Magnetic resonance parallel emission radio frequency pulse design method and device and computer equipment

Abstract

The invention relates to a magnetic resonance parallel emission radio frequency pulse design method and device and computer equipment. According to a preset flip angle and a preset basic flip angle of a target flip pulse in the magnetic resonance sequence, a basic flip pulse is determined, and according to the preset flip angle, the waveform of the basic flip pulse and the flip angle of the basic flip pulse, the target flip pulse is determined; wherein the gradient field waveform in the magnetic resonance sequence is centrosymmetric along the time axis, and the pulse waveform of the target refocusing pulse is symmetric along the time axis. According to the embodiment of the invention, the waveform of the gradient field is centrally symmetric along the time axis, and the pulse waveform of the target refocusing pulse is symmetric along the time axis, so that the design of the target refocusing pulse can meet the average Hamiltonian principle, thereby achieving the purpose of simplifying the calculation, and reducing the complexity of the design of the radio-frequency pulse.

Description

Technical Field

[0001] The present application relates to the field of medical technology, and in particular to a method, device and computer equipment for designing radio frequency pulses for parallel transmission of magnetic resonance. Background Art

[0002] In the process of ultra-high field magnetic resonance imaging, the problem of uneven RF transmission field is easy to occur. In order to solve the problem of uneven RF transmission field, it is often necessary to use a multi-channel parallel transmission coil, and apply parallel transmission RF pulses of different amplitudes and phases to the transmission channels of different coils to reduce standing waves and uniform RF transmission field. Based on the function of RF pulses, RF pulses can be divided into excitation pulses, inversion pulses and refocusing pulses. For example, a body coil with eight channels can independently control different channels to generate RF pulses of different waveforms.

[0003] In the traditional parallel transmission refocusing pulse design, the parameters in the SU(2) expression are directly optimized to solve the parallel transmission RF pulses, which is computationally complex and time-consuming. Summary of the invention

[0004] Based on this, it is necessary to provide a method, device and computer equipment for designing RF pulses for parallel transmission of magnetic resonance that can reduce the complexity of pulse design in order to solve the above technical problems.

[0005] In a first aspect, the present application provides a method for designing radio frequency pulses for parallel transmission of magnetic resonance, comprising:

[0006] Determining a basic refocusing pulse according to a preset flip angle of a target refocusing pulse and a preset basic flip angle in a magnetic resonance sequence;

[0007] Determining the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse;

[0008] Wherein, the gradient field waveform in the magnetic resonance sequence is symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis.

[0009] In one embodiment, determining the basic refocusing pulse according to the preset flip angle of the target refocusing pulse and the preset basic flip angle in the magnetic resonance sequence includes:

[0010] Acquiring the phase of the expected transverse magnetization vector generated by the excitation pulse in the magnetic resonance sequence;

[0011] taking the sum of the phase of the expected transverse magnetization vector and the preset phase as the target phase;

[0012] The basic refocusing pulse is determined according to the preset flip angle, the preset basic flip angle and the target phase.

[0013] In one embodiment, the basic refocusing pulse includes a first basic refocusing pulse and a second basic refocusing pulse; and determining the basic refocusing pulse according to the preset flip angle, the preset basic flip angle and the target phase includes:

[0014] In a case where the preset flip angle is smaller than the preset basic flip angle, determining a first basic refocusing pulse according to a small flip angle approximation principle and the target phase;

[0015] In a case where the preset flip angle is greater than or equal to the preset basic flip angle, determining a second basic refocusing pulse according to a small flip angle approximation principle and the target phase;

[0016] The pulse duration of the first basic refocusing pulse is smaller than the pulse duration of the second basic refocusing pulse, and the flip angle of the first basic refocusing pulse is smaller than the flip angle of the second basic refocusing pulse.

[0017] In one embodiment, the target refocusing pulse includes a first target refocusing pulse, and the step of determining the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse includes:

[0018] Determine a first product result of the preset flip angle and the waveform of the first basic refocusing pulse;

[0019] The first target refocusing pulse is determined according to the ratio of the first product result to the flip angle of the first basic refocusing pulse.

[0020] In one embodiment, the target refocusing pulse includes a second target refocusing pulse, and determining the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse includes:

[0021] Determine a second product result of the preset flip angle and the waveform of the second basic refocusing pulse, and determine a candidate refocusing pulse according to a ratio of the second product result to the flip angle of the second basic refocusing pulse;

[0022] Performing simulation processing on the candidate refocusing pulse to obtain a simulated transverse magnetization vector;

[0023] The candidate refocusing pulse is optimized according to the ideal transverse magnetization vector and the simulated transverse magnetization vector to obtain the second target refocusing pulse; the phase of the ideal transverse magnetization vector is equal to the target phase.

