Method for eliminating electromagnetic interference in real time

Abstract

The invention discloses an electromagnetic interference real-time elimination method, and relates to the technical field of magnetic resonance imaging. The method comprises the following steps: acquiring calibration data; obtaining a convolution kernel based on the calibration data, and determining a convolution kernel coefficient; determining a frequency domain coefficient based on the convolution kernel coefficient; original data are collected, Fourier transform is carried out to obtain corresponding frequency domain data, and the frequency domain data comprise induction coil frequency domain data and receiving coil frequency domain data; and based on the frequency domain coefficient and the frequency domain data of the induction coil, performing frequency domain weighted summation to obtain estimation of the frequency domain of the electromagnetic interference signal of the receiving coil, and based on the estimation, performing elimination from the frequency domain data of the receiving coil to realize electromagnetic interference elimination. According to the method, the convolution operation is replaced by the frequency domain weighting sum, the calculation efficiency is improved, and real-time and stable electromagnetic interference elimination can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic resonance imaging, and in particular to a method for eliminating electromagnetic interference in real time. Background Art

[0002] Traditional magnetic resonance imaging systems require strict electromagnetic shielding to prevent the impact of electromagnetic interference in the environment on imaging quality. However, electromagnetic shielding will greatly limit the application scenarios of magnetic resonance imaging. Multi-channel acquisition technology can be used to simultaneously obtain electromagnetic interference signals in the environment and magnetic resonance signals affected by electromagnetic interference, and eliminate electromagnetic interference on magnetic resonance signals. Existing related technologies include:

[0003] CN107110930A-Noise suppression method and device. In this invention patent, it is proposed to use a transfer function to estimate the electromagnetic interference in the imaging coil, that is, the relationship between the electromagnetic interference signals received by each channel can be described by a transfer function in the frequency domain, and the transfer function is represented by a series of correlation coefficients related to the signal frequency. However, since this method calculates the coefficients of the transfer function for a single frequency point one by one in the frequency domain, it is easily affected by noise; moreover, for frequency bands from multiple interference sources at the same time, the calculated coefficients are prone to deviation.

[0004] CN113176528A-Interference elimination method, medium and device. Aiming at the defects of the aforementioned invention patent, this invention patent proposes to estimate the electromagnetic interference in the imaging coil by convolution in the time domain, which can effectively solve the shortcomings of the aforementioned invention patent and greatly improve the signal-to-noise ratio of imaging. However, the convolution algorithm has a large amount of calculation, which is not conducive to the real-time elimination of electromagnetic interference.

[0005] Therefore, how to achieve real-time and stable electromagnetic interference elimination has become a problem that needs to be solved urgently. Summary of the invention

[0006] In order to overcome the above problems or at least partially solve the above problems, the present invention provides a real-time electromagnetic interference elimination method, which uses frequency domain weighting to replace convolution operations, improves calculation efficiency, and can achieve real-time and stable electromagnetic interference elimination.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] The present invention provides a method for eliminating electromagnetic interference in real time, which realizes multi-channel signal acquisition based on a receiving coil and a plurality of induction coils, wherein the receiving coil is used to receive a magnetic resonance signal, and the induction coil is used to sense an environmental electromagnetic interference signal; the method comprises the following steps:

[0009] Obtain calibration data;

[0010] Obtaining a convolution kernel based on the calibration data and determining a convolution kernel coefficient;

[0011] Determining frequency domain coefficients based on the convolution kernel coefficients;

[0012] Collecting raw data and performing Fourier transform to obtain corresponding frequency domain data, the frequency domain data including induction coil frequency domain data and receiving coil frequency domain data;

[0013] Based on the frequency domain coefficients and the frequency domain data of the induction coil, a frequency domain weighted summation is performed to obtain an estimate of the frequency domain of the electromagnetic interference signal of the receiving coil. Based on the estimate, the electromagnetic interference is eliminated from the frequency domain data of the receiving coil to achieve electromagnetic interference elimination.

