Magnetic resonance imaging method, apparatus, MRI device, and medium

Abstract

This application provides a magnetic resonance imaging method, apparatus, MRI device, and medium. The method improves a first bSSFP sequence to obtain a first sequence such that the total gradient area of ​​the first slice-selective gradient, the first slice-selective convergence gradient, and the first slice-selective complex phase gradient within each first TR in the first sequence is not equal to zero. Based on the first sequence, magnetic resonance scanning is performed on the imaging tissue of the object to be detected, and a target magnetic resonance image of the imaging tissue is reconstructed. Thus, the MRI device applies different additional phases to the imaging protons at different z-positions in the slice-selective direction for each imaging voxel, resulting in different spectral responses for the imaging protons at different z-positions in the slice-selective direction. By superimposing the spectra of multiple imaging protons within a single imaging voxel, the integral averaging of the imaging proton signals at different positions within the imaging voxel can be achieved, thereby avoiding the overall signal of a single imaging voxel being zero, and thus suppressing black band artifacts in the reconstructed magnetic resonance image.

Description

Technical Field

[0001] This application belongs to the field of image processing technology, specifically relating to a magnetic resonance imaging method, device, MRI equipment, and medium. Background Technology

[0002] Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technique. Balanced Steady State Free Precession (bSSFP) sequences are widely used in MRI due to their high signal-to-noise ratio, high tissue contrast, and rapid imaging capabilities.

[0003] However, when the main magnetic field (B0) of the magnetic resonance imaging system is non-uniform, the reconstructed magnetic resonance image of the subject based on the bSSFP sequence will show black band artifacts. Summary of the Invention

[0004] This application provides a magnetic resonance imaging method, apparatus, MRI device, and medium to solve the problem of black band artifacts appearing in the reconstructed magnetic resonance images of the subject under test when the main magnetic field B0 of the magnetic resonance imaging system is non-uniform. This is because the MRI device reconstructs the magnetic resonance image based on the bSSFP sequence when performing magnetic resonance scanning on the subject under test.

[0005] The first aspect of this application provides a magnetic resonance imaging method, the method comprising: Obtain the first sequence, wherein the first sequence is the improved first equilibrium steady-state free precession bSSFP sequence, and each first TR in the first sequence includes the first layer selection gradient, the first layer selection back convergence gradient and the first layer selection complex phase gradient in the layer selection direction. In each first TR in the first sequence, the total gradient area of ​​the first layer selection gradient, the first layer selection back convergence gradient and the first layer selection complex phase gradient is not equal to 0. Based on the first sequence, magnetic resonance scanning is performed on the imaging tissue of the object to be detected, and the first magnetic resonance signal of the imaging tissue is acquired. Based on the first magnetic resonance signal, the target magnetic resonance image is reconstructed.

[0006] Optionally, in the first-layer selected gradient, the first-layer selected back-converging gradient, and the first-layer selected complex phase gradient, at least two gradients have different durations, amplitudes, and / or polarities.

[0007] Optionally, the total gradient area is within a preset threshold range; wherein, the upper limit of the preset threshold range is less than the target gradient area, and the target gradient area refers to the gradient area during the target period of the additional phase change within the imaging voxel.

[0008] Optionally, the target gradient area and the target product are inversely proportional. The upper limit of the preset threshold range is the product of the target gradient area and the first preset coefficient, and the lower limit of the preset threshold range is the product of the target gradient area and the second preset coefficient. The target product is the product of the gyromagnetic ratio of the imaging proton and the layer thickness of the imaging voxel.

[0009] Optionally, the first sequence may further include: multiple second TRs, wherein the multiple first TRs and multiple second TRs are arranged alternately, and the duration of the second TRs is less than the duration of the first TRs.

[0010] Optionally, if the polarity of the second layer-selected gradient in each second TR in the first sequence is the same as the polarity of the first layer-selected gradient, the total gradient area in the layer-selected direction in each second TR is equal to 0. When the polarity of the second layer-selected gradient within each second TR is opposite to that of the first layer-selected gradient, the total gradient area in the layer-selected direction within each second TR is not equal to 0.

[0011] Optionally, before obtaining the first sequence, the method may also include: At least one second bSSFP sequence is obtained, wherein the phase cycle of the RF excitation pulse in each of the at least one second bSSFP sequence is different from the phase cycle of the RF excitation pulse in the first bSSFP sequence, and the duration of the third TR in the second bSSFP sequence is equal to the duration of the first TR. Obtain the second sequence corresponding to each second bSSFP sequence, wherein the second sequence is an improved second bSSFP sequence, and the total gradient area in the layer selection direction within each third TR in the second sequence is not equal to 0; Based on each second sequence, magnetic resonance scanning was performed on the imaging tissue, and the second magnetic resonance signal of the imaging tissue was acquired. Based on at least one set of second magnetic resonance signals, reconstruct at least one second magnetic resonance image that corresponds one-to-one with the second magnetic resonance signals; Based on the first magnetic resonance signal, the target magnetic resonance image is reconstructed, including: Based on the first magnetic resonance signal, reconstruct the first magnetic resonance image; The first magnetic resonance image is weighted and added to at least one second magnetic resonance image to obtain the target magnetic resonance image.

[0012] Optionally, the second sequence may also include: multiple fourth TRs, wherein multiple third TRs and multiple fourth TRs in each second sequence are alternately arranged, and the duration of the fourth TRs is less than the duration of the third TRs.

[0013] A second aspect of this application provides a magnetic resonance imaging apparatus, the apparatus comprising: The acquisition module is used to acquire the first sequence, wherein the first sequence is the improved first equilibrium steady-state free precession bSSFP sequence, and each first TR in the first sequence includes the first layer selection gradient, the first layer selection back convergence gradient and the first layer selection complex phase gradient in the layer selection direction. In each first TR in the first sequence, the total gradient area of ​​the first layer selection gradient, the first layer selection back convergence gradient and the first layer selection complex phase gradient is not equal to 0. The acquisition module is used to perform magnetic resonance scanning on the imaging tissue of the object to be detected based on a first sequence, and to acquire the first magnetic resonance signal of the imaging tissue; The reconstruction module is used to reconstruct the target magnetic resonance image based on the first magnetic resonance signal.

[0014] Optionally, among the stratified gradient, stratified back-convergence gradient, and stratified complex phase gradient, at least two gradients have different durations, amplitudes, and / or polarities.

[0015] Optionally, the total gradient area is within a preset threshold range; wherein, the upper limit of the preset threshold range is less than the target gradient area, and the target gradient area refers to the gradient area during the target period of the additional phase change within the imaging voxel.

[0016] Optionally, the target gradient area and the target product are inversely proportional. The upper limit of the preset threshold range is the product of the target gradient area and the first preset coefficient, and the lower limit of the preset threshold range is the product of the target gradient area and the second preset coefficient. The target product is the product of the gyromagnetic ratio of the imaging proton and the layer thickness of the imaging voxel.

[0017] Optionally, the first sequence may further include: multiple second TRs, wherein the multiple first TRs and multiple second TRs are arranged alternately, and the duration of the second TRs is less than the duration of the first TRs.

[0018] Optionally, if the polarity of the second layer-selected gradient within each second TR in the first sequence is the same as the polarity of the first layer-selected gradient, the total gradient area in the layer-selected direction within each second TR is equal to 0.

[0019] Optionally, the acquisition module is further configured to acquire at least one second bSSFP sequence, wherein the phase cycle of the RF excitation pulse in each of the at least one second bSSFP sequence is different from the phase cycle of the RF excitation pulse in the first bSSFP sequence, and the duration of the third TR in the second bSSFP sequence is equal to the duration of the first TR; acquire a second sequence corresponding to each second bSSFP sequence, wherein the second sequence is an improved second bSSFP sequence, and the total gradient area in the layer selection direction in each third TR in the second sequence is not equal to 0; the acquisition module is further configured to perform magnetic resonance scanning on the imaging tissue based on each second sequence, and acquire the second magnetic resonance signal of the imaging tissue; the reconstruction module is further configured to reconstruct at least one second magnetic resonance image corresponding one-to-one with the second magnetic resonance signal based on at least one set of second magnetic resonance signals; reconstruct a first magnetic resonance image based on the first magnetic resonance signal; and perform weighted summation processing on the first magnetic resonance image and at least one second magnetic resonance image to acquire the target magnetic resonance image.

