Fast positive contrast magnetic resonance imaging method and apparatus based on variable flip angle

Abstract

Embodiments of the present invention disclose a fast positive contrast magnetic resonance imaging method and apparatus based on variable flip angles. The method includes: performing two data acquisitions on the same slice of the same target to respectively obtain fast spin echo data without echo readout gradient offset as original acquisition data, and fast spin echo data with echo readout gradient offset as offset acquisition data; on the same slice of the same target, determining the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data; calculating a target susceptibility matrix according to the target local magnetic field and a pre-constructed target optimization function to achieve positive contrast magnetic resonance imaging. Embodiments of the present invention implement image reconstruction of a local field map combined with a susceptibility map through a magnetic resonance image reconstruction method of sparse under-sampling and background field removal, and further implement imaging of a metal device with a large susceptibility.

Description

Technical Field

[0001] Embodiments of the present invention relate to the field of magnetic resonance technology, and in particular, to a fast positive contrast magnetic resonance imaging method and apparatus based on variable flip angles. Background Art

[0002] Magnetic resonance compatible metal intervention devices are widely used in clinics, such as prostate radioactive seeds, stents, cardiac pacemakers, etc. However, when performing magnetic resonance imaging on the target area implanted with this metal, the magnetized metal device will cause a signal attenuation to the surrounding tissues, resulting in a large black hole in the traditional magnetic resonance image (negative contrast imaging) of this area. This black hole is very difficult to distinguish from tissue voids, blood pools, and low signal-to-noise ratio areas, and this black hole makes it very difficult to accurately locate and evaluate these metal devices. Although the quantitative susceptibility imaging technology based on gradient echo sequences can achieve three-dimensional positive contrast imaging in the case of a short TE, this technology is more commonly used for metal devices with lower magnetic susceptibilities or magnetic nanoparticle imaging, etc. For metal devices with larger magnetic susceptibilities, only ultra-short echo sequences can be used for imaging, but the imaging time is longer. Thus, it can be seen that how to improve the imaging effect of metal device imaging is a technical problem to be solved urgently. Summary of the Invention

[0003] Embodiments of the present invention provide a fast positive contrast magnetic resonance imaging method, apparatus, device, and storage medium based on variable flip angles to achieve imaging of metal devices with larger magnetic susceptibilities and improve the imaging effect of magnetic resonance imaging of metal devices.

[0004] In a first aspect, embodiments of the present invention provide a fast positive contrast magnetic resonance imaging method based on variable flip angles, including:

[0005] Performing two data acquisitions on the same layer of the same target, respectively obtaining fast spin echo data without echo readout gradient offset as original acquisition data, and fast spin echo data with echo readout gradient offset as offset acquisition data;

[0006] On the same layer of the same target, determining the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data;

[0007] Calculating a target susceptibility matrix according to the target local magnetic field and a pre-constructed target optimization function to achieve positive contrast magnetic resonance imaging.

[0008] Optionally, further, determining the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data includes:

[0009] Determine the total magnetic field based on the undersampled phase data of the imaging target;

[0010] Determine the background magnetic field based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data;

[0011] Determine the target local magnetic field according to the total magnetic field and the background field.

[0012] Optionally, further determine the background magnetic field based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data, including:

[0013] Jointly calculate and determine the background magnetic field through the following formula:

[0014]

[0015] χ b =(I - M)χ;

[0016]

[0017] f B =Dχ b *

[0018] where χ b is the background magnetization parameter, M is the matrix of the region of interest (ROI), f is the undersampled phase data of the imaging target, d is the polarization kernel, χ is the magnetic susceptibility matrix of the imaging target, Φ(T shift ) is the offset acquisition data, Φ(0) is the original acquisition data, ΔΦ is the phase difference, γ is the gyromagnetic ratio, is a constant; B0 is the main magnetic field of magnetic resonance imaging, T shift is the readout gradient offset time, D is the convolution operator of the polarization kernel, f B is the background magnetic field.

[0019] Optionally, further determine the target local magnetic field according to the total magnetic field and the background field, including:

[0020] Take the difference between the total magnetic field and the background magnetic field as the target local magnetic field.

[0021] Optionally, further calculate the target magnetic susceptibility matrix according to the target local magnetic field and a pre - constructed target optimization function, including:

[0022] Determine a candidate magnetic susceptibility matrix according to the target local magnetic field and the pre - constructed target optimization function;

[0023] Determine a candidate local magnetic field based on the candidate magnetic susceptibility matrix, and determine a new candidate magnetic susceptibility matrix according to the candidate local magnetic field;

[0024] Iteratively execute the above operations until the iteration stop condition is met, and use the candidate magnetic susceptibility matrix as the target magnetic susceptibility matrix.

