Magnetic resonance imaging apparatus and magnetic resonance imaging method

Abstract

Embodiments disclosed in the specification and drawings relate to a magnetic resonance imaging apparatus and a magnetic resonance imaging method. The present invention easily and appropriately sets the excitation thickness and excitation position of a saturation pulse applied to the outside of the phase encoding direction of an imaging region in a subject. A magnetic resonance imaging apparatus according to an embodiment includes an acquisition unit, a measurement unit, and a calculation unit. The acquisition unit acquires one-dimensional projection data in a phase encoding direction of a subject, which is a subject subject to main imaging. The measurement unit measures the thickness of the subject in the phase encoding direction using the one-dimensional projection data. The calculation unit calculates, on the basis of the thickness of the subject, an excitation thickness and an excitation position of a saturation pulse applied to the outside of the phase encoding direction of an imaging region in the subject when the main imaging is performed.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority of Japanese Patent Application No. 2024-013366, filed on January 31, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The embodiments disclosed in this specification and the accompanying drawings relate to a magnetic resonance imaging apparatus and a magnetic resonance imaging method. BACKGROUND ART

[0004] Conventionally, as a method for highly precisely imaging a small imaging region (Field of View: FOV) in a subject using a Magnetic Resonance Imaging (MRI) apparatus, a local excitation method has been widely used.

[0005] For example, as a general local excitation method, a two-dimensional RF (Radio Frequency) excitation method, an inclined excitation method, and an OVS (Outer Volume Suppression) method are known. The two-dimensional RF (Radio Frequency) excitation method is a method of performing local excitation by applying an RF pulse while performing phase encoding. In addition, the inclined excitation method is a method of performing local excitation by changing the application angle of the excitation pulse and the application angle of the refocusing pulse. In addition, the OVS method is a method of performing local excitation by suppressing signals outside the imaging region by applying a saturation pulse to the outside in the phase encoding direction of the imaging region.

[0006] Among them, in the OVS method, the excitation thickness and excitation position of the saturation pulse vary according to the size of the subject and the position of the imaging region. Therefore, the operator of the MRI apparatus needs to set the excitation thickness and excitation position of the saturation pulse while observing and confirming the structure of the subject, and the workflow becomes complicated. On the other hand, although the complexity of the workflow can be reduced by setting the excitation thickness of the saturation pulse to be large, when the excitation thickness of the saturation pulse is increased, the excitation profile deteriorates, and signal suppression in the part close to the imaging region becomes insufficient. Therefore, it is desirable to set the excitation thickness as thin as possible. SUMMARY OF THE INVENTION

[0007] One of the problems to be solved by the embodiments disclosed in this specification and the accompanying drawings is to easily and appropriately set the excitation thickness and excitation position of the saturation pulse applied to the outside of the phase encoding direction of the imaging region in the subject. However, the problems to be solved by the embodiments disclosed in this specification and the accompanying drawings are not limited to the above problems. The problems corresponding to the respective effects of the respective structures shown in the embodiments described later can also be defined as other problems.

[0008] The MRI apparatus according to the embodiment includes an acquisition unit, a measurement unit, and a calculation unit. The acquisition unit acquires one-dimensional projection data in the phase encoding direction of a subject, which is an object of main imaging. The measurement unit measures the thickness of the subject in the phase encoding direction using the one-dimensional projection data. The calculation unit calculates the excitation thickness and excitation position of the saturation pulse applied to the outside of the phase encoding direction of the imaging region in the subject when performing the main imaging based on the thickness of the subject.

[0009] The magnetic resonance imaging method according to the embodiment includes: a step of acquiring one-dimensional projection data in the phase encoding direction of a subject, which is an object of main imaging; a step of measuring the thickness of the subject in the phase encoding direction using the one-dimensional projection data; and a step of calculating the excitation thickness and excitation position of the saturation pulse applied to the outside of the phase encoding direction of the imaging region in the subject when performing the main imaging based on the thickness of the subject. Description of the Drawings

[0010] Figure 1 is a diagram showing an example of the configuration of the MRI apparatus according to the first embodiment.

[0011] Figure 2 is a diagram showing an outline of the processing performed by the MRI apparatus according to the first embodiment.

[0012] Figure 3 is a diagram showing an example of the processing performed by the MRI apparatus according to the first embodiment.

[0013] Figure 4 is a diagram showing an example of the processing performed by the measurement function according to the first embodiment.

[0014] Figure 5 is a diagram showing an example of the processing performed by the measurement function according to the first embodiment.

[0015] Figure 6 is a diagram showing an example of the processing performed by the calculation function according to the first embodiment.

[0016] Figure 7This is a flowchart showing the processing procedures performed by the respective processing functions of the MRI apparatus according to the first embodiment.

[0017] Figure 8 This is a diagram showing an example of the processing performed by the MRI apparatus according to the second embodiment.

[0018] Figure 9 This is a diagram showing an example of the processing performed by the MRI apparatus according to the second embodiment.

[0019] Figure 10 This is a diagram showing an example of the processing performed by the MRI apparatus according to the third embodiment. Detailed Embodiments

[0020] Hereinafter, embodiments of the MRI apparatus and the MRI method of the present application will be described in detail with reference to the accompanying drawings.

[0021] (First Embodiment)

[0022] Figure 1 This is a diagram showing an example of the structure of the MRI apparatus according to the first embodiment.

[0023] As Figure 1 shown, the 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 radio frequency (RF) coil 4, a local RF coil 5, a transmission circuit 6, a reception circuit 7, an RF shield 8, a gantry 9, an examination table 10, an input interface 11, a display 12, a storage circuit 13, and processing circuits 14 to 17.

[0024] 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 substantially hollow cylindrical shape (including the case where the cross-sectional shape orthogonal to the central axis is elliptical), and generates a static magnetic field in the imaging space formed on its inner peripheral side. For example, the static magnetic field magnet 1 is a superconducting magnet or a permanent magnet, etc. 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.

