WO2020019412A1 - 磁共振成像方法、装置、设备及存储介质 - Google Patents

磁共振成像方法、装置、设备及存储介质 Download PDF

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WO2020019412A1
WO2020019412A1 PCT/CN2018/104180 CN2018104180W WO2020019412A1 WO 2020019412 A1 WO2020019412 A1 WO 2020019412A1 CN 2018104180 W CN2018104180 W CN 2018104180W WO 2020019412 A1 WO2020019412 A1 WO 2020019412A1
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dimensional
target object
data
magnetic resonance
gradient
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French (fr)
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王海峰
梁栋
郑海荣
苏适
丘志浪
史彩云
刘新
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深圳先进技术研究院
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging

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  • Embodiments of the present disclosure relate to the field of image processing technologies, and for example, to a magnetic resonance imaging method, apparatus, device, and storage medium.
  • magnetic resonance imaging As a radiation-free clinical diagnostic image, magnetic resonance imaging is more and more widely used in clinical diagnosis. However, it is difficult for magnetic resonance imaging methods in related technologies to take into account higher image quality and shorter data sampling time, so it is used in clinical practice. In the process, people often need to choose between higher image quality and shorter data sampling time according to their needs.
  • the embodiments of the present disclosure provide a magnetic resonance imaging method, device, device, and storage medium, which solve the technical problem that it is difficult for the magnetic resonance imaging method to take into account both higher image quality and shorter data sampling time.
  • An embodiment of the present disclosure provides a magnetic resonance imaging method, including:
  • the wave-controlled aliasing parallel imaging method (wave-CAIPI) is used to adjust the coding strategy of three-dimension balanced-free free precession (3DbSSFP).
  • the coding strategy includes a coding strategy in a phase direction and a coding strategy in a layer selection direction;
  • Image reconstruction is performed on the three-dimensional under-acquisition data according to the three-dimensional point spread function and the sensitivity map to generate a magnetic resonance image of a target object.
  • An embodiment of the present disclosure further provides a magnetic resonance imaging apparatus, including:
  • a 3D point spread function acquisition module configured to obtain a 3D point spread function of a target object
  • Sensitivity map acquisition module configured to obtain the target object's sum sensitivity map
  • the coding strategy adjustment module is configured to adjust a coding strategy of a balanced steady-state free precession pulse sequence by a wave gradient pulse controllable aliasing parallel imaging method, wherein the coding strategy includes a phase direction coding strategy and a layer selection direction coding strategy ;
  • the three-dimensional under-acquisition data acquisition module is configured to obtain a three-dimensional under-acquisition data of a target object based on a balanced steady-state free precession pulse sequence adjusted based on an encoding strategy, wherein the three-dimensional under-acquisition data is the same as the imaging field of view of the sensitivity map. ;
  • the reconstruction module is configured to perform image reconstruction on the three-dimensional under-acquisition data according to the three-dimensional point spread function and the sensitivity map to generate a magnetic resonance image of a target object.
  • An embodiment of the present disclosure further provides a device, where the device includes:
  • One or more processors are One or more processors;
  • a storage device configured to store one or more programs
  • the one or more processors When the one or more programs are executed by the one or more processors, the one or more processors implement the magnetic resonance imaging method as described above.
  • An embodiment of the present disclosure also provides a storage medium containing computer-executable instructions, which are executed by a computer processor to perform the magnetic resonance imaging method as described above.
  • the magnetic resonance imaging method provided by the embodiment of the present disclosure obtains a magnetic resonance image obtained by balancing a steady-state free precession pulse sequence with a high spatial resolution and a high signal-to-noise ratio, which can more clearly display the tissue structure and effectively reduce the volume effect.
  • wave gradient pulse controllable aliasing parallel imaging method uses sine / The cosine magnetic field gradient disperses the K-space signal, and adjusts the coding strategy of the phase direction and the layer selection direction to reduce the geometric factor, thereby improving the acceleration of the 3D balanced steady-state free precession pulse sequence under the premise of ensuring the image quality. Multiples, and has high robustness.
  • FIG. 1 is a flowchart of a magnetic resonance imaging method according to an embodiment
  • FIG. 2 is a gradient echo sequence diagram provided by an embodiment
  • FIG. 3 is a schematic diagram of a data acquisition strategy based on a wave gradient pulse controllable aliasing parallel imaging method according to an embodiment (2 ⁇ 2 times acceleration);
  • FIG. 4 is a schematic diagram of a data acquisition strategy based on a wave gradient pulse controllable aliasing parallel imaging method according to an embodiment (3 ⁇ 3 times acceleration);
  • FIG. 5 is a sequence diagram of a balanced steady-state free precession pulse after the encoding strategy is adjusted according to an embodiment.
  • FIG. 6 is a flowchart of a method for acquiring a three-dimensional point spread function according to an embodiment
  • FIG. 7 is a two-dimensional balanced steady-state free precession pulse sequence diagram in a layer selection direction according to an embodiment
  • FIG. 9 is a two-dimensional balanced steady-state free precession pulse sequence diagram in which a cosine gradient magnetic field is applied in a layer selection direction according to an embodiment
  • 10 is a two-dimensional balanced steady-state free precession pulse sequence diagram of a cosine gradient magnetic field applied in a phase direction according to an embodiment
  • FIG. 11 is a 2 ⁇ 2 times accelerated test result of a phantom provided by an embodiment
  • FIG. 12 is a 3 ⁇ 3 times accelerated test result of a phantom provided by an embodiment
  • FIG. 13 is a 2 ⁇ 2 times accelerated test result of a human brain according to an embodiment
  • FIG. 14 is a 3 ⁇ 3 times accelerated test result of the human brain according to an embodiment
  • FIG. 15 is a structural block diagram of a magnetic resonance imaging apparatus according to an embodiment
  • FIG. 16 is a schematic structural diagram of a device according to an embodiment.
  • the three-dimensional equilibrium steady-state free precession method has a wide range of applications in the field of magnetic resonance imaging (MRI). It is also called in commercial magnetic resonance: true fast-imaging fast imaging method (steady- stateprecession, true-FISP).
  • the three-dimensional equilibrium steady-state free-rotation method has the characteristics of high spatial resolution of magnetic resonance three-dimensional imaging, which can more clearly display the tissue structure and effectively reduce the volume effect.
  • TR repetition time
  • three-dimensional The equilibrium steady-state free precession method applies zero net magnetic field gradients in three directions (layer selection direction, readout direction, and phase direction). This structure effectively uses the magnetic resonance signals possessed by unspinned spins.
  • the 3D equilibrium steady-state free precession method has a high signal-to-noise ratio; in addition, the 3D equilibrium steady-state free precession method has a structure in which the magnetic field gradient is zero within the repetition time (TR), which makes the 3D equilibrium steady-state free
  • the magnetic resonance image obtained by the screw-in method has a unique T2 / T1 contrast, which is helpful in distinguishing certain specific tissue structures or lesions in clinical diagnosis, such as the heart muscle or tumor.
  • the scanning time is long and the time resolution is low, which limits the application of the technology in many fields, such as for sports tissues (heart and abdomen). Imaging, etc. In addition, too long scanning time can easily cause patient discomfort.
  • Parallel imaging technologies such as sensitivity encoding (SENSE), generalized autocalibrating partially parallel acquisitions (GRAPPA), and partial Fourier reconstruction (PF), only acquire part K Spatial data, and using the prior information contained in multi-channel coils or under-collected K-space to reconstruct the complete image to achieve the purpose of accelerating the acquisition, however, images accelerated by parallel imaging technology will have a root acceleration factor (Where R is the acceleration factor) and the geometric signal factor multiples, and the performance of the multi-channel coil, the accuracy of the prior information, and the reconstruction model have a greater impact on the geometric factor.
  • SENSE sensitivity encoding
  • GRAPPA generalized autocalibrating partially parallel acquisitions
  • PF partial Fourier reconstruction
  • the geometric factor is also called "noise amplification factor".
