A parallel transmission radio frequency sub-pulse sequence generation method, device and storage medium

Abstract

This application relates to a method for generating parallel-transmitted radio frequency (RF) sub-pulse sequences. The method includes: acquiring a first parallel-transmitted RF sub-pulse sequence, which is generated based on a basic parallel-transmitted RF sub-pulse sequence; constructing a pulse sequence optimization function based on the first parallel-transmitted RF sub-pulse sequence; determining an apodization factor based on the pulse sequence optimization function; and generating a second parallel-transmitted RF sub-pulse sequence based on the basic first parallel-transmitted RF sub-pulse sequence and the apodization factor. This application solves the problem in related technologies where, during actual scanning using a fixed time-varying gradient, the main magnetic field in some human body regions is non-uniform, achieving a better goal of exciting a uniform field.

Description

Technical Field

[0001] This application relates to the field of magnetic resonance technology, and in particular to a method, apparatus and storage medium for generating parallel radio frequency sub-pulse sequences. Background Technology

[0002] Currently, imaging examinations, as an indispensable medical aid in clinical diagnosis and treatment, mainly include X-rays, ultrasound, CT scans, and magnetic resonance imaging (MRI). MRI, as a cutting-edge medical imaging technology, offers several advantages over other imaging methods, including: 1. High contrast for soft tissues; 2. No radiation; 3. Non-invasive; 4. Accurate images can be obtained by setting parameters for different tissues. Based on these advantages, in clinical practice, it can assist doctors in more accurately diagnosing patients.

[0003] An MRI system, as a novel high-tech medical device, has a complex and precise internal structure. Its basic components include: a magnet system, gradient coils, radio frequency coils, a spectrometer, and a computer. The spectrometer is the main part of the MRI system. Its functions include: system timing control, sequence execution, gradient pulse generation, and radio frequency pulse generation and reception.

[0004] In the process of magnetic resonance ultra-high field imaging, the multi-channel transmission of radio frequency pulses causes the problem of non-uniformity of the transmission field. While applying parallel transmission pulses, it is necessary to apply time-varying gradients in different directions to improve the uniformity of the transmission field.

[0005] Existing technologies often employ a fixed time-varying gradient and a fixed fundamental RF pulse waveform, followed by optimization of the RF pulse amplitude and phase factors. Current methods commonly use pre-designed gradient waveforms, and then design the amplitude and phase factors for each segment of the multi-channel parallel transmission pulse based on these waveforms. However, they do not consider the RF pulse apodization factor, which may require adjustment, thus limiting their effectiveness in correcting main magnetic field inhomogeneities.

[0006] However, in actual scanning, some areas of the human body (such as the frontal lobe and nasal cavity) have uneven main magnetic fields, and the parallel emission pulses obtained based on traditional methods often cannot achieve good results.

[0007] There is currently no effective solution to the problem that the main magnetic field is uneven in some human body areas when using a fixed time-varying gradient in the actual scanning process. Summary of the Invention

[0008] This embodiment provides a method, apparatus, computer device, and computer-readable storage medium for generating parallel radio frequency sub-pulse sequences to solve the problem in related technologies where, when using a fixed time-varying gradient, the main magnetic field is uneven in some human body areas during actual scanning.

[0009] In a first aspect, this embodiment provides a method for generating parallel transmission radio frequency sub-pulse sequences. The method includes: obtaining a first parallel transmission radio frequency sub-pulse sequence, wherein the first parallel transmission radio frequency sub-pulse sequence is generated based on a parallel transmission radio frequency sub-pulse base sequence; constructing a pulse sequence optimization function based on the first parallel transmission radio frequency sub-pulse sequence; determining an apodization factor based on the pulse sequence optimization function; and generating a second parallel transmission radio frequency sub-pulse sequence based on the first parallel transmission radio frequency sub-pulse base sequence and the apodization factor.

[0010] In some embodiments, constructing a pulse sequence optimization function based on the first parallel transmit radio frequency sub-pulse sequence includes: obtaining a three-dimensional mapping of the test object; setting an expected local excitation state; and generating the pulse sequence optimization function based on the three-dimensional mapping, the expected local excitation state, and the first parallel transmit radio frequency sub-pulse sequence.

[0011] In some embodiments, generating the pulse sequence optimization function based on the three-dimensional mapping, the expected local excitation state, and the first parallel transmitted radio frequency sub-pulse sequence includes: using a minimization criterion to generate the pulse sequence optimization function based on the three-dimensional mapping, the expected local excitation state, and the first parallel transmitted radio frequency sub-pulse sequence.