[0025] The gradient magnetic field coil 2 is arranged inside the static magnetic field magnet 1 and generates a gradient magnetic field in the imaging space where the subject S is arranged. Specifically, the gradient magnetic field coil 2 is formed into a hollow, roughly cylindrical shape (including the case where 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 mutually orthogonal X-axis, Y-axis, and Z-axis, respectively. Based on the current supplied by the gradient magnetic field power supply 3, the X-coil, Y-coil, and Z-coil generate a gradient magnetic field in the imaging space that varies linearly along each axis. 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, Y-axis, and Z-axis constitute the device coordinate system inherent to the MRI device 100.

[0026] 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 individually to the X, Y, and Z coils of the gradient magnetic field coil 2, generating a gradient magnetic field that varies linearly along the mutually orthogonal frequency encoding direction, phase encoding direction, and slice-selective excitation direction. The axes along the frequency encoding direction, the phase encoding direction, and the slice-selective excitation direction constitute a logical coordinate system that defines the slice region or volume region to be imaged.

[0027] Here, gradient magnetic fields along each of the frequency encoding direction, phase encoding direction, and slice-selective excitation direction are superimposed on the static magnetic field generated by the static field magnet 1 to impart spatial position information to the nuclear magnetic resonance (NMR) signals generated from the subject S. Specifically, the gradient magnetic field in the frequency encoding direction modifies the frequency of the NMR signals according to the position in the frequency encoding direction, thereby imparting position information in the frequency encoding direction to the NMR signals. Furthermore, the gradient magnetic field in the phase encoding direction modifies the phase of the NMR signals according to the position in the phase encoding direction, thereby imparting position information in the phase encoding direction to the NMR signals. Furthermore, when capturing two-dimensional MR images (slice images), the gradient magnetic field in the slice-selective excitation direction modifies the frequency of the NMR signals according to the position in the slice-selective excitation direction to determine the position, thickness, and number of slices to be captured. Furthermore, when capturing three-dimensional MR images (volume images), the gradient magnetic field in the slice-selective excitation direction modifies the phase of the NMR signals according to the position in the slice-selective excitation direction, thereby imparting position information in the slice-selective excitation direction to the NMR signals.

[0028] The whole-body RF coil 4 is disposed on the inner peripheral side of the gradient magnetic field coil 2, applies an RF pulse (excitation pulse, etc.) to the subject S disposed in the imaging space, and receives the NMR signal (echo signal, etc.) generated from the subject S due to the influence of the RF pulse. Specifically, the whole-body RF coil 4 is formed in a substantially hollow cylindrical shape (including the case where the cross-sectional shape orthogonal to the central axis is elliptical), and based on the RF pulse signal supplied by the transmission circuit 6, applies an RF pulse to the subject S disposed in the imaging space on its inner peripheral side. Moreover, the whole-body RF coil 4 receives the NMR signal generated from the subject S due to the influence of the RF pulse, and outputs the received NMR signal to the receiving circuit 7. For example, the whole-body RF coil 4 is a birdcage-type coil or a TEM (Transverse Electromagnetic) coil.

[0029] The local RF coil 5 is disposed near the subject S during imaging, and receives the NMR signal generated from the subject S. Specifically, the local RF coil 5 is prepared for each part of the subject S, and is disposed near the part to be imaged when imaging the subject S, receives the NMR signal generated from the subject S due to the influence of the RF pulse applied by the whole-body RF coil 4, 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 formed by combining a plurality of surface coils as coil elements. In addition, the local RF coil 5 may also have a transmission function of applying an RF pulse to the subject.

[0030] The transmission circuit 6 outputs an RF pulse signal corresponding to the resonance frequency (Larmor frequency) inherent to the target atomic nucleus placed in the static magnetic field to the whole-body RF coil 4 or the local RF coil 5. Specifically, the transmission circuit 6 includes a pulse generator, an RF generator, a modulator, and an amplifier. The pulse generator generates the waveform of the RF pulse signal. The RF generator generates an RF signal at the resonance frequency. The modulator generates an RF pulse signal by modulating the amplitude of the RF signal generated by the RF generator using the waveform generated by the pulse generator. The amplifier amplifies the RF pulse signal generated by the modulator and outputs it to the whole-body RF coil 4 or the local RF coil 5.

[0031] The receiving circuit 7 generates NMR data based on the NMR signals 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. Specifically, the receiving circuit 7 includes a selector, a preamplifier, a phase detector, and an A / D (Analog / Digital) converter. The selector selectively inputs the NMR signals output from the whole-body RF coil 4 or the local RF coil 5. The preamplifier amplifies the NMR signals output from the selector. The phase detector detects the phases of the NMR signals output from the preamplifier. The A / D converter generates NMR data by converting the analog signals output from the phase detector into digital signals, and outputs the generated NMR data to the processing circuit 15. In addition, here, not all of the processes described as the processes performed by the receiving circuit 7 necessarily need to be performed by the receiving circuit 7, and a part of the processes (for example, the processes performed by the A / D converter) may be performed by the whole-body RF coil 4 or the local RF coil 5.

[0032] The RF shielding unit 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 influence of the RF pulses generated by the whole-body RF coil 4. Specifically, the RF shielding unit 8 is formed in a substantially hollow cylindrical shape (including the case where the cross-sectional shape orthogonal to the central axis of the cylinder is elliptical), and is disposed in the space on the inner peripheral side of the gradient magnetic field coil 2 so as to cover the outer peripheral surface of the whole-body RF coil 4.