  • the geometric factor is unique to parallel imaging and is a measure of coil separation. The geometric factor depends on the number of repeated acquisitions of each point and the corresponding coil sensitivity difference. It is not a constant, but changes with the image position. It reflects the separation of pixels that are superimposed due to aliasing in a specific RF coil configuration. As the value of the geometric factor increases, the effective signal-to-noise ratio associated with reconstruction decreases. The larger the geometric factor, the smaller the signal-to-noise ratio of the resulting magnetic resonance image.
  • the related art acceleration technology based on the equilibrium steady-state free-spinning method has either a limited acceleration factor or an unstable factor.
  • the embodiment of the present disclosure proposes a magnetic resonance imaging method, device, device, and storage medium. The method is explained.
  • FIG. 1 is a flowchart of a magnetic resonance imaging method provided by this embodiment.
  • the technical solution of this embodiment is applicable to a case where the data collection time is shortened without affecting the quality of magnetic resonance imaging.
  • the method may be performed by a magnetic resonance apparatus provided by an embodiment of the present disclosure, and the apparatus may be implemented in software and / or hardware, and configured to be applied in a processor. As shown in FIG. 1, the method includes the following steps.
  • Step 1010 Obtain a three-dimensional point spread function of the target object.
  • the 3D point spread function of the target object is obtained, and the sampling trajectory in the frequency domain space (K space) is corrected by the 3D point spread function (PSF).
  • Step 1020 Obtain a sensitivity map of the target object.
  • this embodiment adopts a multi-layer parallel acquisition method to acquire magnetic resonance imaging data of a target object. Because different receiving coils have different sensitivities to different layers, it is necessary to use the sensitivity map to separate the images of each layer from the aliased images. For this reason, in this embodiment, the sensitivity map is obtained from the three-dimensional low-resolution data of the target object, and the three-dimensional low-resolution data can be obtained by a three-dimensional low-resolution data acquisition method, such as a gradient echo method, a spin echo method, or a balance Steady-state free spinning method, etc.
  • a three-dimensional low-resolution data acquisition method such as a gradient echo method, a spin echo method, or a balance Steady-state free spinning method, etc.
  • a gradient echo method is used to obtain three-dimensional low-resolution data (see FIG. 2), where the gradient echo method is: the readout of the damaged magnetic field gradient in each repetition time (TR) is applied in the readout direction After the magnetic field gradient.
  • the gradient echo method is: the readout of the damaged magnetic field gradient in each repetition time (TR) is applied in the readout direction After the magnetic field gradient.
  • RF radio frequency
  • the RF spoiler technology is: after the magnetic pulse (Magnetic Resonance, MR) signal of the previous pulse is collected, and before the next RF pulse is excited, the xy plane still retains a fairly strong transverse magnetization vector M xy in each pulse cycle Phase detection pulses are applied after the detection of signals to accelerate the phase loss, so that before the next period of RF pulse excitation, the transverse magnetization vector M xy is destroyed and disappears to zero, so only the longitudinal magnetization vector M z contributes to the next MR signal.
  • MR Magnetic Resonance
  • Step 1030 Adjust the encoding strategy of the balanced steady-state free precession pulse sequence by a wave gradient pulse controllable aliasing parallel imaging method, wherein the encoding strategy includes a phase direction encoding strategy and a layer selection direction encoding strategy.
  • the wave gradient pulse controllable aliasing parallel imaging method not only implements data downsampling in the phase direction and / or layer selection direction based on the traditional multi-layer simultaneous excitation, but also
  • the layer signal adds different linear phases along the phase direction and the layer selection direction to adjust the coding strategy, so that the data collected in the phase direction and the layer selection direction have a linear phase offset, and the data caused by undersampling will be mixed.
  • the overlay is dispersed into the phase direction and the layer selection direction at the same time, making more effective use of the background area in the field of view, making different layers of images form different displacements in the overlay image, increasing the sensitivity difference between layers, further
  • the geometric factor is reduced, and aliasing artifacts that may be caused in the reconstructed image are avoided.
  • the direction perpendicular to the plane is the readout direction, and the intersection of the black dotted lines is the readout line required for full sampling.
  • the readout line required for the undersampling strategy adopted in this embodiment is indicated by a bold solid origin.
  • Figure 3 shows 2 ⁇ 2 times undersampling (2 times undersampling in the phase direction, and 2 times undersampling in the layer selection direction).
  • the total acceleration multiple is 4.
  • the required acquisition time repetition time (TR) ⁇ number of phase encoding lines ( Np) ⁇ number of layer selection lines (Ns) / 4;
  • Figure 4 shows 3 ⁇ 3 times undersampling (3 times undersampling in the phase direction, 3 times undersampling in the layer selection direction), and the total acceleration factor is 9, which is required.
  • Acquisition time repetition time (TR) ⁇ number of phase encoding lines (Np) ⁇ number of layer selection encoding lines (Ns) / 9.
  • the balanced steady-state free-spinning pulse sequence can ensure that the transverse magnetization is not damaged before the next RF pulse is applied, so that the transverse magnetization returns to the original phase, and then the transverse magnetization is carried to the next phase.
  • TR is superimposed on the transverse magnetization pulse generated by the RF pulse. After a certain number of TR repeats, the magnetization reaches a steady state, and the transverse magnetization from two or three consecutive TRs combine to form a powerful signal.
  • a sine gradient magnetic field and a cosine gradient magnetic field with a phase difference of 90 degrees are simultaneously applied in the layer selection direction and the phase direction of a balanced steady-state free precession pulse sequence. It can be understood that, for two sine signals and cosine signals with the same frequency, the phase difference at each moment is 90 degrees.
  • a sine gradient magnetic field is applied between the two-body-encoded gradient pulses in each period of the layer selection direction, and a cosine gradient magnetic field is applied between the two-phase-encoded gradient pulses in each period in the phase direction.
  • Step 1040 Obtain three-dimensional under-acquisition data of the target object based on the balanced steady-state free precession pulse sequence adjusted by the encoding strategy, where the three-dimensional under-acquisition data is the same as the imaging field of the sensitivity map.
  • the imaging field of view of the three-dimensional under-acquisition data is set to be the same as the imaging field of the sensitivity map, and then the three-dimensional under-acquisition data of the target object is obtained based on the balanced steady-state free precession pulse sequence adjusted by the encoding strategy.
  • Step 1050 Perform image reconstruction on the 3D under-acquisition data according to the 3D point spread function and the sensitivity map to generate a magnetic resonance image of the target object.
  • the 3D point spread function is represented by PSF yz (k x , y, z)
  • the sensitivity map is represented by C (x, y, z) indicates that the magnetic resonance reconstruction image can be calculated by the following formula:
  • recon (x, y, z) is the reconstructed image, wave (x, y, z) three-dimensional under-acquisition data, F x and Are the one-dimensional Fourier transform and the inverse one-dimensional Fourier transform along the x direction.
  • the above-mentioned magnetic resonance image reconstruction process corrects the K-space trajectory of three-dimensional under-acquisition data through a three-dimensional point spread function, and separates each layer image from the aliased image by using a sensitivity map.
  • the above method step sequence is the method step sequence of this embodiment.
  • the acquisition order of the three-dimensional point spread function, the sensitivity map, and the three-dimensional under-acquisition data can be arbitrarily combined, but considering that the acquisition time of the three-dimensional under-acquisition data is relatively longer than the acquisition time of the corresponding data of the three-dimensional point spread function and sensitivity map. It is long, so the step of 3D undermined data is put last.
  • the technical solution of the magnetic resonance imaging method provided by this embodiment has a high spatial resolution and a high signal-to-noise ratio by means of a balanced steady-state free precession pulse sequence.
