Endoscopic ultrasonic ringing artifact removal method based on time-frequency analysis filtering

Abstract

Provided is a self-adaptive single-array-element endoscopic ultrasonic ringing artifact removal method based on time-frequency analysis filtering. The method is as follows: acquiring endoscopic single-array-element ultrasonic imaging original data, and performing time-frequency spectrum analysis on adjacent frame signals; according to an optical flow method, obtaining a time-frequency spectrum mutation condition of a time-frequency spectrum of a signal to be processed relative to a reference signal; determining a threshold coefficient and a frequency spectrum distribution condition factor, and determining parameters of a time-frequency filter by means of the two parameters; performing time-frequency filtering on the signal to be processed by means of a time-frequency filter obtained by means of preliminary calculation and performing time domain recovery; performing index calculation on data after the artifact is filtered out by using time-frequency filtering and the original data, and optimizing and adjusting threshold parameters according to whether an index reaches a standard or not; and performing time-frequency filtering, time domain reconstruction, and ultrasonic endoscopic image reconstruction on the data by using a time-frequency filter parameter with the index reaching the standard. According to the method, the ringing artifact can be almost completely removed, an effective echo signal is recovered, and the structural integrity during short-distance imaging is maintained.

Description

Endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering Technical Field

[0001] This invention belongs to the field of interventional ultrasound imaging and relates to a method for removing ringing noise in interventional single-element ultrasound imaging, specifically an adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering. Background Technology

[0002] Currently, interventional single-element ultrasound imaging is often affected by various artifacts. Taking intravascular ultrasound (IVUS) as an example, ultrasound ringing artifact is a typical artifact in interventional single-element ultrasound imaging represented by IVUS.

[0003] Ringing artifacts are artifacts that occur when the ultrasonic transducer, excited by an ultrasonic transceiver, transmits an ultrasonic detection signal that is then received by the transducer itself. The presence of ringing artifacts leaves a series of dense, concentric bright rings in the central region of the ultrasound image. This makes it difficult for interventional single-element ultrasound probes to effectively acquire tissue structure information when close to the tissue being imaged, due to the masking effect of the ringing artifacts, significantly impacting the overall imaging capability of the system.

[0004] Some research findings have been made regarding the characteristics of ringing artifacts. Ringing artifacts are caused by zero drift generated during the use of the ultrasonic transceiver and electromagnetic interference from external equipment, leading to a certain degree of variation in the ultrasonic detection signal. When the ultrasonic detection signal reaches the tissue being imaged and generates an ultrasonic echo signal, a portion of the original detection signal is transmitted through the ultrasonic transducer into the overall ultrasonic signal acquisition. This portion of the ultrasonic detection signal, after coupling, constitutes the ultrasonic ringing artifact signal.

[0005] Currently, methods for removing ringing artifacts worldwide are relatively limited and cannot effectively distinguish between artifacts and normal echo signals. Due to the specific nature of ringing artifacts and their relatively fixed occurrence areas, most methods currently remove ringing artifacts and improve overall image contrast by circularly cropping a fixed area of ​​the reconstructed interventional ultrasound image. However, this method is based on image-end processing, ignoring the size of the ringing artifact area and failing to adjust for changes in external noise and transducer parameters. Furthermore, when the area to be imaged is close to the transducer, causing the effective echo signal to be submerged in ringing artifacts, conventional cropping methods will also remove the effective imaging information near the transducer. Another method is to perform frequency domain filtering on the signal before image reconstruction. This method can only suppress ringing artifacts to a certain extent and also has a suppressive effect on the ultrasound echo signal.

[0006] The aforementioned conventional methods may result in the inability to correctly reconstruct narrower sections near the catheter in interventional single-element ultrasound endoscopic imaging such as IVUS, ultimately affecting the acquisition of structural information of the overall cavity wall.

