Compensation methods, devices, electronic equipment and media in magnetic resonance imaging systems

Abstract

This application provides a compensation method, apparatus, electronic device, and medium in a magnetic resonance imaging (MRI) system. The method includes: acquiring a first characteristic parameter of an ideal gradient waveform and a second characteristic parameter of a target vortex; shifting the magnetic resonance center frequency from a first frequency to a second frequency; calculating a second amplitude parameter of the compensation waveform of the target vortex at each target time point based on the first and second characteristic parameters; inputting the compensation frequency to a first phase accumulator to output a first phase; inputting the first frequency to a second phase accumulator to output a second phase; the compensation frequency is determined based on the compensation waveform; querying a sine and cosine lookup table for the sine and cosine signals corresponding to the target phase; the target phase is the sum of the first and second phases; modulating a radio frequency pulse signal using a cosine signal; and demodulating the magnetic resonance signal using the sine and cosine signals. This method helps to avoid artifacts in the image.

Description

Technical Field

[0001] This application relates to the field of magnetic resonance imaging technology, and in particular to a compensation method, apparatus, electronic device and medium in a magnetic resonance imaging system. Background Technology

[0002] The magnetic fields used in magnetic resonance imaging (MRI) systems include two types: the main magnetic field, which is uniformly distributed in space and is a fundamental condition for generating magnetic resonance signals; and the gradient magnetic field, which is a changing magnetic field. During the scanning process, the gradient magnetic field switches rapidly, inducing changing currents in surrounding conductors, forming eddy currents. Eddy currents typically contain higher-order terms, constant terms, and first-order terms, with the constant term often referred to as the B0 eddy current. The magnetic resonance center frequency is determined by the field strength of the main magnetic field, but the B0 eddy currents cause a time-varying shift in the magnetic resonance center frequency, which can lead to image artifacts.

[0003] In existing technologies, to avoid image artifacts caused by shifts in the magnetic resonance center frequency, a B0 eddy current compensation coil is typically added to the main magnetic field. The B0 eddy current compensation coil generates a B0 eddy current compensation magnetic field. Since the magnetic resonance center frequency is proportional to the magnetic field strength, changing the field strength of the main magnetic field through the B0 eddy current compensation coil also changes the magnetic resonance center frequency of the main magnetic field, thereby compensating for the magnetic resonance center frequency.

[0004] However, in existing technologies, adding a Boolean eddy current compensation coil to the main magnetic field increases the cost of additional hardware. Furthermore, since the Boolean eddy current compensation coil generates its magnetic field by receiving a simulated Boolean eddy current compensation signal, this simulated signal is typically affected by temperature. When the temperature changes, the magnitude of the Boolean eddy current compensation signal drifts or fluctuates, altering the field strength of the Boolean eddy current compensation magnetic field and thus affecting the accuracy of compensating for the magnetic resonance center frequency. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a compensation method, device, electronic device and medium in a magnetic resonance imaging system to improve the accuracy of compensation for the magnetic resonance center frequency, thereby avoiding artifacts in the image.

[0006] In a first aspect, embodiments of this application provide a compensation method in a magnetic resonance imaging system, comprising:

[0007] The first characteristic parameter of the ideal gradient waveform and the second characteristic parameter of the target vortex are obtained; the first characteristic parameter includes the first amplitude parameter at each target time point; the second characteristic parameter includes multiple sets of time constants and amplitude constants; when the target vortex is generated, the magnetic resonance center frequency in the magnetic resonance imaging system shifts from the first frequency to the second frequency.

[0008] Based on the first feature parameter and the second feature parameter, the second amplitude parameter of the compensation waveform of the target eddy current at each of the target time points is calculated, so as to generate the compensation waveform based on the second amplitude parameter at the target time point;

[0009] The compensation frequency is input to a first phase accumulator to output a first phase; and the first frequency is input to a second phase accumulator to output a second phase; the compensation frequency is determined based on the compensation waveform;

[0010] Based on the target phase, the sine and cosine signals corresponding to the target phase are looked up in the sine and cosine lookup table; the target phase is the sum of the first phase and the second phase; the frequencies of the sine and cosine signals are both the second frequency; the second frequency is equal to the sum of the first frequency and the compensation frequency;

[0011] The cosine signal is used to modulate the radio frequency pulse signal so that the frequency of the radio frequency pulse signal is the same as the second frequency; and the sine signal and the cosine signal are used to demodulate the magnetic resonance signal so that the frequency of the magnetic resonance signal is demodulated from the second frequency to the frequency of the baseband signal.

[0012] In conjunction with the first aspect, embodiments of this application provide a first possible implementation of the first aspect, wherein the second characteristic parameter is measured in advance by the following method:

[0013] Within a historical time period, after the target vortex is generated, the waveform of the target vortex is measured;

[0014] The waveform of the target vortex is fitted to obtain the second characteristic parameter.

[0015] In conjunction with the first aspect, this application provides a second possible implementation of the first aspect, wherein the first feature parameter includes a first sub-feature parameter of the ideal gradient waveform in each target direction, and the first sub-feature parameter includes a first sub-amplitude parameter at each target time point; the second feature parameter includes a second sub-feature parameter of the target vortex in each target direction, and the second sub-feature parameter includes multiple sets of sub-time constants and sub-amplitude constants; the target direction includes a first direction, a second direction, and a third direction that are perpendicular to each other;

[0016] The step of calculating the second amplitude parameter of the compensation waveform of the target vortex at each of the target time points based on the first characteristic parameter and the second characteristic parameter includes:

[0017] For each target direction, the first sub-feature parameter corresponding to the target direction is input into the gradient generator corresponding to the target direction, and the sub-gradient waveform of the ideal gradient waveform in the target direction is output.

[0018] For each target direction, the sub-gradient waveform and the second sub-feature parameter corresponding to the target direction are input into the pre-emphasis unit corresponding to the target direction, and the second sub-amplitude parameter of the compensation waveform at each target time point in the target direction is output.