[0033] The gantry 9 has a hollow cavity 9a formed in a substantially cylindrical shape (including the case where the cross-sectional shape orthogonal to the central axis is elliptical), and houses the static magnetic field magnet 1, the gradient magnetic field coil 2, the whole-body RF coil 4, and the RF shielding unit 8. Specifically, the gantry 9 houses them in a state where the whole-body RF coil 4 is disposed on the outer peripheral side of the cavity 9a, the RF shielding unit 8 is disposed on the outer peripheral side of the whole-body RF coil 4, the gradient magnetic field coil 2 is disposed on the outer peripheral side of the RF shielding unit 8, and the static magnetic field magnet 1 is disposed on the outer peripheral side of the gradient magnetic field coil 2. Here, the space inside the cavity 9a of the gantry 9 becomes the imaging space where the subject S is disposed during imaging.

[0034] The examination table 10 includes a top plate 10a on which the subject S is placed, and moves the top plate 10a on which the subject S is placed to the imaging space when imaging the subject S. For example, the examination table 10 is provided such that the long side direction of the top plate 10a is parallel to the central axis of the static magnetic field magnet 1.

[0035] In addition, an example is described herein in which the MRI apparatus 100 has 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. However, the embodiment is not limited thereto. For example, the MRI apparatus 100 may have 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 so as to face each other across the imaging space in which the subject S is disposed. In such an open-type structure, the space sandwiched by the pair of static magnetic field magnets, the pair of gradient magnetic field coils, and the pair of RF coils corresponds to the cavity in the tunnel-type structure.

[0036] The input interface 11 receives input operations of various instructions and various information from the operator. Specifically, the input interface 11 is connected to the processing circuit 17, 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 is implemented by a trackball, a switch button, a mouse, a keyboard, a touch pad for performing input operations through a touch operation surface, a touch screen integrating a display screen and a touch pad, a non-contact input circuit using an optical sensor, a voice input circuit, and the like for setting imaging conditions, a region of interest (ROI), and the like. In addition, in the present specification, the input interface 11 is not limited to devices having physical operation members such as a mouse and a keyboard. For example, an example in which the input interface 11 also includes an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the apparatus and outputs the electrical signal to the control circuit is also included.

[0037] The display 12 displays various information. Specifically, the display 12 is connected to the processing circuit 17, converts data of various information transmitted from the processing circuit 17 into electrical signals for display, and outputs them. For example, the display 1 is implemented by a liquid crystal monitor, a CRT (Cathode Ray Tube) monitor, a touch panel, and the like.

[0038] The storage circuit 13 stores various data. Specifically, the storage circuit 13 is connected to the processing circuits 14 to 17 and stores various data input and output by each processing circuit. For example, the storage circuit 13 is implemented by semiconductor memory elements such as a RAM (Random Access Memory) and a flash memory, a hard disk, an optical disk, and the like.

[0039] The processing circuit 14 has an examination table control function 14a. The examination table control function 14a controls the operation of the examination table 10 by outputting an electric signal for control to the examination table 10. For example, the examination table control function 14a receives an instruction from the operator via the input interface 11 to move the top plate 10a in the longitudinal direction, the up-and-down direction, or the left-and-right direction, and causes the moving mechanism of the top plate 10a of the examination table 10 to operate to move the top plate 10a according to the received instruction.

[0040] The processing circuit 15 has a collection function 15a. The collection function 15a collects NMR data of the subject S by executing various pulse sequences. Specifically, the collection function 15a executes various pulse sequences by driving the gradient magnetic field power supply 3, the transmission circuit 6, and the reception circuit 7 according to the sequence output from the processing circuit 17. Here, the sequence execution data is data representing the pulse sequence, and is information specifying the timing at which the gradient magnetic field power supply 3 supplies current to the gradient magnetic field coil 2 and the intensity of the supplied current, the timing at which the transmission circuit 6 supplies an RF pulse signal to the whole-body RF coil 4 and the intensity of the supplied RF pulse signal, the timing at which the reception circuit 7 samples the NMR signal, etc. Moreover, the collection function 15a receives the NMR data output from the reception circuit 7 as a result of executing the pulse sequence, and stores it in the storage circuit 13. At this time, the NMR data stored in the storage circuit 13 is given position information along the frequency encoding direction, the phase encoding direction, and the slice selection excitation direction by the respective gradient magnetic fields described above, and is stored as k-space data representing two-dimensional or three-dimensional k-space.

[0041] The processing circuit 16 has a generation function 16a. The generation function 16a generates an MR image based on the NMR data collected by the collection function 15a of the processing circuit 15. Specifically, the generation function 16a reads out the NMR data collected by the collection function 15a of the processing circuit 15 from the storage circuit 13 under the control of the processing circuit 17, and performs reconstruction processing such as Fourier transform on the read-out NMR data, thereby generating a two-dimensional or three-dimensional MR image. Moreover, the generation function 16a stores the generated MR image in the storage circuit 13.

[0042] The processing circuit 17 has a photographing control function 17a, an acquisition function 17b, a measurement function 17c, and a calculation function 17d. The photographing control function 17a performs overall control of the MRI apparatus 100 by controlling each component of the MRI apparatus 100. Specifically, the photographing control function 17a causes the display 12 to display a GUI (Graphical User Interface) for receiving input operations of various instructions and various information from the operator, and controls each component of the MRI apparatus 100 according to the input operations received via the input interface 11. For example, the photographing control function 17a receives input of photographing conditions from the operator, and sets a pulse sequence for collecting NMR data of the subject S based on the input photographing conditions. Then, the photographing control function 17a generates sequence execution data representing the set pulse sequence and outputs it to the processing circuit 15, whereby the collection function 15a of the processing circuit 15 executes various pulse sequences. Additionally, for example, the photographing control function 17a reconstructs an MR image based on the k-space data collected by the processing circuit 15 by controlling the generation function 16a of the processing circuit 16. Additionally, for example, the photographing control function 17a reads out the MR image stored in the storage circuit 13 according to a request from the operator, and causes the display 12 to display the read MR image. Furthermore, the acquisition function 17b, the measurement function 17c, and the calculation function 17d will be described later.