[0007] Summary of the Invention

[0008] To address the problem of ringing artifacts in interventional single-element endoscopic ultrasound imaging, which severely affect imaging quality and whose removal effects by existing methods are unsatisfactory, this invention provides an endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering. This method can almost completely remove ringing artifacts, restore effective echo signals, and maintain structural integrity during close-range imaging.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A method for removing ringing artifacts in endoscopic ultrasound based on time-frequency analysis filtering includes the following steps:

[0011] Step 1: Acquire the raw data of endoscopic single-element ultrasound imaging, and perform time-spectrum analysis on adjacent frame signals in the ultrasound data with ultrasound echo signals to obtain the time spectrum of the signal;

[0012] Step 2: Determine the abrupt changes in the time spectrum of the signal to be processed relative to the time spectrum of the reference signal using the optical flow method;

[0013] Step 3: Determine the threshold coefficient and spectral distribution factors, and use these two parameters to determine the parameters of the time-frequency filter;

[0014] Step 4: Perform time-frequency filtering on the signal to be processed using the time-frequency filter obtained from the preliminary calculation, and then perform time-domain recovery;

[0015] Step 5: After removing artifacts using time-frequency filtering, perform index calculations on the data and the original data, and optimize and adjust the threshold parameters based on whether the indexes meet the standards.

[0016] Step 6: Use time-frequency filter parameters that meet the specifications to perform time-frequency filtering, time-domain reconstruction, and ultrasound endoscopic image reconstruction on the data to obtain ultrasound endoscopic images without ringing artifacts.

[0017] An adaptive single-element endoscopic ultrasound ringing artifact removal device based on time-frequency analysis filtering includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the aforementioned adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] This invention can accurately and effectively reduce the "ringing" artifact effect in interventional single-element ultrasound endoscopic imaging, eliminate artifact coverage, improve the signal-to-noise ratio of proximal imaging, and significantly improve the overall structural imaging quality. Attached Figure Description

[0020] Figure 1 shows the composition of the raw ultrasound signal of a single array element;

[0021] Figure 2 is a flowchart of the endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering;

[0022] Figure 3 is the time-frequency spectrum of the reference signal;

[0023] Figure 4 is the time-spectrum image of the signal to be processed;

[0024] Figure 5 is an image of the changes in the time spectrum of the signal to be processed relative to the time spectrum of the reference signal;

[0025] Figure 6 is a comparison matrix (graphicalized) used for comparison with the time-frequency variation portion;

[0026] Figure 7 shows the preliminary calculated image of the time-frequency filter;

[0027] Figure 8 shows the ultrasound echo signal containing ultrasound ringing artifacts and the ultrasound echo signal after removing ultrasound ringing artifacts.

[0028] Figure 9 is an image reconstructed by the method of the present invention containing ringing artifacts;

[0029] Figure 10 is an image reconstructed by the method of the present invention with ringing artifacts removed. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0031] Since in a single-element imaging system, only a "line" pattern can usually be obtained in a single "emission-detection" operation, it is called an A-Line. In this invention, the A-Line signal will be used to represent the signal obtained in a single "emission-detection" operation.

[0032] Research on the existing generation methods of "ringing" artifacts reveals that the generated "ringing" artifacts follow a regular pattern. Ringing artifacts are generated due to the back-coupling of the emitted probe ultrasound into the received signal. Their position within the entire signal is relatively fixed, while their amplitude and shape may vary with hardware temperature and parameter fluctuations. However, adjacent ringing artifacts exhibit a strong similarity. The mixing process of the ultrasonic echo signal and the ringing artifact signal is shown in Figure 1. The ultrasonic excitation signal US...exciting (t) The ringing artifact signal k·C is formed through the coupling effect of the ultrasonic transducer and the influence of temperature and environment on the ringing artifact signal. P (t), and the ultrasound echo signal S reflected by the tissue under ultrasound excitation signal. P (t) are mixed to form the final sampled ultrasonic signal S(t), where k is the coupling effect of the ultrasonic transducer and the proportionality coefficient of temperature and environment.

