit / receive coil 623a and the second transmit / receive coil 623b, similar to the sixth embodiment.

[0158] (Eighth embodiment) Furthermore, while the second embodiment described above illustrates an example using one transmitting coil configured to be adjustable to multiple frequencies and one receiving coil configured to be adjustable to multiple frequencies, the embodiments are not limited to this. For example, in the transmitting and receiving system configuration shown in Figure 10, one transmitting and receiving coil configured to be adjustable to multiple frequencies may be used instead of one transmitting coil and one receiving coil. Such an example will be described below as the eighth embodiment.

[0159] Figure 16 shows an example of the configuration of the transmission and reception system of the MRI apparatus 100 according to the eighth embodiment.

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

[0161] The transmitting / receiving 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 circuit 17 via the processing circuit 15. The transmitting / receiving 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 circuit 17 via the processing circuit 15.

[0162] Furthermore, the MRI apparatus 100 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 Figure 1.

[0163] The pulse generator 161, DAC 162, changeover switch 163, synthesizer 164, first modulator 165a, and second modulator 165b are the same as 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 transmit / receive 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 transmit / receive coil 823.

[0164] Furthermore, the MRI apparatus 100 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 components are included in the receiving circuit 7 shown in Figure 1.

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

[0166] The imaging control function 17a controls the transmitting and receiving coils 823 to transmit RF pulses at frequency A and to receive NMR signals at frequency A. The imaging control function 17a also controls the transmitting and receiving coils 823 to transmit RF pulses at frequency B and to receive NMR signals at frequency B.

[0167] (Ninth embodiment) Furthermore, while the eighth embodiment described above illustrates an example using multiple modulators and multiple detectors, similar to the first embodiment, the embodiments are not limited to this. For example, in the transmitting and receiving system configuration shown in Figure 16, the modulators and detectors may be made common by using modulators and detectors that can be switched to multiple frequencies, similar to the fourth embodiment. Such an example will be described below as the ninth embodiment.

[0168] Figure 17 shows an example of the configuration of the transmitting and receiving system of the MRI apparatus 100 according to the ninth embodiment.

[0169] For example, as shown in Figure 17, the MRI apparatus 100 has a transmit / receive coil 823 configured to be adjustable to frequencies A and B.

[0170] The transmitting and receiving coil 823 is the same as in the eighth embodiment.

[0171] Furthermore, the MRI apparatus 100 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 Figure 1.

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

[0173] Furthermore, the MRI apparatus 100 includes a first preamplifier 871a, a second preamplifier 871b, a selector switch 474, a detector 472, and an ADC 473. For example, these components are included in the receiving circuit 7 shown in Figure 1.

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

[0175] Then, the imaging control function 17a controls the transmitting and receiving coil 823, similar to the eighth embodiment.

[0176] (Other embodiments) In the above-described embodiment, an MRI apparatus 100 having a so-called tunnel-type structure in which the static magnetic field magnet 1, gradient magnetic field coil 2, and whole-body RF coil 4 are each formed in a substantially cylindrical shape was described, but the embodiments are not limited to this. For example, the technology disclosed in this application can also 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 facing each other across the imaging space in which the subject S is placed. In other words, the technology disclosed in this application can be applied to various types of MRI apparatuses as long as they have a static magnetic field magnet that generates a static magnetic field in which the magnetic field strength changes spatially in at least a part of the imaging space in which the subject is placed.

[0177] Furthermore, although the embodiments described above illustrate an example in which the control unit in this specification is implemented by the imaging control function 17a of the processing circuit 17, the embodiments are not limited to this. For example, the control unit in this specification may be implemented not only by the imaging control function 17a described in the embodiments, but also by hardware alone, software alone, or a combination of hardware and software.

[0178] Furthermore, while the above description illustrates an example in which the "processor" reads and executes programs corresponding to each processing function from a memory circuit, the embodiments are not limited to this. The term "processor" refers to circuits such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), Application Specific Integrated Circuit (ASIC), and Programmable Logic Device (e.g., Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (CPLD), and Field Programmable Gate Array (FPGA)). When the processor is a CPU, for example, the processor realizes each processing function by reading and executing programs stored in a memory circuit. On the other hand, when the processor is an ASIC, instead of storing programs in a memory circuit, the processing function is directly incorporated as a logic circuit within the processor's circuit. Note that each processor in this embodiment is not limited to being configured as a single circuit for each processor; multiple independent circuits may be combined to form a single processor, and its processing functions may be realized in this way. Furthermore, the multiple components shown in Figure 1 may be integrated into a single processor to realize its processing function.