[0012] In some embodiments, determining the apodization factor based on the pulse sequence optimization function includes: generating a third parallel transmit radio frequency sub-pulse sequence based on the pulse sequence optimization function; and determining the apodization factor based on the third parallel transmit radio frequency sub-pulse sequence.

[0013] In some embodiments, generating a third parallel transmission radio frequency sub-pulse sequence based on the pulse sequence optimization function includes: solving the pulse sequence optimization function using the conjugate gradient method; and determining the third parallel transmission radio frequency sub-pulse sequence based on the solution result of the pulse sequence optimization function.

[0014] In some embodiments, determining the apodization factor based on the third parallel transmit radio frequency sub-pulse sequence includes: obtaining the amplitude factor and phase factor of the third parallel transmit radio frequency sub-pulse sequence; and determining the apodization factor based on the amplitude factor and phase factor of the third parallel transmit radio frequency sub-pulse sequence.

[0015] In some embodiments, determining the apodization factor based on the amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence includes: obtaining the derivative of the pulse sequence optimization function; and determining the apodization factor based on the amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence and the derivative of the pulse sequence optimization function.

[0016] Secondly, this embodiment provides a parallel transmission radio frequency sub-pulse sequence generation apparatus, the apparatus comprising: an acquisition module for acquiring a first parallel transmission radio frequency sub-pulse sequence, the first parallel transmission radio frequency sub-pulse sequence being generated based on a parallel transmission radio frequency sub-pulse base sequence; a construction module for constructing a pulse sequence optimization function based on the first parallel transmission radio frequency sub-pulse sequence; a determination module for determining an apodization factor based on the pulse sequence optimization function; and a generation module for generating a second parallel transmission radio frequency sub-pulse sequence based on the first parallel transmission radio frequency sub-pulse base sequence and the apodization factor.

[0017] Thirdly, this embodiment provides a computer device including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the parallel transmission radio frequency sub-pulse sequence generation method described in the first aspect above.

[0018] Fourthly, this embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the parallel transmission radio frequency sub-pulse sequence generation method described in the first aspect above.

[0019] Compared with related technologies, the parallel transmission radio frequency sub-pulse sequence generation method, apparatus, and storage medium provided in this embodiment obtain a first parallel transmission radio frequency sub-pulse sequence, which is generated based on a parallel transmission radio frequency sub-pulse base sequence; construct a pulse sequence optimization function based on the first parallel transmission radio frequency sub-pulse sequence; determine an apodization factor based on the pulse sequence optimization function; and generate a second parallel transmission radio frequency sub-pulse sequence based on the first parallel transmission radio frequency sub-pulse base sequence and the apodization factor. This solves the problem in related technologies where the main magnetic field is not uniform in some human body areas during actual scanning when using a fixed time-varying gradient, thus achieving a more uniform radio frequency excitation field.

[0020] Details of one or more embodiments of this application are set forth in the following drawings and description to make other features, objects and advantages of this application more readily apparent. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0022] Figure 1 This is a schematic diagram of the structure of a magnetic resonance imaging system according to this embodiment;

[0023] Figure 2 This is a flowchart of a parallel transmission radio frequency sub-pulse sequence generation method according to this embodiment;

[0024] Figure 3 This is a flowchart of a magnetic resonance parallel emission pulse generation method according to a preferred embodiment;

[0025] Figure 4 This is a flowchart of another magnetic resonance parallel emission pulse generation method according to this preferred embodiment;

[0026] Figure 5 This is a structural block diagram of a parallel transmission radio frequency sub-pulse sequence generation device according to this embodiment. Detailed Implementation

[0027] To better understand the purpose, technical solution, and advantages of this application, the application is described and illustrated below in conjunction with the accompanying drawings and embodiments.

[0028] Unless otherwise defined, the technical or scientific terms used in this application shall have the general meaning as understood by one of ordinary skill in the art to which this application pertains. Words such as “a,” “an,” “an,” “the,” “the,” and “these,” used in this application, do not indicate quantitative limitation and may be singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that comprises a series of steps or modules (units) is not limited to the listed steps or modules (units) but may include steps or modules (units) not listed, or may include other steps or modules (units) inherent to such processes, methods, products, or devices. The terms “connected,” “linked,” and “coupled,” used in this application, are not limited to physical or mechanical connections but may include electrical connections, whether direct or indirect. The term “multiple” used in this application refers to two or more. The "and / or" operator describes the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: A alone, A and B simultaneously, and B alone. Typically, the character " / " indicates that the objects before and after it are in an "or" relationship. The terms "first," "second," and "third," etc., used in this application are merely for distinguishing similar objects and do not represent a specific ordering of the objects.