[0020] Optionally, the second sequence may also include: multiple fourth TRs, wherein multiple third TRs and multiple fourth TRs in each second sequence are alternately arranged, and the duration of the fourth TRs is less than the duration of the third TRs.

[0021] A third aspect of this application provides an MRI device, including: a processor, the processor being connected to a memory, the memory storing a computer program executable on the processor, the computer program being executed by the processor to implement a magnetic resonance imaging method as described in any of the first aspects.

[0022] A fourth aspect of this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements a magnetic resonance imaging method as described in any of the first aspects.

[0023] The fifth aspect of this application provides a computer program product, including a computer program that, when executed by a processor, implements a magnetic resonance imaging method as described in any of the first aspects.

[0024] The magnetic resonance imaging method, apparatus, MRI device, and medium provided in this application embodiment include the following: In the case of non-uniform main magnetic field, the MRI device acquires a first sequence, wherein the first sequence is an improved first equilibrium steady-state free precession bSSFP sequence. Each first TR in the first sequence includes, in the slice selection direction, a first slice selection gradient, a first slice selection reconvergence gradient, and a first slice selection complex phase gradient. In each first TR in the first sequence, the total gradient area of ​​the first slice selection gradient, the first slice selection reconvergence gradient, and the first slice selection complex phase gradient is not equal to 0. Based on the first sequence, the imaging tissue of the object to be detected is subjected to magnetic resonance scanning, and the first magnetic resonance signal of the imaging tissue is acquired. Finally, based on the first magnetic resonance signal, the target magnetic resonance image is reconstructed. Because the total gradient area of ​​each first TR in the first sequence is not equal to 0 in the layer selection direction, different additional phases are applied to the imaging protons at different z positions in the layer selection direction of each imaging voxel, so that the imaging protons at different z positions in the layer selection direction correspond to different spectral responses. By superimposing the spectra of multiple imaging protons in a single imaging voxel, the integral average of the imaging proton signals at different positions in the imaging voxel can be achieved, thereby avoiding the overall signal of a single imaging voxel being zero, and thus suppressing the black band artifacts in the reconstructed magnetic resonance image. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of an MRI device provided in an embodiment of this application; Figure 2 A schematic flowchart of a magnetic resonance imaging method provided in an embodiment of this application; Figure 3 A waveform diagram of a bSSFP sequence provided in an embodiment of this application; Figure 4 A waveform diagram of a first sequence provided in an embodiment of this application; Figure 5 A waveform diagram of another first sequence provided in an embodiment of this application; Figure 6 A waveform diagram of yet another first sequence provided in an embodiment of this application; Figure 7 A schematic flowchart of another magnetic resonance imaging method provided in an embodiment of this application; Figure 8 A schematic diagram of a first bSSFP sequence and a spectral response image of the first sequence provided in an embodiment of this application; Figure 9 A schematic diagram of the signal-to-noise ratio of a magnetic resonance image reconstructed sequentially based on a first bSSFP sequence, a first sequence, and a first sequence including multiple second TRs, provided for an embodiment of this application; Figure 10A contrast diagram of the first bSSFP sequence and the first sequence based on a T1 quantitative water model provided for an embodiment of this application; Figure 11 A contrast comparison diagram of the first bSSFP sequence and the first sequence based on a T2 quantitative water model provided for an embodiment of this application; Figure 12 A contrast diagram of a first bSSFP sequence and a first sequence based on a PD quantitative water model provided in this application embodiment; Figure 13 A schematic diagram of a neck bright blood image reconstructed based on a first bSSFP sequence and a first sequence, respectively, provided for an embodiment of this application; Figure 14 A schematic diagram of a neck black blood image reconstructed based on a first bSSFP sequence and a first sequence, respectively, provided for an embodiment of this application; Figure 15 A schematic diagram of a neck bright blood image reconstructed based on a first bSSFP sequence and a first sequence including multiple second TRs, provided for an embodiment; Figure 16 A schematic diagram of a cross-sectional image of the brain reconstructed based on a first bSSFP sequence and a first sequence including multiple second TRs, provided for an embodiment; Figure 17 A block diagram of a magnetic resonance imaging device provided in an embodiment of this application; Figure 18 This is a schematic diagram of another MRI device provided in an embodiment of this application. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0027] The terms "first," "second," etc., used in this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first" and "second" are generally of the same class, without limiting the number of objects; for example, the first object can be one or more. Furthermore, "or" in this application indicates at least one of the connected objects. For example, "A or B" covers three scenarios: Scenario 1: including A but not B; Scenario 2: including B but not A; Scenario 3: including both A and B. The character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0028] The term "instruction" in this application can be either a direct instruction (or explicit instruction) or an indirect instruction (or implicit instruction). A direct instruction can be understood as one in which the sender explicitly informs the receiver of specific information, the operation to be performed, or the requested result, etc.; an indirect instruction can be understood as one in which the receiver determines the corresponding information based on the instruction sent by the sender, or makes a judgment and determines the operation to be performed or the requested result, etc., based on the judgment result.

[0029] MRI is a non-invasive medical imaging technique that has been widely used in medical imaging. The working principle of MRI is as follows: First, a radio frequency (RF) excitation pulse is applied to the imaging tissue located in the main magnetic field through a radio frequency (RF) transmitting coil. This excites hydrogen protons within the imaging tissue to undergo spin resonance, causing them to deviate from their equilibrium state and generate a magnetic resonance signal. This magnetic resonance signal carries spatial location information under the spatial encoding effect of a gradient magnetic field. Then, it is acquired by a receiving coil to form k-space data. Finally, by performing an inverse Fourier transform on the k-space data, a spatial image of the imaging tissue is reconstructed.

[0030] Figure 1 An MRI device is shown, such as Figure 1 As shown, the MRI device includes: a controller 10, a spectrometer system 20, a main magnet, a gradient system, a radio frequency system, and an auxiliary system. The spectrometer system 20 is connected to the controller 10 and includes a sequence control unit 21. The sequence control unit 21 can generate a pulse sequence based on the pulse sequence parameters issued by the controller 10, and send the pulse sequence to the gradient system and the radio frequency system to control the operation of the gradient system and the radio frequency system.

[0031] The pulse sequence parameters include gradient sequence parameters and radio frequency (RF) pulse sequence parameters. The sequence control unit 21 can be used to generate a gradient sequence based on the gradient sequence parameters and to generate an RF excitation pulse sequence based on the RF excitation pulse sequence parameters. The RF excitation pulse sequence may include multiple RF excitation pulses.

[0032] The main magnet includes a magnet 30. This magnet 30 is used to generate a uniform and stable main magnetic field B0 (i.e., a static magnetic field), which magnetizes hydrogen protons in the imaging tissue to produce a macroscopic longitudinal magnetization vector, providing conditions for the subsequent generation of magnetic resonance signals. This magnet 30 can be a permanent magnet or a superconducting magnet.

[0033] This gradient system is used to provide a gradient magnetic field (i.e., a magnetic field with gradually varying intensity) to achieve spatial localization of magnetic resonance signals. From Figure 1 As can be seen, the gradient system includes a gradient coil 41, a gradient power amplifier 42, and a gradient control unit 43 connected in sequence. The gradient control unit 43 is used to send a gradient sequence based on the sequence control unit 21. The gradient power amplifier 42 controls the gradient coil 43 to generate a spatially linear gradient magnetic field, causing the resonance frequency of the imaging tissue to differ at different spatial locations, thereby spatially encoding the magnetic spin in the imaging tissue. The gradient coil 41 includes three independent gradient coils that spatially encode along three orthogonal spatial directions. Correspondingly, the gradient magnetic field includes a phase-encoded gradient magnetic field, a frequency-encoded gradient magnetic field, and a slice-selective gradient magnetic field.