[0019] For each target time point, the second sub-amplitude parameters in each target direction at that target time point are superimposed to obtain the second amplitude parameter of the compensation waveform at that target time point.

[0020] In conjunction with the first aspect, this application provides a third possible implementation of the first aspect, wherein the modulation of the radio frequency pulse signal using the cosine signal includes:

[0021] The cosine signal is used to modulate the amplitude of the radio frequency pulse waveform to obtain the modulated radio frequency pulse waveform.

[0022] The radio frequency pulse modulation waveform is input into a digital-to-analog converter, and the digital-to-analog converter converts the radio frequency pulse modulation waveform into a radio frequency pulse analog signal;

[0023] The power of the radio frequency pulse analog signal is amplified using a radio frequency power amplifier to obtain the target analog signal;

[0024] The target analog signal is input into a power divider, which then divides the target analog signal into a first analog signal and a second analog signal with equal power.

[0025] The first analog signal and the second analog signal are input into a phase shifter, and the phase of the first analog signal and the second analog signal is changed by the phase shifter so that the phase difference between the first analog signal and the second analog signal is 90 degrees. The first analog signal and the second analog signal with a phase difference of 90 degrees are used as the radio frequency pulse signal.

[0026] In conjunction with the first aspect, this application provides a fourth possible implementation of the first aspect, wherein the demodulation of the magnetic resonance signal using the sine signal and the cosine signal includes:

[0027] The acquired magnetic resonance analog signal is input into an analog-to-digital converter, which converts the magnetic resonance analog signal into a magnetic resonance digital signal.

[0028] The cosine signal and the sine signal are used to perform quadrature demodulation on the magnetic resonance digital signal to obtain a high-frequency digital signal and a low-frequency digital signal of magnetic resonance.

[0029] The high-frequency digital signal of the magnetic resonance is filtered out by a digital filter to obtain the low-frequency digital signal of the magnetic resonance, which is then used as the magnetic resonance signal.

[0030] In conjunction with the first aspect or the fourth possible implementation of the first aspect, embodiments of this application provide a fifth possible implementation of the first aspect, wherein, after obtaining the demodulated magnetic resonance signal, the implementation further includes:

[0031] The magnetic resonance image is obtained by reconstructing the image based on the magnetic resonance signal.

[0032] Secondly, embodiments of this application also provide a compensation device in a magnetic resonance imaging system, comprising:

[0033] The acquisition module is used to acquire the first characteristic parameters of the ideal gradient waveform and the second characteristic parameters of the target vortex; the first characteristic parameters include the first amplitude parameters at each target time point; the second characteristic parameters include multiple sets of time constants and amplitude constants; when the target vortex is generated, the magnetic resonance center frequency in the magnetic resonance imaging system shifts from the first frequency to the second frequency.

[0034] The calculation module is used to calculate the second amplitude parameter of the compensation waveform of the target eddy at each of the target time points according to the first feature parameter and the second feature parameter, so as to generate the compensation waveform according to the second amplitude parameter at the target time point;

[0035] An input module is used to input the compensation frequency to a first phase accumulator and output a first phase; and to input the first frequency to a second phase accumulator and output a second phase; the compensation frequency is determined based on the compensation waveform;

[0036] The query module is used to query the sine and cosine signals corresponding to the target phase in a sine and cosine lookup table based on the target phase; the target phase is the sum of the first phase and the second phase; the frequencies of the sine and cosine signals are both the second frequency; the second frequency is equal to the sum of the first frequency and the compensation frequency;

[0037] A modulation and demodulation module is configured to modulate a radio frequency pulse signal using the cosine signal so that the frequency of the radio frequency pulse signal is the same as the second frequency; and to demodulate a magnetic resonance signal using the sine signal and the cosine signal so that the frequency of the magnetic resonance signal is demodulated from the second frequency to the frequency of the baseband signal.

[0038] In conjunction with the second aspect, this application provides a first possible implementation of the second aspect, wherein the acquisition module further includes, before acquiring the second characteristic parameter of the target vortex, the following:

[0039] The measurement module is used to measure the waveform of the target vortex after it is generated within a historical time period.

[0040] The fitting module is used to fit the waveform of the target vortex to obtain the second feature parameter.

[0041] In conjunction with the second aspect, this application provides a second possible implementation of the second aspect, wherein the first feature parameter includes a first sub-feature parameter of the ideal gradient waveform in each target direction, and the first sub-feature parameter includes a first sub-amplitude parameter at each target time point; the second feature parameter includes a second sub-feature parameter of the target vortex in each target direction, and the second sub-feature parameter includes multiple sets of sub-time constants and sub-amplitude constants; the target direction includes a first direction, a second direction, and a third direction that are perpendicular to each other;

[0042] When the calculation module calculates the second amplitude parameter of the compensation waveform of the target vortex at each of the target time points based on the first feature parameter and the second feature parameter, it is specifically used for:

[0043] For each target direction, the first sub-feature parameter corresponding to the target direction is input into the gradient generator corresponding to the target direction, and the sub-gradient waveform of the ideal gradient waveform in the target direction is output.

[0044] For each target direction, the sub-gradient waveform and the second sub-feature parameter corresponding to the target direction are input into the pre-emphasis unit corresponding to the target direction, and the second sub-amplitude parameter of the compensation waveform at each target time point in the target direction is output.

[0045] For each target time point, the second sub-amplitude parameters in each target direction at that target time point are superimposed to obtain the second amplitude parameter of the compensation waveform at that target time point.

[0046] In conjunction with the second aspect, this application provides a third possible implementation of the second aspect, wherein, when the modulation and demodulation module is used to modulate the radio frequency pulse signal using the cosine signal, it is specifically used for:

[0047] The cosine signal is used to modulate the amplitude of the radio frequency pulse waveform to obtain the modulated radio frequency pulse waveform.