[0043] Here, the processing circuits 14 to 17 are each implemented by a processor, for example. In this case, the processing functions of each processing circuit are stored in the storage circuit 13 in the form of a program that can be executed by a computer, for example. Moreover, each processing circuit realizes the processing function corresponding to each program by reading out and executing each program from the storage circuit 13. In other words, each processing circuit has the respective processing functions shown Figure 1 in the state of reading out each program.

[0044] As described above, the structural example of the MRI apparatus 100 of the present embodiment has been described. Based on this structure, the MRI apparatus 100 of the present embodiment has a function of photographing a subject using the OVS method, which is one of the local excitation methods for highly finely photographing a small photographing area inside the subject. Here, the OVS method is a method of local excitation by applying a saturation pulse to the outside of the phase encoding direction of the photographing area to suppress signals outside the photographing area.

[0045] Generally, in the OVS method, the excitation thickness and excitation position of the saturation pulse vary according to the size of the subject and the position of the imaging region. Therefore, the operator of the MRI apparatus needs to set the excitation thickness and excitation position of the saturation pulse while observing and confirming the structure of the subject, making the workflow complex. On the other hand, although the workflow complexity can be reduced by setting a relatively large excitation thickness for the saturation pulse, when the excitation thickness of the saturation pulse increases, the excitation curve deteriorates, and the signal suppression in the part close to the imaging region becomes insufficient. Therefore, it is desirable to set the excitation thickness as thin as possible.

[0046] Therefore, the MRI apparatus 100 according to the present embodiment is configured to be able to easily and appropriately set the excitation thickness and excitation position of the saturation pulse applied to the outside of the phase encoding direction of the imaging region in the subject.

[0047] Hereinafter, the structure of such an MRI apparatus 100 will be described in detail. In addition, hereinafter, the saturation pulse applied to the outside of the phase encoding direction of the imaging region in the subject when imaging is performed using the OVS method will be referred to as an OVS pulse.

[0048] Figure 2 is a diagram showing an outline of the processing performed by the MRI apparatus 100 according to the first embodiment.

[0049] As Figure 2 shown, when the MRI apparatus 100 performs main imaging using the OVS method, it uses one-dimensional (1-Dimension: 1D) projection data in the phase encoding direction of the subject, which is the object of the main imaging, to measure the thickness of the subject in the phase encoding direction ( Figure 2 in (A)).

[0050] Here, the 1D projection data in the phase encoding direction is data obtained by projecting the subject onto one axis along the phase encoding direction with the frequency encoding direction and the slice selection excitation direction as the respective projection directions, and includes a signal curve representing the distribution of the signals of the subject in the phase encoding direction.

[0051] Then, the MRI apparatus 100 automatically calculates the excitation thickness and excitation position of the OVS pulse based on the measured subject thickness ( Figure 2 in (B)). Here, the excitation thickness is the thickness of the OVS pulse in the phase encoding direction. In addition, the excitation position is the position of the OVS pulse in the phase encoding direction.

[0052] Specifically, the acquisition function 17b of the processing circuit 17 acquires 1D projection data in the phase encoding direction of the subject, which is the object of the main shot. In addition, the measurement function 17c of the processing circuit 17 measures the thickness of the subject in the phase encoding direction using the 1D projection data acquired by the acquisition function 17b. In addition, the calculation function 17d of the processing circuit 17 calculates the excitation thickness and excitation position of the OVS pulse based on the thickness of the subject measured by the measurement function 17c. Here, the acquisition function 17b is an example of an acquisition unit. In addition, the measurement function 17c is an example of a measurement unit. In addition, the calculation function 17d is an example of a calculation unit.

[0053] Figure 3 It is a diagram showing an example of the processing performed by the MRI apparatus 100 of the first embodiment.

[0054] For example, as Figure 3 shown, during the prescan before the main shot, the acquisition function 17b excites a slice acquisition range including the slice of the subject to be shot by the main shot, and collects 1D projection data in the phase encoding direction, thereby acquiring 1D projection data ( Figure 3 (A)).

[0055] For example, the acquisition function 17b controls the collection function 15a of the processing circuit 15 to perform slab excitation of the slice acquisition range at the position of the central coordinate of the shooting area and collect 1D projection data in the phase encoding direction, thereby acquiring 1D projection data in the phase encoding direction. Here, when a plurality of slices of the subject are shot in the main shot, the slice acquisition range is set to include the plurality of slices. When the slice shot by the main shot is one, the slice included in the slice acquisition range may also be one.

[0056] Then, before the main shot is performed, the measurement function 17c measures the thickness of the subject in the phase encoding direction using the 1D projection data acquired by the acquisition function 17b ( Figure 3 (B)), and the calculation function 17d calculates the excitation thickness and excitation position of the OVS pulse based on the thickness of the subject measured by the measurement function 17c ( Figure 3 (C)).

[0057] For example, the measurement function 17c obtains a signal curve representing the distribution of the signals of the subject in the phase encoding direction from the 1D projection data, and measures the thickness of the subject outside the shooting area in the phase encoding direction based on the signal curve.

[0058] Figure 4 and 5This is a diagram showing an example of the processing performed by the measurement function 17c of the first embodiment.

[0059] For example, as Figure 4 shown, based on the signal curve obtained from the 1D projection data, the measurement function 17c measures the thickness thick_sub1 of the subject outside the upper side of the imaging region in the phase encoding direction ( Figure 4 the upper side in Figure 4 ) and the thickness thick_sub2 of the subject outside the lower side of the imaging region in the phase encoding direction (

[0060] the lower side in

[0061] At this time, for example, based on the signal curve obtained from the 1D projection data, the measurement function 17c determines the position where the signal of the subject becomes a specified value in the phase encoding direction, and measures the distance between this position and the position of the edge of the imaging region in the phase encoding direction, thereby measuring the thickness of the subject outside the imaging region in the phase encoding direction.