[0034] The radio frequency system includes an RF transmitting coil 51, an RF power amplifier 52, and an RF control unit 53. The RF coil 51, RF power amplifier 52, and RF control unit 53 are connected sequentially. The RF control unit 53 transmits an RF excitation pulse sequence based on the sequence control unit 21, and controls the RF coil 51 to transmit each RF excitation pulse in the RF excitation pulse sequence via the RF power amplifier 52, thereby exciting hydrogen protons in the imaging tissue to resonate and emit a magnetic resonance signal.

[0035] Please continue reading Figure 1 The radio frequency system may further include a radio frequency receiving coil 54, a coil switching unit 55, a receiving unit 56, and a coil interface unit 57. The radio frequency receiving coil 54 is connected to the coil switching unit 55 via an amplifier. The coil switching unit 55 is also connected to the receiving unit 56 and the coil interface unit 57. The radio frequency receiving coil 54 is used to receive echo signals and can transmit the acquired echo signals to the receiving unit 56. The receiving unit 56 can upload the echo signals to the controller 10, which is used to perform post-processing on the echo signals to ultimately obtain a magnetic resonance image of the imaging tissue.

[0036] The RF receiving coil 54 can be an array coil including multiple coil channels. The coil switching unit 55 is used to switch (i.e., select) the coil channels of the array coil 54. Specifically, the coil switching unit 55 can receive instructions sent by the controller 10 through the coil interface unit 57 and switch the coil channels of the array coil 54 in response to those instructions. When the receiving unit 56 and the selected coil channel are open, the echo signal acquired by that coil channel can be received by the receiving unit 56; otherwise, the echo signal cannot be received by the receiving unit 56. That is, unwanted echo signals can be shielded by the coil switching unit 55.

[0037] In the embodiments of this application, see Figure 1 The RF transmitting coil 51 and the RF receiving coil 54 can be set independently. Alternatively, the RF transmitting coil 51 and the RF receiving coil 54 can be integrated into a single RF coil that can be used for both transmitting and receiving.

[0038] The auxiliary system may include: bed control components and cooling components. Figure 1 (Not shown in the image). This cooling assembly can be used to cool the superconducting coil. The support bed control assembly includes a support bed 51 and a support bed control unit 52. The support bed control unit 52 is used to control the movement of the support bed 51 under the control of the controller 10.

[0039] The MRI device described above is merely an illustrative embodiment and should not be construed as limiting the scope of the MRI device. For example, the MRI device 10 may also include... Figure 1 Other elements not shown, such as memory.

[0040] bSSFP sequences are widely used in magnetic resonance imaging due to their high signal-to-noise ratio, high tissue contrast, and rapid imaging capabilities.

[0041] The bSSFP sequence may include RF excitation pulse sequence, layer-selected gradient sequence, phase-coded gradient sequence, frequency-coded gradient sequence, and position sequence of magnetic resonance signal acquisition. Figure 2 A waveform diagram of a bSSFP sequence provided in an embodiment of this application is shown below. Figure 2 As shown, the first row is an RF excitation pulse sequence, which includes continuous and periodic RF excitation pulses; the second row is a layer selection gradient sequence, which is a gradient sequence to be applied in the layer selection direction, and includes periodic layer selection gradients; the third row is a phase encoding gradient sequence, which includes periodic phase encoding gradients; the fourth row is a frequency encoding gradient sequence, which includes periodic frequency encoding gradients; and the fifth row is a position sequence, which includes the position of magnetic resonance signal acquisition.

[0042] refer to Figure 2 The vertical axis of the RF excitation pulse sequence waveform is the gradient amplitude axis of the RF excitation pulse; the vertical axis of the layer selection gradient sequence waveform is the gradient amplitude axis of the layer selection gradient; the vertical axis of the phase-coded gradient sequence waveform is the gradient amplitude axis of the phase-coded gradient; and the vertical axis of the frequency-coded gradient sequence waveform is the gradient amplitude axis of the frequency-coded gradient. The horizontal axes of the RF excitation pulse sequence waveform, the layer selection gradient sequence waveform, the phase-coded gradient sequence waveform, the frequency-coded gradient sequence waveform, and the position sequence waveform are all time axes. The time interval between any two adjacent RF excitation pulses is TR. For example, TR can be 4 milliseconds (ms). One TR is one period. The layer selection gradient within each TR includes a layer selection gradient 21, and layer selection rephasing gradient 22 and layer selection rewinder gradient 23, which have opposite polarities to the layer selection gradient.

[0043] Within each TR, each layer-selective gradient 21 is applied simultaneously with the RF excitation pulse, the layer-selective re-convergence gradient 22 is applied immediately after the RF excitation pulse is applied, and the layer-selective multiphase gradient 23 is applied before the next RF excitation pulse is applied. Figure 2 Taking the layer selection gradient 21 as positive polarity and the layer selection back-convergence gradient 22 and the layer selection multiphase gradient 23 as negative polarity as an example.

[0044] In related technologies, when the main magnetic field B0 of a magnetic resonance imaging (MRI) system is non-uniform, if an MRI device performs MRI scanning of the imaging tissue of the subject based on a bSSFP sequence, the precession frequency of each imaging proton in the main magnetic field will shift. All imaging protons constituting an imaging voxel will have the same spectral response. When the total accumulated phase of all imaging protons within an imaging voxel is an odd multiple of π, the spectral response of that imaging voxel falls into a signal zero point, resulting in zero signal intensity for that imaging voxel in the reconstructed MRI image. This imaging voxel can be called a zero-signal voxel. Spatially continuous zero-signal voxels then appear as black band artifacts in the MRI image.

[0045] To address the aforementioned issues, this application proposes a magnetic resonance imaging (MRI) method. In cases of non-uniform main magnetic field, this method improves the first bSSFP sequence to obtain a first sequence, ensuring that the total gradient area of ​​the first layer-selective gradient, the first layer-selective convergence gradient, and the first layer-selective complex phase gradient within each first TR in the first sequence is not equal to zero. Based on this first sequence, MRI scanning is performed on the imaging tissue of the target object, and a target MRI image of the imaging tissue is reconstructed. The artifact data in this target MRI image is less than a preset threshold. Because the total gradient area in the layer-selective direction within each first TR in the first sequence is not equal to zero, different additional phases are applied to the imaging protons at different z-positions in the layer-selective direction for each imaging voxel. This results in different spectral responses for the imaging protons at different z-positions in the layer-selective direction. By superimposing the spectra of multiple imaging protons within a single imaging voxel, the integral averaging of the imaging proton signals at different positions within that voxel can be achieved, thus avoiding the overall signal of a single imaging voxel being zero and suppressing black band artifacts in the reconstructed MRI image.

[0046] The technical solution of the magnetic resonance imaging method of this application is described below using several specific embodiments as examples: Figure 3 This is a flowchart illustrating a magnetic resonance imaging method provided in an embodiment of this application. This method can be applied to... Figure 1 The controller 10 in the MRI device shown, such as Figure 3 As shown, the flow of the method in this embodiment is as follows: S31: Obtain the first sequence.

[0047] The first sequence is the improved first equilibrium steady-state free precession bSSFP sequence. Each first TR in the first sequence includes the first layer selection gradient, the first layer selection back convergence gradient, and the first layer selection complex phase gradient in the layer selection direction. In each first TR in the first sequence, the total gradient area of ​​the first layer selection gradient, the first layer selection back convergence gradient, and the first layer selection complex phase gradient is not equal to 0.

[0048] In some embodiments, the controller may pre-store a first bSSFP sequence and adjust the first target gradient within each first TR in the first bSSFP sequence to obtain a first sequence.