[0048] The radio frequency pulse modulation waveform is input into a digital-to-analog converter, and the digital-to-analog converter converts the radio frequency pulse modulation waveform into a radio frequency pulse analog signal;

[0049] The power of the radio frequency pulse analog signal is amplified using a radio frequency power amplifier to obtain the target analog signal;

[0050] The target analog signal is input into a power divider, which then divides the target analog signal into a first analog signal and a second analog signal with equal power.

[0051] The first analog signal and the second analog signal are input into a phase shifter, and the phase of the first analog signal and the second analog signal is changed by the phase shifter so that the phase difference between the first analog signal and the second analog signal is 90 degrees. The first analog signal and the second analog signal with a phase difference of 90 degrees are used as the radio frequency pulse signal.

[0052] In conjunction with the second aspect, this application provides a fourth possible implementation of the second aspect, wherein, when the modulation and demodulation module is used to demodulate the magnetic resonance signal using the sine signal and the cosine signal, it is specifically used for:

[0053] The acquired magnetic resonance analog signal is input into an analog-to-digital converter, which converts the magnetic resonance analog signal into a magnetic resonance digital signal.

[0054] The cosine signal and the sine signal are used to perform quadrature demodulation on the magnetic resonance digital signal to obtain a high-frequency digital signal and a low-frequency digital signal of magnetic resonance.

[0055] The high-frequency digital signal of the magnetic resonance is filtered out by a digital filter to obtain the low-frequency digital signal of the magnetic resonance, which is then used as the magnetic resonance signal.

[0056] In conjunction with the second aspect or the fourth possible implementation of the second aspect, embodiments of this application provide a fifth possible implementation of the second aspect, which further includes:

[0057] The image reconstruction module is used to reconstruct the image based on the magnetic resonance signal to obtain a magnetic resonance image.

[0058] Thirdly, embodiments of this application also provide an electronic device, including: a processor, a memory, and a bus, wherein the memory stores machine-readable instructions executable by the processor, and when the electronic device is running, the processor communicates with the memory via the bus, and when the machine-readable instructions are executed by the processor, the steps in any of the possible implementations of the first aspect described above are performed.

[0059] Fourthly, embodiments of this application also provide a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the steps in any of the possible implementations of the first aspect described above.

[0060] This application provides a compensation method, apparatus, electronic device, and medium in a magnetic resonance imaging (MRI) system. The magnetic resonance center frequency and the frequency of the radio frequency (RF) pulse signal are the same. When the magnetic resonance center frequency differs from the RF pulse signal frequency, image artifacts occur. Therefore, when the magnetic resonance center frequency shifts, this application changes the frequencies of the RF pulse and the magnetic resonance signal to make the magnetic resonance center frequency the same as the RF pulse signal frequency, and makes the frequency of the magnetic resonance signal the frequency of the baseband signal, thereby avoiding image artifacts. While existing technologies directly correct the magnetic resonance center frequency using a Boolean eddy current compensation coil, this application demodulates the magnetic resonance signal and modulates the RF pulse signal entirely in the digital domain, thus indirectly compensating for the magnetic resonance center frequency. The method in this application does not require an additional Boolean eddy current compensation coil and is therefore unaffected by temperature, which helps improve the accuracy of magnetic resonance center frequency compensation.

[0061] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0062] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0063] Figure 1 The diagram illustrates the ideal gradient waveform, the actual gradient waveform, and the waveform of the B0 eddy current provided in the embodiments of this application.

[0064] Figure 2A flowchart of a compensation method in a magnetic resonance imaging system provided in an embodiment of this application is shown;

[0065] Figure 3 This paper shows a schematic diagram of the structure of the first phase accumulator, the second phase accumulator, the first register, and the second register provided in an embodiment of this application.

[0066] Figure 4 This paper shows a schematic diagram of the structure of the sequence controller, gradient generator, pre-emphasis unit, and fourth adder provided in an embodiment of this application.

[0067] Figure 5 A schematic diagram of the structure of the radio frequency transmitting unit provided in the embodiment of this application is shown;

[0068] Figure 6 A schematic diagram of the structure of the radio frequency receiving unit provided in the embodiment of this application is shown;

[0069] Figure 7 This paper shows a schematic diagram of the structure of a compensation device in a magnetic resonance imaging system provided in an embodiment of the present application;

[0070] Figure 8 A schematic diagram of the structure of an electronic device provided in an embodiment of this application is shown. Detailed Implementation

[0071] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0072] To facilitate understanding, the generation process of B0 eddy currents in this application is first described: The magnetic resonance imaging system includes a gradient coil and a conductor. The gradient coil is used to generate a gradient magnetic field according to the received ideal gradient waveform. When the gradient magnetic field switches gradients, eddy currents are generated in the conductor. The eddy currents include linear eddy currents and constant B0 eddy currents. Figure 1 The diagram illustrates the ideal gradient waveform, the actual gradient waveform, and the waveform of the B0 eddy current provided in the embodiments of this application. Figure 1As shown, during the process of generating a gradient magnetic field, the magnetic resonance imaging system sends an ideal gradient waveform to the gradient coil. After receiving the ideal gradient waveform, the gradient coil outputs the actual gradient waveform. The actual gradient waveform is different from the ideal gradient waveform. The actual gradient waveform is affected by linear eddy currents, while the magnetic resonance center frequency is affected by B0 eddy currents.

[0073] Considering the low accuracy of compensating for the center frequency of magnetic resonance using B0 eddy current compensation coils in the prior art, this application provides a compensation method, device, electronic device, and medium in a magnetic resonance imaging system to improve the accuracy of compensating for the center frequency of magnetic resonance and thus avoid artifacts in the image. The following is a description through embodiments.