[0024] In one embodiment, the method further comprises:

[0025] Obtain the main magnetic field inhomogeneity and the sensitivity matrix of each transmission channel under parallel transmission pre-scan;

[0026] The excitation pulse is determined according to each of the sensitivity matrices and the main magnetic field inhomogeneity.

[0027] In a second aspect, the present application also provides a radio frequency pulse design device for parallel transmission of magnetic resonance, comprising:

[0028] A first determination module is used to determine a basic refocusing pulse according to a preset flip angle of a target refocusing pulse and a preset basic flip angle in a magnetic resonance sequence;

[0029] A second determination module, configured to determine the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse;

[0030] Wherein, the gradient field waveform in the magnetic resonance sequence is symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis.

[0031] In a third aspect, the present application further provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0032] Determining a basic refocusing pulse according to a preset flip angle of a target refocusing pulse and a preset basic flip angle in a magnetic resonance sequence;

[0033] Determining the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse;

[0034] Wherein, the gradient field waveform in the magnetic resonance sequence is symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis.

[0035] In a fourth aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the following steps are implemented:

[0036] Determining a basic refocusing pulse according to a preset flip angle of a target refocusing pulse and a preset basic flip angle in a magnetic resonance sequence;

[0037] Determining the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse;

[0038] Wherein, the gradient field waveform in the magnetic resonance sequence is symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis.

[0039] In a fifth aspect, the present application further provides a computer program product, including a computer program, which implements the following steps when executed by a processor:

[0040] Determining a basic refocusing pulse according to a preset flip angle of a target refocusing pulse and a preset basic flip angle in a magnetic resonance sequence;

[0041] Determining the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse;

[0042] Wherein, the gradient field waveform in the magnetic resonance sequence is symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis.

[0043] The above-mentioned method, device and computer equipment for designing radio frequency pulses for parallel transmission of magnetic resonance determine the basic refocusing pulse according to the preset flip angle and the preset basic flip angle of the target refocusing pulse in the magnetic resonance sequence, and determine the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse; wherein the gradient field waveform in the magnetic resonance sequence is centrally symmetric along the time axis, and the pulse waveform of the target refocusing pulse is symmetric along the time axis. In the embodiment of the present application, the gradient field waveform is pre-set to be centrally symmetric along the time axis, and the pulse waveform of the target refocusing pulse is symmetric along the time axis, so that the design of the target refocusing pulse can meet the average Hamiltonian principle, so as to achieve the purpose of simplifying the calculation and reduce the complexity of the radio frequency pulse design. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments of the present application or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0045] Figure 1 A diagram of an application environment of a method for designing radio frequency pulses for parallel transmission of magnetic resonance in one embodiment;

[0046] Figure 2 A schematic flow chart of a method for designing radio frequency pulses for parallel transmission of magnetic resonance in one embodiment;

[0047] Figure 3 is a schematic diagram of a gradient pulse in one embodiment;

[0048] Figure 4A schematic diagram of a process of determining a basic refocusing pulse in one embodiment;

[0049] Figure 5 is a schematic diagram of an excitation pulse in one embodiment;

[0050] Figure 6 is a schematic diagram of the phase of the expected transverse magnetization vector in one embodiment;

[0051] Figure 7 is a schematic flow chart of a method for determining a second target refocusing pulse in one embodiment;

[0052] Figure 8 A schematic flow chart of a method for designing radio frequency pulses for parallel transmission of magnetic resonance in another embodiment;

[0053] Fig. 9 A structural block diagram of a device for designing radio frequency pulses for parallel transmission of magnetic resonance in one embodiment. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0055] At present, the existing design method for small flip angle of parallel transmitted RF pulses is to apply time-varying gradient pulses in three directions of xyz or two directions of xy while applying multi-channel RF pulses. The integral of the gradient pulse over time can be analogous to reading k-space, which is called "excitation k-space". However, the design method of RF pulses under small flip angles is difficult to apply to the design of RF pulses under large flip angles. For large flip scenarios (i.e., flip angles greater than 90 degrees), the existing technology is to solve the parameters based on the SU(2) expression Then solve the parallel transmitted RF pulses: , , , is the target rotation angle of RF pulse b (that is, the target flip angle of RF pulse), R(b) represents the regularization function for multi-channel RF pulses, which is used to constrain the specific absorption ratio (SAR). The above method is difficult to apply to the design of longer refocusing pulses (one type of RF pulse). Therefore, regardless of the small flip angle or large flip angle scenario, RF pulses need to use an iterative optimization algorithm, which is a complex process and takes a long time to calculate.