[0025] Optionally, further determine the candidate magnetic susceptibility matrix according to the target local magnetic field and the pre-constructed target optimization function, including:

[0026] Solve the candidate magnetic susceptibility matrix based on the target optimization function using the first-order primal-dual algorithm;

[0027] The target optimization function is: where λ is the regularization parameter, f L is the target local magnetic field, M1 is the mask matrix, χ is the candidate magnetic susceptibility matrix, D is the convolution operator of the polarization kernel, M is a matrix; G represents the gradient operator in three directions in three-dimensional space.

[0028] Optionally, further perform two data acquisitions on the same slice of the same target, and respectively obtain fast spin echo data without echo readout gradient offset as the original acquisition data, and fast spin echo data with echo readout gradient offset as the offset acquisition data, including:

[0029] Use an asymmetric slice selection excitation pulse to excite the target area, and offset for each echo readout gradient to obtain fast spin echo data without echo readout gradient offset as the original acquisition data, and fast spin echo data with echo readout gradient offset as the offset acquisition data.

[0030] In a second aspect, an embodiment of the present invention further provides a fast positive contrast magnetic resonance imaging device based on a variable flip angle, including:

[0031] A data acquisition module, configured to perform two data acquisitions on the same slice of the same target, and respectively obtain fast spin echo data without echo readout gradient offset as the original acquisition data, and fast spin echo data with echo readout gradient offset as the offset acquisition data;

[0032] A local magnetic field determination module, configured to determine the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data on the same slice of the same target;

[0033] A magnetic resonance imaging module, configured to calculate the target magnetic susceptibility matrix according to the target local magnetic field and the pre-constructed target optimization function, and implement fast positive contrast magnetic resonance imaging.

[0034] In a third aspect, an embodiment of the present invention further provides a computer device, the device includes:

[0035] One or more processors;

[0036] A storage device for storing one or more programs;

[0037] When the one or more programs are executed by the one or more processors, the one or more processors implement the fast positive-contrast magnetic resonance imaging method based on variable flip angles provided in any embodiment of the present invention.

[0038] In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, it implements the fast positive-contrast magnetic resonance imaging method based on variable flip angles provided in any embodiment of the present invention.

[0039] In the embodiments of the present invention, two data acquisitions are performed on the same layer of the same target to respectively obtain fast spin echo data without echo readout gradient offset as original acquisition data, and fast spin echo data with echo readout gradient offset as offset acquisition data; on the same layer of the same target, the target local magnetic field generated by the metal device in the target area is determined based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data; according to the target local magnetic field and the pre-constructed target optimization function, the target susceptibility matrix is calculated to achieve positive-contrast magnetic resonance imaging. Through the magnetic resonance image reconstruction method based on sparse under-sampling and background field removal, the image reconstruction of the local field map combined with the susceptibility map is realized, and further the imaging of the metal device with a large susceptibility is realized. Description of the Drawings

[0040] Figure 1 is a schematic flowchart of a fast positive-contrast magnetic resonance imaging method based on variable flip angles provided in Embodiment 1 of the present invention;

[0041] Figure 2 is a schematic diagram of a positive-contrast magnetic resonance imaging sequence provided in Embodiment 2 of the present invention;

[0042] Figure 3 is a schematic structural diagram of a fast positive-contrast magnetic resonance imaging device provided in Embodiment 3 of the present invention;

[0043] Figure 4 is a schematic structural diagram of a computer device provided in Embodiment 4 of the present invention. Detailed Embodiments

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. In addition, it should be noted that for the sake of description, only the parts related to the present invention rather than all the structures are shown in the accompanying drawings.

[0045] Embodiment 1

[0046] Figure 1 FIG. is a schematic flowchart of a fast positive contrast magnetic resonance imaging method based on a variable flip angle provided by Embodiment 1 of the present invention. This embodiment is applicable to the situation during magnetic resonance scanning and imaging, especially applicable to the situation of magnetic resonance imaging of an imaging target containing a metal device. This method can be executed by a fast positive contrast magnetic resonance imaging device based on a variable flip angle, and the fast positive contrast magnetic resonance imaging device based on a variable flip angle can be implemented in a software and / or hardware manner. For example, the fast positive contrast magnetic resonance imaging device based on a variable flip angle can be configured in a computer device. As Figure 1 shown, the method includes:

[0047] S110. Perform two data acquisitions on the same layer of the same target, respectively obtaining fast spin echo data without echo readout gradient offset as original acquisition data, and fast spin echo data with echo readout gradient offset as offset acquisition data.

[0048] Embodiment 1 of the present invention proposes a fast positive contrast magnetic resonance imaging method based on a variable flip angle. By offsetting the position of the echo readout gradient on the basis of the fast spin echo sequence, data can be acquired in a very short offset time to determine the phase difference. By taking the difference of the phases, background field processing can be avoided, and then combined with an image reconstruction algorithm, a susceptibility image can be reconstructed. A stable positive contrast image of the implanted metal device is obtained, and finally a fast positive contrast magnetic resonance imaging technology with application value is formed, providing a safe and non-invasive technical guarantee for the accurate positioning and evaluation of the implanted device.