  • the magnetic resonance image can more clearly display the tissue structure and effectively reduce Volume effect, meanwhile, the T2 / T1 weighted contrast characteristic of this magnetic resonance image can help to distinguish some specific tissue structures or lesions, such as myocardium or tumor, in clinical diagnosis;
  • wave gradient pulse controllable aliasing parallel imaging method uses The sine / cosine magnetic field gradient disperses the K-space signal, and adjusts the coding strategy of the phase direction and layer selection direction to reduce the geometric factor, thereby improving the 3D equilibrium steady-state free-rotation pulse sequence under the premise of ensuring image quality Speedup, and has high robustness.
  • FIG. 6 is a flowchart of a method for acquiring a three-dimensional point spread function according to an embodiment. This embodiment optimizes the three-dimensional point spread function of the target object based on the above embodiment.
  • Step 10110 Obtain mapping data of the target object based on the balanced steady-state free precession pulse sequence.
  • two-dimensional mapping data of the target object in the layer selection direction and two-dimensional mapping data in the phase direction are obtained. For example, as shown in FIG. 7, based on a two-dimensional balanced steady-state free precession pulse sequence in the layer selection direction, two-dimensional mapping data of the target object in the layer selection direction, that is, two-dimensional mapping data in the xz plane is obtained; as shown in FIG. 8. As shown in the figure, two-dimensional mapping data of the target object in the phase direction is obtained based on the two-dimensional equilibrium steady-state free precession pulse sequence in the phase direction, that is, two-dimensional mapping data in the xy plane.
  • a cosine magnetic field gradient is applied in the layer selection direction of the two-dimensional balanced steady-state free precession pulse sequence to obtain the gradient two-dimensional mapping data of the target object in the layer selection direction.
  • a cosine magnetic field gradient is applied in the layer selection direction of the two-dimensional balanced steady-state free-spinning pulse sequence in the layer selection direction, and based on the two-dimensional balanced steady-state free rotation in which the cosine magnetic field gradient is added in the layer selection direction.
  • the progressive pulse sequence acquires the gradient two-dimensional mapping data of the target object in the layer selection direction, that is, the two-dimensional mapping data of the xz plane.
  • a cosine magnetic field gradient is applied in the phase direction of the two-dimensional balanced steady-state free precession pulse sequence to obtain gradient two-dimensional mapping data in the phase direction.
  • a cosine magnetic field gradient is applied in the phase direction of a two-dimensional balanced steady-state free-running pulse sequence in the phase direction, and based on a two-dimensional balanced steady-state free-running pulse sequence in which a cosine magnetic field gradient is added in the phase direction Obtain the gradient two-dimensional mapping data of the target object in the phase direction, that is, the two-dimensional mapping data of the xy plane.
  • the time required to collect mapping data in the layer selection direction is 2 ⁇ repetition time (TR) ⁇ number of layer selection coding lines (Ns), including the time when the cosine magnetic field gradient is applied in the layer selection direction and the time when the cosine magnetic field gradient is not applied;
  • the time required to acquire phase direction mapping data is 2 ⁇ repetition time (TR) ⁇ number of phase encoding lines (Np), including the time when the cosine magnetic field gradient is applied in the phase direction and the time when the cosine magnetic field gradient is not applied. Since the above mapping data collects two-dimensional data, the required scanning time is shorter.
  • Step 10120 Obtain a three-dimensional point spread function of the target object according to the mapping data.
  • the three-dimensional point spread function can be obtained directly from the three-dimensional mapping data, or the three-dimensional point spread function can be obtained from the two-dimensional point spread function of two intersecting planes. This embodiment uses the latter to reduce the acquisition time of mapping data.
  • a three-dimensional point is calculated based on the two-dimensional mapping data in the layer selection direction and the two-dimensional mapping data in the phase direction, and the two-dimensional gradient data in the layer selection direction and the two-dimensional gradient data in the phase direction. Diffusion function.
  • a two-dimensional point spread function in the layer selection direction is obtained based on the two-dimensional map data in the layer selection direction and the gradient two-dimensional map data in the layer selection direction.
  • the two-dimensional map data of the gradient is waveP z
  • the cosine magnetic field gradient in the layer selection direction is collected.
  • a two-dimensional point spread function in the phase direction is obtained based on a two-dimensional map function in the phase direction and a gradient two-dimensional map function in the phase direction.
  • a gradient-dimensional map data is acquired waveP y
  • no phase sinusoidal magnetic field gradient direction (FIG. 8) acquired two-dimensional
  • the mapping data is P y
  • a three-dimensional point spread function is obtained based on the two two-dimensional point spread functions.
  • PSF yz (k x , y, z) PSF z (k x , z) ⁇ PSF y (k x , y), which is the value of any point (k x , y, z) in the three-dimensional point spread function PSF yz
  • PSF yz (k x , z) PSF yz (k x , z).
  • a two-dimensional point spread function in a layer selection direction is determined by two-dimensional mapping data with and without a cosine magnetic field gradient applied in a layer selection direction; through a phase direction
  • the two-dimensional mapping data with and without the cosine magnetic field gradient is applied to determine the two-dimensional point spread function in the phase direction, and then the two-dimensional point spread function in the layer selection direction and the two-dimensional point spread in the phase direction are determined.
  • the function determines the three-dimensional point spread function. Compared with determining three-dimensional point spread function through three-dimensional mapping data, the time for collecting mapping data can be greatly reduced, and the time for collecting magnetic resonance imaging data can be reduced.
  • a phantom and a human brain test are performed on a magnetic resonance imaging system, and the feasibility of the magnetic resonance imaging method described in any of the foregoing embodiments of the present disclosure is confirmed.
  • Fig. 11 and Fig. 12 show the results of the simulation test.
  • Figure a in Figure 11 and Figure a in Figure 12 are MRI images obtained based on the Fourier transform method;
  • Figure b in Figure 11 and Figure b in Figure 12 are MRI images obtained based on the sensitivity coding method;
  • FIG. C in FIG. 11 and FIG. C in FIG. 12 are MRI images obtained based on the magnetic resonance imaging method according to the embodiment of the present disclosure;
  • FIG. E in FIG. 11 and FIG. E in FIG. 12 are geometric factors corresponding to the magnetic resonance imaging method according to the embodiment of the present disclosure during image reconstruction.
  • Figure 13 and Figure 14 show the results of the human brain test.
  • Figure a in Figure 13 and Figure a in Figure 14 are MRI images obtained based on the Fourier transform method;
  • Figure b in Figure 13 and Figure b in Figure 14 are MRI images obtained based on the sensitivity coding method;
  • FIG. C in FIG. 13 and FIG. C in FIG. 14 are MRI images obtained based on the magnetic resonance imaging method according to the embodiment of the present disclosure;
  • FIG. E in FIG. 13 and FIG. E in FIG. 14 are geometric factors corresponding to the magnetic resonance imaging method according to the embodiment of the present disclosure during the image reconstruction process.
  • the magnetic resonance imaging method has a lower geometric factor (g-factor) (see FIG. E in FIG. 13 and FIG. E in FIG. 14).
  • g-factor geometric factor
  • the acceleration factor is large, the reconstructed The image has better image quality (see Figure c in Figure 14).
  • This embodiment compares the actual magnetic resonance imaging data acquisition time and image quality of the phantom and the human body, and illustrates that the magnetic resonance imaging method described in the foregoing embodiment of the present disclosure can pass the larger Accelerating multiples reduces data collection time, which is conducive to improving the patient experience and clinical promotion.
  • FIG. 15 is a structural block diagram of a magnetic resonance imaging apparatus according to an embodiment.