[0029] This embodiment provides a magnetic resonance imaging system. Figure 1 This is a schematic diagram of the structure of a magnetic resonance imaging system according to this embodiment. In this embodiment, a multi-channel magnetic resonance imaging system is used as an example. A multi-channel magnetic resonance imaging system is based on multiple independent transmit coils, utilizing multiple channels to independently transmit radio frequency pulses and excite the sample through the coils, thereby acquiring different echo signals. For example... Figure 1 As shown, the magnetic resonance imaging system includes: a computer 10, a display 20, a memory 30, a pulse program generator 40, a transmit channel 50, a receive channel 60, a magnet 70, a gradient coil 80, a radio frequency coil 90, a gradient driver 100, and a gradient controller 110.

[0030] The gradient coil 80 is arranged around the magnet 70 and consists of three sets of coils arranged according to the three basic layers of X, Y and Z. It can provide any frequency-coded gradient, phase-coded gradient and layer-selective gradient.

[0031] Start the number of radio frequency transmission channels 50 corresponding to the radio frequency target pulse waveform, and use the radio frequency transmission channels to simultaneously transmit the frequency-adjusted radio frequency target pulse waveform.

[0032] In a magnetic resonance imaging (MRI) system, the radio frequency (RF) magnetic field superimposed on the radio frequency (RF) coil and perpendicular to the main magnetic field B0 is called a radio frequency pulse (RF pulse). RF pulses with specified parameters are emitted to drive the RF coil and generate the RF magnetic field, which is usually referred to as the Bt field in MRI. RF pulses have specific frequency, amplitude, and bandwidth (frequency range). The center position and bandwidth of the RF frequency are crucial for MRI, being essential parameters for spatial localization and achieving the required contrast. Therefore, for the RF generation system in MRI, parameters such as pulse intensity, duration, and interval significantly affect the quality of MRI imaging. In this embodiment, the RF pulse used is a slice-selective RF pulse, also known as a soft pulse. Typical soft pulses include Sinc-type pulses and Gaussian-type pulses. Within a certain frequency range, it maintains a specific RF intensity B1.

[0033] Preferably, in this embodiment, the multi-channel independent transmission of RF pulses can be achieved by using a DAC to output multiple RF pulse signals with independently adjustable phase, frequency, and amplitude in parallel. Furthermore, leveraging the flexibility of FPGA development and the advantages of its built-in IP core reduces the complexity and cost of system design. Using an FPGA to implement DDS functionality and RF waveform modulation, and employing independent high-performance DACs to output multiple RF signals in parallel, provides excellent flexibility in design and high-performance DAC selection. The IP core provided by the FPGA chip facilitates the implementation of DDS and modulation waveform functions, reducing the difficulty and cost of solution design and implementation; and enables the parallel output of multiple RF signals with independently adjustable phase, frequency, and amplitude.

[0034] This embodiment provides a method for generating parallel transmission radio frequency sub-pulse sequences. This embodiment uses the application of this method to a terminal as an example for illustration. It can be understood that this method can also be applied to a server, and can also be applied to a system including a terminal and a server, and can be implemented through the interaction between the terminal and the server. Figure 2 This is a flowchart of a parallel transmission radio frequency sub-pulse sequence generation method according to this embodiment, as follows: Figure 2 As shown, the process includes the following steps:

[0035] Step S202: Obtain the first parallel transmission radio frequency sub-pulse sequence, which is generated based on the parallel transmission radio frequency sub-pulse base sequence.

[0036] Specifically, upon power-on, the RF coils transmit a basic RF sub-pulse sequence in parallel. This basic sequence can be a commonly used one, such as a Spin Echo sequence, Gradient Echo sequence, or Inversion Recovery sequence, or it can be a custom-designed sequence. Based on the hardware parameters and the basic sequence, the sub-pulse sequence to be transmitted by each RF coil is calculated, including the RF waveform and phase encoding. The initial sub-pulse sequence transmitted by each RF coil is the basic RF sub-pulse sequence. The basic RF sub-pulse sequences of each RF coil are combined into a parallel-transmitted RF sub-pulse sequence. This combination can be achieved using methods such as linear combination or square root weighting. Parallel transmission refers to the process of different RF pulse waveforms being transmitted by different transmission channels of the RF coils. As needed, the above steps can be repeated to generate multiple parallel-transmitted RF sub-pulse sequences to further improve imaging quality and efficiency.

