Ultrasonic shock wave signal gain optimization method based on time reversal mirror

Abstract

The invention discloses an ultrasonic shock wave signal gain optimization method based on a time reversal mirror. The method comprises the following steps: S1, acquiring transmission characteristics of a channel; s2, performing system modeling of the virtual time reversal mirror based on the transmission characteristics; and S3, carrying out optimization processing on the TRM excitation signal. The ultrasonic shock wave amplitude is remarkably enhanced, the cracking capacity of the ultrasonic shock wave on high-hardness calcified plaques is improved, the ultrasonic shock wave enhancement device is suitable for shock wave enhancement application scenes in various acoustic systems, and the success rate and reliability of percutaneous coronary intervention therapy are improved.

Description

Technical Field

[0001] This invention belongs to the field of signal processing and ultrasonic shock wave control technology, and particularly relates to a method for optimizing the gain of ultrasonic shock wave signals based on a time-reversal mirror. Background Technology

[0002] Chronic total occlusion (CTO) is a complex lesion of coronary artery disease, characterized by the long-term accumulation of plaque along the inner wall of the artery, leading to severe narrowing or even complete occlusion of the vessel. Percutaneous coronary intervention (PCI) is widely used in the treatment of CTO due to its minimally invasive nature and rapid recovery. However, the proximal end of the occluded vessel often forms a hard, stubborn fibrous cap due to calcification and fibrosis, making it difficult to insert the guidewire and thus affecting the success rate of PCI in opening CTO lesions.

[0003] By emitting pulsed shock waves, calcified plaques within blood vessels can be effectively broken up, the lumen expanded, and vascular compliance improved, thereby reducing the difficulty of guidewire puncture and increasing the success rate of CTO-PCI surgery. Currently, shock wave generation methods mainly include electrical spark discharge, chemical explosion, electromagnetic pistons, and laser irradiation. However, these methods have certain limitations in application. For example, they require high-voltage drive, the physical process is difficult to precisely control, and the shock wave parameters are difficult to adjust flexibly after the hardware system is fixed.

[0004] In contrast, piezoelectric transducers offer advantages such as high controllability and integration, and are considered a more ideal method for generating shock waves. However, a drawback of this technology is the relatively small amplitude of the generated shock waves. To address this issue, Time-Reversal Mirror (TRM) technology can be introduced. The principle behind this technology is to use a low-amplitude broadband signal to achieve time-focused energy at the target location, thereby forming a stronger, shorter pulse.

[0005] However, current research on TRM signal gain optimization is still relatively lacking, resulting in the shock wave energy generated by TRM technology being insufficient to break up high-hardness calcified plaques. Therefore, a method for optimizing ultrasonic shock wave signal gain based on a time-reversal mirror is needed. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a method for optimizing the gain of ultrasonic shock wave signals based on a time-reversal mirror (TRM). By combining virtual time-reversal mirror modeling, frequency-domain windowing, and frequency-domain iterative weighting strategies, the TRM excitation signal is preprocessed and frequency-domain modulated, thereby indirectly controlling the TRM response signal. This significantly enhances the amplitude of the ultrasonic shock wave, improving its ability to dissolve high-hardness calcified plaques. This method improves the system's output energy through signal processing strategies without requiring high-voltage drive, offering advantages such as flexible parameter adjustment, strong adaptability, and ease of implementation. It is suitable for shock wave enhancement applications in various acoustic systems and helps improve the success rate and reliability of percutaneous coronary intervention.

[0007] To achieve the above objectives, the present invention provides a method for optimizing the gain of ultrasonic shock wave signals based on a time-reversal mirror, comprising:

[0008] S1. Obtain the transmission characteristics of the channel;

[0009] S2. System modeling of the virtual time-reversal mirror based on the aforementioned transmission characteristics;

[0010] S3. Optimize the TRM excitation signal.

[0011] Optionally, the transmission characteristics of the channel can be obtained, including:

[0012] The signal generator produces a voltage pulse signal in the form of a sinc function, which is converted into an ultrasonic signal by a piezoelectric transducer and then input to one end of the dispersive waveguide. At the other end, the piezoelectric transducer receives the response signal, records the response signal as a voltage signal, and estimates the transfer function based on the spectrum of the input signal and the response signal.

[0013] Optionally, the process of modeling the virtual time-reversal mirror system based on the transmission characteristics includes: reversing the received signal on the time axis to obtain its complex conjugate in the frequency domain, multiplying the spectrum of the reversed signal with the transfer function, and restoring the time-domain TRM response signal through inverse fast Fourier transform.