  • the device is configured to execute the magnetic resonance imaging device provided in any of the foregoing embodiments, and the device may be implemented by software or hardware. As shown in Figure 15, the device includes:
  • the three-dimensional point spread function acquisition module 11 is set to acquire the three-dimensional point spread function of the target object;
  • the sensitivity map acquisition module 12 is set to acquire the target object's sum sensitivity map;
  • the coding strategy adjustment module 13 is set to controllable mixing by wave gradient pulses
  • the superimposed parallel imaging method adjusts the encoding strategy of the balanced steady-state free precession pulse sequence, wherein the encoding strategy includes the encoding strategy in the phase direction and the encoding strategy in the layer selection direction;
  • the three-dimensional under-acquisition data acquisition module 14 is set to be based on the encoding strategy
  • the adjusted balanced steady-state free precession pulse sequence acquires three-dimensional under-acquisition data of the target object, wherein the three-dimensional under-acquisition data is the same as the imaging field of view of the sensitivity map;
  • the reconstruction module 15 is configured to diffuse according to the three-dimensional point diffusion
  • the function and the sensitivity map perform image reconstruction on the three-dimensional under-acquisition data to generate a magnetic resonance image of a target object
  • the magnetic resonance image obtained by balancing the steady-state free-rotation pulse sequence has high spatial resolution and high signal-to-noise ratio, which can more clearly display the tissue structure and effectively reduce
  • the volume effect and the T2 / T1 weighted contrast characteristic of this magnetic resonance image are helpful for distinguishing certain specified tissue structures or lesions, such as myocardium or tumor, in clinical diagnosis;
  • wave gradient pulse controllable aliasing parallel imaging method Use the sine / cosine magnetic field gradient to disperse the K-space signal, and adjust the phase direction and layer selection direction coding strategy to reduce the geometric factor, so as to ensure the image quality, improve the three-dimensional equilibrium steady-state free precession pulse Acceleration multiple of the sequence, and has high robustness.
  • the magnetic resonance imaging apparatus provided by this embodiment can execute the magnetic resonance imaging method provided by any embodiment of the present disclosure, and has the corresponding functional modules and beneficial effects of executing the method.
  • FIG. 16 is a schematic structural diagram of a device according to an embodiment.
  • the device includes a processor 201, a memory 202, an input device 203, and an output device 204; the number of processors 201 in the device may be one or more, and one processor 201 is taken as an example in FIG. 16; the device The processor 201, the memory 202, the input device 203, and the output device 204 may be connected through a bus or other methods. In FIG. 16, the connection through a bus is taken as an example.
  • the memory 202 is a computer-readable storage medium, and can be used to store software programs, computer-executable programs, and modules, such as program instructions / modules corresponding to the magnetic resonance imaging method in the embodiment of the present disclosure (for example, a three-dimensional point spread function acquisition module 11. Sensitivity map acquisition module 12, encoding strategy adjustment module 13, three-dimensional under-acquisition data acquisition module 14, and reconstruction module 15).
  • the processor 201 executes one or more functional applications and data processing of the device by running software programs, instructions, and modules stored in the memory 202, that is, the above-mentioned magnetic resonance imaging method is implemented.
  • the memory 202 may mainly include a storage program area and a storage data area, where the storage program area may store an operating system and application programs required for at least one function; the storage data area may store data created according to the use of the terminal, and the like.