[0049] Specifically, after adopting an appropriate variable flip angle, the tissue signal remains in a steady state for most of the time in the echo train, greatly improving the acquisition efficiency of the T2-weighted image. Each readout gradient is offset by a very short T shift (0.3 - 0.8 ms) time, so that the effective echo time is very short. While avoiding serious signal loss, the phase change caused by the difference in the magnetic susceptibility of the tissue itself is obtained, realizing the data acquisition of the positive contrast magnetic resonance imaging of the implanted radioactive particles.

[0050] Based on this, two data acquisitions are performed on the same layer of the same target to respectively obtain fast spin echo data without echo readout gradient offset as the original acquisition data, and fast spin echo data with echo readout gradient offset as the offset acquisition data, including: using an asymmetric slice selection excitation pulse to excite the target area, offsetting for each echo readout gradient, obtaining fast spin echo data without echo readout gradient offset as the original acquisition data, and fast spin echo data with echo readout gradient offset as the offset acquisition data. In order to shorten the echo time while achieving precise slice selection, an asymmetric slice selection excitation pulse (Slab - selected Excitation RFPulse) can be used to excite the target area. At the same time, each readout gradient is offset by a very short time (0.3 - 0.8 ms), so that the effective echo time is very short, obtaining fast spin echo data without echo readout gradient offset as the original acquisition data, and fast spin echo data with echo readout gradient offset as the offset acquisition data.

[0051] S120. On the same layer of the same target, determine the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data.

[0052] After obtaining the original acquisition data and the offset acquisition data of the same layer, the phase contrast generated by the magnetic susceptibility difference of the tissue itself is obtained, and then the target local magnetic field generated by the metal device in the target area can be solved by combining the phase contrast information with the sampling parameters.

[0053] In one implementation, determining the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data includes: determining the total magnetic field according to the undersampled phase data of the imaging target; determining the background magnetic field based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data; determining the target local magnetic field according to the total magnetic field and the background field. It can be understood that the total magnetic field is obtained by superimposing the background magnetic field and the target local magnetic field, and the total magnetic field can be obtained according to the undersampled phase data of the imaging target. Based on this, if the target local magnetic field needs to be solved, only the background magnetic field needs to be calculated. Among them, the determination method of the total magnetic field can refer to the calculation method in the prior art and will not be limited here.

[0054] In this embodiment, determining the target local magnetic field according to the total magnetic field and the background field includes: taking the difference between the total magnetic field and the background magnetic field as the target local magnetic field. Suppose, f L is the target local magnetic field, f is the total magnetic field, f B is the background magnetic field, then it can be through f L = f - fB Solve for the target local magnetic field.

[0055] In an embodiment of the present invention, the background magnetic field is determined based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data, including: jointly calculating and determining the background magnetic field through the following formula:

[0056]

[0057] χ b =(I - M)χ;

[0058]

[0059] f B =Dχ b * ;

[0060] where χ b is the background magnetization parameter, M is the matrix of the region of interest (ROI), f is the undersampled phase data of the imaging target, d is the polarization kernel, χ is the magnetic susceptibility matrix of the imaging target, Φ(T shift ) is the offset acquisition data, Φ(0) is the original acquisition data, ΔΦ is the phase difference, γ is the gyromagnetic ratio, is a constant; B0 is the main magnetic field of magnetic resonance imaging, T shift is the readout gradient offset time, D is the convolution operator of the polarization kernel, f B is the background magnetic field.

[0061] To correct the influence of background magnetic field void gaps, magnetic field inhomogeneity, etc. on the field map. The background magnetic field is fitted with the dipole field generated by a group of dipoles outside the region of interest (ROI), and a weighted minimization model is used to obtain the background magnetization χ b :

[0062]

[0063] where χ b =(I - M)χ, Ω is the undersampling matrix, d is the polarization kernel, D is the convolution operator of the polarization kernel. M is the ROI matrix, where the target region value is 1. Φ(T shift ) is the phase data acquired after gradient offset, Φ(0) is the phase data before gradient offset, χ is the magnetic susceptibility map of the target, that is, the magnetic susceptibility matrix of the imaging target.

[0064] After determining χ b , calculate the background magnetic field f through f B =Dχ b * ​B 。

[0065] S130. Calculate the target magnetic susceptibility matrix according to the target local magnetic field and the pre-constructed target optimization function, and realize positive contrast magnetic resonance imaging.