[0056] The RF pulse design method for parallel transmission of magnetic resonance provided in the embodiment of the present application can be applied to Figure 1In the application environment shown in FIG. 1 , a computer device may be a server, and its internal structure diagram may be as shown in FIG. Figure 1 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. Among them, the processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store relevant data of radio frequency pulse design. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a radio frequency pulse design method is implemented. Optionally, the server can be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server providing cloud computing services.

[0057] Those skilled in the art will understand that Figure 1 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0058] In an exemplary embodiment, Figure 2 As shown, a method for designing RF pulses for parallel transmission of magnetic resonance is provided, and the method is applied to Figure 1 The computer device in the example is used for explanation, including the following S201 to S202. Among them:

[0059] S201, determining a basic refocusing pulse according to a preset flip angle of a target refocusing pulse and a preset basic flip angle in a magnetic resonance sequence.

[0060] The gradient field waveform in the magnetic resonance sequence is symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis.

[0061] The preset flip angle is the flip angle of the target refocusing pulse to be designed, that is, the actual flip angle of each target refocusing pulse in the magnetic resonance sequence. Optionally, the preset flip angle can be determined based on the imaging effect to be achieved, such as signal intensity, contrast, and energy deposition limitation.

[0062] The preset basic flip angle is a flip angle set in the process of designing the target refocusing pulse.

[0063] Optionally, the magnetic resonance sequence may include a fast spin echo sequence, etc. Since the fast spin echo sequence includes a large number of refocusing pulses, the B1+ field effect is very obvious. The inhomogeneity of the B1+ field can cause abnormal bright and dark areas in the medical image, which are so-called dielectric artifacts. These artifacts may mask or imitate lesions, thereby misleading the diagnosis.

[0064] According to the principle of designing RF pulses by the Shinnar-Le Roux algorithm, the effect of any RF pulse is equivalent to the generation of a rotation matrix, so the process of optimizing RF pulses is equivalent to the process of optimizing the rotation matrix. According to the Average Hamilitonian Theory (AHT), the SU (2) rotation matrix U can be expressed as: , , U1 is the effect of the RF pulse on the system, , U init The initial energy state of the system is caused by the inhomogeneity of the gradient field and the main magnetic field, that is, the gradient field and the main magnetic field do not change the rotation state, and only the application of the radio frequency pulse will lead to the generation of the rotation matrix. Main magnetic field inhomogeneity The influence of, r is the spatial position, that is, (x, y, z), k r To excite K space, that is, (k x , k y , k z ), is the Pauli matrix in the z direction. （0） , A （1） Magnus expansion term, A （0） It is independent of the waveform of the gradient pulse and the focusing pulse, and can be approximated by a small flip angle. （1） It is related to the waveform of the gradient pulse and the focusing pulse. When the inhomogeneity of the main magnetic field is ignored, Under the influence of , when the pulse waveform of the gradient pulse is symmetrical along the time dimension, and the pulse waveform of the focusing pulse is symmetrical along the time dimension, A （1） Therefore, in the embodiment of the present application, the gradient field waveform in the magnetic resonance sequence is symmetrical along the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis, such as Figure 3 As shown, Figure 3 is a schematic diagram of a gradient pulse in one embodiment, Figure 3 The gradient pulses shown satisfy the AHT theory. That is, , where G is the gradient pulse, is the total duration of the gradient pulse, is the target focusing pulse, is the total duration of the target refocusing pulse.

[0065] In the embodiment of the present application, the excitation pulse can be optimized based on the main magnetic field inhomogeneity obtained by the parallel transmission pre-scan and the sensitivity matrix of each transmission channel, and the phase of the expected transverse magnetization vector generated by the excitation pulse is obtained. The target phase is determined based on the difference between the phase of the expected transverse magnetization vector and the preset phase, and the basic refocusing pulse is determined based on the preset flip angle, the preset basic flip angle and the target phase. The basic refocusing pulse can be a first basic refocusing pulse with a preset flip angle less than a preset basic flip angle (in a small flip angle scenario), or a second basic refocusing pulse with a preset flip angle greater than or equal to the preset basic flip angle (in a large flip angle scenario).

[0066] In a possible implementation, the correspondence between each excitation pulse and the target phase can be established in advance, and the excitation pulse can be optimized based on the main magnetic field inhomogeneity obtained by the parallel emission pre-scan and the sensitivity matrix of each emission channel. The target phase can be obtained based on the correspondence between each excitation pulse and the phase, and the basic refocusing pulse can be determined based on the preset flip angle, the preset basic flip angle and the target phase.

[0067] S202, determining a target refocusing pulse according to a preset flip angle, a waveform of a basic refocusing pulse, and a flip angle of the basic refocusing pulse.