  • the memory 202 may include a high-speed random access memory, and may further include a non-volatile memory, such as at least one magnetic disk storage device, a flash memory device, or other non-volatile solid-state storage device.
  • the memory 202 may include memory remotely set relative to the processor 201, and these remote memories may be connected to the device through a network. Examples of the above network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.
  • the input device 203 may be configured to receive inputted numeric or character information and generate key signal inputs related to user settings and function control of the device.
  • the output device 204 may include a display device such as a display screen, for example, a display screen of a user terminal.
  • the above device further includes a collector 205, which is configured to obtain a three-dimensional point spread function of the target object, obtain a target object and a sensitivity map, and adjust the balance and stability by a wave gradient pulse controllable aliasing parallel imaging method.
  • the encoding strategy of the state free precession pulse sequence and the balanced steady-state free precession pulse sequence adjusted based on the encoding strategy are used to obtain the 3D undermined data of the target object.
  • An embodiment of the present disclosure further provides a storage medium including computer-executable instructions, which are executed by a computer processor to perform a magnetic resonance imaging method, the method including:
  • the storage medium provided by this embodiment includes computer-executable instructions, and the computer-executable instructions are not limited to the method operations described above, and may also perform related operations in the magnetic resonance imaging method provided by any embodiment of the present disclosure. operating.
  • the present disclosure can be implemented by software and necessary general-purpose hardware, and of course, can also be implemented by hardware, but the former is a better implementation in many cases.
  • the technical solution of the present disclosure that is essential or contributes to related technologies may be embodied in the form of a software product.
  • the computer software product may be stored in a computer-readable storage medium, such as a computer floppy disk, Read-only memory (ROM), random access memory (RAM), flash memory (FLASH), hard disk or optical disk, etc., including multiple instructions to make a computer device (can be a personal computer , Server, or network device, etc.) execute the magnetic resonance imaging method described in any embodiment of the present disclosure.
  • the multiple units and modules included are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be realized;
  • the names of each functional unit are only for the convenience of distinguishing from each other, and are not used to limit the protection scope of the present disclosure.

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  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

一种磁共振成像方法、装置、设备及存储介质，磁共振成像方法包括：获取目标对象的三维点扩散函数（1010）；获取目标对象的灵敏度图（1020）；通过波浪梯度脉冲可控混叠并行成像方法调整平衡稳态自由旋进脉冲序列的编码策略，其中，编码策略包括相位方向的编码策略和选层方向的编码策略（1030）；基于编码策略调整后的平衡稳态自由旋进脉冲序列，获取目标对象的三维欠采数据，其中，三维欠采数据的灵敏度图的成像视野相同（1040）；根据三维点扩散函数和灵敏度图对三维欠采数据进行图像重建，以生成目标对象的磁共振图像（1050）。

Description

磁共振成像方法、装置、设备及存储介质
本公开要求申请日为2018年07月23日、申请号为201810815138.5的中国专利申请的优先权，该申请的全部内容通过引用结合在本公开中。
技术领域
本公开实施例涉及图像处理技术领域，例如涉及一种磁共振成像方法、装置、设备及存储介质。
背景技术
作为无辐射的临床诊断影像，磁共振图像越来越广泛地应用于临床诊断，但相关技术中的磁共振成像方法很难兼顾较高的图像质量和较短的数据采样时间，因此在临床使用过程中，人们往往需要根据需求的侧重点在较高的图像质量和较短的数据采样时间之间进行选择。
发明内容
本公开实施例提供了一种磁共振成像方法、装置、设备及存储介质，解决磁共振成像方法很难兼顾较高的图像质量和较短的数据采样时间的技术问题。
本公开实施例提供了一种磁共振成像方法，包括：
获取目标对象的三维点扩散函数(point spread function，PSF)；
获取目标对象的灵敏度图(sensitivity map)；
通过波浪梯度脉冲可控混叠并行成像方法(wave controlled aliasing in parallel imaging，wave-CAIPI)调整平衡稳态自由旋进脉冲序列(three-dimension balanced steady-state free precession，3D bSSFP)的编码策略，其中，所述编码策略包括相位方向的编码策略和选层方向的编码策略；
基于编码策略调整后的平衡稳态自由旋进脉冲序列，获取目标对象的三维欠采数据，其中，所述三维欠采数据与所述灵敏度图的成像视野相同；