[0074] Example 1:

[0075] To facilitate understanding of this embodiment, a compensation method in a magnetic resonance imaging system disclosed in this application will first be described in detail. Figure 2 A flowchart of a compensation method in a magnetic resonance imaging system provided in an embodiment of this application is shown, as follows: Figure 2 As shown, the process includes the following steps S101-S105:

[0076] S101: Obtain the first characteristic parameter of the ideal gradient waveform and the second characteristic parameter of the target vortex; the first characteristic parameter includes the first amplitude parameter at each target time point; the second characteristic parameter includes multiple sets of time constants and amplitude constants; when the target vortex is generated, the magnetic resonance center frequency in the magnetic resonance imaging system shifts from the first frequency to the second frequency.

[0077] In embodiments of this application, the target time point includes the current time point and at least one historical time point, with the same time interval between each target time point. The target eddy current is a B0 eddy current. The first amplitude parameter represents the amplitude of the ideal gradient waveform at the target time point. The amplitude constant represents the waveform amplitude of the target eddy current at the time point corresponding to the time constant.

[0078] S102: Calculate the second amplitude parameter of the compensation waveform of the target vortex at each target time point based on the first characteristic parameter and the second characteristic parameter, so as to generate the compensation waveform based on the second amplitude parameter at the target time point.

[0079] In one specific embodiment, the first feature parameter and the second feature parameter are input into the following difference equation:

[0080] w k (n)-β k w k (n-1)=α k(p(n)-p(n-1))

[0081] Where n and n-1 represent two adjacent target time points, p(n) represents the first amplitude parameter of the ideal gradient waveform at target time point n, and p(n-1) represents the first amplitude parameter of the ideal gradient waveform at target time point n-1; w(n) represents the second amplitude parameter of the compensation waveform at target time point n, and w(n-1) represents the second amplitude parameter of the compensation waveform at target time point n-1. α k Let β represent the amplitude constant of the Kth group. k This represents the time constant of the Kth group, where K represents the group number. The compensation waveform is the same as the waveform of the target vortex.

[0082] S103: Input the compensation frequency to the first phase accumulator and output the first phase; and input the first frequency to the second phase accumulator and output the second phase; the compensation frequency is determined according to the compensation waveform.

[0083] The compensation frequency of the compensation waveform is determined based on the compensation waveform. This compensation frequency is then input into the first phase accumulator, which outputs the first phase. The first frequency is then input into the second phase accumulator, which outputs the second phase.

[0084] In one specific embodiment Figure 3 The diagram illustrates the structure of the first phase accumulator, the second phase accumulator, the first register, and the second register provided in the embodiments of this application. Figure 3 As shown, the compensation frequency is input to the first phase accumulator through the first register. The first phase accumulator is composed of a first adder and a third register. The output of the third register is used as feedback input to the first adder. The output of the third register is the first phase to compensate for the frequency change.

[0085] Similarly, the first frequency is input to the second phase accumulator through the second register. The second phase accumulator is composed of a second adder and a fourth register. The output of the fourth register is used as feedback input to the second adder. The output of the fourth register is the second phase that changes with the first frequency.

[0086] like Figure 3 As shown, the first phase and the second phase are input into the third adder. In the third adder, the sum of the first phase and the second phase is calculated, and the sum of the first phase and the second phase is used as the target phase.

[0087] S104: Based on the target phase, look up the sine and cosine signals corresponding to the target phase in the sine and cosine lookup table; the target phase is the sum of the first phase and the second phase; the frequencies of the sine and cosine signals are both the second frequency; the second frequency is equal to the sum of the first frequency and the compensation frequency.

[0088] The sine and cosine lookup table contains the correspondence between the target phase and the sine and cosine signals.

[0089] Since the target phase is the sum of the first phase and the second phase, the frequency of the first phase is the compensation frequency, and the frequency of the second phase is the first frequency, the frequency of the target phase is the sum of the compensation frequency and the first frequency, that is, the frequency of the target phase is the second frequency.

[0090] S105: Modulate the radio frequency pulse signal using a cosine signal so that the frequency of the radio frequency pulse signal is the same as the second frequency; and demodulate the magnetic resonance signal using a sine signal and a cosine signal so that the frequency of the magnetic resonance signal is demodulated from the second frequency to the frequency of the baseband signal.

[0091] In this application, a cosine signal is used to modulate the radio frequency pulse signal to raise its frequency to a second frequency; sine and cosine signals are used to demodulate the magnetic resonance signal to lower its frequency from the second frequency to the baseband signal frequency. The baseband signal has a lower frequency, and its signal spectrum starts near zero, exhibiting a low-pass form.

[0092] In the embodiments of this application, the method is applied to a magnetic resonance imaging (MRI) system. In an MRI system, a uniform strong magnetic field is generated by a main magnetic field, causing the hydrogen nuclei in the human body to undergo spin polarization. The magnetically polarized hydrogen nuclei generate a magnetic moment in the human body. Without external magnetic field excitation other than the main magnetic field, this magnetic moment remains stable, with its direction coaxial with the main magnetic field. When an external uniform radio frequency magnetic field is present, i.e., when a radio frequency pulse signal is used to excite a substance containing hydrogen nuclei with non-zero spin, nuclear magnetic resonance occurs. After the radio frequency pulse signal stops, nuclear magnetic relaxation occurs, generating a magnetic resonance signal. This magnetic resonance signal is then acquired using an induction coil. Therefore, in this application, the radio frequency pulse signal is used to excite the hydrogen nuclei in the human body, and the magnetic resonance signal is used to generate a magnetic resonance image.

[0093] In one possible implementation, before performing step S101, the method further includes: pre-measuring the second characteristic parameter. Specifically, the second characteristic parameter is pre-measuring by the following steps S1001-S1002:

[0094] S1001: Measure the waveform of the target vortex after it is generated within a historical time period.

[0095] S1002: Fit the waveform of the target vortex to obtain the second characteristic parameter.