[0014] In order to improve the computational efficiency, the present invention replaces the convolution operation with the weighted sum in the frequency domain after obtaining the convolution kernel coefficient. The frequency domain coefficient is multiplied with the frequency domain data of the induction coil to obtain the weighted frequency domain data; and the weighted frequency domain data of all the induction coils are added to obtain an estimate of the frequency domain of the electromagnetic interference signal of the receiving coil, and the electromagnetic interference can be eliminated by eliminating it from the frequency domain data of the receiving coil. The present invention uses the weighted sum in the frequency domain to replace the convolution operation, which improves the computational efficiency and can achieve real-time and stable electromagnetic interference elimination.

[0015] Furthermore, the calibration data includes electromagnetic interference signals sensed by the multi-channel induction coil and electromagnetic interference signals received by the receiving coil; the calibration data is used to estimate the coupling relationship between electromagnetic interference signals received by different channels.

[0016] Furthermore, the method for obtaining calibration data comprises the following steps:

[0017] Before or after acquiring the magnetic resonance signal, a pre-scan is performed with the transmitting radio frequency coil turned off to acquire calibration data.

[0018] Furthermore, the method for obtaining calibration data comprises the following steps:

[0019] For signals collected multiple times, the electromagnetic interference signal is obtained and used as calibration data by subtracting the signal data collected twice adjacently.

[0020] Furthermore, the method for obtaining calibration data comprises the following steps:

[0021] Perform an internal scan to acquire calibration data using the dead time during the MRI scan.

[0022] Furthermore, the above method for determining frequency domain coefficients based on convolution kernel coefficients includes the following steps:

[0023] Pad the convolution kernel coefficients with zeros to make the convolution kernel coefficients and the induction coil frequency domain data have the same length;

[0024] After zero padding, a one-dimensional Fourier transform is performed and flipped along the frequency domain direction to obtain the frequency domain coefficients.

[0025] Furthermore, the method for performing frequency domain weighted summation based on the frequency domain coefficients and the frequency domain data of the induction coil to obtain an estimate of the frequency domain of the electromagnetic interference signal of the receiving coil includes the following steps:

[0026] Multiply the frequency domain coefficients by the frequency domain data of the induction coils of each channel respectively to obtain weighted frequency domain data of the corresponding induction coils;

[0027] The weighted frequency domain data of all induction coils are added together to obtain a frequency domain estimate of the electromagnetic interference signal of the receiving coil, and the estimate is eliminated from the frequency domain data of the receiving coil to achieve electromagnetic interference elimination.

[0028] Furthermore, the real-time electromagnetic interference elimination method further includes the following steps:

[0029] After the electromagnetic interference is eliminated, image reconstruction is performed to obtain the final magnetic resonance image with the interference eliminated.

[0030] The present invention has at least the following advantages or beneficial effects:

[0031] The present invention provides a method for eliminating electromagnetic interference in real time. After obtaining the convolution kernel coefficient, the convolution operation is replaced by the weighted sum in the frequency domain to improve the calculation efficiency; the frequency domain coefficient is multiplied by the frequency domain data of the induction coil to obtain the weighted frequency domain data; and the weighted frequency domain data of all the induction coils are added to obtain an estimation of the frequency domain of the electromagnetic interference signal of the receiving coil, and the estimation is eliminated from the frequency domain data of the receiving coil to achieve electromagnetic interference elimination. The present invention uses the weighted sum in the frequency domain to replace the convolution operation, improves the calculation efficiency, and can achieve real-time and stable electromagnetic interference elimination. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 A flowchart of a method for real-time elimination of electromagnetic interference according to an embodiment of the present invention;

[0034] Figure 2 This is a block diagram of the magnetic resonance imaging system;

[0035] Figure 3 Schematic diagram of a convolution kernel in an embodiment of the present invention;

[0036] Figure 4 Schematic diagram of calculating frequency domain coefficients from convolution kernel coefficients in an embodiment of the present invention;

[0037] Figure 5 A structural block diagram of an electronic device provided by an embodiment of the present invention.

[0038] Description of reference numerals: 101, memory; 102, processor; 103, communication interface. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0042] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0043] In the description of the embodiments of the present invention, "plurality" means at least 2.

[0044] Example:

[0045] like Figure 1 As shown, an embodiment of the present invention provides a method for real-time elimination of electromagnetic interference, which realizes multi-channel signal acquisition based on a receiving coil and a plurality of induction coils, wherein the receiving coil is used to receive a magnetic resonance signal, and the induction coil is used to sense an environmental electromagnetic interference signal; the method comprises the following steps:

[0046] Acquire calibration data; the calibration data includes electromagnetic interference signals sensed by the multi-channel induction coil and electromagnetic interference signals received by the receiving coil; the calibration data is a pure electromagnetic interference signal, which is used to estimate the coupling relationship of electromagnetic interference signals received by different channels.