[0014] Optionally, the process of optimizing the TRM excitation signal includes: preprocessing the signal after time-reversal mirror processing and frequency-domain adaptive modulation.

[0015] Optionally, the signal preprocessing process includes: using zero-filling to improve spectral resolution and bandpass filtering the signal to focus on the center frequency of the piezoelectric transducer.

[0016] Optionally, the frequency-domain adaptive modulation process includes: designing a frequency-selective modulation function to amplify or suppress different frequency components of the TRM excitation signal.

[0017] Optionally, the process of designing the frequency-selective modulation function includes using a frequency-domain windowing method, which applies a Gaussian window function to the TRM excitation signal in the frequency domain to enhance key frequency components near the center frequency and suppress energy leakage in non-target frequency bands.

[0018] Optionally, the process of designing the frequency-selective modulation function includes using a frequency-domain iterative weighting method, based on the spectral characteristics of the TRM excitation signal, increasing the excitation amplitude in the frequency band that contributes the main output energy, and iteratively updating the weighting strategy to improve the shock wave gain.

[0019] Technical Effects of this Invention: This invention discloses a method for optimizing the gain of ultrasonic shock wave signals based on a time-reversal mirror (TRM). By preprocessing and frequency-domain modulating the TRM excitation signal, the amplitude of the TRM response signal can be significantly improved, enhancing the focusing of the ultrasonic shock wave in the target area and effectively improving the effect on high-hardness calcified plaques. It requires no high-voltage drive, features a simple structure, flexible control, and high integration, and offers strong controllability during operation, facilitating engineering deployment and application. For the frequency-domain adaptive modulation process, this invention proposes two optimization strategies to meet the needs of different application scenarios: Frequency-domain windowing method: Simple to implement and computationally inexpensive, suitable for applications requiring rapid deployment or real-time response. This method effectively suppresses signal components in non-target frequency bands, improving the concentration and peak intensity of the output signal. Frequency-domain iterative weighting method: Based on multi-round traversal search to obtain the optimal weight combination, although computationally complex, it can achieve a more significant gain improvement under offline optimization conditions, suitable for systems with higher performance requirements. This method can dynamically adjust the weighting strategy according to the frequency response characteristics of the system, without relying on a preset fixed weighting scheme, and can also ensure that each weighting moves towards the optimization goal, thus having stronger adaptability. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0021] Figure 1 This is a flowchart illustrating an ultrasonic shock wave signal gain optimization method based on a time-reversal mirror according to an embodiment of the present invention.

[0022] Figure 2 This embodiment of the invention demonstrates the energy focusing effect of a dispersive signal propagating in a waveguide after being processed by a time-reversal mirror (TRM);

[0023] Figure 3This invention illustrates the coefficient changes of two modulation methods, Windowed-TRM and Weighted-TRM, during the spectral processing of the TRM excitation signal.

[0024] Figure 4 The figure shows a comparison of time-domain simulation results of the traditional TRM and the windowed-optimized TRM method in the embodiments of the present invention, where (a) is the TRM excitation signal and the Windowed-TRM excitation signal, and (b) is a magnified view of the TRM response signal and the Windowed-TRM response signal.

[0025] Figure 5 This is an embodiment of the present invention. Figure 4 Corresponding frequency domain power spectrum comparison chart;

[0026] Figure 6 The figure shows a comparison of time-domain simulation results of the traditional TRM and the iterative weighted optimization TRM method in the embodiments of the present invention, where (a) is the TRM excitation signal and the Weighted-TRM excitation signal, and (b) is a magnified view of the TRM response signal and the Weighted-TRM response signal.

[0027] Figure 7 This is an embodiment of the present invention. Figure 6 Corresponding frequency domain power spectrum comparison chart;

[0028] Figure 8 The shock wave results were obtained using the traditional TRM method in the physical experiment of this invention embodiment.

[0029] Figure 9 The shock wave results were obtained using the Weighted-TRM method in the physical experiment of this invention. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0032] like Figure 1 As shown, this embodiment provides a method for optimizing the gain of ultrasonic shock wave signals based on a time-reversal mirror, including:

[0033] S1. Obtain the transmission characteristics of the channel;

[0034] S2. System modeling based on a virtual time-reversal mirror;

[0035] Optimization of S3 and TRM excitation signals.