[0066] The positive contrast imaging algorithm is based on the magnetic susceptibility imaging model to solve the magnetic susceptibility intensity distribution of the scanned object. When reconstructing the magnetic susceptibility image using the local field map information of the imaging target, it is an ill-posed inverse problem (the polarization kernel is irreversible at the magic angle of 55°). Based on this, the sparse characteristic of the magnetic susceptibility gradient information can be fully utilized, and the L1 norm constraint is introduced to solve the optimal solution of this ill-posed problem. Combining the characteristic that the magnetic susceptibility of the metal intervention device is much larger than that of human tissues, the constraint matrix M1 is added to improve the reconstruction quality of the positive contrast image, where M1 is a mask matrix, the value of the target area is 1, and the background noise and the low-signal area around the metal are 0.

[0067] In an embodiment of the present invention, calculating the target magnetic susceptibility matrix according to the target local magnetic field and the pre-constructed target optimization function includes: determining a candidate magnetic susceptibility matrix according to the target local magnetic field and the pre-constructed target optimization function; determining a candidate local magnetic field based on the candidate magnetic susceptibility matrix, and determining a new candidate magnetic susceptibility matrix according to the candidate local magnetic field; iteratively executing the above operations until the iteration stop condition is satisfied, and taking the candidate magnetic susceptibility matrix as the target magnetic susceptibility matrix. In this embodiment, the target magnetic susceptibility matrix is obtained by iteratively seeking the optimal solution. Generally speaking, first calculate the magnetic susceptibility matrix through the target optimization function, then substitute the magnetic susceptibility matrix into the solution formula of the background magnetization to obtain the iterative target local magnetic field, and then calculate the magnetic susceptibility matrix based on the iterative target local magnetic field and the target optimization function, and repeat the iterative operation until the iteration ends, and take the magnetic susceptibility matrix at the end of the iteration as the target magnetic susceptibility matrix. Among them, the iteration end condition can be that the number of iterations reaches the set number of times, and / or the difference between two consecutive iterations is less than the set threshold.

[0068] Preferably, determining the candidate magnetic susceptibility matrix according to the target local magnetic field and the pre-constructed target optimization function includes: solving the candidate magnetic susceptibility matrix based on the target optimization function by using the first-order primal-dual algorithm; the target optimization function is: where λ is the regularization parameter, f L is the target local magnetic field, M1 is the mask matrix, χ is the candidate magnetic susceptibility matrix, D is the convolution operator of the polarization kernel, and M is the matrix; G represents the gradient operator in three directions in the three-dimensional space. In the target optimization function, the regularization parameter λ is used to ensure the consistency and sparsity of the data. Solving the target optimization function by using the first-order primal-dual algorithm can effectively solve the function, making the obtained target magnetic susceptibility matrix more accurate.

[0069] In the embodiment of the present invention, two data acquisitions are performed on the same layer of the same target to respectively obtain fast spin echo data without echo readout gradient offset as the original acquisition data, and fast spin echo data with echo readout gradient offset as the offset acquisition data; on the same layer of the same target, based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data, the target local magnetic field generated by the metal device in the target area is determined; according to the target local magnetic field and the pre-constructed target optimization function, the target susceptibility matrix is calculated to achieve positive contrast magnetic resonance imaging. Through the magnetic resonance image reconstruction method based on sparse under-sampling and background field removal, the image reconstruction of the local field map combined with the susceptibility map is realized, and thus the imaging of the metal device with a large susceptibility is realized.

[0070] Embodiment 2

[0071] Figure 2 It is a schematic diagram of a positive contrast magnetic resonance imaging sequence provided by Embodiment 2 of the present invention. On the basis of the above embodiment, a preferred embodiment is provided.

[0072] Figure 2 Schematically shows an improved variable flip angle timing diagram. Figure 2 Among them, the first pulse is a 90° slice selection excitation pulse, and then α is a variable flip angle refocusing pulse. The variable flip angle of this sequence needs to meet the CPMG (Carr-Purcell-Meiboom-Gill) condition. Figure 2 C is the flip angle chain. Figure 2 D is the undersampling Mask.

[0073] Adopt Figure 2 When performing magnetic resonance data acquisition using the sequence shown, an asymmetric slice selection excitation pulse (Slab-selected Excitation RF Pulse) is used to shorten the echo time while achieving accurate slice selection. At the same time, each readout gradient is offset for a very short T shift (0.3 - 0.8 ms) time, so that the effective echo time is very short. While avoiding serious signal loss, the phase change caused by the difference in the magnetic susceptibility of the tissue itself is obtained, and the data acquisition of the positive contrast magnetic resonance imaging of implanted radioactive particles is realized.

[0074] In this embodiment, the positive contrast image reconstruction with alternating iteration of the field map and the susceptibility map specifically includes two parts: the solution of the local field map and the reconstruction of the susceptibility map.

[0075] (1) Adopt Figure 2The undersampled phase data f of the imaging target, i.e., the total field map, is obtained from the shown sequence. To correct the influence of the background field (such as void gaps, magnetic field inhomogeneity, etc.) on the field map, a dipole field generated by a group of dipoles outside the region of interest (ROI) is used to fit the background field, and a weighted minimization model is adopted here to obtain the background magnetization χ b , and the susceptibility map of the target is χ.