[0037] Furthermore, if the basic waveform of each radio frequency subpulse basic sequence is set as x(t), then the waveform actually used to control the generated parallel transmission radio frequency subpulse sequence is: X(t). The computer generates the first parallel transmission radio frequency subpulse sequence based on the parallel radio frequency subpulse basic sequence by introducing an apodization factor. The first parallel transmission radio frequency subpulse sequence is generated based on the radio frequency subpulse basic sequence and the apodization factor: b1(α,t)=m(α,t)·X(t), where α represents the apodization factor.

[0038] Furthermore, in magnetic resonance imaging (MRI) systems, pulse sequences are used to excite and probe magnetic resonance signals. Pulse sequence optimization aims to obtain high-quality images. The apodization factor α is a parameter of the radio frequency sub-pulse, referring to the degree of correction applied to the fundamental waveform after apodization. When optimizing the pulse sequence, the signal intensity can be controlled by adjusting the apodization factor, thereby achieving better image quality.

[0039] Step S204: Construct a pulse sequence optimization function based on the first parallel transmitted radio frequency sub-pulse sequence.

[0040] Specifically, the computer constructs a pulse sequence optimization function to optimize the first parallel transmitted radio frequency sub-pulse sequence. The pulse sequence optimization function adopts an optimization algorithm, which can improve imaging quality and efficiency.

[0041] In some embodiments, constructing a pulse sequence optimization function based on a first parallel transmit radio frequency sub-pulse sequence includes: obtaining a three-dimensional mapping of the test object; setting an expected local excitation state; and generating a pulse sequence optimization function based on the three-dimensional mapping, the expected local excitation state, and the first parallel transmit radio frequency sub-pulse sequence.

[0042] Specifically, the spectrometer pre-scans the test object to obtain a 3D B1map. The B1map acquires the overall 3D contour of the object, obtaining information on the contour and the distribution of the excitation field (generated by radio frequency). Obtaining the 3D B1map allows for a better understanding of the test object's morphology and structure, facilitating the design of optimized pulse sequences. The pulse sequence optimization function includes information from the 3D B1map. The spectrometer sets the expected local excitation state and generates the pulse sequence optimization function based on the 3D B1map, the expected local excitation state, and the first parallel-transmitted radio frequency sub-pulse sequence.

[0043] In some embodiments, generating a pulse sequence optimization function based on a three-dimensional mapping, a anticipated local excitation state, and a first parallel transmit radio frequency sub-pulse sequence includes: using a minimization criterion to generate a pulse sequence optimization function based on a three-dimensional mapping, a anticipated local excitation state, and a first parallel transmit radio frequency sub-pulse sequence.

[0044] Specifically, the pulse sequence optimization function can be as follows:

[0045]

[0046] Where argmin(·) is the minimum function, A is the system matrix, and A=iγexp(i2π(xk) x +yk y +zk z +Δω(tT))), where exp is an exponential function with base e, T is the pulse duration, k=∫g(t)dt, and the corresponding k x =∫g x (t)dt,k y =∫g y (t)dt,k z =∫g z (t)dt, g(t) is the gradient waveform, b is the desired RF pulse, W is the weight matrix used to balance the weights of the excitation region and the non-excitation region, S is the acquired B1 map, λ is the regularization coefficient, such as the number 8, d is the expected shape of the local excitation, which is determined by the selected shape mask and the folding angle θ: d=mask·sinθ.

[0047] Step S206: Determine the apodization factor based on the pulse sequence optimization function.

[0048] Specifically, the apodization factor α is determined based on the pulse sequence optimization function, including: iteratively optimizing the first parallel transmitted radio frequency sub-pulse sequence using the conjugate gradient method, setting the total number of iterations, and obtaining the third parallel transmitted radio frequency sub-pulse sequence. The amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence can be obtained based on the third parallel transmitted radio frequency sub-pulse sequence. The apodization factor can be obtained based on the pulse sequence optimization function, the amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence. Furthermore, the first parallel transmission RF sub-pulse sequence is generated from each RF sub-pulse base sequence x(t), and the resulting parallel transmission RF sub-pulse sequence X(t) is generated by introducing an apodization factor, resulting in b1(α,t) = m(α,t)·X(t). The second parallel transmission RF sub-pulse sequence is obtained by constructing a pulse sequence optimization function based on the first parallel transmission RF sub-pulse sequence, and obtaining a unique apodization factor. In the process of calculating the unique apodization factor, the pulse sequence optimization function is iteratively optimized, and the number of iterations is set. The resulting parallel transmission RF sub-pulse sequence is the third parallel transmission RF sub-pulse sequence. That is, the second parallel transmission RF sub-pulse sequence is obtained by obtaining a unique apodization factor based on the third parallel transmission RF sub-pulse sequence.