[0036] Specifically, S1 includes:

[0037] S1.1 Provide a shock wave generating device, including a signal generator, a piezoelectric transducer (i.e., an ultrasonic probe), and a dispersive waveguide;

[0038] S1.2 The signal generator produces a voltage pulse signal x(t) in the form of a sinc function. This signal is converted into an ultrasonic signal by a piezoelectric transducer and input to one end of a dispersive waveguide. At the other end, a low-amplitude broadband signal is received by the piezoelectric transducer and recorded as a voltage signal y(t). This propagation process can be represented by the following formula:

[0039]

[0040] Where h^(t) is the estimated channel impulse response function, and n(t) is the interference noise. This represents the convolution operation.

[0041] The impulse response function characterizes the system's response behavior under unit impulse excitation and is a time-domain description of the system's transmission characteristics.

[0042] S1.3 To simplify modeling and calculation (time-domain convolution corresponds to frequency-domain multiplication) and to more intuitively analyze the variation characteristics of different frequency components, the signal needs to be converted from the time domain to the frequency domain for processing. By acquiring the input and output signals, the spectrum is calculated using the Fast Fourier Transform (FFT), and then the transfer function of the dispersive waveguide is estimated using the following formula.

[0043]

[0044] Where Y(f) and X(f) represent the spectrum of the response signal y(t) and the excitation signal x(t), respectively, * denotes complex conjugate, and ε is a small constant introduced to avoid the denominator being zero.

[0045] This transfer function represents the frequency domain transmission characteristics of the channel, which can describe the amplitude and phase changes of a signal propagating in a complex medium, providing a foundation for the subsequent simulation modeling of a virtual time-reversal mirror.

[0046] Specifically, S2 includes:

[0047] S2.1 The virtual time-reversal mirror modeling refers to calculating the backpropagation response of a system in a simulation environment using the channel transfer function and the time-reversed result of the received signal, without the need for actual backpropagation experiments. This allows for the prediction and optimization of the TRM focusing performance. The modeling process mainly includes: reversing the received signal on the time axis (equivalent to taking its complex conjugate in the frequency domain), multiplying its spectrum by the transfer function to obtain the TRM response in the frequency domain, and finally restoring the TRM response signal in the time domain using the inverse fast Fourier transform (IFFT).

[0048] S2.2 The core idea of ​​the virtual time-reversal mirror technology is that: only one probe signal needs to be sent in the real environment and the echo signal recorded to complete the channel estimation, and then the propagation process of time reversal is reconstructed through a simulation model. According to the reciprocity principle of sound wave propagation in a linear time-invariant system, after time reversal processing, the frequency components that were originally propagating dispersedly in the dispersive medium can be resynchronized at the sound source, thereby forming a concentrated shock wave pulse.

[0049] S2.3. The specific operation is as follows: During the simulation, the time-reversed signal y(-t) is re-inputted into the system as the TRM excitation signal. The estimated channel transfer function TF(f) is used to simulate the reverse propagation process of "receiver transmitting in reverse and original transmitter receiving," thereby forming a spatiotemporally focused TRM response signal q(t) at the original signal source location. The time-domain representation of this process is as follows:

[0050]

[0051] in This constitutes a virtual time reversal channel.

[0052] In practical calculations, using the frequency domain form is more efficient; therefore, the spectrum of the TRM response signal is obtained as follows:

[0053] Q(f)=FFT(y(-t))·TF(f)=Y * (f)·TF(f);

[0054] Finally, the time-domain representation of the TRM response signal can be obtained through IFFT as follows:

[0055]

[0056] S2.4 Through the above simulation modeling process, without the need for complex physical backpropagation experiments, the TRM response focusing effect under different input signal conditions can be quickly predicted, thus providing a clear energy distribution reference and response evaluation basis for the subsequent design and optimization strategy of frequency domain modulation function.

[0057] Specifically, S3 includes:

[0058] S3.1 Signal preprocessing: To improve the resolution of the spectrum, zero-filling is used to improve the accuracy of the Fast Fourier Transform (FFT). At the same time, the signal is bandpass filtered to focus on the center frequency of the piezoelectric transducer, remove irrelevant frequency band interference, and improve the stability of the system.