[0068] In the embodiment of the present application, according to the above analysis, it can be known that a first basic refocusing pulse less than a preset basic flip angle and a second basic refocusing pulse greater than or equal to the preset basic flip angle can be obtained. Therefore, the first target refocusing pulse can be determined by scalar multiplication according to the preset flip angle, the waveform of the first basic refocusing pulse and the flip angle of the first basic refocusing pulse. The candidate refocusing pulse can be obtained by scalar multiplication according to the preset flip angle, the waveform of the second basic refocusing pulse and the flip angle of the second basic refocusing pulse, and the second target refocusing pulse can be obtained by optimizing the candidate refocusing pulse.

[0069] In a possible implementation, a candidate refocusing pulse may be obtained by scalar multiplication according to a preset flip angle, the waveform of the second basic refocusing pulse and the flip angle of the second basic refocusing pulse, and the candidate refocusing pulse may be directly used as the second target refocusing pulse.

[0070] In the above-mentioned RF pulse design method for parallel transmission of magnetic resonance, the basic refocusing pulse is determined according to the preset flip angle and the preset basic flip angle of the target refocusing pulse in the magnetic resonance sequence, and the target refocusing pulse is determined according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse; wherein the gradient field waveform in the magnetic resonance sequence is centrally symmetric along the time axis, and the pulse waveform of the target refocusing pulse is symmetric along the time axis. In the embodiment of the present application, the gradient field waveform is pre-set to be centrally symmetric along the time axis, and the pulse waveform of the target refocusing pulse is symmetric along the time axis, so that the design of the target refocusing pulse can meet the average Hamiltonian principle, so as to achieve the purpose of simplifying the calculation and reduce the complexity of the RF pulse design.

[0071] Figure 4 FIG. 1 is a flow chart of a basic refocusing pulse determination method in an embodiment, as shown in FIG. Figure 4 As shown, the embodiment of the present application relates to a possible implementation method of determining a basic refocusing pulse according to a preset flip angle and a preset basic flip angle of a target refocusing pulse in a magnetic resonance sequence, including the following steps:

[0072] S401, acquiring the phase of the expected transverse magnetization vector generated by the excitation pulse in the magnetic resonance sequence.

[0073] In the embodiment of the present application, the excitation pulse is a pulse obtained after optimization, such as Figure 5 As shown, Figure 5 Schematic diagram of an excitation pulse in one embodiment. ,according to An expected transverse magnetization vector generated by an excitation pulse in a magnetic resonance sequence is acquired, where the expected transverse magnetization vector includes a phase and an amplitude of the expected transverse magnetization vector. For the excitation pulse The corresponding sensitivity matrix of each transmission channel, For the excitation pulse The corresponding system matrix. Figure 6 As shown, Figure 6 is a schematic diagram of the phase of the expected transverse magnetization vector in one embodiment, namely, Figure 5 The phase of the expected transverse magnetization vector resulting from the excitation pulse is shown.

[0074] S402: taking the sum of the expected transverse magnetization vector phase and the preset phase as the target phase.

[0075] Optionally, the preset phase may be 90 degrees, or a phase infinitely close to 90 degrees.

[0076] In the embodiment of the present application, taking the preset phase of 90 degrees as an example, in order to meet the CPMG condition, the sum of the phase of the expected transverse magnetization vector and 90 degrees is used as the target phase for the input of the subsequent target refocusing pulse design to meet the Carr-Purcell-Meiboom-Gill (CPMG) condition. The CPMG sequence includes a 90° excitation pulse and a series of 180° refocusing pulses.

[0077] S403, determining a basic refocusing pulse according to a preset flip angle, a preset basic flip angle and a target phase.

[0078] In the embodiment of the present application, when the preset flip angle is less than the preset basic flip angle, a first basic refocusing pulse with a shorter pulse can be determined based on the preset flip angle and the target phase using the small flip angle approximation principle; when the preset flip angle is greater than or equal to the preset basic flip angle, a second basic refocusing pulse with a longer pulse can be determined based on the preset flip angle and the target phase using the small flip angle approximation principle. The pulse duration of the first basic refocusing pulse is less than the pulse duration of the second basic refocusing pulse, and the flip angle of the first basic refocusing pulse is less than the flip angle of the second basic refocusing pulse.

[0079] In a possible implementation, when the preset flip angle is less than the preset basic flip angle, the preset flip angle and the target phase are input into a pre-trained first pulse prediction model to obtain a first basic refocusing pulse; when the preset flip angle is greater than or equal to the preset basic flip angle, the preset flip angle and the target phase are input into a pre-trained second pulse prediction model to obtain a second basic refocusing pulse. The first pulse prediction model and the second pulse prediction model can be time series models such as autoregression, moving average, autoregression moving average, etc., or can be RF-Adaboost ensemble learning models.