[0049] Furthermore, taking the first parallel transmitted radio frequency sub-pulse sequence b1(α,t) as a Sinc function as an example, b1(α,t) can be expressed as:

[0050] b1(α,t)=at0[(1-α)+αcos(πt\Nt0)]sin(πt / t0) / (πt) (b)

[0051] In some embodiments, determining the apodization factor based on the amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence includes: obtaining the derivative of the pulse sequence optimization function; and determining the apodization factor based on the amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence and the derivative of the pulse sequence optimization function.

[0052] Specifically, by taking the derivative of the pulse sequence optimization function with respect to the apodization factor α, we obtain the derivative function of the pulse sequence optimization function. The derivative function can be expressed as:

[0053]

[0054] The first derivative Since it is independent of the apodization factor α, a unique set of apodization factors can be obtained based on the amplitude factor and phase factor of the fixed third parallel transmit RF sub-pulse sequence.

[0055] Step S208: Generate a second parallel transmission radio frequency subpulse sequence based on the first parallel transmission radio frequency subpulse basic sequence and the apodization factor.

[0056] Specifically, according to steps S202 to S206, a unique set of apodization factors is obtained. After obtaining the unique set of apodization factors, the base waveforms of different sub-pulses of different channels are changed according to the apodization factors to obtain the radio frequency sub-pulse waveforms of different sub-pulses of different channels. The radio frequency sub-pulse waveforms of different sub-pulses of different channels are processed in parallel to obtain the second parallel transmission radio frequency sub-pulse sequence.

[0057] Through the above steps, a first parallel-transmitted radio frequency sub-pulse sequence is obtained, which is generated based on the parallel-transmitted radio frequency sub-pulse base sequence; a pulse sequence optimization function is constructed based on the first parallel-transmitted radio frequency sub-pulse sequence; an apodization factor is determined based on the pulse sequence optimization function; and a second parallel-transmitted radio frequency sub-pulse sequence is generated based on the parallel-transmitted radio frequency sub-pulse base sequence and the apodization factor. This solves the problem in related technologies where the main magnetic field is not uniform in some human body areas during actual scanning when using a fixed time-varying gradient, thus achieving the goal of better exciting a uniform field.

[0058] The present embodiment will now be described and illustrated through preferred embodiments.

[0059] Figure 3 This is a flowchart of a method for generating parallel emission pulses in magnetic resonance according to a preferred embodiment of this invention. Figure 3 As shown, the method for generating parallel emission pulses in magnetic resonance includes the following steps:

[0060] Step S302: Select the gradient waveform pre-RF pulse base waveform.

[0061] Specifically, if the base waveform for each channel is set to x(t), then the actual RF sub-pulse waveform used to control the generation is:

[0062] b2(α,t)=m(α,t)·x(t) (d)

[0063] Where x(t) represents the original radio frequency subpulse waveform, m(α,t) represents the modulation function, where α represents the adjustable apodization factor. By adjusting different apodization factors, different radio frequency subpulse waveforms are generated.

[0064] Step S304: Optimize and obtain the amplitude factor and phase factor of each parallel transmission sub-pulse.

[0065] Specifically, in the design of parallel transmit pulses, a series of radio frequency (RF) sub-pulses is often used, where RF sub-pulses are applied sequentially at fixed intervals, while a fixed time-varying gradient is applied on different axes. In this scenario, the optimization process for parallel transmit pulses involves jointly optimizing the waveforms, amplitude factors, and phase factors of different RF sub-pulses. The optimization function expression is as follows:

[0066]

[0067] A = exp(i2π(xk) x +yk y +zk z +Δω(tT))) (f)

[0068] k=∫g(t)dt (g)

[0069] Where argmin(·) is the minimum function, b is the radio frequency pulse, k is the final obtained three-dimensional excitation K-space, A is the system matrix, determined by the gradient waveform and main magnetic field inhomogeneity generated in each iteration, S is the acquired three-dimensional B1 map, the smoothness of the three-dimensional B1 map needs to be adjustable in actual iteration, and λ is the regularization coefficient, usually the number 8 is used. The weighted 2-norm is represented by the weighting matrix W, where W is the weight matrix used to balance the weights of the excitation and non-excitation regions, and ||·||2 is the 2-norm. d represents the expected shape of the local excitation, determined by the selected shape mask and the fold angle θ. Specifically, d can be obtained using formula (e).