[0033] This invention provides a method for removing ringing artifacts in endoscopic ultrasound based on time-frequency analysis filtering. The method is based on time-frequency spectrum analysis, which, according to the strong correlation between ringing artifacts between two adjacent A-line intervals, removes the relatively unchanged portions of the time-frequency spectrum, retaining the changing portions to eliminate the relatively fixed signal of the ringing artifact. As shown in Figure 2, the specific steps include:

[0034] Step 1: Acquire raw data from endoscopic single-element ultrasound imaging. Acquire ultrasound data containing ultrasound echo signals and ultrasound data containing only ultrasound ringing artifacts. Perform time-spectrum analysis on the signals between two adjacent A-line intervals in the ultrasound data containing ultrasound echo signals. Specific steps are as follows:

[0035] Step 11: Acquire a frame of B-sacn ultrasound data using an endoscopic ultrasound imaging system. The ultrasound data contains H groups of ultrasound A-line signals. Each ultrasound A-line signal consists of ultrasound ringing artifacts and ultrasound echo signals. The ultrasound data is obtained by converting the acoustic signals into electrical signals using an ultrasound transducer and finally acquiring them through a data acquisition card.

[0036] Step 12: Extract the signals of two adjacent A-line intervals from the ultrasound A-line signals of group H, and perform continuous wavelet transform or short-time Fourier transform on them to obtain the time spectrum of the two adjacent A-line interval signals, which are S e (w m ,t n ) M×N and S r (w m ,t n ) M×N As shown in Figures 3 and 4, where w m The vertical axis representing the frequency of the time spectrum, t n The horizontal axis represents the number of sampling points of the time spectrum. The calculated time spectrum is an M×N matrix, where M and N are the frequency resolution and time resolution of the time spectrum, respectively.

[0037] Step 2: Determine the abrupt changes in the time spectrum of the signal to be processed relative to the time spectrum of the reference signal using the optical flow method. The specific steps are as follows:

[0038] Step 21: Based on the time spectrum of the signal obtained in Step 1, select one frame of the time spectrum as the reference signal S. e (w m ,t n ) M×N ;

[0039] Step 22: Calculate S in the time spectrum using the optical flow method. r (w m ,t n ) M×N For S e (w m ,t n ) M×N The relatively changing part is obtained by taking the moving portion D of the time spectrum of the signal to be processed relative to the time spectrum of the reference signal. M×N The calculated motion portion of the time spectrum is shown in Figure 5, and the calculation formula is D. M×N =S e (w,t n ) M×N -S r (w,t n ) M×N .

[0040] Step 3: Determine the threshold coefficient and spectral distribution factors; these two parameters are used to determine the parameters of the time-frequency filter. The specific steps are as follows:

[0041] Step 3.1: Determine the threshold coefficient eff to decide whether the portion of the spectrum with a relative rate of change greater than the threshold coefficient is retained, and the portion with a relative rate of change less than the threshold coefficient is discarded.

[0042] Step 3.2: Simultaneously add the spectral distribution factor Γ(w) of ultrasound ringing artifacts. m ):

[0043] Γ(w m ) is the Fourier transform of the ringing artifact u0(t) itself, representing the frequency distribution of the ringing artifact. By adding this factor, the probability of removing the part with a wider frequency distribution can be increased.

[0044] Step 3.3: The reference time spectrum S e (w m ,t n ) M×N Multiply by the threshold coefficient eff, and simultaneously add the spectral distribution factor Γ(w) m ), to determine the final comparison matrix M com (m,n):

[0045] The calculated comparison matrix is ​​shown in Figure 6.

[0046] Step 3.4: Compare matrix M com (m,n) represents the moving portion D of the time spectrum of the signal to be processed relative to the time spectrum of the reference signal. M×N Compare them, and select D from them. M×N China-Belgium M com The larger elements of (m,n) are set to 1, and the smaller elements are set to 0, resulting in the preliminary time-frequency filter A(m,n):

[0047] The preliminary calculated time-frequency filter image is shown in Figure 7.

[0048] Step 4: Apply time-frequency filtering to the signal to be processed using the time-frequency filter obtained from the preliminary calculations, and then perform time-domain recovery. The specific steps are as follows:

[0049] Step 41: Use the initially obtained time-frequency filter A(m,n) to perform time-frequency filtering on the time spectrum of the signal to be processed, and obtain the time-frequency filtered time spectrum S. result (w,t n ): S result (w m ,t n )=A(m,n)·S e (w m ,t n )

[0050] Step 42: Filter the time-frequency spectrum S result (w,t n Perform inverse time-frequency transformation to recover the time domain signal and obtain the ultrasonic echo signal without ultrasonic ringing artifacts. The recovered time domain signal is shown in Figure 8.