[0096] In this embodiment of the application, the waveform curve of the target vortex changing over time is measured, and the waveform curve of the target vortex is subjected to multi-exponential fitting to obtain the second characteristic parameter.

[0097] In one possible implementation, the first characteristic parameter includes a first sub-characteristic parameter of the ideal gradient waveform in each target direction, and the first sub-characteristic parameter includes a first sub-amplitude parameter at each target time point; the second characteristic parameter includes a second sub-characteristic parameter of the target vortex in each target direction, and the second sub-characteristic parameter includes multiple sets of sub-time constants and sub-amplitude constants; the target direction includes a first direction, a second direction, and a third direction that are perpendicular to each other; when performing step S102: calculating the second amplitude parameter of the compensation waveform of the target vortex at each target time point based on the first characteristic parameter and the second characteristic parameter, the specific steps can be as follows:

[0098] S1021: For each target direction, the first sub-feature parameter corresponding to the target direction is input into the gradient generator corresponding to the target direction, and the sub-gradient waveform of the ideal gradient waveform in the target direction is output.

[0099] In the embodiments of this application, the first direction, the second direction, and the third direction refer to the three directions X, Y, and Z at the physical layer. Figure 4 The following is a schematic diagram of the structure of the sequence controller, gradient generator, pre-emphasis unit, and fourth adder provided in the embodiments of this application, as shown below. Figure 4 As shown, there are three gradient generators: X gradient generator, Y gradient generator, and Z gradient generator, and three pre-emphasis units: X pre-emphasis unit, Y pre-emphasis unit, and Z pre-emphasis unit.

[0100] The sequence controller provides the first sub-feature parameters required by the X gradient generator, Y gradient generator, and Z gradient generator respectively. Specifically, the first sub-feature parameter R... X Provided to the X gradient generator, the first sub-feature parameter R Y The first sub-feature parameter R is provided to the Y gradient generator. Z It is provided to the Z gradient generator. Each gradient generator outputs a sub-gradient waveform, which represents the waveform of the ideal gradient waveform in each target direction. In other words, the sub-gradient waveform is a set of waveform amplitudes in a time series.

[0101] S1022: For each target direction, input the sub-gradient waveform and the second sub-feature parameter corresponding to the target direction into the pre-emphasis unit corresponding to the target direction, and output the second sub-amplitude parameter of the compensation waveform at each target time point in the target direction.

[0102] like Figure 4 As shown, the sub-gradient waveform U output by the X gradient generator is... X The input is given to the X pre-emphasis unit, and the second sub-feature parameter H is also input. X The input is fed into the X pre-emphasis unit, where the sub-gradient waveform U is... X The first sub-feature parameter R on X Second sub-feature parameter H X The parameters are input into the difference equation to obtain the second sub-amplitude parameter of the compensation waveform in the X direction at each target time point. Refer to step S102 for details.

[0103] Similarly, the Y pre-emphasis unit outputs the second sub-amplitude parameter of the compensation waveform in the Y direction at each target time point, and the Z pre-emphasis unit outputs the second sub-amplitude parameter of the compensation waveform in the Z direction at each target time point.

[0104] In the embodiments of this application, the transfer function of the pre-emphasis unit is:

[0105]

[0106] Among them, A n T is the sub-amplitude constant in the second sub-feature parameter. n is the sub-time constant in the second sub-characteristic parameter, and N is the number of sets of the second sub-characteristic parameters of the target vortex. H(s) is the ratio of the Laplace transform of the response (i.e., output) of a linear system (in this case, the pre-emphasized unit) to the Laplace transform of the excitation (i.e., input), where s is a variable related to input / output.

[0107] The difference equation is obtained by discretizing the transfer function H(S) through the inverse Laplace transform. The transfer function describes the input-output relationship of the system in the complex frequency domain. After the inverse Laplace transform, the input-output relationship in the time domain is obtained. After discretization, the difference equation is obtained. The output can be calculated from the input, the amplitude constant and time constant of the eddy current compensation.

[0108] S1023: For each target time point, the second sub-amplitude parameters in each target direction at that target time point are superimposed to obtain the second amplitude parameter of the compensation waveform at that target time point.

[0109] like Figure 4As shown, the second sub-amplitude parameters of the compensation waveforms in each target direction output by the X pre-emphasis unit, Y pre-emphasis unit, and Z pre-emphasis unit at each target time point are input into the fourth adder. In the fourth adder, for each target time point, the second sub-amplitude parameters in each target direction at that target time point are superimposed to obtain the second amplitude parameter of the compensation waveform at that target time point.

[0110] In one possible implementation, when performing step S105, which modulates the radio frequency pulse signal using a cosine signal, the specific steps S1051-S1055 can be performed as follows:

[0111] S1051: Use a cosine signal to modulate the amplitude of the radio frequency pulse waveform to obtain the modulated radio frequency pulse waveform.

[0112] S1052: Input the radio frequency pulse modulation waveform into the digital-to-analog converter, and convert the radio frequency pulse modulation waveform into a radio frequency pulse analog signal through the digital-to-analog converter.

[0113] S1053: Use an RF power amplifier to amplify the power of the RF pulse analog signal to obtain the target analog signal.

[0114] S1054: Input the target analog signal into the power divider, and the power divider divides the target analog signal into a first analog signal and a second analog signal with the same power.

[0115] S1055: Input the first analog signal and the second analog signal into the phase shifter, change the phase of the first analog signal and the second analog signal through the phase shifter, so that the phase difference between the first analog signal and the second analog signal is 90 degrees, and use the first analog signal and the second analog signal with a phase difference of 90 degrees as radio frequency pulse signals.