[0070] d = mask·sinθ (h)

[0071] Select the RF pulse waveform and gradient waveform for each channel of the base layer. Set the parallel transmission gradient path to "5-spokes", with the z-direction gradient used for layer selection and the x and y-direction gradients used for the excitation field within the uniform layer. Set each channel's RF pulse to consist of 5 sub-pulses, each sub-pulse corresponding one-to-one with the plateau period of the layer selection gradient. Set the base waveform for the sub-pulses to the Sinc waveform; then the Sinc function expression is:

[0072] b2(t)=at0[(1-α)+αcos(πt\Nt0)]sin(πt / t0) / (πt) (i)

[0073] b2(α,t)=m(α,t)·x(t) (j)

[0074] Where α represents the apodization factor, t0 is the reciprocal of the pulse bandwidth, a is the amplitude, N is the larger of the number of zero crossings to the left and right of the pulse center, and the initial value of the apodization factor is set to 0.

[0075] Furthermore, with a preset total number of iterations, the amplitude factor and phase factor of each sub-pulse in each channel are optimized using the conjugate gradient method. The amplitude of the function, i.e., the amplitude factor in this embodiment, and the phase of the function, i.e., the phase factor in this embodiment, can be clearly obtained from the function expression of the sub-pulse.

[0076] Step S306: Optimize the apodization factor for each channel and each sub-pulse.

[0077] Specifically, after optimizing the amplitude factor and phase factor of each parallel transmission sub-pulse in step S304, the amplitude factor and phase factor of each sub-pulse in each channel are fixed, and the first derivative of the optimization function with respect to the apodization factor is calculated.

[0078] Specifically, first, with a preset total number of iterations, the amplitude and phase factors of each sub-pulse segment in each channel are optimized using the conjugate gradient method. Then, with the amplitude and phase factors of each sub-pulse segment in each channel fixed, the first derivative of the optimization function with respect to the apodization factor is calculated:

[0079]

[0080] The first derivative is independent of the apodization factor, so a unique set of apodization factors can be obtained based on the fixed magnitude factor and phase factor.

[0081] Step S308: Jointly adjust the apodization factor, amplitude factor and phase factor of each sub-pulse of each channel.

[0082] Specifically, after obtaining the apodization factor, the base waveforms of different sub-pulses in different channels are changed according to the apodization factor, and then the amplitude factor and phase factor of different sub-pulses in different channels are recalculated.

[0083] By jointly adjusting the apodization factor, amplitude factor, and phase factor of each sub-pulse in each channel, a better uniform field can be excited.

[0084] In one embodiment, such as Figure 4 The diagram provided illustrates a flowchart of a magnetic resonance radio frequency pulse sequence generation method according to a preferred embodiment of the present invention. In this embodiment, the method includes the following steps:

[0085] Step S402: Design the gradient RF basic waveform.

[0086] Specifically, the gradient waveform and RF pulses of which number of sub-RF pulses should be used can be determined according to the specific application. If the sequence is 3D volume excitation, hard pulses can be selected as the sub-RF pulses; if the function is 2D layer selection, Sinc, SLR, Gauss pulses, etc. can be selected as the sub-RF pulses; if it is a gradient waveform in the corresponding layer direction, a rectangular waveform should be selected; if the function is 3D slab (3D layer block excitation, i.e., three-dimensional excitation of a relatively thick layer), Sinc, SLR, Gauss pulses, etc. can be selected as the sub-RF pulses, and the corresponding z-direction gradient waveform is a rectangular wave or a triangular waveform.

[0087] Step S404: Add a delay factor and an apodization factor to generate an RF waveform.

[0088] Specifically, different delay factors β are added for different RF sub-pulses. After adding the delay factor, the expression for the RF sub-pulse is:

[0089] b3(α,β,t)=at0[(1-α)+αcos(πt\Nt0)]sin(π(t-β) / t0) / (π(t-β)) (l)

[0090] Step S406: Construct the optimization function and determine the number of iterations M.

[0091] Specifically, the optimization function then becomes:

[0092]

[0093] Step S408: Perform conjugate gradient calculation to obtain the magnitude factor and phase factor after iteration.