根据所述三维点扩散函数和所述灵敏度图对所述三维欠采数据进行图像重建，以生成目标对象的磁共振图像。
本公开实施例还提供了一种磁共振成像装置，包括：
三维点扩散函数获取模块，设置为获取目标对象的三维点扩散函数；
灵敏度图获取模块，设置为获取目标对象的和灵敏度图；
编码策略调整模块，设置为通过波浪梯度脉冲可控混叠并行成像方法调整平衡稳态自由旋进脉冲序列的编码策略，其中，所述编码策略包括相位方向的编码策略和选层方向的编码策略；
三维欠采数据获取模块，设置为基于编码策略调整后的平衡稳态自由旋进脉冲序列，获取目标对象的三维欠采数据，其中，所述三维欠采数据与所述灵敏度图的成像视野相同；
重建模块，设置为根据所述三维点扩散函数和所述灵敏度图对所述三维欠采数据进行图像重建，以生成目标对象的磁共振图像。
本公开实施例还提供了一种设备，所述设备包括：
一个或多个处理器；
存储装置，设置为存储一个或多个程序；
当所述一个或多个程序被所述一个或多个处理器执行，使得所述一个或多个处理器实现如上所述的磁共振成像方法。
本公开实施例还提供了一种包含计算机可执行指令的存储介质，所述计算机可执行指令在由计算机处理器执行时用于执行如上所述的磁共振成像方法。
本公开实施例提供的磁共振成像方法通过平衡稳态自由旋进脉冲序列所获得的磁共振图像具有高空间分辨率和高信噪比，能够更清晰的显示组织结构，有效的降低了容积效应，同时该磁共振图像特有的T2/T1加权对比度，在临床诊断中有助于分辨某些特定的组织结构或病灶，如心肌或肿瘤等；波浪梯度脉冲可控混叠并行成像方法利用正弦/余弦磁场梯度分散K空间信号，并对相位方向和选层方向的编码策略进行调整，达到降低几何因子的目的，从而在保证图像质量的前提下，提高三维平衡稳态自由旋进脉冲序列的加速倍数，且具有较高的鲁棒性。
附图说明
图1是一实施例提供的磁共振成像方法的流程图；
图2是一实施例提供的梯度回波序列图；
图3是一实施例提供的基于波浪梯度脉冲可控混叠并行成像方法的数据采集策略示意图(2×2倍加速)；
图4是一实施例提供的基于波浪梯度脉冲可控混叠并行成像方法的数据采 集策略示意图(3×3倍加速)；
图5是一实施例提供的编码策略调整后的平衡稳态自由旋进脉冲序列图。
图6是一实施例提供的三维点扩散函数获取方法的流程图；
图7是一实施例提供的选层方向上的二维平衡稳态自由旋进脉冲序列图；
图8是一实施例提供的相位方向上的二维平衡稳态自由旋进脉冲序列图；
图9是一实施例提供的选层方向施加余弦梯度磁场的二维平衡稳态自由旋进脉冲序列图；
图10是一实施例提供的相位方向施加余弦梯度磁场的二维平衡稳态自由旋进脉冲序列图；
图11是一实施例提供的仿体2×2倍加速测试结果；
图12是一实施例提供的仿体3×3倍加速测试结果；
图13是一实施例提供的人脑2×2倍加速测试结果；
图14是一实施例提供的人脑3×3倍加速测试结果；
图15是一实施例提供的磁共振成像装置的结构框图；
图16为一实施例提供的设备的结构示意图。
具体实施方式
以下将参照本公开实施例中的附图，通过实施方式描述本公开的技术方案，显然，所描述的实施例是本公开一部分实施例，而不是全部的实施例。
三维平衡稳态自由旋进方法在磁共振成像(magnetic resonance imaging，MRI)领域有着广泛的应用，在商用磁共振中也被称为：真稳态进动快速成像方法(true fast imaging with steady-state precession，true-FISP)。三维平衡稳态自由旋进方法具有磁共振三维成像的高空间分辨率的特点，能够更清晰的显示组织结构，有效的降低了容积效应；在每个重复时间(repetition time，TR)内，三维平衡稳态自由旋进方法在三个方向(选层方向、读出方向和相位方向)所施加的净磁场梯度为零，该结构有效的利用了未散相自旋子所具有的磁共振信号，使得三维平衡稳态自由旋进方法具有很高的信噪比；此外，三维平衡稳态自由旋进方法在重复时间(TR)内的磁场梯度为零这一结构，使通过三维平衡稳态自由旋进方法获得的磁共振图像具有独特的T2/T1对比度，该对比度在临床诊断中有助于分辨某些特定的组织结构或病灶，如心肌或肿瘤等。然而，由于该 方法的磁共振三维成像所需采集的数据量大，扫描的时间很长，时间分辨率较低，限制了该技术在诸多领域的应用，如针对运动组织(心脏和腹部)的成像等；此外，过长的扫描时间也容易引起病患的不适。
为了减少平衡稳态自由旋进方法的数据采集时间，相关技术利用并行成像技术(parallel imaging，PI)和压缩感知技术(compressed sensing，CS)进行加速。并行成像技术，如灵敏度编码技术(sensitivity encoding，SENSE)、整体自动校准部分并行采集技术(generalized autocalibrating partially parallel acquisitions，GRAPPA)和部分傅里叶重建技术(partial Fourier reconstruction，PF)，仅采集部分K空间数据，并利用多通道线圈或欠采K空间所含有的先验信息，重建完整图像，以实现加速采集的目的，然而通过并行成像技术加速后的图像会有根号加速倍数(
Figure PCTCN2018104180-appb-000001
其中R为加速倍数)和几何因子倍数的信噪比损失，且多通道线圈的性能、先验信息的准确性和重建模型对几何因子的影响较大，因此，在保证图像质量的前提下，利用并行成像技术加速所获得的加速倍数有限，通常为2至4倍。压缩感知技术通过在目标函数中添加L-1范数的约束，对欠采数据进行重建，通常能达到4倍以上加速，但是，压缩感知技术中L-1范数的正则化参数往往需要人为选取，不恰当的正则化参数会导致重建图像出现过渡平滑的问题。
几何因子也被称为“噪声放大因子”，几何因子是并行成像特有的，是对线圈分离的一个度量。几何因子取决于每一个点被重复采集的个数以及对应的线圈敏感性差异，并不是一个常数，而是随图像位置变化而变化，反映在特定射频线圈配置下分离因混叠而叠加的像素的能力，几何因子数值增加则与重建有关的有效信噪比减小。几何因子越大，则最终得到的磁共振图像的信噪比越小。
综上，相关技术中基于平衡稳态自由旋进方法的加速技术，要么加速倍数有限，要么存在不稳定因素。为了在保证成像质量的前提下，进一步减少基于平衡稳态自由旋进方法的数据采集时间，本公开实施例提出了一种磁共振成像方法、装置、设备及存储介质，下面先对磁共振成像方法进行说明。
实施例一
图1是本一实施例提供的磁共振成像方法的流程图。本实施例的技术方案适用于在不影响磁共振成像质量的前提下缩短数据采集时间的情况。该方法可以由本公开实施例提供的磁共振装置来执行，该装置可以采用软件和/或硬件的 方式实现，并配置在处理器中应用。如图1所示，该方法包括如下步骤。
步骤1010、获取目标对象的三维点扩散函数。
获取目标对象的三维点扩散函数，并通过三维点扩散函数(point spread function，PSF)对频域空间(K空间)采样轨迹进行校正。
步骤1020、获取目标对象的灵敏度图。
为了加快磁共振图像的数据采集速度，本实施例采用多层并行采集的方法获取目标对象的磁共振成像数据。由于不同的接收线圈对不同层面有不一样的灵敏度，因此需要利用灵敏度图将每一层的图像从混叠图像中分离出来。为此，本实施例通过目标对象的三维低分辨率数据求取灵敏度图，而且三维低分辨率数据可通过三维低分辨率数据采集方法获取，比如基于梯度回波方法、自旋回波方法或平衡稳态自由旋进方法等。
本实施例采用梯度回波方法获取三维低分辨率数据(参见图2所示)，其中，梯度回波方法为：每个重复时间(TR)内的损毁磁场梯度施加在读出方向的读出磁场梯度之后。本实施例还可以采用添加了射频(Radio Frequency，RF)扰相技术的梯度回波方法。其中，RF扰相技术为：在前一次脉冲的磁共振(Magnetic Resonance，MR)信号采集后，下一个RF脉冲激发前，xy平面仍保留相当强的横向磁化矢量M xy，在每个脉冲周期的信号检测后施加扰相脉冲，使失相位加快，从而在下一周期的RF脉冲激发前，横向磁化矢量M xy被破坏消失为零，因而只有纵向磁化矢量M z对下一个MR信号有贡献。
步骤1030、通过波浪梯度脉冲可控混叠并行成像方法调整平衡稳态自由旋进脉冲序列的编码策略，其中，编码策略包括相位方向的编码策略和选层方向的编码策略。
不同于传统并行成像方法的数据采集策略，波浪梯度脉冲可控混叠并行成像方法在传统多层同时激发的基础上，不仅在相位方向和/或选层方向实现数据降采样，并且对来自不同层信号在沿相位方向和选层方向添加不同的线性相位以对编码策略进行调整，从而使沿相位方向和选层方向所采集的数据具有线性的相位偏移，以及将欠采样所导致的混叠同时分散到相位方向和选层方向，更有效地利用了视野中的背景区域，使不同层的图像在混叠图像中形成不同的位移，增大了层与层之间的灵敏度差异，进一步降低了几何因子，同时避免了重建图像中可能会引起的混叠伪影。
在一实施例中，如图3和图4所示，垂直于本平面方向(同时垂直于相位 方向和选层方向)为读出方向，黑色虚线交点为全采样所需采集的读出线，本实施例所采用的欠采样策略所需采集的读出线由加粗实心原点表示。图3所示为2×2倍欠采样(相位方向2倍欠采样，选层方向2倍欠采样)，总加速倍数为4，所需采集时间＝重复时间(TR)×相位编码线数(Np)×选层编码线数(Ns)/4；图4所示为3×3倍欠采样(相位方向3倍欠采样，选层方向3倍欠采样)，总加速倍数为9，所需采集时间＝重复时间(TR)×相位编码线数(Np)×选层编码线数(Ns)/9。
在一实施例中，平衡稳态自由旋进脉冲序列可确保横向磁化在每个TR末期，下一个RF脉冲施加前不被损毁而使横向磁化回到原来相位，然后横向磁化被带到下一个TR，叠加到RF脉冲产生的横向磁化脉冲中，一定数量的TR重复后，磁化达到稳态，来自两个或三个连续TR横向磁化联合形成强大信号。