[0080] In an embodiment of the present application, the phase of the expected transverse magnetization vector generated by the excitation pulse in the magnetic resonance sequence is obtained. In order to meet the CPMG condition, the sum of the phase of the expected transverse magnetization vector and the preset phase is used as the target phase, and the basic refocusing pulse is determined according to the preset flip angle, the preset basic flip angle and the target phase. The present application can design the corresponding basic refocusing pulses of different flip angles in parallel by the phase of the expected transverse magnetization vector generated by the excitation pulse, thereby improving the efficiency of determining the basic refocusing pulse.

[0081] In one embodiment, when the preset flip angle is less than the preset basic flip angle, a first basic refocusing pulse is determined according to the small flip angle approximation principle and the target phase; when the preset flip angle is greater than or equal to the preset basic flip angle, a second basic refocusing pulse is determined according to the small flip angle approximation principle and the target phase; wherein the pulse duration of the first basic refocusing pulse is less than the pulse duration of the second basic refocusing pulse, and the flip angle of the first basic refocusing pulse is less than the flip angle of the second basic refocusing pulse.

[0082] The Small Tip-angle Approximation (STA) principle can be used to simplify the design process of RF pulses by converting complex nonlinear problems into linear problems, making them easier to analyze and calculate. In the image reconstruction process, the small tip-angle approximation can help more accurately recover images from K-space data, especially when using fast spin echo sequences.

[0083] In an embodiment of the present application, when designing a target refocusing pulse with a variable flip angle, two basic refocusing pulses need to be designed, one is a first basic refocusing pulse for presetting a flip angle less than 90 degrees, at which time the pulse duration of the first basic refocusing pulse is shorter, and the flip angle of the first basic refocusing pulse can be around 60 degrees to 80 degrees.

[0084] Another basic refocusing pulse is used to preset a second basic refocusing pulse with a flip angle greater than 90 degrees. In this case, the flip angle of the second basic refocusing pulse can be 90 degrees or greater than 90 degrees. Optionally, the flip angle of the second basic refocusing pulse is 90 degrees to 150 degrees. The second basic refocusing pulse has a longer pulse duration to prevent the RF pulse voltage from being too high.

[0085] In an embodiment of the present application, when the preset flip angle is less than the preset basic flip angle, the first basic refocusing pulse is determined according to the small flip angle approximation principle and the target phase; when the preset flip angle is greater than or equal to the preset basic flip angle, the second basic refocusing pulse is determined according to the small flip angle approximation principle and the target phase. In an embodiment of the present application, the first basic refocusing pulse and the second basic refocusing pulse are obtained on the basis that the pulse waveform of the gradient pulse is symmetrical along the time axis and the pulse waveform of the target refocusing pulse is symmetrical along the time axis, so that the design of the second basic refocusing pulse can also adopt the small flip angle approximation principle. Moreover, this method can minimize scalar multiplication, that is, it simplifies the amount of data for subsequently determining the target refocusing pulse based on the first basic refocusing pulse, the second basic refocusing pulse and scalar multiplication, and reduces the complexity of the target refocusing pulse design.

[0086] In one embodiment, a target refocusing pulse is determined based on a preset flip angle, a waveform of a basic refocusing pulse and a flip angle of the basic refocusing pulse, including: determining a first product result of the preset flip angle and the waveform of a first basic refocusing pulse; and determining a first target refocusing pulse based on a ratio of the first product result to the flip angle of the first basic refocusing pulse.

[0087] In the embodiment of the present application, the first target refocusing pulse can be obtained by scalar multiplication based on the preset flip angle, the flip angle of the first basic refocusing pulse and the waveform of the first basic refocusing pulse, that is, according to A first target focusing pulse is determined, wherein: is a preset flip angle, and the preset flip angle at this time is a flip angle smaller than the preset basic flip angle. is the waveform of the first basic refocusing pulse, is the flip angle of the first basic focusing pulse.

[0088] In an embodiment of the present application, a first product result of a preset flip angle and the waveform of a first basic refocusing pulse is determined; based on the ratio of the first product result to the flip angle of the first basic refocusing pulse, a first target refocusing pulse is determined. There is no need to use an iterative solution method to obtain the first target refocusing pulse, thereby reducing the complexity of the calculation of the first target refocusing pulse.