[0116] Figure 5 A schematic diagram of the structure of the radio frequency transmitting unit provided in the embodiment of this application is shown, as follows: Figure 5 As shown, the radio frequency (RF) transmitting unit includes: a first multiplier, a digital-to-analog converter (DAC), an RF power amplifier, a power divider, a phase shifter, and a transmitting coil. After receiving the cosine signal, the RF transmitting unit modulates the RF pulse waveform using the first multiplier. The modulated RF pulse waveform is then converted into an RF pulse analog signal by the DAC. This analog signal is then converted into an RF pulse signal by the RF power amplifier, power divider, and phase shifter. The RF pulse signal is then input to the transmitting coil to excite the magnetic resonance signal.

[0117] In one possible implementation, when performing step S105 to demodulate the magnetic resonance signal using sine and cosine signals, the specific steps S1056-S1058 can be performed as follows:

[0118] S1056: The acquired magnetic resonance analog signal is input into the analog-to-digital converter, which converts the magnetic resonance analog signal into a magnetic resonance digital signal.

[0119] S1057: Use cosine and sine signals to perform quadrature demodulation on the magnetic resonance digital signal to obtain the magnetic resonance high-frequency digital signal and the magnetic resonance low-frequency digital signal.

[0120] S1058: The high-frequency digital signal of magnetic resonance is filtered out by a digital filter to obtain the low-frequency digital signal of magnetic resonance, so as to use the low-frequency digital signal of magnetic resonance as the magnetic resonance signal.

[0121] Figure 6 A schematic diagram of the structure of the radio frequency receiving unit provided in the embodiment of this application is shown, as follows: Figure 6 As shown, the radio frequency (RF) receiving unit includes an analog-to-digital converter (ADC), a second multiplier, a third multiplier, and a digital filter. After receiving the sine and cosine signals, the RF receiving unit inputs the acquired magnetic resonance analog signal into the ADC. The ADC converts the magnetic resonance analog signal into a magnetic resonance digital signal. The second and third multipliers then perform quadrature demodulation on the digitized magnetic resonance digital signal using the cosine and sine signals. After digital filtering, the demodulated signal yields a low-frequency magnetic resonance digital signal, which is used as the magnetic resonance signal for image reconstruction.

[0122] In one possible implementation, after obtaining the demodulated magnetic resonance signal, the method further includes: performing image reconstruction based on the magnetic resonance signal to obtain a magnetic resonance image.

[0123] Example 2:

[0124] Based on the same technical concept, embodiments of this application also provide a compensation device in a magnetic resonance imaging system. Figure 7 This application provides a schematic diagram of the structure of a compensation device in a magnetic resonance imaging system, as shown in the embodiment of the present application. Figure 7 As shown, the device includes:

[0125] The acquisition module 701 is used to acquire the first characteristic parameters of the ideal gradient waveform and the second characteristic parameters of the target vortex; the first characteristic parameters include the first amplitude parameters at each target time point; the second characteristic parameters include multiple sets of time constants and amplitude constants; when the target vortex is generated, the magnetic resonance center frequency in the magnetic resonance imaging system shifts from the first frequency to the second frequency.

[0126] The calculation module 702 is used to calculate the second amplitude parameter of the compensation waveform of the target eddy at each of the target time points according to the first feature parameter and the second feature parameter, so as to generate the compensation waveform according to the second amplitude parameter at the target time point;

[0127] The input module 703 is used to input the compensation frequency to a first phase accumulator and output a first phase; and to input the first frequency to a second phase accumulator and output a second phase; the compensation frequency is determined based on the compensation waveform;

[0128] The query module 704 is used to query the sine and cosine signals corresponding to the target phase in a sine and cosine lookup table according to the target phase; the target phase is the sum of the first phase and the second phase; the frequencies of the sine signal and the cosine signal are both the second frequency; the second frequency is equal to the sum of the first frequency and the compensation frequency;

[0129] The modulation and demodulation module 705 is used to modulate the radio frequency pulse signal using the cosine signal so that the frequency of the radio frequency pulse signal is the same as the second frequency; and to demodulate the magnetic resonance signal using the sine signal and the cosine signal so that the frequency of the magnetic resonance signal is demodulated from the second frequency to the frequency of the baseband signal.

[0130] Optionally, before acquiring the second characteristic parameter of the target vortex, the acquisition module 701 further includes:

[0131] The measurement module is used to measure the waveform of the target vortex after it is generated within a historical time period.

[0132] The fitting module is used to fit the waveform of the target vortex to obtain the second feature parameter.

[0133] Optionally, the first feature parameter includes a first sub-feature parameter of the ideal gradient waveform in each target direction, the first sub-feature parameter including a first sub-amplitude parameter at each target time point; the second feature parameter includes a second sub-feature parameter of the target vortex in each target direction, the second sub-feature parameter including multiple sets of sub-time constants and sub-amplitude constants; the target direction includes a first direction, a second direction and a third direction that are perpendicular to each other;

[0134] When the calculation module 702 calculates the second amplitude parameter of the compensation waveform of the target vortex at each of the target time points based on the first characteristic parameter and the second characteristic parameter, it is specifically used for:

[0135] For each target direction, the first sub-feature parameter corresponding to the target direction is input into the gradient generator corresponding to the target direction, and the sub-gradient waveform of the ideal gradient waveform in the target direction is output.

[0136] For each target direction, the sub-gradient waveform and the second sub-feature parameter corresponding to the target direction are input into the pre-emphasis unit corresponding to the target direction, and the second sub-amplitude parameter of the compensation waveform at each target time point in the target direction is output.

[0137] For each target time point, the second sub-amplitude parameters in each target direction at that target time point are superimposed to obtain the second amplitude parameter of the compensation waveform at that target time point.

[0138] Optionally, when the modulation and demodulation module 705 is used to modulate the radio frequency pulse signal using the cosine signal, it is specifically used for:

[0139] The cosine signal is used to modulate the amplitude of the radio frequency pulse waveform to obtain the modulated radio frequency pulse waveform.