如图5所示，通过波浪梯度脉冲可控混叠并行成像方法，在平衡稳态自由旋进脉冲序列的选层方向和相位方向同时施加相位相差90度的正弦梯度磁场和余弦梯度磁场。可以理解的是，对于频率相同的两正弦信号和余弦信号，每一刻的相位差为90度。在一实施例中，在选层方向的每个周期的两体层编码梯度脉冲之间施加正弦梯度磁场，在相位方向的每个周期的两相位编码梯度脉冲之间施加余弦梯度磁场。
步骤1040、基于编码策略调整后的平衡稳态自由旋进脉冲序列获取目标对象的三维欠采数据，其中，三维欠采数据与灵敏度图的成像视野相同。
将三维欠采数据的成像视野设置成与灵敏度图的成像视野相同，然后基于编码策略调整后的平衡稳态自由旋进脉冲序列获取目标对象的三维欠采数据。
步骤1050、根据三维点扩散函数和灵敏度图对三维欠采数据进行图像重建，以生成目标对象的磁共振图像。
根据三维点扩散函数和灵敏度图对三维欠采数据进行图像重建，以生成目标对象的磁共振图像，例如，若三维点扩散函数用PSF yz(k x，y，z)表示，灵敏度图用C(x，y，z)表示，磁共振重建图像可由以下公式计算得到：
Figure PCTCN2018104180-appb-000002
其中，recon(x，y，z)为重建图像，wave(x，y，z)三维欠采数据，F x和
Figure PCTCN2018104180-appb-000003
为沿x方向的一维傅里叶变换和一维傅里叶逆变换。
上述磁共振图像重建过程通过三维点扩散函数对三维欠采数据进行K空间 轨迹的校正，通过灵敏度图将每一层图像从混叠图像中分离出来。
上述方法步骤顺序为本实施例的方法步骤顺序。在一实施例中，三维点扩散函数、灵敏度图和三维欠采数据的获取顺序可以任意组合，但考虑到三维欠采数据的采集时间相对于三维点扩散函数和灵敏度图对应数据的采集时间要长，所以将三维欠采数据的步骤放在最后。
本实施例提供的磁共振成像方法的技术方案通过平衡稳态自由旋进脉冲序列所获得的磁共振图像具有高空间分辨率和高信噪比，能够更清晰的显示组织结构，有效的降低了容积效应，同时该磁共振图像特有的T2/T1加权对比度，在临床诊断中有助于分辨某些特定的组织结构或病灶，如心肌或肿瘤等；波浪梯度脉冲可控混叠并行成像方法利用正弦/余弦磁场梯度分散K空间信号，并对相位方向和选层方向的编码策略进行调整，达到降低几何因子的目的，从而在保证图像质量的前提下，提高三维平衡稳态自由旋进脉冲序列的加速倍数，且具有较高的鲁棒性。
实施例二
图6是一实施例提供的三维点扩散函数获取方法的流程图。本实施例在上述实施例的基础上，对获取目标对象的三维点扩散函数进行了优化。
本实施例提供的方法包括如下步骤：
步骤10110、基于平衡稳态自由旋进脉冲序列获取目标对象的映射数据。
基于二维平衡稳态自由旋进脉冲序列，获取目标对象在选层方向上的二维映射数据和相位方向上的二维映射数据。例如，如图7所示，基于选层方向的二维平衡稳态自由旋进脉冲序列，获取目标对象在选层方向上的二维映射数据，即xz平面的二维映射数据；如图8所示，基于相位方向上的二维衡平衡稳态自由旋进脉冲序列获取目标对象在相位方向的二维映射数据，即xy平面的二维映射数据。
在二维平衡稳态自由旋进脉冲序列的选层方向施加余弦磁场梯度，以获取目标对象在选层方向上的梯度二维映射数据。例如，如图9所示，在选层方向的二维平衡稳态自由旋进脉冲序列的选层方向施加余弦磁场梯度，基于在选层方向添加了余弦磁场梯度的二维平衡稳态自由旋进脉冲序列获取目标对象在选层方向上的梯度二维映射数据，也就是xz平面的二维映射数据。
在二维平衡稳态自由旋进脉冲序列的相位方向施加余弦磁场梯度，以获取 相位方向上的梯度二维映射数据。例如，如图10所示，在相位方向的二维平衡稳态自由旋进脉冲序列的相位方向施加余弦磁场梯度，基于在相位方向添加了余弦磁场梯度的二维平衡稳态自由旋进脉冲序列获取目标对象在相位方向的梯度二维映射数据，也就是xy平面的二维映射数据。
综上，采集选层方向的映射数据所需时间为2×重复时间(TR)×选层编码线数(Ns)，包括选层方向上施加了余弦磁场梯度和没有施加余弦磁场梯度的时间；采集相位方向映射数据所需时间为2×重复时间(TR)×相位编码线数(Np)，包括相位方向上施加了余弦磁场梯度和没有施加余弦磁场梯度的时间。由于上述映射数据所采集的是二维数据，因此所需扫描时间较短。
步骤10120、根据映射数据求取目标对象的三维点扩散函数。
在一实施例中，三维点扩散函数可以根据三维映射数据直接求取，也可以根据两个相交平面的二维点扩散函数求取三维点扩散函数。本实施例采用后者，以减少映射数据的采集时间。在一实施例中，基于选层方向上的二维映射数据和相位方向上的二维映射数据，以及选层方向上的梯度二维映射数据和相位方向上的梯度二维映射数据计算三维点扩散函数。
基于选层方向上的二维映射数据和选层方向上的梯度二维映射数据求取选层方向上的二维点扩散函数。在一实施例中，若选层方向施加余弦磁场梯度(如图9所示)所采集的梯度二维映射数据为waveP z，选层方向无余弦磁场梯度(如图7所示)所采集的二维映射数据为P z，则选层方向上的二维点扩散函数PSF z中任意点(k x，z)的值为：PSF z(k x，z)＝waveP z(k x，z)/P z(k x，z)。
基于相位方向上的二维映射函数和相位方向上的梯度二维映射函数求取相位方向上的二维点扩散函数。在一实施例中，若相位方向施加正弦磁场梯度(如图10所示)所采集的梯度二维映射数据为waveP y，相位方向无正弦磁场梯度(如图8所示)所采集的二维映射数据为P y，则相位方向上的二维点扩散函数PSF y中任意点(k x，y)的值为：PSF y(k x，y)＝waveP y(k x，y)/P y(k x，y)。
在选层方向上的二维点扩散函数和相位方向上的二维点扩散函数确定后，基于这两个二维点扩散函数求取三维点扩散函数。例如，PSF yz(k x，y，z)＝PSF z(k x，z)·PSF y(k x，y)，即三维点扩散函数PSF yz中任意点(k x，y，z)的值为PSF yz(k x，z)。
本实施例提供的磁共振成像方法的技术方案，通过选层方向上施加了余弦磁场梯度和没有施加余弦磁场梯度的二维映射数据，确定选层方向上的二维点 扩散函数；通过相位方向上施加了余弦磁场梯度和没有施加余弦磁场梯度的二维映射数据，确定相位方向上的二维点扩散函数，然后通过选层方向上的二维点扩散函数和相位方向上的二维点扩散函数确定三维点扩散函数。相较于通过三维映射数据确定三维点扩散函数可以大大降低映射数据采集的时间，进而减少磁共振成像数据采集时间。
实施例三
本实施例在磁共振成像系统上进行了仿体和人脑测试，证实了本公开前述任意实施例所述的磁共振成像方法的可行性。
图11和图12为仿体测试结果，扫描参数如下：回波时间(echo of time，TE)＝2.41毫秒(ms)，重复时间(TR)＝4.81ms，翻转角(flip angle，FA)＝50°，带宽(bandwidth)＝579赫兹/像素(Hz/pixel)，体素尺寸(voxel size)＝1×1×1立方毫米(mm 3)，扫描矩阵尺寸＝192×192×192，正弦/余弦磁场梯度周期数＝5，正弦/余弦磁场梯度最大幅度＝4毫特斯拉/米(mT/m)，当加速倍数为2×2倍时，扫描时间为45秒(s)(图11)；当加速倍数为3×3倍时，扫描时间为20s(图12)。
图11中的图a和图12中的图a为基于傅里叶变换方法所获得的MRI图像；图11中的图b和图12中的图b为基于灵敏度编码方法所获得的MRI图像；图11中的图c和图12中的图c为基于本公开实施例所述磁共振成像方法所获得的MRI图像；图11中的图d和图12中的图d为灵敏度编码方法在图像重建过程中所对应的几何因子；图11中的图e和图12中的图e为本公开实施例所述磁共振成像方法在图像重建过程中所对应的几何因子。
从仿体测试结果中可以看到，相对于传统灵敏度编码技术(sensitivity encoding，SENSE)的几何因子(参见图11中的图d和图12中的图d所示)，本公开实施例的几何因子(g-factor)有了大幅度的下降(参见图11中e图和图12中e图所示)，在加速倍数较大的情况下，具有更好的图像质量(参见图12中的图c所示)。
图13和图14所示为人脑测试结果，扫描参数如下：回波时间(TE)＝2.17ms，重复时间(TR)＝4.34ms，翻转角(FA)＝30°，带宽＝633Hz/pixel，体素尺寸＝1×1×1mm 3，扫描矩阵尺寸＝208×208×208，正弦/余弦磁场梯度周期数＝5，正弦/余弦磁场梯度最大幅度＝6mT/m；当加速倍数为2×2倍时，扫描时间为48s (图13)；当加速倍数为3×3倍时，扫描时间为21s(图14)。
图13中的图a和图14中的图a为基于傅里叶变换方法所获得的MRI图像；图13中图b和图14中的图b为基于灵敏度编码方法所获得的MRI图像；图13中的图c和图14中的图c为基于本公开实施例所述磁共振成像方法所获得的MRI图像；图13中的图d和图14中的图d为灵敏度编码方法在图像重建过程中所对应的几何因子；图13中的图e和图14中的图e为本公开实施例所述磁共振成像方法在图像重建过程中所对应的几何因子。
同仿体测试结果类似，在人脑测试中，相对于传统灵敏度编码技术(SENSE)的几何因子(参见图13中的图d和图14中的图d所示)，本公开实施例所述的磁共振成像方法具有更低的几何因子(g-factor)(参见图13中的图e和图14中的图e所示)，在加速倍数较大的情况下，本公开实施例重建的图像具有更好的图像质量(参见图14中的图c所示)。
本实施例通过在仿体和人体的实际磁共振成像数据采集时间和图像质量进行对比，说明了前述本公开实施例所述的磁共振成像方法可以在保证成像质量的前提下，通过较大的加速倍数降低数据采集时间，有利于提升病人体验以及临床推广。
实施例四
图15是一实施例提供的磁共振成像装置的结构框图。该装置用于执行上述任意实施例所提供的磁共振成像装置，该装置可选为软件或硬件实现。如图15所示，该装置包括：