[0089] Figure 7 FIG. 4 is a flow chart of a method for determining a second target focusing pulse in an embodiment. Figure 7 As shown, the embodiment of the present application relates to another possible implementation method of how to determine the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse, including the following steps:

[0090] S701, determining a second multiplication result of a preset flip angle and a waveform of a second basic refocusing pulse, and determining a candidate refocusing pulse according to a ratio of the second multiplication result to the flip angle of the second basic refocusing pulse.

[0091] In the embodiment of the present application, similarly, according to Determine candidate refocusing pulses, where is a preset flip angle, where the preset flip angle is a flip angle greater than or equal to a preset basic flip angle. is the waveform of the second basic refocusing pulse, is the flip angle of the second basic focusing pulse.

[0092] S702, performing simulation processing on the candidate refocusing pulse to obtain a simulated transverse magnetization vector.

[0093] In the embodiment of the present application, the candidate refocusing pulse may be simulated using the Bloch simulation method to obtain a simulated transverse magnetization vector, where the obtained simulated transverse magnetization vector includes an amplitude and a phase of the simulated transverse magnetization vector.

[0094] S703, optimizing the candidate refocusing pulse according to the ideal transverse magnetization vector and the simulated transverse magnetization vector to obtain a second target refocusing pulse; the phase of the ideal transverse magnetization vector is equal to the target phase.

[0095] In the embodiment of the present application, the desired transverse magnetization vector corresponding to the second target refocusing pulse and the simulated transverse magnetization vector obtained above can be used to optimize the candidate refocusing pulse to obtain the second target refocusing pulse. That is, the candidate refocusing pulse is optimized by using the difference between the amplitude of the simulated transverse magnetization vector and the amplitude of the desired transverse magnetization vector, until the difference between the amplitude of the simulated transverse magnetization vector and the amplitude of the desired transverse magnetization vector is less than a preset difference value threshold, or there is no difference between the amplitude of the pseudo-transverse magnetization vector and the amplitude of the desired transverse magnetization vector, thereby obtaining the second target refocusing pulse. For example, the 2-norm distance between the amplitude of the simulated transverse magnetization vector and the amplitude of the desired transverse magnetization vector is calculated, and the scalar error of the candidate refocusing pulse is optimized by using the 2-norm distance to obtain the second target refocusing pulse.

[0096] In the embodiment of the present application, the second product result of the preset flip angle and the waveform of the second basic refocusing pulse is determined, and the candidate refocusing pulse is determined according to the ratio of the second product result to the flip angle of the second basic refocusing pulse, and the candidate refocusing pulse is simulated to obtain a simulated transverse magnetization vector, and the candidate refocusing pulse is optimized according to the ideal transverse magnetization vector and the simulated transverse magnetization vector to obtain the second target refocusing pulse. In the embodiment of the present application, in the large flip angle scenario, the second target refocusing pulse is obtained by scalar multiplication, which reduces the complexity of the design of the second target refocusing pulse, and the candidate refocusing pulse obtained based on the scalar multiplication is optimized by using the ideal transverse magnetization vector and the simulated transverse magnetization vector, which improves the accuracy of the determination of the second target refocusing pulse.

[0097] In one embodiment, the method further includes: acquiring the main magnetic field inhomogeneity and the sensitivity matrix of each transmission channel under the parallel transmission pre-scan; and determining the excitation pulse according to each sensitivity matrix and the main magnetic field inhomogeneity.

[0098] In the embodiment of the present application, the main magnetic field inhomogeneity under the parallel transmission pre-scan is obtained. And the sensitivity matrix B1 Map of each transmitting channel. According to the magnetic field inhomogeneity And each sensitivity matrix, determine the system matrix A can be expressed as .in, is the gyromagnetic ratio, which is approximately equal to 42.576MHz / T1, T1 is the total duration of the excitation pulse, (x, y, z) is the spatial coordinate, and the spatial coordinate is determined based on the acquired sensitivity matrix and the main magnetic field inhomogeneity, (k x , k y , k z ) is the excitation K space (the integration of the gradient waveform with respect to time can be analogously read as K space, which is called the excitation K space).

[0099] according to Determine the excitation pulse , where S is the sensitivity matrix of each emission channel, d is the expected excitation shape, , mask represents the contour information of the scanned object, and R(b1) represents the regularization function for the multi-channel excitation pulse, which is used to constrain SAR.

[0100] Optionally, the pulse waveform of the excitation pulse may be selected from a SPINS path in addition to a kt-points path.

[0101] In an embodiment of the present application, the main magnetic field inhomogeneity and the sensitivity matrix of each transmission channel under the parallel transmission pre-scan are obtained; based on each sensitivity matrix and the main magnetic field inhomogeneity, the excitation pulse is determined, laying the foundation for the subsequent determination of the target refocusing pulse based on the phase of the expected transverse magnetization vector generated by the excitation pulse.