[0059] S3.2, Frequency Domain Adaptive Modulation:

[0060] To further enhance the energy focusing effect of the TRM excitation signal, this invention adaptively modulates the signal y(-t) after processing by the time-reversal mirror to form a TRM excitation signal s(t) with optimized characteristics. By designing a frequency-selective modulation function o(t), targeted amplification or suppression of different frequency components of the TRM excitation signal is achieved. The above process can be expressed as:

[0061]

[0062] Since convolution in the time domain corresponds to multiplication in the frequency domain, in practice, a fast Fourier transform is used to transform the signal from the time domain to the frequency domain, and the TRM excitation signal is processed in the frequency domain in the simulation environment:

[0063] S(f))=O(f)·Y * (f);

[0064] Among them, S(f), O(f), Y * (f) are the frequency domain representations of s(t), o(t), and y(-t), respectively.

[0065] This invention proposes two methods for constructing the frequency domain modulation function O(t):

[0066] S3.2.1 Frequency Domain Windowing Method: By applying a Gaussian window function to the TRM excitation signal in the frequency domain, the key frequency components near the center frequency are enhanced, energy leakage in non-target frequency bands is suppressed, and the bandwidth is controlled to compress the main lobe.

[0067] The specific implementation method is as follows: Analyze the spectral characteristics of the system's transfer function, and combine its peak value with the center frequency of the piezoelectric transducer to select a suitable center frequency of the Gaussian window function; set the bandwidth of the window function to control the frequency range of energy concentration. The expression for the Gaussian window function is:

[0068]

[0069] Where f center σ is the center frequency of the Gaussian window, and σ is the standard deviation, which can be calculated using the principle of full width at half height (FWHM).

[0070] The spectrum of the TRM excitation signal after the Gaussian window is as follows:

[0071] S windowed (f)=O(f)·Y * (f)=G(f)·Y * (f).

[0072] S3.2.2 Frequency Domain Iterative Weighting Method: Based on the spectral characteristics of the original TRM excitation signal, the excitation amplitude is increased in the frequency band that contributes the main output energy, while other frequency bands are kept unchanged or moderately suppressed.

[0073] The specific implementation method is as follows: Construct a weighting function W(f), which has the following form:

[0074]

[0075] Where k is used to control the weighting intensity, f low and f high These are the left and right endpoints of the weighted interval, respectively.

[0076] The optimization process is as follows: Iterate through different frequency bands to change the weighting factor and adjust the spectrum of the TRM excitation signal; in each round, evaluate the current weighting effect by calculating the ratio of the peak-to-peak value of the TRM response signal to the TRM excitation signal in the time domain; select the set of weighting parameters that maximizes the gain and use the updated TRM excitation signal as the input for the next iteration; continuously iterate and update the weighting strategy to gradually increase the shock wave gain; terminate the optimization when the gain converges or reaches the iteration limit and output the final TRM excitation signal.

[0077] The specific implementation process of this embodiment includes the following steps:

[0078] Channel estimation, virtual time-reversal mirror modeling, adaptive modulation processing, and experimental verification.

[0079] In this embodiment, a 10mm diameter, 3000mm long aluminum rod is used as a dispersive waveguide, and the piezoelectric transducer is a Doppler ultrasonic probe, model DPL1P24. During the simulation, the excitation and response signals are bandpass filtered in the 0.75-1.6MHz frequency band to remove irrelevant frequency interference.

[0080] The implementation process of a virtual time reversal mirror is as follows: Figure 2 As shown. For easier observation and comparison, the amplitude was scaled by a factor of 0.009 when plotting the original excitation signal. Simulation results show that the signal re-emitted after processing by the time-reversal mirror can be clearly focused at the waveguide source, and the resulting TRM response signal exhibits a short pulse form, demonstrating good energy concentration characteristics.

[0081] Simulation comparison results of shock waves generated by traditional TRM and frequency-domain windowed optimized TRM are as follows: Figure 4 , Figure 5 As shown in the figure. Simulation results show that the windowed-TRM response signal has a narrower main lobe width, significantly reduced spectral leakage, and more concentrated energy distribution after windowing. Compared with the traditional TRM method, its gain is improved by 39.08%, verifying the effectiveness of the windowing strategy in improving signal focusing ability.

[0082] Furthermore, Figure 6 and Figure 7 Simulation results show the generation of shock waves using a traditional TRM and a frequency-domain iteratively weighted optimized TRM. The simulation results demonstrate that the spectrum of the Weighted-TRM response signal obtained after iterative weighting is sharper, and the energy concentration of the main lobe is significantly better than that of the windowing method. The Weighted-TRM gain is increased by 55.29% compared to the traditional TRM, showing superior energy enhancement performance.