[0049] In other embodiments, the controller may pre-store a first sequence obtained by adjusting the first target gradient within each first TR in the first bSSFP sequence.

[0050] It should be noted that the first gradient in the first TR of the first bSSFP sequence in the layer selection direction includes: the first layer selection gradient, the first layer selection back-convergence gradient and the first layer selection complex phase gradient, and the first target gradient is one of the first layer selection back-convergence gradient and the first layer selection complex phase gradient.

[0051] The first layer-selective gradient is applied during the RF excitation pulse to select the imaging plane. To maintain a steady-state signal, the first layer-selective convergence gradient and the first layer-selective complex phase gradient need to compensate for the phase accumulation caused by the first layer-selective gradient, so that the integral of the gradient in the layer-selective direction within the first TR is 0, i.e., the total gradient area in the layer-selective direction is 0. In other words, the first layer-selective convergence gradient and the first layer-selective complex phase gradient can determine the total gradient area in the layer-selective direction. Therefore, the controller can adjust the first layer-selective convergence gradient or the first layer-selective complex phase gradient within each first TR in the first bSSFP sequence so that the total gradient area in the layer-selective direction within each first TR in the acquired first sequence is not equal to 0.

[0052] In some embodiments, the first sequence may be obtained by adjusting at least one of the duration, amplitude, and polarity of the first target gradient in the first layer selected back-converging gradient and the first layer selected complex phase gradient.

[0053] S32: Based on the first sequence, perform magnetic resonance scanning on the imaging tissue of the object to be detected, and acquire the first magnetic resonance signal of the imaging tissue.

[0054] The imaging tissue refers to the biological tissue or anatomical structure of the object to be scanned to generate an image. It can be any tissue in the human or animal body that has an MRI signal response, including but not limited to: liver, spleen, heart, breast, and uterus. The first magnetic resonance signal refers to the electromagnetic signal emitted by the imaging protons in the imaging tissue after frequency encoding and phase encoding, following the application of a first RF excitation pulse based on a first sequence in a strong magnetic field.

[0055] After placing the object to be detected in the main magnetic field B0, the controller can apply a first sequence to the imaging tissue of the object to be detected, scan the imaging tissue, and repeatedly perform signal acquisition within multiple first TRs to acquire the first magnetic resonance signal of the imaging tissue.

[0056] S33: Reconstruct the target magnetic resonance image based on the first magnetic resonance signal.

[0057] It should be noted that the first magnetic resonance signal is k-space data. After filling the k-space completely based on the first magnetic resonance signal, the controller performs an inverse Fourier transform on the data in the k-space to reconstruct the complex form of the first magnetic resonance image. The controller then takes the amplitude value of the first magnetic resonance image to obtain the amplitude image, i.e., the target magnetic resonance image.

[0058] Since the controller reconstructs the target magnetic resonance image based on the first sequence, different additional phases are applied to the imaging protons at different z positions in the layer selection direction for each imaging voxel, so that the imaging protons at different z positions in the layer selection direction correspond to different spectral responses. By superimposing the spectra of multiple imaging protons in a single imaging voxel, the integral average of the imaging proton signals at different positions in the imaging voxel can be achieved, thereby avoiding the overall signal of a single imaging voxel being zero, and thus reducing the black band artifact data in the target magnetic resonance image.

[0059] Specifically, an imaging voxel includes multiple imaging protons in three directions. The layer selection direction refers to the spatial direction in which the layer selection gradient is applied, which can be the z-axis direction. In the layer selection direction within the first TR, the total accumulated phase of imaging protons at different z-positions in the main magnetic field B0 is... This can be expressed by the following formula:

[0060] in, Indicates the gyromagnetic ratio of the imaging proton. This represents the z-position coordinate of the imaging proton along the layer selection direction. This represents the total gradient area of ​​the layer selection gradient. Therefore, it can be understood that the change in the total gradient area of ​​the layer selection gradient determines the total accumulated phase of each imaging proton. When the total gradient area of ​​the layer selection gradient is not equal to 0, the total accumulated phase of the imaging protons at different z positions in the layer selection direction is not equal to 0. Therefore, the first sequence in which the total gradient area of ​​the layer selection gradient within each first TR is not equal to 0 applies different additional phases to the imaging protons at different z positions in the layer selection direction for each imaging voxel, resulting in different spectral responses for the imaging protons at different z positions in the layer selection direction.

[0061] In summary, under the condition of non-uniform main magnetic field, a first sequence is acquired, wherein the first sequence is an improved first equilibrium steady-state free precession bSSFP sequence. Each first TR in the first sequence includes, in the layer selection direction, a first layer selection gradient, a first layer selection reconvergence gradient, and a first layer selection complex phase gradient. Within each first TR in the first sequence, the total gradient area of ​​the first layer selection gradient, the first layer selection reconvergence gradient, and the first layer selection complex phase gradient is not equal to 0. Based on the first sequence, magnetic resonance scanning is performed on the imaging tissue of the object to be detected, and the first magnetic resonance signal of the imaging tissue is acquired. Finally, based on the first magnetic resonance signal, the target magnetic resonance image is reconstructed. Because the total gradient area of ​​each first TR in the first sequence is not equal to 0 in the layer selection direction, different additional phases are applied to the imaging protons at different z positions in the layer selection direction of each imaging voxel, so that the imaging protons at different z positions in the layer selection direction correspond to different spectral responses. By superimposing the spectra of multiple imaging protons in a single imaging voxel, the integral average of the imaging proton signals at different positions in the imaging voxel can be achieved, thereby avoiding the overall signal of a single imaging voxel being zero, and thus suppressing the black band artifacts in the reconstructed magnetic resonance image.

[0062] Optionally, in the first-layer selected gradient, the first-layer selected back-converging gradient, and the first-layer selected complex phase gradient, at least two gradients have different durations, amplitudes, and / or polarities.

[0063] Among them, reference Figure 2 The first TR includes: a first-layer selected gradient 21, a first-layer selected back-converging gradient 22, and a first-layer selected complex phase gradient 23. The controller can adjust the duration, amplitude, and / or polarity of the first target gradient in the first-layer selected back-converging gradient 22 and the first-layer selected complex phase gradient 23, so that at least two gradients in the first-layer selected gradient 21, the first-layer selected back-converging gradient 22, and the first-layer selected complex phase gradient 23 have different durations, amplitudes, and / or polarities, and the total gradient area of ​​the first-layer selected gradient 21, the first-layer selected back-converging gradient 22, and the first-layer selected complex phase gradient 23 is not equal to 0.

[0064] It is understandable that, when the controller adjusts the first target gradient within each first TR in the first bSSFP sequence to obtain the first sequence, the gradient area of ​​the first target gradient is the integral of the gradient intensity of the first target gradient over time. Possible ways to adjust the gradient area of ​​the first target gradient may include, but are not limited to, the following: One possible implementation is as follows: Given a fixed duration for the first target gradient and that the polarity of the first target gradient is either positive or negative, the controller can adjust the magnitude of the first target gradient. This adjustment can increase or decrease the magnitude; for example, the controller can increase the magnitude of the first target gradient.

[0065] Another possible implementation is that, with the magnitude and polarity of the first target gradient remaining constant, the controller can adjust the duration of the first target gradient. This adjustment can be either lengthening or shortening the duration; for example, the controller can lengthen the duration of the first target gradient.

[0066] Another possible implementation is that, with the duration of the first target gradient remaining constant, the controller can both change the polarity of the first target gradient and adjust its magnitude.

[0067] Another possible implementation is to change only the polarity of the first target gradient, while keeping both the magnitude and duration of the first target gradient constant. For example, Figure 4 A waveform diagram of a first sequence provided in an embodiment of this application, such as... Figure 4 As shown, the time interval between each two adjacent first RF excitation pulses in the first row is the first TR. The first target gradient in each first TR includes a first layer-selected gradient 41, a first layer-selected back-convergence gradient 42, and a first layer-selected complex phase gradient 43. The first layer-selected complex phase gradient 43 is the first target gradient, and its polarity is opposite to that of the first layer-selected back-convergence gradient 42.