[0102] Figure 8 FIG. 1 is a flow chart of a method for designing a radio frequency pulse for parallel transmission of magnetic resonance in another embodiment. Figure 8 As shown, the following steps are included:

[0103] S801, obtaining the main magnetic field inhomogeneity and the sensitivity matrix of each transmission channel under parallel transmission pre-scan;

[0104] S802, determining an excitation pulse according to each sensitivity matrix and the main magnetic field inhomogeneity;

[0105] S803, acquiring the phase of the expected transverse magnetization vector generated by the excitation pulse;

[0106] S804, taking the sum of the expected transverse magnetization vector phase and the preset phase as the target phase;

[0107] S805, when the preset flip angle is less than the preset basic flip angle, determining a first basic refocusing pulse according to a small flip angle approximation principle and a target phase;

[0108] S806, determining a first product result of a preset flip angle and a waveform of a first basic refocusing pulse, and determining a first target refocusing pulse according to a ratio of the first product result to the flip angle of the first basic refocusing pulse;

[0109] S807, when the preset flip angle is greater than or equal to the preset basic flip angle, determine the second basic refocusing pulse according to the small flip angle approximation principle and the target phase; wherein the pulse duration of the first basic refocusing pulse is smaller than the pulse duration of the second basic refocusing pulse, and the flip angle of the first basic refocusing pulse is smaller than the flip angle of the second basic refocusing pulse;

[0110] S808, determining a second multiplication result of a preset flip angle and a waveform of a second basic refocusing pulse, and determining a candidate refocusing pulse according to a ratio of the second multiplication result to the flip angle of the second basic refocusing pulse;

[0111] S809, performing simulation processing on the candidate focusing pulse to obtain a simulated transverse magnetization vector;

[0112] S810, optimizing the candidate refocusing pulse according to the ideal transverse magnetization vector and the simulated transverse magnetization vector to obtain a second target refocusing pulse; the phase of the ideal transverse magnetization vector is equal to the target phase.

[0113] In the embodiment of the present application, the gradient field waveform is pre-set to be symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis, so that the design of the target refocusing pulse can satisfy the average Hamiltonian principle to achieve the purpose of simplifying the calculation and reduce the complexity of the RF pulse design.

[0114] It should be understood that, although the steps in the flowcharts involved in the above embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above embodiments may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0115] Based on the same inventive concept, the embodiment of the present application also provides a device for designing a radio frequency pulse for parallel transmission of magnetic resonance for implementing the radio frequency pulse design method for parallel transmission of magnetic resonance. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in the embodiments of one or more devices for designing a radio frequency pulse for parallel transmission of magnetic resonance provided below can refer to the limitations of the method for designing a radio frequency pulse for parallel transmission of magnetic resonance above, and will not be repeated here.

[0116] In an exemplary embodiment, Fig. 9 As shown, a radio frequency pulse design device for parallel transmission of magnetic resonance is provided, comprising: a first determination module 11 and a second determination module 12, wherein:

[0117] A first determination module 11 is used to determine a basic refocusing pulse according to a preset flip angle of a target refocusing pulse and a preset basic flip angle in a magnetic resonance sequence;

[0118] A second determination module 12 is used to determine a target refocusing pulse according to a preset flip angle, a waveform of a basic refocusing pulse and a flip angle of the basic refocusing pulse;

[0119] The gradient field waveform in the magnetic resonance sequence is symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis.

[0120] In one embodiment, the first determination module 11 is specifically used to obtain the phase of the expected transverse magnetization vector generated by the excitation pulse in the magnetic resonance sequence; take the sum of the phase of the expected transverse magnetization vector and the preset phase as the target phase; and determine the basic refocusing pulse according to the preset flip angle, the preset basic flip angle and the target phase.

[0121] In one embodiment, the first determination module 11 is specifically used to determine the first basic refocusing pulse according to the small flip angle approximation principle and the target phase when the preset flip angle is less than the preset basic flip angle; and to determine the second basic refocusing pulse according to the small flip angle approximation principle and the target phase when the preset flip angle is greater than or equal to the preset basic flip angle; wherein the pulse duration of the first basic refocusing pulse is less than the pulse duration of the second basic refocusing pulse, and the flip angle of the first basic refocusing pulse is less than the flip angle of the second basic refocusing pulse.

[0122] In one embodiment, the second determination module 12 is specifically used to determine a first product result of a preset flip angle and a waveform of a first basic refocusing pulse; and determine a first target refocusing pulse according to a ratio of the first product result to the flip angle of the first basic refocusing pulse.