[0094] Specifically, the total number of iterations is preset, and the amplitude factor and phase factor of each sub-pulse in each channel are optimized using the conjugate gradient method. The number of calculations, n, is then counted.

[0095] Step S410: Determine whether the number of calculations n in step S408 has reached the number of iterations M. If yes, proceed to step S412; otherwise, proceed to step S408.

[0096] Specifically, determine whether the number of calculations n in step S408 has reached the number of iterations M. If the number of calculations n is less than the number of iterations M, then continue to execute step S408 to calculate the amplitude factor and phase factor after iteration; otherwise, execute step S412.

[0097] Step S412: Optimize the apodization factor and delay factor of the first radio frequency waveform.

[0098] Specifically, based on the calculated amplitude and phase factors obtained after the iteration when the number of calculations reaches M, the amplitude and phase factors of each sub-pulse in each channel are then fixed, and the first derivative of the optimization function with respect to the apodization factor is calculated:

[0099]

[0100] The first derivative is independent of the apodization factor and the delay factor. Therefore, the apodization factor and delay factor of the first radio frequency waveform are optimized based on the fixed amplitude factor and phase factor.

[0101] Step S414: Substitute the sequence into the scan.

[0102] Specifically, an optimized radio frequency pulse sequence can be obtained based on the apodization factor and delay factor of the first radio frequency waveform, and the optimized radio frequency pulse sequence is substituted into the sequence for scanning.

[0103] In the design of parallel-emission excitation layer selection pulses, a common scenario is that the excitation pulses are symmetrical, in which case the application time of the excitation pulses coincides perfectly with the plateau period of the layer selection gradient. However, this design cannot completely solve the problem of non-uniform RF excitation field.

[0104] By adjusting the amplitude factor, phase factor, apodization factor, and time delay factor of different radio frequency sub-pulses, the goal of deeply optimizing the radio frequency transmission field can be achieved.

[0105] It should be noted that the specific limitations of the above steps can be found in the specific limitations of a magnetic resonance pulse sequence generation method described above, and will not be repeated here.

[0106] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they may be executed in other orders. Moreover, at least some of the steps in the flowcharts of the embodiments described above may include...

[0107] It should be noted that the steps shown in the above process or in the flowchart of the accompanying figures can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0108] This embodiment also provides a parallel transmission radio frequency sub-pulse sequence generation device, which is used to implement the above embodiments and preferred embodiments, and will not be repeated as described previously. The terms "module," "unit," "subunit," etc., used below can refer to a combination of software and / or hardware that performs a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0109] Figure 5 This is a structural block diagram of a parallel transmission radio frequency sub-pulse sequence generation device according to this embodiment, as shown below. Figure 5 As shown, the generating apparatus includes:

[0110] The acquisition module 510 is used to acquire the first parallel transmission radio frequency sub-pulse sequence, which is generated based on the parallel transmission radio frequency sub-pulse base sequence.

[0111] The construction module 520 is used to construct a pulse sequence optimization function based on the first parallel transmitted radio frequency sub-pulse sequence;

[0112] The determination module 530 is used to determine the apodization factor based on the pulse sequence optimization function;

[0113] The generation module 540 is used to generate a second parallel transmission radio frequency subpulse sequence based on the basic sequence of parallel transmission radio frequency subpulses and the apodization factor.

[0114] It should be noted that the above modules can be functional modules or program modules, and can be implemented through software or hardware. For modules implemented through hardware, the above modules can reside in the same processor; or the above modules can be located in different processors in any combination.

[0115] This embodiment also provides an electronic device including a memory and a processor, the memory storing a computer program and the processor being configured to run the computer program to perform the steps in any of the above method embodiments.

[0116] Optionally, the electronic device may further include a transmission device and an input / output device, wherein the transmission device is connected to the processor and the input / output device is connected to the processor.

[0117] Optionally, in this embodiment, the processor can be configured to perform the following steps via a computer program:

[0118] S1, Obtain the first parallel transmission radio frequency sub-pulse sequence, which is generated based on the parallel transmission radio frequency sub-pulse base sequence.

[0119] S2, construct a pulse sequence optimization function based on the first parallel transmitted radio frequency sub-pulse sequence.

[0120] S3. Determine the apodization factor based on the pulse sequence optimization function.

[0121] S4. Generate a second parallel transmission radio frequency sub-pulse sequence based on the basic sequence of parallel transmission radio frequency sub-pulses and the apodization factor.