三维点扩散函数获取模块11，设置为获取目标对象的三维点扩散函数；灵敏度图获取模块12，设置为获取目标对象的和灵敏度图；编码策略调整模块13，设置为通过波浪梯度脉冲可控混叠并行成像方法调整平衡稳态自由旋进脉冲序列的编码策略，其中，所述编码策略包括相位方向的编码策略和选层方向的编码策略；三维欠采数据获取模块14，设置为基于编码策略调整后的平衡稳态自由旋进脉冲序列获取目标对象的三维欠采数据，其中，所述三维欠采数据与所述灵敏度图的成像视野相同；重建模块15，设置为根据所述三维点扩散函数和所述灵敏度图对所述三维欠采数据进行图像重建，以生成目标对象的磁共振图像。
本实施例提供的磁共振成像装置的技术方案，通过平衡稳态自由旋进脉冲 序列所获得的磁共振图像具有高空间分辨率和高信噪比，能够更清晰的显示组织结构，有效的降低了容积效应，同时该磁共振图像特有的T2/T1加权对比度，在临床诊断中有助于分辨某些指定的组织结构或病灶，如心肌或肿瘤等；波浪梯度脉冲可控混叠并行成像方法利用正弦/余弦磁场梯度分散K空间信号，并对相位方向和选层方向的编码策略进行调整，达到降低几何因子的目的，从而在保证图像质量的前提下，提高三维平衡稳态自由旋进脉冲序列的加速倍数，且具有较高的鲁棒性。
本实施例所提供的磁共振成像装置可执行本公开任意实施例所提供的磁共振成像方法，具备执行方法相应的功能模块和有益效果。
实施例五
图16为一实施例提供的设备的结构示意图。如图16所示，该设备包括处理器201、存储器202、输入装置203以及输出装置204；设备中处理器201的数量可以是一个或多个，图16中以一个处理器201为例；设备中的处理器201、存储器202、输入装置203以及输出装置204可以通过总线或其他方式连接，图16中以通过总线连接为例。
存储器202作为一种计算机可读存储介质，可用于存储软件程序、计算机可执行程序以及模块，如本公开实施例中的磁共振成像方法对应的程序指令/模块(例如，三维点扩散函数获取模块11、灵敏度图获取模块12、编码策略调整模块13、三维欠采数据获取模块14以及重建模块15)。处理器201通过运行存储在存储器202中的软件程序、指令以及模块，从而执行设备的一种或多种功能应用以及数据处理，即实现上述的磁共振成像方法。
存储器202可主要包括存储程序区和存储数据区，其中，存储程序区可存储操作系统、至少一个功能所需的应用程序；存储数据区可存储根据终端的使用所创建的数据等。此外，存储器202可以包括高速随机存取存储器，还可以包括非易失性存储器，例如至少一个磁盘存储器件、闪存器件、或其他非易失性固态存储器件。在一些实例中，存储器202可包括相对于处理器201远程设置的存储器，这些远程存储器可以通过网络连接至设备。上述网络的实例包括但不限于互联网、企业内部网、局域网、移动通信网及其组合。
输入装置203可设置为接收输入的数字或字符信息，以及产生与设备的用户设置以及功能控制有关的键信号输入。
输出装置204可包括显示屏等显示设备，例如，用户终端的显示屏。
在一实施例中，上述设备还包括采集器205，采集器205设置为获取目标对象的三维点扩散函数，获取目标对象的和灵敏度图，通过波浪梯度脉冲可控混叠并行成像方法调整平衡稳态自由旋进脉冲序列的编码策略并基于编码策略调整后的平衡稳态自由旋进脉冲序列获取目标对象的三维欠采数据。
实施例六
本公开一实施例还提供一种包含计算机可执行指令的存储介质，所述计算机可执行指令在由计算机处理器执行时用于执行一种磁共振成像方法，该方法包括：
获取目标对象的三维点扩散函数；获取目标对象的灵敏度图；通过波浪梯度脉冲可控混叠并行成像方法调整平衡稳态自由旋进脉冲序列的编码策略，其中，所述编码策略包括相位方向的编码策略和选层方向的编码策略；基于编码策略调整后的平衡稳态自由旋进脉冲序列获取目标对象的三维欠采数据，其中，所述三维欠采数据与所述灵敏度图的成像视野相同；根据所述三维点扩散函数和所述灵敏度图对所述三维欠采数据进行图像重建，以生成目标对象的磁共振图像。
当然，本实施例所提供的一种包含计算机可执行指令的存储介质，计算机可执行指令不限于如上所述的方法操作，还可以执行本公开任意实施例所提供的磁共振成像方法中的相关操作。
通过以上关于实施方式的描述，所属领域的技术人员可以了解到，本公开可借助软件及必需的通用硬件来实现，当然也可以通过硬件实现，但很多情况下前者是更佳的实施方式。基于这样的理解，本公开的技术方案本质上或者说对相关技术做出贡献的部分可以以软件产品的形式体现出来，该计算机软件产品可以存储在计算机可读存储介质中，如计算机的软盘、只读存储器(Read-Only Memory，ROM)、随机存取存储器(Random Access Memory，RAM)、闪存(FLASH)、硬盘或光盘等，包括多个指令用以使得一台计算机设备(可以是个人计算机、服务器或者网络设备等)执行本公开任意实施例所述的磁共振成像方法。
在一实施例中，上述磁共振成像装置的实施例中，所包括的多个单元和模块只是按照功能逻辑进行划分的，但并不局限于上述的划分，只要能够实现相 应的功能即可；另外，每个功能单元的名称也只是为了便于相互区分，并不用于限制本公开的保护范围。
注意，上述仅为本公开的实施例及所运用技术原理。

Claims (10)

  1. 一种磁共振成像方法，包括：
    获取目标对象的三维点扩散函数；
    获取所述目标对象的灵敏度图；
    通过波浪梯度脉冲可控混叠并行成像方法调整平衡稳态自由旋进脉冲序列的编码策略，其中，所述编码策略包括相位方向的编码策略和选层方向的编码策略；
    基于所述编码策略调整后的平衡稳态自由旋进脉冲序列获取所述目标对象的三维欠采数据，其中，所述三维欠采数据与所述灵敏度图的成像视野相同；
    根据所述三维点扩散函数和所述灵敏度图对所述三维欠采数据进行图像重建，以生成所述目标对象的磁共振图像。
  2. 根据权利要求1所述的方法，其中，所述获取目标对象的三维点扩散函数，包括：
    基于所述平衡稳态自由旋进脉冲序列获取所述目标对象的映射数据；
    根据所述映射数据求取所述目标对象的三维点扩散函数。
  3. 根据权利要求2所述的磁共振成像方法，其中，所述基于所述平衡稳态自由旋进脉冲序列获取所述目标对象的映射数据，包括：
    基于二维平衡稳态自由旋进脉冲序列获取所述目标对象在所述选层方向上的二维映射数据和所述相位方向上的二维映射数据；
    在所述二维平衡稳态自由旋进脉冲序列的选层方向施加余弦磁场梯度，以获取所述目标对象在所述相位方向上的梯度二维映射数据；
    在所述二维平衡稳态自由旋进脉冲序列的相位方向施加余弦磁场梯度，以获取所述目标对象在所述选层方向上的梯度二维映射数据；
    所述根据所述映射数据求取所述目标对象的三维点扩散函数，包括：
    基于所述选层方向上的二维映射数据、所述相位方向上的二维映射数据、所述选层方向上的梯度二维映射数据以及所述相位方向上的梯度二维映射数据计算所述三维点扩散函数。
  4. 根据权利要求3所述的磁共振成像方法，其中，所述基于所述选层方向上的二维映射数据、所述相位方向上的二维映射数据、所述选层方向上的梯度二维映射数据以及所述相位方向上的梯度二维映射数据计算所述三维点扩散函数，包括：
    基于所述选层方向上的二维映射数据和所述选层方向上的梯度二维映射数 据求取所述选层方向上的二维点扩散函数；
    基于所述相位方向上的二维映射函数和所述相位方向上的梯度二维映射函数求取所述相位方向上的二维点扩散函数；
    基于所述选层方向上的二维点扩散函数和所述相位方向上的二维点扩散函数求取所述三维点扩散函数。
  5. 根据权利要求1-4任一项所述的磁共振成像方法，其中，所述获取所述目标对象的灵敏度图，包括：
    获取所述目标对象的三维低分辨率数据；
    根据所述三维低分辨率数据计算所述目标对象的灵敏度图。
  6. 根据权利要求5所述的磁共振成像方法，其中，所述获取所述目标对象的三维低分辨率数据，包括：
    基于梯度回波脉冲序列、自旋回波脉冲序列或所述平衡稳态自由旋进脉冲序列获取所述目标对象的三维低分辨率数据。
  7. 根据权利要求1-6任一项所述的磁共振成像方法，其中，所述通过波浪梯度脉冲可控混叠并行成像方法调整平衡稳态自由旋进脉冲序列的编码策略，其中，所述编码策略包括相位方向的编码策略和选层方向的编码策略，包括：
    在所述平衡稳态自由旋进脉冲序列的相位方向和所述平衡稳态自由旋进脉冲序列的选层方向同时分别施加相位相差90度的正弦磁场梯度和余弦磁场梯度，以调整所述平衡稳态自由旋进脉冲序列的编码策略。
  8. 一种磁共振成像装置，包括：
    三维点扩散函数获取模块，设置为获取目标对象的三维点扩散函数；
    灵敏度图获取模块，设置为获取所述目标对象的和灵敏度图；
    编码策略调整模块，设置为通过波浪梯度脉冲可控混叠并行成像方法调整平衡稳态自由旋进脉冲序列的编码策略，其中，所述编码策略包括相位方向的编码策略和选层方向的编码策略；
    三维欠采数据获取模块，设置为基于编码策略调整后的平衡稳态自由旋进脉冲序列获取所述目标对象的三维欠采数据，其中，所述三维欠采数据与所述灵敏度图的成像视野相同；
    重建模块，设置为根据所述三维点扩散函数和所述灵敏度图对所述三维欠采数据进行图像重建，以生成所述目标对象的磁共振图像。
  9. 一种设备，所述设备包括：
    一个或多个处理器；
    存储装置，设置为存储一个或多个程序；
    当所述一个或多个程序被所述一个或多个处理器执行，使得所述一个或多个处理器实现如权利要求1-7中任一项所述的磁共振成像方法。
  10. 一种包含计算机可执行指令的存储介质，所述计算机可执行指令在由计算机处理器执行时用于执行如权利要求1-7中任一项所述的磁共振成像方法。
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