[0062] For example, after removing the background noise (noise) included in the 1D projection data, the measurement function 17c obtains a signal curve from the 1D projection data, and based on this signal curve, determines the position where the signal of the subject becomes zero in the phase encoding direction. Then, the measurement function 17c measures the thickness of the subject outside the imaging region in the phase encoding direction by measuring the distance between the determined position where the signal of the subject becomes zero and the position of the edge of the imaging region in the phase encoding direction.

[0062] For example, as Figure 5 shown, based on the signal curve obtained from the 1D projection data, the measurement function 17c determines the coordinate y1_zero of the position where the signal of the subject becomes zero (zero) and the coordinate y1_edge of the position of the edge of the imaging region from the center coordinate of the imaging region to one side in the phase encoding direction. Then, the measurement function 17c measures the thickness thick_sub1 of the subject outside the one side of the imaging region in the phase encoding direction by measuring the distance abs(y1_zero - y1_edge) between the determined coordinates y1_zero and y1_edge. In addition, the measurement function 17c performs the same processing from the center coordinate of the imaging region to the other side in the phase encoding direction, and measures the thickness thick_sub2 of the subject outside the other side of the imaging region in the phase encoding direction.

[0063] In addition, here, the measurement function 17c determines the position where the signal of the subject becomes zero in the phase encoding direction after removing the background noise included in the 1D projection data, but the implementation is not limited thereto. For example, the measurement function 17c may also use a threshold value set to a size capable of removing the background noise to determine the position where the signal of the subject becomes the threshold value in the phase encoding direction. In this case, the measurement function 17c may not remove the background noise included in the 1D projection data.

[0064] In addition, for example, the calculation function 17d calculates the excitation thickness and excitation position of the OVS pulse based on the thickness of the subject measured by the measurement function 17c, the center position of the imaging region, and the size of the imaging region.

[0065] Figure 6 It is a diagram showing an example of the processing performed by the calculation function 17d of the first embodiment.

[0066] For example, as Figure 6 shown, the calculation function 17d calculates the excitation thickness thick_sut1 of the first OVS pulse applied to the outside of one side ( Figure 6 the upper side in Figure 6 ) of the imaging region in the phase encoding direction and the excitation thickness thick_sut2 of the second OVS pulse applied to the outside of the other side (

[0067] the lower side in

[0068] ) of the imaging region in the phase encoding direction.

[0069] Y1 = y + FOVy / 2 + thick_sat1 / 2

[0070] Y2 = y - FOVy / 2 - thick_sat1 / 2

[0071] In addition, for example, the calculation function 17d receives the excitation width OVSx in the frequency encoding direction of the OVS pulse from the operator, and calculates the coordinate X1 in the frequency encoding direction of the first OVS pulse and the coordinate X2 in the frequency encoding direction of the second OVS pulse according to the formulas X1 = OVSx / 2 and X2 = OVSx / 2.

[0072] Moreover, after the calculation function 17d calculates the excitation thickness and excitation position of the OVS pulse, the imaging control function 17a of the processing circuit 17 applies the OVS pulse based on the calculated excitation thickness and excitation position, thereby performing the main imaging of the subject using the OVS method.

[0073] The above describes each processing function of the processing circuit 17. As described above, the processing circuit 17 is implemented by a processor, for example. In this case, each processing function of the processing circuit 17 is stored in the storage circuit 13 in the form of a program executable by a computer, for example. Moreover, the processing circuit 17 reads and executes each program from the storage circuit 13 to implement the processing functions corresponding to the respective programs.

[0074] Figure 7 It is a flowchart showing the processing procedure of the processing performed by each processing function of the MRI apparatus 100 according to the first embodiment.

[0075] For example, as Figure 7 shown, in the present embodiment, first, the acquisition function 17b acquires 1D projection data in the phase encoding direction of the subject, which is the object of the main imaging (step S101). The processing of this step S101 is realized, for example, by the processing circuit 17 reading and executing a prescribed program corresponding to the acquisition function 17b from the storage circuit 13.

[0076] Then, the measurement function 17c measures the subject thickness in the phase encoding direction using the 1D projection data acquired by the acquisition function 17b (step S102). The processing of this step S102 is realized, for example, by the processing circuit 17 reading and executing a prescribed program corresponding to the measurement function 17c from the storage circuit 13.

[0077] Then, the calculation function 17d calculates the excitation thickness and excitation position of the OVS pulse based on the subject thickness measured by the measurement function 17c (step S103). The processing of this step S103 is realized, for example, by the processing circuit 17 reading and executing a prescribed program corresponding to the calculation function 17d from the storage circuit 13.

[0078] Then, the imaging control function 17a performs main imaging of the subject using the OVS method by applying an OVS pulse based on the excitation thickness and excitation position calculated by the calculation function 17d (step S104). The process of this step S104 is realized, for example, by the processing circuit 17 reading out and executing a prescribed program corresponding to the imaging control function 17a from the storage circuit 13.

[0079] As described above, in the first embodiment, the acquisition function 17b acquires 1D projection data in the phase encoding direction of the subject, which is the object of main imaging. In addition, the measurement function 17c measures the subject thickness in the phase encoding direction using the 1D projection data acquired by the acquisition function 17b. Further, the calculation function 17d calculates the excitation thickness and excitation position of the OVS pulse based on the subject thickness measured by the measurement function 17c.