[0076]

[0077] Where:

[0078] χ b =(I - M)χ (2)

[0079]

[0080] Ω is the undersampling matrix, d is the polarization kernel, D is the convolution operator of the polarization kernel. M is the ROI matrix, where the value of the target area is 1. Φ(T shift ) is the phase data acquired after gradient offset, and Φ(0) is the phase data obtained when the gradient is not offset.

[0081] Then the background field is: f B = Dχ b * , and thus the local field is f L = f - f B .

[0082] (2) Susceptibility map reconstruction

[0083] The positive contrast imaging algorithm is based on the susceptibility imaging model to solve the susceptibility intensity distribution of the scanned object. When reconstructing the susceptibility image using the local field map information of the imaging target, it is an ill-posed inverse problem (the polarization kernel is irreversible at the magic angle of 55°). Therefore, the sparse characteristic of the susceptibility gradient information can be fully utilized, and the L1 norm constraint is introduced to solve the optimal solution of this ill-posed problem. Combining the fact that the susceptibility of the metal intervention device is much larger than that of human tissues, a constraint matrix M1 is added to improve the quality of positive contrast image reconstruction, where M1 is the Mask matrix, with the value of the target area being 1, and the background noise and the low-signal area around the metal being 0. The reconstruction formula is shown in equation (1):

[0084]

[0085] λ is the regularization parameter to ensure the consistency and sparsity of the data. To effectively solve the function (4), the first-order primal-dual algorithm is used to solve the objective function χ.

[0086] The magnetic susceptibility map χ obtained by formula solving, in combination with formula (1) and formula (2), further optimizes the solution of the local field map f L , and repeat this step until an optimal magnetic susceptibility map χ is obtained, that is, an optimized positive contrast image.

[0087] The embodiment of the present invention proposes a novel variable flip angle positive contrast imaging sequence. A time shift is performed on each readout gradient, and the background field processing algorithm is combined with the shifted and unshifted imaging data to obtain a preliminary local field map. The magnetic susceptibility map is obtained by using the magnetic susceptibility image reconstruction algorithm in combination with the local field map, and the magnetic susceptibility map and the local field map are alternately iteratively solved to obtain a more optimized magnetic susceptibility map, with better positive contrast visualization effect and more accurate positioning. Compared with the existing positive contrast imaging technology, the compressed sensing reconstruction model of sparse under-sampling and background field removal proposed in the embodiment of the present invention realizes the alternating iterative reconstruction of the local field map and the magnetic susceptibility map. It can be applied to imaging of smaller interventional / implanted metal devices, can achieve three-dimensional positive contrast visualization, has a faster imaging speed, and more accurate positioning.

[0088] Embodiment III

[0089] Figure 3 is a schematic structural diagram of a fast positive contrast magnetic resonance imaging device based on a variable flip angle provided by Embodiment III of the present invention. The fast positive contrast magnetic resonance imaging device based on a variable flip angle can be implemented in software and / or hardware. For example, the fast positive contrast magnetic resonance imaging device based on a variable flip angle can be configured in a computer device. As Figure 3 shown, the device includes a data acquisition module 310, a local magnetic field determination module 320, and a magnetic resonance imaging module 330, where:

[0090] The data acquisition module 310 is used to perform two data acquisitions on the same layer of the same target, and respectively obtain fast spin echo data without echo readout gradient offset as the original acquisition data, and fast spin echo data with echo readout gradient offset as the offset acquisition data;

[0091] The local magnetic field determination module 320 is used to determine the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data on the same layer of the same target;

[0092] The magnetic resonance imaging module 330 is used to calculate the target magnetic susceptibility matrix according to the target local magnetic field and the pre-constructed target optimization function to realize positive contrast magnetic resonance imaging.

[0093] In an embodiment of the present invention, by performing two data acquisitions on the same layer of the same target, fast spin echo data without echo readout gradient offset is obtained as the original acquisition data, and fast spin echo data with echo readout gradient offset is obtained as the offset acquisition data; on the same layer of the same target, based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data, the target local magnetic field generated by the metal device in the target area is determined; according to the target local magnetic field and the pre-constructed target optimization function, the target susceptibility matrix is calculated to achieve positive contrast magnetic resonance imaging. In an embodiment of the present invention, through a magnetic resonance image reconstruction method of sparse under-sampling and background field removal, the image reconstruction of the local field map and the susceptibility map is realized, and further, the imaging of the metal device with a large susceptibility is realized.

[0094] Optionally, on the basis of the above solution, the local magnetic field determination module 320 is specifically configured to:

[0095] Determine the total magnetic field according to the under-sampled phase data of the imaging target;

[0096] Determine the background magnetic field based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data;

[0097] Determine the target local magnetic field according to the total magnetic field and the background field.