[0047] Obtaining a convolution kernel based on the calibration data and determining a convolution kernel coefficient;

[0048] Determining frequency domain coefficients based on the convolution kernel coefficients;

[0049] Collecting raw data and performing Fourier transform to obtain corresponding frequency domain data, the frequency domain data including induction coil frequency domain data and receiving coil frequency domain data;

[0050] Based on the frequency domain coefficients and the frequency domain data of the induction coil, a frequency domain weighted sum is performed to obtain an estimate of the frequency domain of the electromagnetic interference signal of the receiving coil, and based on the estimate, the electromagnetic interference is eliminated from the frequency domain data of the receiving coil to achieve electromagnetic interference elimination;

[0051] Furthermore, it includes: multiplying the frequency domain coefficients with the frequency domain data of the induction coils of each channel respectively to obtain weighted frequency domain data of the corresponding induction coils; adding the weighted frequency domain data of all induction coils to obtain a frequency domain estimate of the electromagnetic interference signal of the receiving coil, and eliminating it from the frequency domain data of the receiving coil to achieve electromagnetic interference elimination.

[0052] The present invention is a technical research and development for the electromagnetic interference problem in magnetic resonance imaging. Here, the principle of magnetic resonance imaging is briefly explained. Figure 2 As shown. The operator sends instructions to the spectrometer through the computer, and the spectrometer generates gradient waveforms and RF signal waveforms according to the instructions; the gradient waveform is amplified by the gradient amplifier, and the gradient coil forms the gradient of the magnetic field, thereby realizing spatial gradient encoding; and the RF signal is amplified by the RF amplifier and emitted by the transmitting RF coil, thereby exciting the protons (hydrogen nuclei) in the imaging area; and the excited protons will emit RF signals, which are received by the receiving RF coil, amplified by the receiving RF amplifier, converted into digital signals by the spectrometer, and transmitted to the computer for processing to obtain images for display.

[0053] The present invention realizes efficient real-time elimination of electromagnetic interference through multi-channel acquisition, and adopts two types of receiving radio frequency coils: one type of coil is used to receive magnetic resonance signals (receiving coil), but due to the lack of electromagnetic shielding, it will inevitably be affected by electromagnetic interference; the other type of coil is used to sense environmental electromagnetic interference signals (sensing coil). When designing, it is necessary to increase the signal-to-noise ratio that the coil can provide as much as possible, that is, for the receiving coil, it should be able to receive magnetic resonance signals as sensitively as possible, and be affected as little as possible by electromagnetic interference and thermal noise; for the sensing coil, it should be able to sense environmental electromagnetic interference as sensitively as possible, and receive as little magnetic resonance signals as possible, and may also be affected as little as possible by thermal noise. Both types of coils need to reduce the influence of thermal noise as much as possible. In practical applications, the coil resistance can be minimized to the greatest extent by cooling, thereby reducing the influence of thermal noise.

[0054] First, a convolution kernel is obtained from the calibration data. The convolution kernel can be used to estimate the electromagnetic interference in the receiving coil from the electromagnetic interference signal measured by the induction coil and eliminate it. More specifically, in the present invention, the electromagnetic interference signal received by the receiving coil can be estimated by the electromagnetic interference signal sensed by the induction coil through a convolution operation (e.g. Figure 3 Assume that the size of the convolution kernel is 2K+1, and the t-th sample of the r-th channel of the receiving coil is represented as s r,t ; The induction coil has a total of M channels, and the jth sample of the i-th channel of the induction coil is represented by s i,j , then we can have the following formula

[0055]

[0056] where c i,j The time-invariant convolution kernel coefficients can be estimated from the calibration signal.

[0057] In order to improve the computational efficiency, the present invention replaces the convolution operation with the weighted sum in the frequency domain after obtaining the convolution kernel coefficient. The frequency domain coefficient is multiplied with the frequency domain data of the induction coil to obtain the weighted frequency domain data; and the weighted frequency domain data of all the induction coils are added to obtain an estimate of the frequency domain of the electromagnetic interference signal of the receiving coil, and the electromagnetic interference can be eliminated by eliminating it from the frequency domain data of the receiving coil. The present invention uses the weighted sum in the frequency domain to replace the convolution operation, which improves the computational efficiency and can achieve real-time and stable electromagnetic interference elimination.