[0080] According to this configuration, the operator of the MRI apparatus does not need to set the excitation thickness and excitation position of the OVS pulse, and the work flow is improved. In addition, the OVS pulse can be applied with the minimum excitation thickness regardless of the size of the subject and the position of the imaging region, and local excitation can be appropriately performed. Therefore, according to the first embodiment, the excitation thickness and excitation position of the OVS pulse can be easily and appropriately set.

[0081] The first embodiment has been described above, but the above-described first embodiment can also be implemented by appropriately changing a part of the processing functions of the processing circuit 17 of the MRI apparatus 100. Therefore, hereinafter, some modification examples related to the first embodiment will be described as other embodiments. In addition, in the following embodiments, the description will focus on the differences from the first embodiment, and detailed descriptions of repeated contents will be omitted.

[0082] (Second Embodiment)

[0083] For example, in the above-described first embodiment, the calculation function 17d calculates the excitation thickness and excitation position of the OVS pulse based on the subject thickness measured by the measurement function 17c, the center position of the imaging region, and the size of the imaging region. However, as is well known, the RF curve of the OVS pulse is not rectangular and has side lobes, and signal folding occurs in the side lobe portion.

[0084] Therefore, for example, the calculation function 17d may also calculate the excitation thickness and excitation position of the OVS pulse by considering the side lobes of the OVS pulse, and suppress the signal folding caused by the side lobes of the OVS pulse. Hereinafter, such an example will be described as the second embodiment.

[0085] For example, the calculation function 17d calculates the sidelobe width of the OVS pulse, and calculates the excitation thickness and excitation position of the OVS pulse in such a manner that the OVS pulse is applied at intervals of at least the size of the sidelobe width from the imaging region.

[0086] Figure 8 and 9 is a diagram showing an example of the processing performed by the MRI apparatus 100 of the second embodiment.

[0087] For example, as ​ shown, after the calculation function 17d calculates the excitation thickness thick_sut1 of the first OVS pulse applied to the outside of one side of the imaging region in the phase encoding direction and the excitation thickness thick_sut2 of the second OVS pulse applied to the outside of the other side of the imaging region in the phase encoding direction by the same method as in the first embodiment, the calculation function 17d calculates the RF curve of each OVS pulse and calculates the sidelobe width of the RF curve.

[0088] Moreover, for example, as ​ shown, when the coordinate in the frequency encoding direction is represented by x or X, the coordinate in the phase encoding direction is represented by y or Y, the size of the imaging region in the phase encoding direction is set to FOVy, the center coordinate of the imaging region is set to (x, y), the excitation center coordinate of the first OVS pulse is set to (X1, Y1), and the excitation center coordinate of the second OVS pulse is set to (X2, Y2), the calculation function 17d calculates the coordinate Y1 in the phase encoding direction of the excitation center coordinate of the first OVS pulse and the coordinate Y2 in the phase encoding direction of the excitation center coordinate of the second OVS pulse according to the following formulas.

[0089] Y1 = y + FOVy / 2 + thick_sat1 / 2 + sidelobe width of the first OVS pulse

[0090] Y2 = y - FOVy / 2 - thick_sat1 / 2 - sidelobe width of the second OVS pulse

[0091] Accordingly, the first OVS pulse and the second OVS pulse are applied at intervals of at least the size of the sidelobe width from the imaging region. In addition, the interval between the OVS pulse and the imaging region does not necessarily need to be the same as the sidelobe width of the OVS pulse. For example, an interval obtained by adding a predetermined width to the sidelobe width of the OVS pulse may be set to more reliably suppress signal folding back.

[0092] In the above-described second embodiment, the acquisition function 17b calculates the sidelobe width of the OVS pulse, and calculates the excitation thickness and excitation position of the OVS pulse in such a manner that the OVS pulse is applied at intervals of at least the size of the sidelobe width from the imaging region.

[0093] Therefore, according to the second embodiment, it is possible to suppress the signal folding caused by the sidelobes of the OVS pulse. In addition, it is possible to prevent reshooting in the case where signal folding occurs, and it is possible to suppress the extension of the time required for shooting.

[0094] (Third Embodiment)

[0095] In addition, for example, in the above-described first embodiment, in the pre-scan before the main shooting, the acquisition function 17b excites the slice shooting range including the slice of the subject to be shot by the main shooting, and collects 1D projection data in the phase encoding direction, thereby obtaining 1D projection data. However, the method of collecting 1D projection data is not limited to this.

[0096] For example, the acquisition function 17b may also obtain 1D projection data for calculating the excitation thickness and excitation position of the OVS pulse by generating 1D projection data in the phase encoding direction based on the shooting data normally collected in the pre-scan. Hereinafter, such an example will be described as the third embodiment.

[0097] For example, the acquisition function 17b obtains 1D projection data by generating 1D projection data in the phase encoding direction based on the shooting data for positioning the subject collected before the main shooting.

[0098] ​ It is a diagram showing an example of the processing performed by the MRI apparatus 100 according to the third embodiment.

[0099] For example, as ​ shown, the acquisition function 17b acquires the positioning images (slice 1 to slice n) of a plurality of slices of the subject collected in the pre-scan performed before the main shooting from the storage circuit 13 ( ​ (A)).

[0100] Here, the positioning image (also referred to as a Locator image) is an image of the subject used to determine the position of the shooting area in the main shooting, and is, for example, multi-slice data or volume data of the subject.

[0101] Then, the acquisition function 17b virtually generates 1D projection data in the phase encoding direction by accumulating the signals of the acquired plurality of positioning images in the slice selection excitation direction and then projecting in the frequency encoding direction as the projection direction ( ​ (B)).

[0102] Then, similar to the first embodiment, the measurement function 17c measures the thickness of the subject in the phase encoding direction using the 1D projection data acquired by the acquisition function 17b ( ​ of (C)), and the calculation function 17d calculates the excitation thickness and excitation position of the OVS pulse based on the thickness of the subject measured by the measurement function 17c ( ​ of (D)).