[0098] Optionally, on the basis of the above solution, the local magnetic field determination module 320 is specifically configured to:

[0099] Jointly calculate and determine the background magnetic field through the following formula:

[0100]

[0101] χ b =(I - M)χ;

[0102]

[0103] f B =Dχ b *

[0104] where χ b is the background magnetization parameter, M is the region of interest (ROI) matrix, f is the under-sampled phase data of the imaging target, d is the polarization kernel, χ is the susceptibility matrix of the imaging target, Φ(T shift ) is the offset acquisition data, Φ(0) is the original acquisition data, ΔΦ is the phase difference, γ is the gyromagnetic ratio, is a constant; B0 is the main magnetic field of magnetic resonance imaging, T shift is the readout gradient offset time, D is the convolution operator of the polarization kernel, f Bis the background magnetic field.

[0105] Optionally, based on the above solution, the local magnetic field determination module 320 is specifically configured to:

[0106] Take the difference between the total magnetic field and the background magnetic field as the target local magnetic field.

[0107] Optionally, based on the above solution, the magnetic resonance imaging module 330 is specifically configured to:

[0108] Determine a candidate susceptibility matrix according to the target local magnetic field and a pre-constructed target optimization function;

[0109] Determine a candidate local magnetic field based on the candidate susceptibility matrix, and determine a new candidate susceptibility matrix according to the candidate local magnetic field;

[0110] Iteratively execute the above operations until the iteration stop condition is satisfied, and take the candidate susceptibility matrix as the target susceptibility matrix.

[0111] Optionally, based on the above solution, the magnetic resonance imaging module 330 is specifically configured to:

[0112] Solve the candidate susceptibility matrix based on the target optimization function by using the first-order primal-dual algorithm;

[0113] The target optimization function is: where λ is the regularization parameter, f L is the target local magnetic field, M1 is the mask matrix, χ is the candidate susceptibility matrix, D is the convolution operator of the polarization kernel, and M is the matrix; G represents the gradient operator in three directions in the three-dimensional space.

[0114] Optionally, based on the above solution, the data acquisition module 310 is specifically configured to:

[0115] Use an asymmetric slice selection excitation pulse to excite the target region, shift each echo readout gradient, obtain fast spin echo data without echo readout gradient shift as the original acquisition data, and fast spin echo data with echo readout gradient shift as the offset acquisition data

[0116] The fast positive contrast magnetic resonance imaging device based on variable flip angle provided by the embodiments of the present invention can execute the fast positive contrast magnetic resonance imaging method provided by any embodiment of the present invention, and has the corresponding functional modules and beneficial effects for executing the method.

[0117] Embodiment 4

[0118] Figure 4 is a schematic structural diagram of a computer device provided by Embodiment 4 of the present invention. Figure 4A block diagram of an exemplary computer device 412 suitable for implementing embodiments of the present invention is shown. Figure 4 The computer device 412 shown is merely an example and should not impose any limitation on the functionality and scope of use of the embodiments of the present invention.

[0119] As Figure 4 shown, the computer device 412 appears in the form of a general-purpose computing device. The components of the computer device 412 may include, but are not limited to: one or more processors 416, a system memory 428, and a bus 418 that connects different system components (including the system memory 428 and the processor 416).

[0120] The bus 418 represents one or more of several types of bus architectures, including a memory bus or memory controller, a peripheral bus, a graphics acceleration port, a processor 416, or a local bus using any of the various bus architectures. By way of example, these architectures include, but are not limited to, Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MAC) bus, Enhanced ISA bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus.

[0121] The computer device 412 typically includes a variety of computer system-readable media. These media can be any available media that can be accessed by the computer device 412, including volatile and non-volatile media, removable and non-removable media.

[0122] The system memory 428 may include computer system-readable media in the form of volatile memory, such as random access memory (RAM) 440 and / or cache memory 442. The computer device 412 may further include other removable / non-removable, volatile / non-volatile computer system storage media. By way of example only, a storage device 444 may be used for reading and writing on non-removable, non-volatile magnetic media ( Figure 4 not shown, commonly referred to as a "hard disk drive"). Although Figure 4 not shown in the figure, a disk drive for reading and writing on a removable non-volatile disk (such as a "floppy disk") and an optical disk drive for reading and writing on a removable non-volatile optical disk (such as a CD-ROM, DVD-ROM, or other optical media) may be provided. In these cases, each drive may be connected to the bus 418 through one or more data media interfaces. The memory 428 may include at least one program product having a set (e.g., at least one) of program modules configured to perform the functions of the embodiments of the present invention.

[0123] A program / utilities 440 having a set (at least one) of program modules 442 can be stored, for example, in a memory 428. Such program modules 442 include, but are not limited to, an operating system, one or more application programs, other program modules, and program data. Each or some combination of these examples may include an implementation of a network environment. The program modules 442 generally execute the functions and / or methods in the embodiments described in the present invention.