[0068] Understandably, if the polarity of the first layer selected gradient 41 is positive, and the polarity of the first layer selected convergence gradient 42 and the first layer selected complex phase gradient 43 is negative, then the controller can select the first layer selected complex phase gradient 43 as the first target gradient and only adjust its polarity from negative to positive.

[0069] Optionally, when the controller adjusts the first target gradient within each first TR in the first bSSFP sequence, the total gradient area in the layer selection direction is within a preset threshold range. The upper limit of the preset threshold range is less than the target gradient area. The target gradient area refers to the gradient area when the additional phase change within the imaging voxel reaches a target period. In other words, the target gradient area refers to the total gradient area corresponding to when the additional phase change along the layer selection direction within an imaging voxel reaches a complete period (e.g., 2π).

[0070] The controller can pre-store the target period; for example, the target period could be 2. .

[0071] Optionally, the target gradient area and the target product are inversely proportional. The upper limit of the preset threshold range is the product of the target gradient area and the first preset coefficient, and the lower limit of the preset threshold range is the product of the target gradient area and the second preset coefficient. The target product is the product of the gyromagnetic ratio of the imaging proton and the layer thickness of the imaging voxel.

[0072] The target gradient area can be expressed by the following formula:

[0073] Thickness represents the thickness of the voxel in the z-direction, i.e., the layer thickness.

[0074] The controller can also pre-store a first preset coefficient and a second preset coefficient. For example, the first preset coefficient can be 60% and the second preset coefficient can be 20%.

[0075] That is, the upper limit of the preset threshold range can be the range of variation of the additional phase within the voxel reaching 2. The maximum gradient area corresponding to 60% of the time, and the lower limit of the preset threshold range can be the minimum gradient area corresponding to the range of variation of the additional phase within the voxel reaching 20% ​​of 2PI.

[0076] It should be noted that the larger the total gradient area in the first TR of the first sequence in the layer selection direction, the greater the phase difference between imaging protons at different z positions within each imaging voxel. During signal reception, the signal vectors of these imaging protons are added together. For voxels at the resonance frequency, phase dispersion leads to a decrease in the vector sum, thereby reducing the signal amplitude and resulting in a low signal-to-noise ratio of the reconstructed magnetic resonance image. For voxels that were originally near the black band, phase dispersion leads to an increase in the vector sum, thereby increasing the signal amplitude and reducing black band artifacts.

[0077] Therefore, it is understandable that when the total gradient area is less than the lower limit of the preset threshold range, the magnetic resonance image obtained by the MRI device scanning the imaging tissue based on the first sequence contains more artifact data; when the total gradient area is greater than the upper limit of the preset threshold range, the magnetic resonance image obtained by the MRI device scanning the imaging tissue based on the first sequence contains less artifact data than the preset threshold, but the signal-to-noise ratio of the magnetic resonance image is low; when the total gradient area is within the preset threshold range, the magnetic resonance image obtained by the MRI device scanning the imaging tissue based on the first sequence contains less artifact data than the preset threshold, and the signal-to-noise ratio of the magnetic resonance image is high.

[0078] Therefore, by limiting the range of the total gradient area, the controller not only suppresses black band artifacts in the reconstructed magnetic resonance image, but also helps to improve the signal-to-noise ratio of the reconstructed magnetic resonance image, thereby further improving the imaging quality of the reconstructed magnetic resonance image.

[0079] In some embodiments, when the main magnetic field is not uniform, the controller may also apply an additional modulation gradient in the layer selection direction within each first TR in the first bSSFP sequence to obtain the first sequence.

[0080] The modulation gradient can be positive or negative, and it has a duration of a preset time and an amplitude of a preset magnitude. The controller can pre-store the preset time and preset amplitude; for example, the preset time could be 1e-3 seconds (s), and the preset amplitude could be 2... / (γ·Thickness) * 60% / 1e-3 Tesla per meter (T / m).

[0081] Optionally, the first sequence may further include: multiple second TRs, wherein the multiple first TRs and multiple second TRs are arranged alternately, and the duration of the second TRs is less than the duration of the first TRs.

[0082] Figure 5 A waveform diagram of another first sequence provided in an embodiment of this application, as shown below. Figure 5 As shown, multiple first TRs and multiple second TRs are arranged alternately, and the controller applies a second RF excitation pulse and a second gradient in the layer selection direction in each of the multiple second TRs.

[0083] The controller can pre-store the first TR and the second TR. For example, the first TR can be 4ms and the second TR can be 2ms.

[0084] It is understandable that, since the duration of the second TR is not equal to that of the first TR, the phase accumulation caused by the non-uniformity of the main magnetic field B0 in the second TR is different from that caused by the non-uniformity of the main magnetic field B0 in the first TR. By alternately executing the first TR and the second TR, the image signal-to-noise ratio can be improved while reducing black band artifacts.

[0085] It should be noted that while the controller applies the first RF excitation pulse and the first gradient in the layer selection direction in each first TR, it also performs magnetic resonance signal acquisition. In the second TR, it only applies the second RF excitation pulse and the second gradient in the layer selection direction without performing magnetic resonance signal acquisition, which can reduce the duration of the second TR.

[0086] Optionally, if the polarity of the second layer-selected gradient within each second TR in the first sequence is the same as the polarity of the first layer-selected gradient, the total gradient area in the layer-selected direction within each second TR is equal to 0.

[0087] Among them, reference Figure 5In the waveform of the first sequence, within each second TR, the second gradient in the layer selection direction includes a second layer selection gradient 51 and a second layer selection back-convergence gradient 52. The polarity of the second layer selection gradient 51 is positive, the polarity of the second layer selection back-convergence gradient 52 is negative, and the gradient area of ​​the second layer selection gradient 51 is equal to the gradient area of ​​the second layer selection back-convergence gradient 52. The polarity of the first layer selection gradient 41 applied within the first TR is positive, the polarity of the first layer selection back-convergence gradient 42 applied within the first TR is negative, and the polarity of the first layer selection complex phase gradient 43 is positive. Therefore, the polarity of the second layer selection gradient 51 is the same as the polarity of the first layer selection gradient 41. The total gradient area of ​​the first sequence within the second TR is equal to 0, while the total gradient area within the first TR is not equal to 0.

[0088] Optionally, if the polarity of the second layer-selected gradient within each second TR is opposite to the polarity of the first layer-selected gradient, the total gradient area in the layer-selected direction within each second TR is not equal to 0.

[0089] Figure 6 A waveform diagram of another first sequence provided in the embodiments of this application, as shown below. Figure 6 As shown, in this first sequence, within each second TR, the second gradient in the layer selection direction includes only one second layer selection gradient 61, which has a negative polarity. The first layer selection gradient 41 applied within the first TR has a positive polarity, while the first layer selection regression gradient 42 and the first layer selection complex phase gradient 43 applied within the first TR have negative polarities. Therefore, the polarity of the second layer selection gradient 61 is opposite to that of the first layer selection gradient 41, and the total gradient area of ​​the first sequence within the first and second TRs is not equal to 0. Thus, compared to applying a layer selection regression gradient within the second TR, the duration of the second TR required without applying a layer selection regression gradient within the second TR is shorter, thereby reducing the complexity caused by adding multiple second TRs.

[0090] Optionally, the phase of the RF excitation pulse applied in the first TR and the phase of the RF excitation pulse applied in the second TR may be the same or different. For example, if the phase of the RF excitation pulse applied in the first TR and the phase of the RF excitation pulse applied in the second TR are different, the phase of the RF excitation pulse applied in each of the first TRs may be 0°, and the phase applied in each of the second TRs may be 180°.