[0103] In addition, here, the acquisition function 17b generates 1D projection data in the phase encoding direction based on the localization image of the subject, but other types of captured data collected during pre-scanning can also be used instead of the localization image. For example, the acquisition function 17b can also generate 1D projection data in the phase encoding direction based on the sensitivity map data (map data) for luminance correction or parallel imaging collected during pre-scanning.

[0104] As described above, in the third embodiment, the acquisition function 17b acquires 1D projection data for calculating the excitation thickness and excitation position of the OVS pulse by generating 1D projection data in the phase encoding direction based on captured data such as localization images and sensitivity maps that are typically collected during pre-scanning before main imaging.

[0105] Therefore, according to the third embodiment, there is no need to add new data collection during pre-scanning to calculate the excitation thickness and excitation position of the OVS pulse, and it is possible to suppress the extension of the imaging time required.

[0106] As described above, the first to third embodiments have been described. However, for example, in the first and second embodiments, the one-dimensional projection data can also be MR data collected by applying only the gradient magnetic field in the phase encoding direction without applying the gradient magnetic field in the frequency encoding direction and the gradient magnetic field in the slice selection excitation direction. As a result, the collection time of the one-dimensional projection data can be shortened, and the excitation thickness and excitation position of the OVS pulse can be easily and appropriately set without extending the entire imaging time.

[0107] In addition, in the above-described first to third embodiments, an example of calculating the excitation thickness and excitation position of the OVS pulse used when imaging a three-dimensional imaging region has been described, but the methods described in each embodiment can also be similarly applied to calculating the excitation thickness and excitation position of a two-dimensional saturation pulse applied to the outside in the phase encoding direction of a two-dimensional imaging region when imaging a two-dimensional imaging region.

[0108] (Other Embodiments)

[0109] In addition, in the above-described embodiments, the processing circuits 14 to 17 are each implemented by a single processor, but the embodiments are not limited thereto. For example, each processing circuit may also be constituted by combining a plurality of independent processors, and each processing function is realized by each processor executing a program. In addition, the processing functions of each processing circuit may be appropriately dispersed or integrated into a single or multiple processing circuits. In the above description, the single storage circuit 13 stores programs corresponding to the respective processing functions, but the embodiments are not limited thereto. For example, it may be configured such that a plurality of storage circuits are dispersedly arranged for each processing circuit, and each processing circuit reads out a corresponding program from a separate storage circuit.

[0110] In addition, in the above-described embodiments, an example has been described in which the acquisition unit, measurement unit, and calculation unit in this specification are respectively realized by the acquisition function, measurement function, and display control function of the processing circuit, but the embodiments are not limited thereto. For example, the acquisition unit, measurement unit, and calculation unit in this specification can be realized not only by the acquisition function, measurement function, and calculation function described in the embodiments, but also by only hardware, only software, or a combination of hardware and software to achieve the same functions.

[0111] In addition, in the above description, an example has been described in which the "processor" reads out and executes a program corresponding to each processing function from the storage circuit, but the embodiments are not limited thereto. The term "processor" refers to, for example, 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)), etc. When the processor is, for example, a CPU, the processor realizes each processing function by reading out and executing a program stored in the storage circuit. On the other hand, when the processor is an ASIC, instead of storing the program in the storage circuit, the processing function is directly incorporated into the circuit of the processor as a logic circuit. In addition, each processor in this embodiment is not limited to the case where each processor is configured as a single circuit, and a processor may also be constituted by combining a plurality of independent circuits to realize its processing function. And ​Multiple constituent elements therein are integrated into one processor to implement its processing functions.

[0112] Here, a program executed by the processor is pre-loaded into a ROM (Read Only Memory), a storage circuit, etc. and provided. This program can also be recorded in a computer-readable storage medium such as a CD (Compact Disk)-ROM, FD (Flexible Disk), CD-R (Recordable), DVD (Digital Versatile Disk), etc. in a format installable in these devices or in an executable format file. Additionally, this program can also be stored on a computer connected to a network such as the Internet and provided or distributed by downloading via the network. For example, this program is composed of modules including the above-mentioned respective functional units. As actual hardware, by reading and executing the program from a storage medium such as a ROM by the CPU and loading it onto the main storage device, each module is generated on the main storage device.

[0113] In addition, in the above-described embodiments, each constituent element of each illustrated device is functionally conceptual, and physically it is not necessarily configured as illustrated. That is, the specific form of dispersion or integration of each device is not limited to the illustrated form, and can be dispersed or integrated functionally or physically in any unit according to various loads, usage conditions, etc. to form all or part of it. And all or any part of each processing function performed in each device can be implemented by a CPU and a program analyzed and executed by the CPU, or can be implemented as hardware based on wired logic.

[0114] In addition, all or part of the processing described as being automatically performed in each of the above-described embodiments can also be manually performed, or all or part of the processing described as being manually performed can also be automatically performed by a known method. In addition to this, the processing procedures, control procedures, specific names, and information including various data and parameters shown in the above description and the drawings can be arbitrarily changed unless otherwise specifically noted.

[0115] According to at least one of the above-described embodiments, it is possible to easily and appropriately set the excitation thickness and excitation position of the saturation pulse applied to the outside in the phase encoding direction of the imaging region in the subject.

[0116] Some embodiments have been described, but 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, changes, and combinations of the embodiments can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and its equivalents.

[0117] Regarding the above embodiments, the following remarks are disclosed as an aspect and optional features of the invention.

[0118] (Remark 1)

[0119] A magnetic resonance imaging apparatus, comprising:

[0120] An acquisition unit that acquires one-dimensional projection data in the phase encoding direction of a subject, which is the object of main imaging;

[0121] A measurement unit that measures the thickness of the subject in the phase encoding direction using the one-dimensional projection data; and

[0122] A calculation unit that calculates the excitation thickness and excitation position of a saturation pulse applied to the outside of the imaging region in the phase encoding direction within the subject during the main imaging based on the thickness of the subject.