[0124] The computer device 412 can also communicate with one or more external devices 414 (such as a keyboard, a pointing device, a display 424, etc.), and can also communicate with one or more devices that enable a user to interact with the computer device 412, and / or communicate with any device that enables the computer device 412 to communicate with one or more other computing devices (such as a network card, a modem, etc.). Such communication can be carried out through an input / output (I / O) interface 422. Moreover, the computer device 412 can also communicate with one or more networks (such as a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) through a network adapter 420. As shown in the figure, the network adapter 420 communicates with other modules of the computer device 412 through a bus 418. It should be understood that although not shown in the figure, other hardware and / or software modules can be used in conjunction with the computer device 412, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems, etc.

[0125] The processor 416 executes various functional applications and data processing by running programs stored in the system memory 428. For example, it implements the fast positive contrast magnetic resonance imaging method based on a variable flip angle provided by the embodiments of the present invention. The method includes:

[0126] Performing two data acquisitions on the same slice of the same target, respectively obtaining fast spin echo data without echo readout gradient offset as original acquisition data, and fast spin echo data with echo readout gradient offset as offset acquisition data;

[0127] On the same slice of the same target, determining the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data;

[0128] Calculating a target magnetic susceptibility matrix according to the target local magnetic field and a pre-constructed target optimization function to achieve positive contrast magnetic resonance imaging.

[0129] Of course, those skilled in the art can understand that the processor can also implement the technical solution of the fast positive-contrast magnetic resonance imaging method based on variable flip angles provided in any embodiment of the present invention.

[0130] Embodiment 5

[0131] Embodiment 5 of the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, it implements the fast positive-contrast magnetic resonance imaging method based on variable flip angles provided in the embodiments of the present invention. The method includes:

[0132] Perform two data acquisitions on the same slice of the same target, and respectively obtain fast spin echo data without echo readout gradient offset as the original acquisition data, and fast spin echo data with echo readout gradient offset as the offset acquisition data;

[0133] On the same slice of the same target, determine the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data;

[0134] Calculate the target susceptibility matrix according to the target local magnetic field and the pre-constructed target optimization function to achieve positive-contrast magnetic resonance imaging.

[0135] Of course, for a computer-readable storage medium provided in the embodiments of the present invention, the computer program stored thereon is not limited to the above method operations, and can also execute the related operations of the fast positive-contrast magnetic resonance imaging method based on variable flip angles provided in any embodiment of the present invention.

[0136] The computer storage medium of the embodiments of the present invention can adopt any combination of one or more computer-readable media. The computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the above. More specific examples (non-exhaustive list) of the computer-readable storage medium include: an electrical connection having one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this document, the computer-readable storage medium can be any tangible medium that contains or stores a program, and the program can be used by or in combination with an instruction execution system, apparatus, or device.

[0137] A computer-readable signal medium may include a data signal propagated in a baseband or as part of a carrier wave, which carries computer-readable program code. Such a propagated data signal may take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the foregoing. The computer-readable signal medium may also be any computer-readable medium other than a computer-readable storage medium, which can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device.

[0138] The program code contained on a computer-readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

[0139] The computer program code for performing the operations of the present invention may be written in one or more programming languages or combinations thereof. The programming languages include object-oriented programming languages such as Java, Smalltalk, C++, and also include conventional procedural programming languages such as the "C" language or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, executed as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., through the Internet using an Internet service provider).

[0140] Embodiment 5

[0141] This embodiment provides a magnetic resonance imaging system, including a main magnet, a radio frequency coil, and a processor; the main magnet is used to generate a main magnetic field; the radio frequency coil is used to transmit radio frequency pulses, refocusing pulses, and receive magnetic resonance signals; the processor is used to execute the fast positive contrast magnetic resonance imaging method based on variable flip angle provided in any embodiment of the present invention.

[0142] Furthermore, the processor is specifically used to: determine the refocusing pulse parameters according to the precession frequencies of the imaging protons in different substances. The specific determination method of the refocusing pulse parameters may refer to the foregoing embodiments and will not be elaborated herein.

[0143] In the magnetic resonance imaging system provided by the embodiment of the present invention, a processor determines the frequency parameter of the refocusing pulse according to the precession frequency difference of different substances in the subject. During imaging, the processor controls the main magnet to generate a main magnetic field, controls the radio frequency transmitting coil to emit radio frequency pulses to excite the target area of the subject, controls the radio frequency transmitting coil to emit refocusing pulses to refocus the magnetic resonance signals of the target area, and controls the radio frequency receiving coil to receive the magnetic resonance signals to generate magnetic resonance image data, so that only the magnetic resonance signals of the target imaging substances are refocused, realizing the reasonable suppression of the magnetic resonance signals of interfering imaging substances without the need for additional pulses, and overcoming the problems of poor imaging effect caused by the sensitivity of traditional signal suppression to the radio frequency field and the non-uniformity of the radio frequency field.