[0122] It should be noted that the specific examples in this embodiment can refer to the examples described in the above embodiments and optional implementations, and will not be repeated in this embodiment.

[0123] Furthermore, in conjunction with the parallel transmission radio frequency sub-pulse sequence generation method provided in the above embodiments, this embodiment can also provide a storage medium for implementation. The storage medium stores a computer program; when executed by a processor, the computer program implements any of the parallel transmission radio frequency sub-pulse sequence generation methods in the above embodiments.

[0124] It should be understood that the specific embodiments described herein are merely illustrative of the application and not intended to limit it. All other embodiments derived by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0125] Obviously, the accompanying drawings are merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar situations based on these drawings without any creative effort. Furthermore, it is understood that although the work done in this development process may be complex and lengthy, for those skilled in the art, certain design, manufacturing, or production modifications made based on the technical content disclosed in this application are merely conventional technical means and should not be considered as insufficient disclosure of this application.

[0126] The term "embodiment" in this application refers to a specific feature, structure, or characteristic described in connection with an embodiment that may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily imply the same embodiment, nor does it imply that it is mutually exclusive with or independent of other embodiments. It will be clearly or implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0127] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of patent protection. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. A method for generating parallel transmission radio frequency sub-pulse sequences, characterized in that, The method includes: Obtain a first parallel transmission radio frequency sub-pulse sequence, which is generated based on the parallel transmission radio frequency sub-pulse base sequence; Based on the first parallel transmitted radio frequency sub-pulse sequence, construct a pulse sequence optimization function; The apodization factor is determined based on the pulse sequence optimization function. A second parallel transmission radio frequency subpulse sequence is generated based on the basic sequence of the parallel transmission radio frequency subpulse and the apodization factor; The step of determining the apodization factor based on the pulse sequence optimization function includes: Based on the pulse sequence optimization function, a third parallel transmission radio frequency sub-pulse sequence is generated; Obtain the amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence; Obtain the derivative of the pulse sequence optimization function; The apodization factor is determined based on the amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence and the derivative of the pulse sequence optimization function.

2. The method for generating parallel transmission radio frequency sub-pulse sequences according to claim 1, characterized in that, The step of constructing a pulse sequence optimization function based on the first parallel transmitted radio frequency sub-pulse sequence includes: Obtain a 3D mapping of the test object; Set the desired local excitation state; The pulse sequence optimization function is generated based on the three-dimensional mapping, the expected local excitation state, and the first parallel transmission radio frequency sub-pulse sequence.

3. The parallel transmission radio frequency sub-pulse sequence generation method according to claim 2, characterized in that, The step of generating the pulse sequence optimization function based on the three-dimensional mapping, the expected local excitation state, and the first parallel transmission radio frequency sub-pulse sequence includes: The pulse sequence optimization function is generated based on the minimization criterion, the three-dimensional mapping, the expected local excitation state, and the first parallel transmission radio frequency sub-pulse sequence.

4. The method for generating parallel transmission radio frequency sub-pulse sequences according to claim 1, characterized in that, The step of generating the third parallel transmission radio frequency sub-pulse sequence according to the pulse sequence optimization function includes: The conjugate gradient method is used to solve the pulse sequence optimization function; The third parallel transmission radio frequency sub-pulse sequence is determined based on the solution result of the pulse sequence optimization function.

5. A parallel transmission radio frequency sub-pulse sequence generation device, characterized in that, The device includes: The acquisition module is used to acquire a first parallel transmission radio frequency sub-pulse sequence, which is generated based on the parallel transmission radio frequency sub-pulse base sequence. The construction module is used to construct a pulse sequence optimization function based on the first parallel transmitted radio frequency sub-pulse sequence; The determining module is configured to determine an apodization factor based on the pulse sequence optimization function; wherein, determining the apodization factor based on the pulse sequence optimization function includes: Based on the pulse sequence optimization function, a third parallel transmission radio frequency sub-pulse sequence is generated; Obtain the amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence; Obtain the derivative of the pulse sequence optimization function; The apodization factor is determined based on the amplitude factor and phase factor of the third parallel transmitted radio frequency sub-pulse sequence and the derivative of the pulse sequence optimization function; The generation module is used to generate a second parallel transmission radio frequency subpulse sequence based on the basic sequence of the parallel transmission radio frequency subpulse and the apodization factor.

6. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 4.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the parallel transmission radio frequency sub-pulse sequence generation method according to any one of claims 1 to 4.

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