[0123] (Remark 2)

[0124] Alternatively, the acquisition unit may excite a slice imaging range including a slice of the subject to be imaged by the main imaging, and collect one-dimensional projection data in the phase encoding direction, thereby acquiring the one-dimensional projection data.

[0125] (Remark 3)

[0126] Alternatively, the measurement unit may obtain a signal curve representing the signal distribution of the subject in the phase encoding direction based on the one-dimensional projection data, and measure the thickness of the subject outside the imaging region in the phase encoding direction based on the signal curve.

[0127] (Remark 4)

[0128] Alternatively, the measurement unit may determine, based on the signal curve, a position where the signal of the subject becomes a specified value in the phase encoding direction, and measure the distance between this position and the position of the edge of the imaging region in the phase encoding direction, thereby measuring the thickness of the subject.

[0129] (Remark 5)

[0130] Alternatively, the calculation unit may calculate the excitation thickness and excitation position of the saturation pulse based on the thickness of the subject, the central position of the imaging region, and the size of the imaging region.

[0131] (Note 6)

[0132] Alternatively, the calculation unit may calculate the sidelobe width of the saturation pulse, and calculate the excitation thickness and excitation position of the saturation pulse in such a way that the saturation pulse is applied at intervals separated from the imaging region by at least the size of the sidelobe width.

[0133] (Note 7)

[0134] Alternatively, the acquisition unit may acquire the one-dimensional projection data in the phase encoding direction by generating the one-dimensional projection data in the phase encoding direction from the imaging data for positioning the subject collected before the main imaging.

[0135] (Note 8)

[0136] Alternatively, the one-dimensional projection data may be nuclear magnetic resonance data collected by applying only the gradient magnetic field in the phase encoding direction without applying the gradient magnetic field in the frequency encoding direction and the gradient magnetic field in the slice selection excitation direction.

[0137] (Note 9)

[0138] Alternatively, the saturation pulse applied to the outside of the imaging region in the phase encoding direction may be an OVS pulse, i.e., a band suppression pulse.

[0139] (Note 10)

[0140] Alternatively, the excitation thickness may be the thickness of the saturation pulse in the phase encoding direction.

[0141] (Note 11)

[0142] Alternatively, the excitation position may be the position of the saturation pulse in the phase encoding direction.

[0143] (Note 12)

[0144] A magnetic resonance imaging method, comprising:

[0145] a step of acquiring one-dimensional projection data in the phase encoding direction of a subject, which is an object of main imaging;

[0146] a step of measuring the thickness of the subject in the phase encoding direction using the one-dimensional projection data; and

[0147] A step of calculating an excitation thickness and an excitation position of a saturation pulse applied to the outside of the phase encoding direction of a shooting region in the subject during the main shooting based on the thickness of the subject.

Claims

1. A magnetic resonance imaging apparatus, characterized in that, Comprising: An acquisition unit that acquires one-dimensional projection data in the phase encoding direction of a subject, which is the object of main imaging; A measurement unit that measures the thickness of the subject in the phase encoding direction by using the one-dimensional projection data; And A calculation unit that calculates the excitation thickness and excitation position of a saturation pulse applied to the outside of the imaging region in the phase encoding direction within the subject during the main imaging, based on the thickness of the subject.

2. The magnetic resonance imaging apparatus according to claim 1, wherein The acquisition unit excites a slice imaging range including the slice of the subject to be imaged by the main imaging, and performs one-dimensional projection data collection in the phase encoding direction, thereby acquiring the one-dimensional projection data.

3. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein The measurement unit obtains a signal curve representing the distribution of signals of the subject in the phase encoding direction from the one-dimensional projection data, and measures the thickness of the subject outside the imaging region in the phase encoding direction based on the signal curve.

4. The magnetic resonance imaging apparatus according to claim 3, wherein The measurement unit determines, in the phase encoding direction, the position where the signal of the subject becomes a specified value based on the signal curve, and measures the distance between this position and the position of the edge of the imaging region in the phase encoding direction, thereby measuring the thickness of the subject.

5. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein The calculation unit calculates the excitation thickness and excitation position of the saturation pulse based on the thickness of the subject, the central position of the imaging region, and the size of the imaging region.

6. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein The calculation unit calculates the sidelobe width of the saturation pulse, and calculates the excitation thickness and excitation position of the saturation pulse in such a manner that the saturation pulse is applied at an interval at least separating the sidelobe width from the imaging region.

7. The magnetic resonance imaging apparatus according to claim 1, wherein The acquisition unit acquires the one-dimensional projection data by generating the one-dimensional projection data in the phase encoding direction from the positioning imaging data of the subject collected before the main imaging.

8. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein The one-dimensional projection data is nuclear magnetic resonance data collected by applying only the gradient magnetic field in the phase encoding direction without applying the gradient magnetic field in the frequency encoding direction and the gradient magnetic field in the slice selection excitation direction.

9. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein The saturation pulse applied to the outside of the imaging region in the phase encoding direction is an OVS pulse, i.e., a band suppression pulse.

10. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein The excitation thickness is the thickness of the saturation pulse in the phase encoding direction.

11. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein The excitation position is a position in the phase encoding direction of the saturation pulse.

12. A magnetic resonance imaging method, characterized in that, Comprising: A step of acquiring one-dimensional projection data in the phase encoding direction of an object to be examined, which is the subject of the main imaging; A step of measuring the thickness of the subject in the phase encoding direction using the one-dimensional projection data; And A step of calculating the excitation thickness and excitation position of a saturation pulse applied to the outside of the imaging region in the subject during the main imaging based on the thickness of the subject.

Images