[0140] The radio frequency pulse modulation waveform is input into a digital-to-analog converter, and the digital-to-analog converter converts the radio frequency pulse modulation waveform into a radio frequency pulse analog signal;

[0141] The power of the radio frequency pulse analog signal is amplified using a radio frequency power amplifier to obtain the target analog signal;

[0142] The target analog signal is input into a power divider, which then divides the target analog signal into a first analog signal and a second analog signal with equal power.

[0143] The first analog signal and the second analog signal are input into a phase shifter, and the phase of the first analog signal and the second analog signal is changed by the phase shifter so that the phase difference between the first analog signal and the second analog signal is 90 degrees. The first analog signal and the second analog signal with a phase difference of 90 degrees are used as the radio frequency pulse signal.

[0144] Optionally, when the modulation and demodulation module 705 is used to demodulate the magnetic resonance signal using the sine signal and the cosine signal, it is specifically used for:

[0145] The acquired magnetic resonance analog signal is input into an analog-to-digital converter, which converts the magnetic resonance analog signal into a magnetic resonance digital signal.

[0146] The cosine signal and the sine signal are used to perform quadrature demodulation on the magnetic resonance digital signal to obtain a high-frequency digital signal and a low-frequency digital signal of magnetic resonance.

[0147] The high-frequency digital signal of the magnetic resonance is filtered out by a digital filter to obtain the low-frequency digital signal of the magnetic resonance, which is then used as the magnetic resonance signal.

[0148] Optional, also includes:

[0149] The image reconstruction module is used to reconstruct the image based on the magnetic resonance signal to obtain a magnetic resonance image.

[0150] For details on the specific implementation methods, steps, and principles, please refer to the description in Example 1, which will not be repeated here.

[0151] Example 3:

[0152] Based on the same technical concept, embodiments of this application also provide an electronic device. Figure 8 This application provides a schematic diagram of the structure of an electronic device according to an embodiment of the present application. Figure 8 As shown, the electronic device 800 includes a processor 801, a memory 802, and a bus 803. The memory stores machine-readable instructions that can be executed by the processor. When the electronic device is running, the processor 801 communicates with the memory 802 through the bus 803. The processor 801 executes the machine-readable instructions to perform the steps of the method described in Embodiment 1.

[0153] For details on the specific implementation methods, steps, and principles, please refer to the description in Example 1, which will not be repeated here.

[0154] Example 4:

[0155] Based on the same technical concept, Embodiment 4 of this application also provides a computer-readable storage medium storing a computer program, which is executed by a processor to perform the steps of the method described in Embodiment 1.

[0156] For details on the specific implementation methods, steps, and principles, please refer to the description in Example 1, which will not be repeated here.

[0157] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0158] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the shown or discussed mutual couplings, direct couplings, or communication connections may be through some communication interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.

[0159] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0160] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0161] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a processor-executable, non-volatile, computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0162] Finally, it should be noted that the above-described embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The scope of protection of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this application. Such modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims.

Claims

1. A method of compensation in a magnetic resonance imaging system, characterized by, The method comprises: obtaining first characteristic parameters of an ideal gradient waveform and second characteristic parameters of a target eddy current; the first characteristic parameters comprise first amplitude parameters at respective target time points; the second characteristic parameters comprise multiple sets of time constants and amplitude constants; a magnetic resonance center frequency in a magnetic resonance imaging system is shifted from a first frequency to a second frequency after the target eddy current is generated; the target time points comprise a current time point and at least one historical time point; calculating second amplitude parameters of a compensation waveform of the target eddy current at the respective target time points according to the first characteristic parameters and the second characteristic parameters, so as to generate the compensation waveform according to the second amplitude parameters at the target time points; wherein the first characteristic parameters and the second characteristic parameters are input into the following difference equation: n and n-1 represent two adjacent target time points respectively, p(n) represents a first amplitude parameter corresponding to the ideal gradient waveform at the target time point n, p(n-1) represents a first amplitude parameter corresponding to the ideal gradient waveform at the target time point n-1; w(n) represents a second amplitude parameter corresponding to the compensation waveform at the target time point n, w(n-1) represents a second amplitude parameter corresponding to the compensation waveform at the target time point n-1; α k represents the Kth group of amplitude constants, β k represents the Kth group of time constants, K represents the number of groups; a first register is used to input a compensation frequency into a first phase accumulator, and a first phase varying with the compensation frequency is output; and a second register is used to input the first frequency into a second phase accumulator, and a second phase varying with the first frequency is output; the compensation frequency is determined according to the compensation waveform; the first phase accumulator is composed of a first adder and a third register, and an output of the third register is input as feedback into the first adder; the second phase accumulator is composed of a second adder and a fourth register, and an output of the fourth register is input as feedback into the second adder; the first phase and the second phase are input into a third adder, and a sum of the first phase and the second phase is calculated in the third adder; a target phase is the sum of the first phase and the second phase; the target phase is used to query a sine signal and a cosine signal corresponding to the target phase in a sine-cosine query table; the sine signal and the cosine signal both have the second frequency; the second frequency is equal to a sum of the first frequency and the compensation frequency; the cosine signal is used to modulate a radio frequency pulse signal, so that the radio frequency pulse signal has the same frequency as the second frequency; and the sine signal and the cosine signal are used to demodulate a magnetic resonance signal, so that the frequency of the magnetic resonance signal is demodulated from the second frequency to a frequency of a baseband signal.

2. The method of claim 1, wherein, The second characteristic parameters are measured in advance by the following method: a waveform of the target eddy current is measured in a historical time period after the target eddy current is generated; the waveform of the target eddy current is fitted to obtain the second characteristic parameters.