[0123] In one embodiment, the second determination module 12 is specifically used to determine a second product result of a preset flip angle and a waveform of a second basic refocusing pulse, and determine a candidate refocusing pulse according to a ratio of the second product result to the flip angle of the second basic refocusing pulse; simulate the candidate refocusing pulse to obtain a simulated transverse magnetization vector; optimize the candidate refocusing pulse according to the ideal transverse magnetization vector and the simulated transverse magnetization vector to obtain a second target refocusing pulse; the phase of the ideal transverse magnetization vector is equal to the target phase.

[0124] In one embodiment, the first determination module 11 is further used to obtain the main magnetic field inhomogeneity and the sensitivity matrix of each transmission channel in the parallel transmission pre-scan; and determine the excitation pulse according to each sensitivity matrix and the main magnetic field inhomogeneity.

[0125] Each module in the above-mentioned RF pulse design device for parallel transmission of magnetic resonance can be implemented in whole or in part by software, hardware and a combination thereof. Each of the above-mentioned modules can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute the operations corresponding to each of the above modules.

[0126] In an exemplary embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps of any of the above method embodiments when executing the computer program.

[0127] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of any of the above method embodiments are implemented.

[0128] In one embodiment, a computer program product is provided, including a computer program, which implements the steps of any of the above method embodiments when executed by a processor.

[0129] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0130] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, an artificial intelligence (AI) processor, etc., but are not limited to this.

[0131] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0132] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for designing radio frequency pulses for parallel transmission of magnetic resonance, characterized in that: The method comprises: Determining a basic refocusing pulse according to a preset flip angle of a target refocusing pulse and a preset basic flip angle in a magnetic resonance sequence; Determining the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse; Wherein, the gradient field waveform in the magnetic resonance sequence is symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis.

2. The method according to claim 1, characterized in that The step of determining the basic refocusing pulse according to the preset flip angle of the target refocusing pulse and the preset basic flip angle in the magnetic resonance sequence comprises: Acquiring the phase of the expected transverse magnetization vector generated by the excitation pulse in the magnetic resonance sequence; taking the sum of the phase of the expected transverse magnetization vector and the preset phase as the target phase; The basic refocusing pulse is determined according to the preset flip angle, the preset basic flip angle and the target phase.

3. The method according to claim 2, characterized in that The basic refocusing pulse includes a first basic refocusing pulse and a second basic refocusing pulse; The step of determining the basic refocusing pulse according to the preset flip angle, the preset basic flip angle and the target phase comprises: In a case where the preset flip angle is smaller than the preset basic flip angle, determining a first basic refocusing pulse according to a small flip angle approximation principle and the target phase; In a case where the preset flip angle is greater than or equal to the preset basic flip angle, determining a second basic refocusing pulse according to a small flip angle approximation principle and the target phase; The pulse duration of the first basic refocusing pulse is smaller than the pulse duration of the second basic refocusing pulse, and the flip angle of the first basic refocusing pulse is smaller than the flip angle of the second basic refocusing pulse.

4. The method according to claim 3, characterized in that The target refocusing pulse includes a first target refocusing pulse, and determining the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse includes: Determine a first product result of the preset flip angle and the waveform of the first basic refocusing pulse; The first target refocusing pulse is determined according to the ratio of the first product result to the flip angle of the first basic refocusing pulse.

5. The method according to claim 3, characterized in that: The target refocusing pulse includes a second target refocusing pulse, and determining the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse includes: Determine a second product result of the preset flip angle and the waveform of the second basic refocusing pulse, and determine a candidate refocusing pulse according to a ratio of the second product result to the flip angle of the second basic refocusing pulse; Performing simulation processing on the candidate refocusing pulse to obtain a simulated transverse magnetization vector; The candidate refocusing pulse is optimized according to the ideal transverse magnetization vector and the simulated transverse magnetization vector to obtain the second target refocusing pulse; the phase of the ideal transverse magnetization vector is equal to the target phase.

6. The method according to claim 2, characterized in that The method further comprises: Obtain the main magnetic field inhomogeneity and the sensitivity matrix of each transmission channel under parallel transmission pre-scan; The excitation pulse is determined according to each of the sensitivity matrices and the main magnetic field inhomogeneity.

7. A radio frequency pulse design device, characterized in that: The device comprises: A first determination module is used to determine a basic refocusing pulse according to a preset flip angle of a target refocusing pulse and a preset basic flip angle in a magnetic resonance sequence; A second determination module, configured to determine the target refocusing pulse according to the preset flip angle, the waveform of the basic refocusing pulse and the flip angle of the basic refocusing pulse; Wherein, the gradient field waveform in the magnetic resonance sequence is symmetrical along the center of the time axis, and the pulse waveform of the target refocusing pulse is symmetrical along the time axis.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

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