[0144] Note that the above is only the preferred embodiment of the present invention and the applied technical principle. Those skilled in the art will understand that the present invention is not limited to the specific embodiments here, and various obvious changes, re-adjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments only. Without departing from the concept of the present invention, more other equivalent embodiments can be included, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A fast positive contrast magnetic resonance imaging method based on variable flip angle, characterized in that Including: Performing two data acquisitions on the same layer of the same target, respectively obtaining fast spin echo data without echo readout gradient offset as original acquisition data, and fast spin echo data with echo readout gradient offset as offset acquisition data; On the same layer of the same target, determining the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data; Calculating a target susceptibility matrix according to the target local magnetic field and a pre-constructed target optimization function to achieve positive contrast magnetic resonance imaging; Wherein, the determining the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data includes: Determining the total magnetic field according to the undersampled phase data of the imaging target; Determining the background magnetic field based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data; Determining the target local magnetic field according to the total magnetic field and the background magnetic field; Wherein, the determining the background magnetic field based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data includes: Jointly calculating and determining the background magnetic field through the following formula: ； ； ； ； Among them, is the background magnetization matrix, is the mask matrix, where the target region value is 1, and the background noise and the low-signal region around the metal are 0, is the difference of is the undersampled phase data of the imaging target, d is the polarization kernel, is the susceptibility matrix of the imaging target, is the offset acquisition data, is the original acquisition data, is the phase difference, is the gyromagnetic ratio and is a constant; is the main magnetic field of magnetic resonance imaging, is the readout gradient offset time, is the convolution operator of the polarization kernel, is the background magnetic field.

2. The method according to claim 1, wherein The determining the target local magnetic field according to the total magnetic field and the background magnetic field includes: Taking the difference between the total magnetic field and the background magnetic field as the target local magnetic field.

3. The method according to claim 1, wherein The calculating a target susceptibility matrix according to the target local magnetic field and a pre-constructed target optimization function includes: Solving the target susceptibility matrix based on the target optimization function by using the first-order primal-dual algorithm; The target optimization function is as follows: , where is the undersampling matrix, is the regularization parameter, is the target local magnetic field, is the mask matrix, where the value of the target region is 1, and the background noise and the low-signal region around the metal are 0, is the target magnetic susceptibility matrix, is the convolution operator of the polarization kernel; G represents the gradient operator in three directions in the three-dimensional space.

4. The method according to claim 1, wherein The performing two data acquisitions on the same layer of the same target, respectively obtaining fast spin echo data without echo readout gradient offset as original acquisition data, and fast spin echo data with echo readout gradient offset as offset acquisition data includes: Using an asymmetric layer selection excitation pulse to excite the target area, offsetting for each echo readout gradient, obtaining fast spin echo data without echo readout gradient offset as original acquisition data, and fast spin echo data with echo readout gradient offset as offset acquisition data.

5. A fast positive-contrast magnetic resonance imaging device based on variable flip angles, characterized in that, Including: A data acquisition module, configured to perform two data acquisitions on the same layer of the same target, respectively obtaining fast spin echo data without echo readout gradient offset as original acquisition data, and fast spin echo data with echo readout gradient offset as offset acquisition data; A local magnetic field determination module, configured to determine the target local magnetic field generated by the metal device in the target area based on the phase difference and sampling parameters between the original acquisition data and the offset acquisition data on the same layer of the same target; A magnetic resonance imaging module, configured to calculate a target susceptibility matrix according to the target local magnetic field and a pre-constructed target optimization function to achieve positive contrast magnetic resonance imaging; Wherein, the local magnetic field determination module is specifically configured to: Determine the total magnetic field according to the undersampled phase data of the imaging target; Determine the background magnetic field based on the phase difference and sampling parameters between the original acquired data and the offset acquired data; Determine the target local magnetic field according to the total magnetic field and the background magnetic field; Wherein, the local magnetic field determination module is specifically configured to: Jointly calculate and determine the background magnetic field through the following formula: ； ； ； ； Among them, is the background magnetization matrix, is the mask matrix, where the target region value is 1, and the background noise and the low-signal region around the metal are 0. is the difference of is the undersampled phase data of the imaging target, d is the polarization kernel, is the magnetic susceptibility matrix of the imaging target, is the offset acquisition data, is the original acquisition data, is the phase difference, is the gyromagnetic ratio and is a constant; is the main magnetic field of magnetic resonance imaging, is the readout gradient offset time, is the convolution operator of the polarization kernel, is the background magnetic field.

6. A computer device, characterized in that, The device includes: One or more processors; A storage device for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the fast positive contrast magnetic resonance imaging method based on variable flip angle as described in any one of claims 1-4.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the fast positive contrast magnetic resonance imaging method based on variable flip angle as described in any one of claims 1-4.

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