[0091] In this process, after the object to be detected is placed in the main magnetic field B0, the controller can apply a first sequence including multiple second TRs to the imaging tissue of the object to be detected, scan the imaging tissue, and repeatedly perform signal acquisition within multiple first TRs to acquire the third magnetic resonance signal of the imaging tissue.

[0092] Therefore, since the phase accumulation caused by the non-uniformity of the main magnetic field B0 in the second TR is different from the phase accumulation caused by the non-uniformity of the main magnetic field B0 in the first TR, by alternately executing the first TR and the second TR, the spectral response of the original single first TR can be changed, thereby reducing the black band artifacts in the magnetic resonance image reconstructed based on the first sequence which also includes multiple second TRs, while improving the signal-to-noise ratio of the magnetic resonance image.

[0093] Figure 7 This is a schematic flowchart of another magnetic resonance imaging method provided in an embodiment of this application. Figure 7 Is Figure 2 Based on the illustrated embodiment, at least one second sequence can be obtained, and the target magnetic resonance image can be reconstructed based on the first sequence and at least one second sequence. This method can be applied to... Figure 1 The controller 10 in the MRI device shown, such as Figure 7 As shown, the flow of the method in this embodiment is as follows: S71: Obtain at least one second bSSFP sequence.

[0094] In this sequence, the phase cycle of the RF excitation pulse in each of the at least one second bSSFP sequence is different from the phase cycle of the RF excitation pulse in the first bSSFP sequence, and the duration of the third TR in the second bSSFP sequence is equal to the duration of the first TR.

[0095] The controller can pre-store at least one second bSSFP sequence. It should be noted that when there are multiple second bSSFP sequences, the phase cycle of the RF excitation pulse in each of the multiple second bSSFP sequences is different. For example, if the phase cycle of the RF excitation pulse in the first bSSFP sequence is 0°→180°→0°→180°, and assuming there are two second bSSFP sequences, then the phase cycles of the RF excitation pulse in these two second bSSFP sequences could be 0°→90°→180°→270° and 0°→270°→180°→90°, respectively.

[0096] S72: Obtain the second sequence corresponding to each second bSSFP sequence.

[0097] The second sequence is the improved second bSSFP sequence, and the total gradient area in the layer selection direction within each third TR in the second sequence is not equal to 0.

[0098] The third gradient in the layer selection direction within each third TR of each second bSSFP sequence includes: a third layer selection gradient, a third layer selection back-convergence gradient, and a third layer selection complex phase gradient. Among the third layer selection gradient, the third layer selection back-convergence gradient, and the first layer selection complex phase gradient, at least two gradients have different durations, amplitudes, and / or polarities.

[0099] In some embodiments, the controller may adjust at least one of the duration, amplitude, and polarity of the second target gradient, such that at least two of the third-layer selected gradient, the third-layer selected back-converging gradient, and the third-layer selected complex phase gradient have different durations, amplitudes, and / or polarities, and the total gradient area of ​​the third-layer selected gradient, the third-layer selected back-converging gradient, and the third-layer selected complex phase gradient is not equal to 0. The second target gradient is one of the third-layer selected back-converging gradient and the third-layer selected complex phase gradient.

[0100] Optionally, the controller can also pre-store a second sequence.

[0101] S73: Based on each second sequence, perform magnetic resonance scanning on the imaging tissue and acquire the second magnetic resonance signal of the imaging tissue.

[0102] The second magnetic resonance signal refers to the electromagnetic signal emitted by the imaging protons in the imaging tissue after frequency and phase encoding, following the application of a third RF excitation pulse based on a second sequence in a strong magnetic field.

[0103] After the object to be detected is placed in the main magnetic field B0, the controller can apply each second sequence to the imaging tissue of the object to be detected, scan the imaging tissue, and repeatedly perform signal acquisition in multiple third TRs to acquire the second magnetic resonance signal of the imaging tissue.

[0104] S74: Based on at least one set of second magnetic resonance signals, reconstruct at least one second magnetic resonance image that corresponds one-to-one with the second magnetic resonance signals.

[0105] It should be noted that the second magnetic resonance signal is also k-space data. For each group of second magnetic resonance signals, after the k-space is filled completely based on the second magnetic resonance signal, the controller performs an inverse Fourier transform on the data in the k-space to reconstruct the complex form of the second magnetic resonance image.

[0106] S75: Based on the first magnetic resonance signal, reconstruct the first magnetic resonance image, and perform weighted addition processing on the first magnetic resonance image and at least one second magnetic resonance image to obtain the target magnetic resonance image.

[0107] Specifically, after filling the k-space completely based on the first magnetic resonance signal, the controller performs an inverse Fourier transform on the data in the k-space to reconstruct the complex form of the first magnetic resonance image. The controller then performs a weighted summation of the first magnetic resonance image with at least one second magnetic resonance image to obtain a weighted initial magnetic resonance image; finally, the controller takes the amplitude value of the weighted initial magnetic resonance image to obtain the target magnetic resonance image.

[0108] It should be noted that both the first magnetic resonance image and at least one second magnetic resonance image include amplitude and phase information. When the first magnetic resonance image and at least one second magnetic resonance image are weighted and added together, the weights of the first magnetic resonance image and each of the second magnetic resonance images are also complex numbers.

[0109] It should also be noted that if the phase of the RF excitation pulse is shifted by an angle in either the first or second bSSFP sequence, the entire spectral response will shift along the frequency axis. Therefore, the position of the black band artifact in the reconstructed magnetic resonance image will differ under different RF phase cycles. Thus, the controller utilizes the RF phase shift to weightedly add the complex images reconstructed from the first sequence and at least one second sequence under different RF phase cycles. This allows the position of the signal zero point in the target magnetic resonance image to be filled by other non-zero signals, thereby further suppressing the black band artifact in the reconstructed magnetic resonance image.

[0110] Optionally, if the first sequence further includes multiple second TRs, the second sequence further includes multiple fourth TRs, wherein multiple third TRs in each second sequence are alternately arranged with multiple fourth TRs, and the duration of the fourth TRs is less than the duration of the third TRs.

[0111] The controller can pre-store the third TR and the fourth TR. For example, the third TR can be 4ms and the fourth TR can be 2ms.

[0112] It should be noted that the controller applies a fourth RF excitation pulse and a fourth gradient in the layer selection direction within the fourth TR in each second sequence.

[0113] Understandably, since the duration of the fourth TR is not equal to that of the third TR, the phase accumulation caused by the inhomogeneity of the main magnetic field B0 in the fourth TR is different from that caused by the inhomogeneity of the main magnetic field B0 in the third TR. By alternately executing the third TR and the fourth TR, the signal zero point that was originally under a single third TR can oscillate in time instead of being fixed in the same spatial position, thereby reducing the black band artifacts in the magnetic resonance image reconstructed based on the second sequence that also includes multiple fourth TRs.

[0114] It should be noted that while the controller applies the third RF excitation pulse and the third gradient in the layer selection direction in each third TR, it also performs magnetic resonance signal acquisition. In the fourth TR, it only applies the fourth RF excitation pulse and the fourth gradient in the layer selection direction, without performing magnetic resonance signal acquisition, in order to reduce the time of the fourth TR.

[0115] In some embodiments, when the polarity of the fourth layer-selected gradient in each fourth TR in the second sequence is the same as the polarity of the third layer-selected gradient in the third TR, the total gradient area in the layer-selected direction in each fourth TR in the second sequence is equal to 0.

[0116] Within each fourth TR, the fourth gradient in the layer selection direction can include a fourth layer selection gradient and a fourth layer selection back-convergence gradient. The polarity of the fourth layer selection gradient is positive, the polarity of the fourth layer selection back-convergence gradient is negative, and the gradient area of ​​the fourth layer selection gradient is equal to the gradient area of ​​the fourth layer selection back-convergence gradient.

[0117] In other embodiments, when the polarity of the fourth layer-selection gradient in each fourth TR is opposite to the polarity of the third layer-selection gradient in the third TR, the total gradient area in the layer-selection direction in each fourth TR is not equal to 0.