[0058] Furthermore, the method for obtaining calibration data comprises the following steps:

[0059] Before or after acquiring the magnetic resonance signal, a pre-scan is performed with the transmitting radio frequency coil turned off to acquire calibration data.

[0060] Furthermore, the method for obtaining calibration data comprises the following steps:

[0061] For signals collected multiple times, the electromagnetic interference signal is obtained and used as calibration data by subtracting the signal data collected twice adjacently.

[0062] Furthermore, the method for obtaining calibration data comprises the following steps:

[0063] Perform an internal scan to acquire calibration data using the dead time during the MRI scan.

[0064] In some embodiments of the present invention, the collected calibration signal (calibration data) includes the electromagnetic interference signal c sensed by the multi-channel induction coil. sen , and the electromagnetic interference signal c received by the receiving coil rec , then the coupling function F can be estimated so that F(c sen )=c rec Then, in the subsequent data collection, the electromagnetic interference signal s sensed by the induction coil can be sen The electromagnetic interference signal s received by the receiving coil is estimated by the coupling function rec , that is, s rec =F(c sen ). The calibration signal can be obtained in the following three ways.

[0065] (a) Pre-scan, that is, before (or after) acquiring magnetic resonance signals, with the transmitting radio frequency coil turned off (so that no magnetic resonance signals are generated), calibration signal data is acquired.

[0066] (b) For signals that have been acquired multiple times, it can be considered that the magnetic resonance signals acquired two times in close proximity are theoretically unchanged, while the electromagnetic interference signal changes randomly; by subtracting two close acquisitions, the electromagnetic interference signal can be retained as a calibration signal, while the magnetic resonance signal can be eliminated to the greatest extent.

[0067] (c) Intra-scan, which uses the dead time during the scanning process to collect the calibration signal.

[0068] Furthermore, the above method for determining frequency domain coefficients based on convolution kernel coefficients includes the following steps:

[0069] Pad the convolution kernel coefficients with zeros to make the convolution kernel coefficients and the induction coil frequency domain data have the same length;

[0070] After zero padding, a one-dimensional Fourier transform is performed and flipped along the frequency domain direction to obtain the frequency domain coefficients.

[0071] In some embodiments of the present invention, in order to improve the computational efficiency, after obtaining the convolution kernel coefficient, the above convolution operation can be replaced by the weighted sum in the frequency domain. Figure 4 As shown, the convolution kernel coefficients are padded with zeros to make them consistent with the length of the frequency domain data of the induction coil, and then a one-dimensional Fourier transform is performed and flipped along the frequency direction to obtain the frequency domain coefficients.

[0072] Furthermore, the real-time electromagnetic interference elimination method further includes the following steps:

[0073] After the electromagnetic interference is eliminated, image reconstruction is performed to obtain the final magnetic resonance image with the interference eliminated.

[0074] like Figure 5 As shown, in a third aspect, an embodiment of the present application provides an electronic device, which includes a memory 101 for storing one or more programs and a processor 102. When the one or more programs are executed by the processor 102, any method in the first aspect described above is implemented.

[0075] The memory 101, the processor 102 and the communication interface 103 are directly or indirectly electrically connected to each other to achieve data transmission or interaction. For example, these elements can be electrically connected to each other through one or more communication buses or signal lines. The memory 101 can be used to store software programs and modules, and the processor 102 executes various functional applications and data processing by executing the software programs and modules stored in the memory 101. The communication interface 103 can be used to communicate signaling or data with other node devices.

[0076] Among them, the memory 101 can be, but is not limited to, a random access memory (RAM), a read only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable read-only memory (EEPROM), etc.