[0179] Here, the program executed by the processor is provided pre-installed in ROM (Read Only Memory) or memory circuits. This program may also be provided as a file in an installable or executable format on computer-readable storage media such as CD (Compact Disk)-ROM, FD (Flexible Disk), CD-R (Recordable), or DVD (Digital Versatile Disk). Alternatively, this program may be stored on a computer connected to a network such as the Internet and provided or distributed by downloading it via the network. For example, this program consists of modules containing the functional units described above. In actual hardware, the CPU reads the program from a storage medium such as ROM and executes it, loading each module onto the main memory and generating it in the main memory.

[0180] According to at least one embodiment described above, the sensitivity of the RF coil can be improved when the magnetic field strength of the static magnetic field changes spatially.

[0181] 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 carried out in a variety of 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 variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

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

Claims

1. A static magnetic field magnet generates a static magnetic field in which the magnetic field strength changes spatially, Multiple transmitting and receiving coils transmit high-frequency pulses to a subject placed in a static magnetic field where the magnetic field strength changes spatially, and receive nuclear magnetic resonance signals generated from the subject due to the influence of the high-frequency pulses. A control unit that controls the plurality of transmitting and receiving coils to transmit the high-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 system equipped with the following features.

2. The control unit controls the plurality of transmitting and receiving coils to switch the frequency for receiving the nuclear magnetic resonance signal, with reference to the frequency for transmitting the high-frequency pulse. The magnetic resonance imaging apparatus according to claim 1.

3. The control unit controls the plurality of transmitting and receiving coils to switch the frequency for receiving the nuclear magnetic resonance signal based on the position of the imaging slice. The magnetic resonance imaging apparatus according to claim 1 or 2.

4. The control unit controls the plurality of transmitting and receiving coils to sequentially transmit the high-frequency pulses at each of the plurality of frequencies and to sequentially receive the nuclear magnetic resonance signal at each of the plurality of frequencies. A magnetic resonance imaging apparatus according to any one of claims 1 to 3.

5. The control unit transmits the high-frequency pulse in a bandwidth including the plurality of frequencies and controls the plurality of transmitting and receiving coils to simultaneously receive the nuclear magnetic resonance signal at each of the plurality of frequencies. A magnetic resonance imaging apparatus according to any one of claims 1 to 3.

6. The aforementioned multiple frequencies are adjusted to resonant frequencies corresponding to the magnetic field strength of the static magnetic field at the position of each of the multiple transmitting and receiving coils. The control unit performs parallel imaging using the plurality of transmitting and receiving coils. The magnetic resonance imaging apparatus according to claim 5.

7. The receiving coil is configured to be adjustable to the aforementioned multiple frequencies, The control unit switches the frequency of the receiving coil to receive the nuclear magnetic resonance signal at each of the plurality of frequencies. A magnetic resonance imaging apparatus according to any one of claims 1 to 4.

8. The control unit controls the other transmitting and receiving coils to enter a decoupled state when one of the plurality of transmitting and receiving coils transmits the high-frequency pulse. The magnetic resonance imaging apparatus according to claim 7.

9. The control unit controls the plurality of transmitting and receiving coils so that each transmitting and receiving coil is in a state where it can receive the nuclear magnetic resonance signal simultaneously. The magnetic resonance imaging apparatus according to claim 8.

10. A static magnetic field magnet generates a static magnetic field in which the magnetic field strength changes spatially. Multiple transmitting and receiving coils transmit high-frequency pulses to a subject placed in a static magnetic field where the magnetic field strength changes spatially, and receive nuclear magnetic resonance signals generated from the subject due to the influence of the high-frequency pulses. The receiving coil receives the nuclear magnetic resonance signal generated from the subject due to the influence of the high-frequency pulse. The control unit controls the plurality of transmitting and receiving coils to transmit the high-frequency pulses 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, including the following.

Images