[0118] Within each fourth TR, the fourth gradient in the layer selection direction may include only one fourth layer selection gradient, and the polarity of this fourth layer selection gradient is negative.

[0119] Furthermore, after placing the object to be detected in the main magnetic field B0, the controller can apply various second sequences, including multiple fourth TRs, to the imaging tissue of the object to be detected, scan the imaging tissue, and repeatedly perform signal acquisition within multiple third TRs to acquire the second magnetic resonance signal of the imaging tissue.

[0120] Therefore, since the phase accumulation caused by the inhomogeneity of the main magnetic field B0 in the fourth TR is different from the phase accumulation caused by the inhomogeneity of the main magnetic field B0 in the third TR, by alternately executing the third TR and the fourth TR, the spectral response of the original single third TR can be changed, thereby reducing the black band artifacts in the magnetic resonance image reconstructed based on the second sequence which also includes multiple fourth TRs, while improving the signal-to-noise ratio of the magnetic resonance image.

[0121] It is understood that the controller can reconstruct a third magnetic resonance image based on a first sequence that also includes multiple second TRs, and reconstruct a fourth magnetic resonance image corresponding one-to-one with the second sequence based on at least one second sequence that also includes multiple fourth TRs. The controller performs a weighted summation of the third magnetic resonance image and at least one fourth magnetic resonance image to obtain a fifth magnetic resonance image. Taking the amplitude of this fifth magnetic resonance image yields a further optimized target magnetic resonance image. Here, the third magnetic resonance image, each of the fourth magnetic resonance images, and the fifth magnetic resonance image are all complex images.

[0122] In this embodiment of the application, under the same changing main magnetic field B0, the spectral response of the first bSSFP sequence and the first sequence are measured respectively. Figure 8 A schematic diagram of the first bSSFP sequence and the spectral response image of the first sequence is shown, as follows. Figure 8 As shown, the left image is the spectral response image of the first bSSFP sequence, and the right image is the spectral response image of the first sequence. It can be seen that when the main magnetic field B0 is non-uniform, the spectral response image of the first bSSFP sequence includes two obvious black band artifacts, while the spectral response image of the first sequence does not have black band artifacts. Therefore, the magnetic resonance image reconstructed based on the first sequence provided in this application embodiment has a high quality.

[0123] In summary, under the condition of non-uniform main magnetic field, a first sequence is acquired, wherein the first sequence is an improved first equilibrium steady-state free precession bSSFP sequence. Each first TR in the first sequence includes, in the layer selection direction, a first layer selection gradient, a first layer selection reconvergence gradient, and a first layer selection complex phase gradient. Within each first TR in the first sequence, the total gradient area of ​​the first layer selection gradient, the first layer selection reconvergence gradient, and the first layer selection complex phase gradient is not equal to 0. Based on the first sequence, magnetic resonance scanning is performed on the imaging tissue of the object to be detected, and the first magnetic resonance signal of the imaging tissue is acquired. Finally, based on the first magnetic resonance signal, the target magnetic resonance image is reconstructed. Because the total gradient area of ​​each first TR in the first sequence is not equal to 0 in the layer selection direction, different additional phases are applied to the imaging protons at different z positions in the layer selection direction of each imaging voxel, so that the imaging protons at different z positions in the layer selection direction correspond to different spectral responses. By superimposing the spectra of multiple imaging protons in a single imaging voxel, the integral average of the imaging proton signals at different positions in the imaging voxel can be achieved, thereby avoiding the overall signal of a single imaging voxel being zero, and thus suppressing the black band artifacts in the reconstructed magnetic resonance image.

[0124] Figure 9The diagram illustrates the signal-to-noise ratio (SNR) of magnetic resonance (MRI) images reconstructed sequentially based on a first bSSFP sequence, a first sequence, and a first sequence including multiple second TRs. Experimental calculations show that the SNR of the MRI image reconstructed based on the first bSSFP sequence is 38.6, the SNR of the MRI image reconstructed based on the first sequence is 39.5, and the SNR of the MRI image reconstructed based on the first sequence including multiple second TRs is 70.8. Therefore, the SNR of the MRI image reconstructed based on the first sequence provided in this embodiment is comparable to that of the MRI image reconstructed based on the first bSSFP sequence, while the SNR of the MRI image reconstructed based on the first sequence including multiple second TRs provided in this embodiment is the highest.

[0125] Figure 10 A contrast diagram of the first bSSFP sequence and the first sequence is shown in the quantitative water model based on longitudinal relaxation time (T1); Figure 11 A contrast diagram of the first bSSFP sequence and the first sequence is shown in the quantitative water model based on transverse relaxation time (T2); Figure 12 A contrast diagram of the first bSSFP sequence and the first sequence of the first sequence in a quantitative water model based on proton density (PD) is shown; as follows: Figures 10 to 12 The images on the left show the contrast of the bSSFP sequence, and the images on the right show the contrast of the first sequence. Figures 10 to 12 It can be seen that the contrast of the first sequence provided in this application embodiment is relatively small compared with the contrast of the first bSSFP sequence. This can suppress the black band artifacts in the reconstructed magnetic resonance image without changing the physical properties of the imaging tissue in the magnetic resonance image, thus ensuring the reliability of the magnetic resonance image.

[0126] Figure 13 A schematic diagram of a bright blood image of the neck reconstructed based on the first bSSFP sequence and the first sequence is shown. Figure 14 A schematic diagram of the neck black blood images reconstructed based on the first bSSFP sequence and the first sequence is shown. Figure 13 As shown, the left image is a bright blood image of the neck reconstructed based on the first bSSFP sequence, and the right image is a bright blood image of the neck reconstructed based on the first sequence; as Figure 14 As shown, the left images in the first and second rows are both neck black blood images reconstructed based on the first bSSFP sequence, and the right images in the first and second rows are both neck black blood images reconstructed based on the first sequence. Figure 13 and Figure 14 As can be seen from this embodiment, the first sequence provided can effectively suppress black band artifacts in the reconstructed magnetic resonance image.

[0127] Figure 15A schematic diagram shows a bright blood image of the neck reconstructed based on a first bSSFP sequence and a first sequence that also includes multiple second TRs. Figure 16 A schematic diagram shows cross-sectional images of the brain reconstructed based on a first bSSFP sequence and a first sequence that also includes multiple second TRs. (See diagram.) Figure 15 As shown, the upper image is a bright blood image of the neck reconstructed based on the first bSSFP sequence, and the lower image is a bright blood image of the neck reconstructed based on the first sequence, which also includes multiple second TRs; as Figure 16 As shown, the left images in the first, second, and third rows are cross-sectional images of the brain at different layers reconstructed based on the first bSSFP sequence, while the right images in the first, second, and third rows are cross-sectional images of the brain at different layers reconstructed based on the first sequence, which also includes multiple second TRs.

[0128] from Figures 15 to 16 As can be seen, compared with the first bSSFP sequence, the magnetic resonance images reconstructed based on the first sequence provided in this application embodiment, and the magnetic resonance images reconstructed based on the first sequence provided in this application which also includes multiple second TRs, do not have black band artifacts. The method provided in this application embodiment can obtain magnetic resonance images with high imaging quality.

[0129] Figure 17 A block diagram of a magnetic resonance imaging device provided in an embodiment of this application, such as... Figure 17 As shown, the device includes: an acquisition module 1701, a collection module 1702, and a reconstruction module 1703. The acquisition module 1701 is used to acquire a first sequence, wherein the first sequence is an improved first equilibrium steady-state free precession bSSFP sequence. Each first TR in the first sequence includes, in the layer selection direction, a first layer selection gradient, a first layer selection convergence gradient, and a first layer selection complex phase gradient. In each first TR in the first sequence, the total gradient area of ​​the first layer selection gradient, the first layer selection convergence gradient, and the first layer selection complex phase gradient is not equal to 0. The collection module 1702 is used to perform magnetic resonance scanning on the imaging tissue of the object to be detected based on the first sequence and acquire the first magnetic resonance signal of the imaging tissue. The reconstruction module 1703 is used to reconstruct the target magnetic resonance image based on the first magnetic resonance signal.