[0083] Based on simulation optimization, the modulated Weighted-TRM excitation signal was transmitted in an actual shock wave generating device, and the Weighted-TRM response signal was acquired at the receiving end. This signal was then compared with the measured results of the unprocessed TRM excitation signal after transmission. The experimental verification results for the frequency domain iterative weighting method are as follows: Figure 8 , Figure 9 As shown in the figure. Experimental results show that the measured gain of the Weighted-TRM is 60.03% higher than that of the traditional TRM, effectively verifying the significant role of the signal gain optimization method based on time-reversal mirror and adaptive modulation proposed in this invention in enhancing ultrasonic shock wave signals.

[0084] This invention discloses a method for optimizing the gain of ultrasonic shock wave signals based on a time-reversal mirror (TRM). By preprocessing and frequency-domain modulating the TRM excitation signal, the amplitude of the TRM response signal can be significantly improved, enhancing the focusing of the ultrasonic shock wave in the target area and effectively improving the effect on high-hardness calcified plaques. It requires no high-voltage drive, features a simple structure, flexible control, and high integration, and offers strong controllability during operation, facilitating engineering deployment. For the frequency-domain adaptive modulation process, this invention proposes two optimization strategies to meet the needs of different application scenarios: Frequency-domain windowing method: Simple to implement and computationally inexpensive, suitable for applications requiring rapid deployment or real-time response. This method effectively suppresses signal components in non-target frequency bands, improving the concentration and peak intensity of the output signal. Frequency-domain iterative weighting method: Based on multi-round traversal search to obtain the optimal weight combination, although computationally complex, it can achieve a more significant gain improvement under offline optimization conditions, suitable for systems with higher performance requirements. This method can dynamically adjust the weighting strategy according to the frequency response characteristics of the system, without relying on a preset fixed weighting scheme, and ensures that each weighting moves towards the optimization goal, thus exhibiting stronger adaptability.

[0085] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for optimizing the gain of ultrasonic shock wave signals based on a time-reversal mirror, characterized in that, include: S1. Obtain the transmission characteristics of the channel; S2. System modeling of the virtual time-reversal mirror based on the aforementioned transmission characteristics; S3. Optimize the TRM excitation signal.

2. The ultrasonic shock wave signal gain optimization method based on a time-reversal mirror as described in claim 1, characterized in that, The transmission characteristics of the channel include: The signal generator produces a voltage pulse signal in the form of a sinc function, which is converted into an ultrasonic signal by a piezoelectric transducer and then input to one end of the dispersive waveguide. At the other end, the piezoelectric transducer receives the response signal, records the response signal as a voltage signal, and estimates the transfer function based on the spectrum of the input signal and the response signal.

3. The ultrasonic shock wave signal gain optimization method based on a time-reversal mirror as described in claim 1, characterized in that, The process of modeling the virtual time-reversal mirror system based on the transmission characteristics includes: reversing the received signal on the time axis to obtain its complex conjugate in the frequency domain, multiplying the spectrum of the reversed signal with the transfer function, and restoring the time domain TRM response signal through inverse fast Fourier transform.

4. The ultrasonic shock wave signal gain optimization method based on a time-reversal mirror as described in claim 1, characterized in that, The process of optimizing the TRM excitation signal includes: signal preprocessing and frequency domain adaptive modulation of the signal after time-reversal mirror processing.

5. The ultrasonic shock wave signal gain optimization method based on a time-reversal mirror as described in claim 4, characterized in that, The signal preprocessing process includes: using zero-filling to improve spectral resolution and bandpass filtering the signal to focus on the center frequency of the piezoelectric transducer.

6. The ultrasonic shock wave signal gain optimization method based on a time-reversal mirror as described in claim 4, characterized in that, The process of frequency-domain adaptive modulation includes: designing a frequency-selective modulation function to amplify or suppress different frequency components of the TRM excitation signal.

7. The ultrasonic shock wave signal gain optimization method based on a time-reversal mirror as described in claim 6, characterized in that, The process of designing a frequency-selective modulation function includes using a frequency-domain windowing method. By applying a Gaussian window function to the TRM excitation signal in the frequency domain, the key frequency components near the center frequency are enhanced and energy leakage in non-target frequency bands is suppressed.

8. The ultrasonic shock wave signal gain optimization method based on a time-reversal mirror as described in claim 6, characterized in that, The process of designing a frequency-selective modulation function involves using a frequency-domain iterative weighting method. Based on the spectral characteristics of the TRM excitation signal, the excitation amplitude is increased in the frequency band that contributes the main output energy, and the weighting strategy is updated iteratively to improve the shock wave gain.

Images