[0077] The processor 102 may be an integrated circuit chip with signal processing capability. The processor 102 may be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it may also be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0078] In the embodiments provided in the present application, it should be understood that the disclosed method and system can also be implemented in other ways. The method and system embodiments described above are merely schematic. For example, the flowcharts and block diagrams in the accompanying drawings show the possible architecture, functions and operations of the method and system, method and computer program product according to multiple embodiments of the present application. In this regard, each box in the flowchart or block diagram can represent a module, a program segment or a part of a code, and the module, a program segment or a part of a code contains one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or the flowchart, and the combination of boxes in the block diagram and / or the flowchart can be implemented with a dedicated hardware-based system that performs a specified function or action, or can be implemented with a combination of dedicated hardware and computer instructions.

[0079] In addition, the functional modules in the various embodiments of the present application may be integrated together to form an independent part, or each module may exist separately, or two or more modules may be integrated to form an independent part.

[0080] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium on which a computer program is stored, and when the computer program is executed by the processor 102, a method as in any one of the first aspects described above is implemented. If the function is implemented in the form of a software function module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or part of the contribution to the prior art or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a disk or an optical disk.

[0081] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0082] It will be apparent to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above, and that the present application can be implemented in other specific forms without departing from the spirit or essential features of the present application. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the present application is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present application. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for real-time elimination of electromagnetic interference, characterized in that: Implementing multi-channel signal acquisition based on a receiving coil and a plurality of induction coils, wherein the receiving coil is used to receive magnetic resonance signals, and the induction coil is used to sense environmental electromagnetic interference signals; The following steps are involved: Obtain calibration data; Obtaining a convolution kernel based on the calibration data and determining a convolution kernel coefficient; Determining frequency domain coefficients based on the convolution kernel coefficients; Collecting raw data and performing Fourier transform to obtain corresponding frequency domain data, the frequency domain data including induction coil frequency domain data and receiving coil frequency domain data; Based on the frequency domain coefficients and the frequency domain data of the induction coil, a frequency domain weighted summation is performed to obtain an estimate of the frequency domain of the electromagnetic interference signal of the receiving coil. Based on the estimate, the electromagnetic interference is eliminated from the frequency domain data of the receiving coil to achieve electromagnetic interference elimination.

2. The method for real-time elimination of electromagnetic interference according to claim 1, characterized in that: The calibration data includes electromagnetic interference signals sensed by the multi-channel induction coil and electromagnetic interference signals received by the receiving coil; the calibration data is used to estimate the coupling relationship between electromagnetic interference signals received by different channels.

3. The method for real-time elimination of electromagnetic interference according to claim 1, characterized in that: The method for obtaining calibration data comprises the following steps: Before or after acquiring magnetic resonance signals, a pre-scan is performed with the transmitting radio frequency coil turned off to acquire calibration data.

4. The method for real-time elimination of electromagnetic interference according to claim 1, characterized in that: The method for obtaining calibration data comprises the following steps: For signals collected multiple times, the electromagnetic interference signal is obtained and used as calibration data by subtracting the signal data collected twice adjacently.

5. The method for real-time elimination of electromagnetic interference according to claim 1, characterized in that: The method for obtaining calibration data comprises the following steps: Perform an internal scan to acquire calibration data using the dead time during the MRI scan.

6. The method for real-time elimination of electromagnetic interference according to claim 1, characterized in that: The method for determining frequency domain coefficients based on convolution kernel coefficients comprises the following steps: Pad the convolution kernel coefficients with zeros to make the convolution kernel coefficients and the induction coil frequency domain data have the same length; After zero padding, a one-dimensional Fourier transform is performed and flipped along the frequency domain direction to obtain frequency domain coefficients.

7. The method for real-time elimination of electromagnetic interference according to claim 1, characterized in that: The method of performing frequency domain weighted summation based on the frequency domain coefficients and the frequency domain data of the induction coil to obtain an estimation of the frequency domain of the electromagnetic interference signal of the receiving coil comprises the following steps: Multiply the frequency domain coefficients by the frequency domain data of the induction coils of each channel respectively to obtain weighted frequency domain data of the corresponding induction coils; The weighted frequency domain data of all induction coils are added together to obtain a frequency domain estimate of the electromagnetic interference signal of the receiving coil, and the estimate is eliminated from the frequency domain data of the receiving coil to achieve electromagnetic interference elimination.

8. The method for real-time elimination of electromagnetic interference according to claim 1, characterized in that: The following steps are also included: After the electromagnetic interference is eliminated, image reconstruction is performed to obtain the final magnetic resonance image with interference eliminated.

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