[0130] Optionally, in the first-layer selected gradient, the first-layer selected back-converging gradient, and the first-layer selected complex phase gradient, at least two gradients have different durations, amplitudes, and / or polarities.

[0131] Optionally, the total gradient area is within a preset threshold range; wherein, the upper limit of the preset threshold range is less than the target gradient area, and the target gradient area refers to the gradient area during the target period of the additional phase change within the imaging voxel.

[0132] Optionally, the target gradient area and the target product are inversely proportional. The upper limit of the preset threshold range is the product of the target gradient area and the first preset coefficient, and the lower limit of the preset threshold range is the product of the target gradient area and the second preset coefficient. The target product is the product of the gyromagnetic ratio of the imaging proton and the layer thickness of the imaging voxel.

[0133] Optionally, the first sequence may further include: multiple second TRs, wherein the multiple first TRs and multiple second TRs are arranged alternately, and the duration of the second TRs is less than the duration of the first TRs.

[0134] Optionally, if the polarity of the second layer-selected gradient within each second TR in the first sequence is the same as the polarity of the first layer-selected gradient, the total gradient area in the layer-selected direction within each second TR is equal to 0.

[0135] Optionally, the acquisition module 1701 is further configured to acquire at least one second bSSFP sequence, wherein the phase cycle of the RF excitation pulse in each of the at least one second bSSFP sequence is different from the phase cycle of the RF excitation pulse in the first bSSFP sequence, and the duration of the third TR in the second bSSFP sequence is equal to the duration of the first TR; acquire a second sequence corresponding to each second bSSFP sequence, wherein the second sequence is an improved second bSSFP sequence, and the total gradient area in the layer selection direction in each third TR in the second sequence is not equal to 0; the acquisition module 1702 is further configured to perform magnetic resonance scanning on the imaging tissue based on each second sequence, and acquire the second magnetic resonance signal of the imaging tissue; the reconstruction module 1703 is further configured to reconstruct at least one second magnetic resonance image corresponding one-to-one with the second magnetic resonance signal based on at least one set of second magnetic resonance signals; reconstruct a first magnetic resonance image based on the first magnetic resonance signal; and perform weighted summation processing on the first magnetic resonance image and at least one second magnetic resonance image to acquire the target magnetic resonance image.

[0136] Optionally, the second sequence may also include: multiple fourth TRs, wherein multiple third TRs and multiple fourth TRs in each second sequence are alternately arranged, and the duration of the fourth TRs is less than the duration of the third TRs.

[0137] The apparatus in this embodiment can be used to execute the solutions of the above method embodiments. Its implementation principle and technical effect are similar, and will not be described again here.

[0138] Figure 18 This is a schematic diagram of the structure of another MRI device provided in an embodiment of this application, as shown below. Figure 18As shown, the MRI device 10 includes a memory 1801, a processor 1802, and a computer program stored in the memory 1801 and executable on the processor 1802. When the processor 1802 executes the computer program, it implements the magnetic resonance imaging method of the above embodiment.

[0139] The processor 1802 may be a central processing unit (CPU), a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof.

[0140] This application also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the magnetic resonance imaging method as described above.

[0141] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the magnetic resonance imaging method as described above.

[0142] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0143] From the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of computer software products plus necessary general-purpose hardware platforms, and of course, they can also be implemented by hardware. The computer software product is stored in a storage medium (such as ROM, RAM, magnetic disk, optical disk, etc.) and includes several instructions to cause the terminal or network-side device to execute the methods described in the embodiments of this application.

[0144] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other implementations under the guidance of this application without departing from the spirit and scope of the claims. All of these implementations are within the protection scope of this application.

Claims

1. A magnetic resonance imaging method, characterized in that, The method includes: Obtain a first sequence, wherein the first sequence is an improved first equilibrium steady-state free precession bSSFP sequence, and each first TR of the first sequence includes the following in the layer selection direction: first layer selection gradient, first layer selection back convergence gradient and first layer selection complex phase gradient. In each first TR of the first sequence, the total gradient area of ​​the first layer selection gradient, the first layer selection back convergence gradient and the first layer selection complex phase gradient is not equal to 0. Based on the first sequence, magnetic resonance scanning is performed on the imaging tissue of the object to be detected, and the first magnetic resonance signal of the imaging tissue is acquired. Based on the first magnetic resonance signal, the target magnetic resonance image is reconstructed.

2. The method according to claim 1, characterized in that, In the first layer selected gradient, the first layer selected back-convergence gradient, and the first layer selected complex phase gradient, at least two gradients have different durations, amplitudes, and / or polarities.

3. The method according to claim 1, characterized in that, The total gradient area is within a preset threshold range; wherein, the upper limit of the preset threshold range is less than the target gradient area, and the target gradient area refers to the gradient area during the target period of the additional phase change within the imaging voxel.

4. The method according to claim 3, characterized in that, The target gradient area is inversely proportional to the target product. The upper limit of the preset threshold range is the product of the target gradient area and the first preset coefficient, and the lower limit of the preset threshold range is the product of the target gradient area and the second preset coefficient. The target product is the product of the gyromagnetic ratio of the imaging proton and the layer thickness of the imaging voxel.

5. The method according to any one of claims 1 to 4, characterized in that, The first sequence further includes: a plurality of second TRs, wherein the plurality of first TRs and the plurality of second TRs are alternately arranged, and the duration of the second TRs is less than the duration of the first TRs.

6. The method according to claim 5, characterized in that, When the polarity of the second layer-selected gradient within each second TR in the first sequence is the same as the polarity of the first layer-selected gradient, the total gradient area in the layer-selected direction within each second TR is equal to 0. When the polarity of the second layer-selected gradient within each second TR is opposite to the polarity of the first layer-selected gradient, the total gradient area in the layer-selected direction within each second TR is not equal to 0.

7. The method according to any one of claims 1 to 4, characterized in that, Prior to obtaining the first sequence, the method further includes: At least one second bSSFP sequence is obtained, wherein the phase cycle of the RF excitation pulse in each of the at least one second bSSFP sequence is different from the phase cycle of the RF excitation pulse in the first bSSFP sequence, and the duration of the third TR in the second bSSFP sequence is equal to the duration of the first TR. Obtain a second sequence corresponding to each of the second bSSFP sequences, wherein the second sequence is an improved second bSSFP sequence, and the total gradient area in the layer selection direction within each of the third TRs in the second sequence is not equal to 0; Based on each of the second sequences, magnetic resonance scanning is performed on the imaging tissue, and the second magnetic resonance signal of the imaging tissue is acquired; Based on at least one set of the second magnetic resonance signals, reconstruct at least one second magnetic resonance image that corresponds one-to-one with the second magnetic resonance signals; The process of reconstructing the target magnetic resonance image based on the first magnetic resonance signal includes: Based on the first magnetic resonance signal, reconstruct the first magnetic resonance image; The first magnetic resonance image is weighted and added to at least one second magnetic resonance image to obtain the target magnetic resonance image.

8. The method according to claim 7, characterized in that, The second sequence further includes: a plurality of fourth TRs, wherein the plurality of third TRs in each of the second sequences are alternately arranged with the plurality of fourth TRs, and the duration of the fourth TRs is less than the duration of the third TRs.

9. An MRI device, characterized in that, The MRI device includes a processor connected to a memory storing a computer program executable on the processor, the processor being configured to implement the magnetic resonance imaging method as described in any one of claims 1 to 8 when the computer program is executed by the processor.

10. A computer-readable storage medium, characterized in that, A computer program is stored on the computer-readable storage medium, which, when executed by a processor, implements the magnetic resonance imaging method as described in any one of claims 1 to 8.

Images