3. The method of claim 1, wherein, The first characteristic parameters comprise first sub-characteristic parameters of the ideal gradient waveform in respective target directions, and the first sub-characteristic parameters comprise first sub-amplitude parameters at respective target time points; the second characteristic parameters comprise second sub-characteristic parameters of the target eddy current in the respective target directions, and the second sub-characteristic parameters comprise multiple sets of sub-time constants and sub-amplitude constants; the target directions comprise a first direction, a second direction and a third direction perpendicular to each other; The calculation of the second amplitude parameters of the compensation waveform of the target eddy current at the respective target time points according to the first characteristic parameters and the second characteristic parameters comprises: For each of the target directions, the first sub-feature parameter corresponding to the target direction is input into a gradient generator corresponding to the target direction, and a sub-gradient waveform of the ideal gradient waveform in the target direction is output; For each of the target directions, the sub-gradient waveform corresponding to the target direction and the second sub-feature parameter are input into a pre-emphasis unit corresponding to the target direction, and a second sub-amplitude parameter of the compensation waveform in the target direction at each of the target time points is output; For each of the target time points, the second sub-amplitude parameters in each of the target directions at the target time point are superimposed to obtain the second amplitude parameter of the compensation waveform at the target time point.

4. The method of claim 1, wherein, The use of the cosine signal to modulate the radio frequency pulse signal comprises: using the cosine signal to amplitude modulate the radio frequency pulse waveform to obtain a modulated radio frequency pulse modulation waveform; inputting the radio frequency pulse modulation waveform into a digital-to-analog converter, and converting the radio frequency pulse modulation waveform into a radio frequency pulse analog signal through the digital-to-analog converter; using a radio frequency power amplifier to amplify the power of the radio frequency pulse analog signal to obtain a target analog signal; inputting the target analog signal into a power divider, and dividing the target analog signal into a first analog signal and a second analog signal with the same power through the power divider; inputting the first analog signal and the second analog signal into a phase shifter, changing the phase of the first analog signal and the second analog signal through the phase shifter so that the phase difference between the first analog signal and the second analog signal is 90 degrees, and taking the first analog signal and the second analog signal with a phase difference of 90 degrees as the radio frequency pulse signal.

5. The method of claim 1, wherein, The use of the sine signal and the cosine signal to demodulate the magnetic resonance signal comprises: inputting the acquired magnetic resonance analog signal into an analog-to-digital converter, and converting the magnetic resonance analog signal into a magnetic resonance digital signal through the analog-to-digital converter; using the cosine signal and the sine signal to quadrature demodulate the magnetic resonance digital signal to obtain a magnetic resonance high frequency digital signal and a magnetic resonance low frequency digital signal; filtering out the magnetic resonance high frequency digital signal through a digital filter to obtain the magnetic resonance low frequency digital signal, and taking the magnetic resonance low frequency digital signal as the magnetic resonance signal.

6. The method of claim 1 or 5, wherein, After obtaining the demodulated magnetic resonance signal, it further comprises: reconstructing an image according to the magnetic resonance signal to obtain a magnetic resonance image.

7. A compensation device in a magnetic resonance imaging system, characterized by It comprises: an acquisition module for acquiring first feature parameters of an ideal gradient waveform and second feature parameters of a target eddy current; the first feature parameters include first amplitude parameters at each target time point; the second feature parameters include multiple groups of time constants and amplitude constants; when the target eddy current is generated, the magnetic resonance center frequency in the magnetic resonance imaging system is shifted from a first frequency to a second frequency; the target time points include a current time point and at least one historical time point; The computing module is configured to calculate a second amplitude parameter of the compensation waveform of the target eddy current at each of the target time points according to the first characteristic parameter and the second characteristic parameter, so as to generate the compensation waveform according to the second amplitude parameter at the target time points. The first characteristic parameter and the second characteristic parameter are input into the following difference equation: n and n-1 represent two adjacent target time points respectively, p(n) represents a first amplitude parameter corresponding to the ideal gradient waveform at the target time point n, p(n-1) represents a first amplitude parameter corresponding to the ideal gradient waveform at the target time point n-1; w(n) represents a second amplitude parameter corresponding to the compensation waveform at the target time point n, w(n-1) represents a second amplitude parameter corresponding to the compensation waveform at the target time point n-1; α k represents the Kth group of amplitude constants, β k represents the Kth group of time constants, K represents the number of groups; The input module is configured to input the compensation frequency through a first register into a first phase accumulator, and output a first phase varying at the compensation frequency; and input the first frequency through a second register into a second phase accumulator, and output a second phase varying at the first frequency; the compensation frequency is determined according to the compensation waveform; the first phase accumulator is composed of a first adder and a third register, and an output of the third register is input as feedback into the first adder; the second phase accumulator is composed of a second adder and a fourth register, and an output of the fourth register is input as feedback into the second adder; the first phase and the second phase are input into a third adder, and a sum of the first phase and the second phase is calculated in the third adder; The query module is configured to query a sine signal and a cosine signal corresponding to the target phase in a cosine lookup table according to the target phase; the target phase is a sum of the first phase and the second phase; the sine signal and the cosine signal both have the second frequency; the second frequency is equal to a sum of the first frequency and the compensation frequency; The modulation and demodulation module is configured to modulate a radio frequency pulse signal using the cosine signal, so that the radio frequency pulse signal has the same frequency as the second frequency; and demodulate a magnetic resonance signal using the sine signal and the cosine signal, so that the frequency of the magnetic resonance signal is demodulated from the second frequency to a frequency of a baseband signal.

8. The apparatus of claim 7, wherein, Further comprising: The measurement module is configured to measure a waveform of the target eddy current when the target eddy current is generated in a historical time period; The fitting module is configured to fit the waveform of the target eddy current to obtain the second characteristic parameter.

9. An electronic device, comprising: The processor, the memory and the bus, the memory stores machine readable instructions executable by the processor, when the electronic device is running, the processor and the memory communicate through the bus, the machine readable instructions are executed by the processor to execute the steps of the method of any one of claims 1 to 6. The computer readable storage medium stores a computer program, and the computer program is executed by the processor to execute the steps of the method of any one of claims 1 to 6.

10. A computer-readable storage medium, characterized in that, ​

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