[0051] Step 5: After removing artifacts using time-frequency filtering, calculate the performance indicators using the original data and optimize the threshold parameters based on whether the indicators meet the standards. The specific steps are as follows:

[0052] Step 51: Perform ultrasound ringing artifact removal on all ultrasound data containing ultrasound echo signals to obtain ultrasound echo signals u free of ringing artifacts. clear num (t), this signal is the num-th among all A-line signals, and is superimposed and mixed with ultrasound data containing only ringing artifacts to simulate the actual ultrasound echo signal u. mix num (t);

[0053] Step 52: Repeat the ultrasonic ringing artifact removal method to simulate the actual ultrasonic echo signal u. mixnum (t) Perform ultrasonic ringing artifact removal to obtain the ultrasonic echo signal u after artifact removal. cleaned num (t), this signal is compared with the ultrasonic echo signal u that does not contain ringing artifacts. clear num The correlation coefficient of the signal (t) is calculated, and the filtering process is repeated. The correlation coefficient between the recovered ultrasound echo signal and the original ultrasound echo signal is optimized by adjusting the value of the threshold coefficient eff.

[0054] Step 6: Perform time-frequency filtering on the data using time-frequency filter parameters that meet the specified standards, reconstruct the time domain, and then reconstruct the ultrasound endoscopic image. Compare the artifact removal effects. Figure 9 shows the image reconstructed using the method of this invention, which contains ringing artifacts, and Figure 10 shows the image reconstructed using the method of this invention, which removes ringing artifacts. As can be seen from Figures 9 and 10, removing ringing artifacts allows the image near the center of the image to be restored and is no longer affected by ultrasound ringing artifacts.

[0055] The present invention also provides an adaptive single-element endoscopic ultrasound ringing artifact removal device based on time-frequency analysis filtering. The device includes a memory and a processor, wherein the memory stores a computer program and the processor executes the computer program to realize the above-mentioned adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering.

Claims

1. An adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering, characterized in that... The method includes the following steps: Step 1: Acquire the raw data of endoscopic single-element ultrasound imaging, and perform time-spectrum analysis on adjacent frame signals in the ultrasound data with ultrasound echo signals to obtain the time spectrum of the signal; Step 2: Determine the abrupt changes in the time spectrum of the signal to be processed relative to the time spectrum of the reference signal using the optical flow method; Step 3: Determine the threshold coefficient and spectral distribution factors, and use these two parameters to determine the parameters of the time-frequency filter; Step 4: Perform time-frequency filtering on the signal to be processed using the time-frequency filter obtained from the preliminary calculation, and then perform time-domain recovery; Step 5: After removing artifacts using time-frequency filtering, perform index calculations on the data and the original data, and optimize and adjust the threshold parameters based on whether the indexes meet the standards. Step 6: Use time-frequency filter parameters that meet the specifications to perform time-frequency filtering, time-domain reconstruction, and ultrasound endoscopic image reconstruction on the data to obtain ultrasound endoscopic images without ringing artifacts.

2. The adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering according to claim 1, characterized in that... The specific steps of step 1 are as follows: Step 11: Acquire a frame of ultrasound B-scan data using an ultrasound endoscopic imaging system. The ultrasound data contains H groups of ultrasound A-line signals. Each ultrasound A-line signal consists of ultrasound ringing artifacts and ultrasound echo signals. Step 12: Extract the signals of two adjacent A-line intervals from the ultrasound A-line signals of group H, and perform continuous wavelet transform or short-time Fourier transform on them to obtain the time spectrum of the two adjacent A-line interval signals, which are S e (w m ,t n ) M×N and S r (w m ,t n ) M×N , where w m The vertical axis representing the frequency of the time spectrum, t n represent The number of sampling points on the horizontal axis of the time spectrum is used to calculate the time spectrum as an M×N matrix, where M and N are the frequency resolution and time resolution of the time spectrum, respectively.

3. The adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering according to claim 1, characterized in that... The specific steps of step 2 are as follows: Step 21: Based on the time spectrum of the signal obtained in Step 1, select one frame of the time spectrum as the reference signal S. e (w m ,t n ) M×N ; Step 22: Calculate S in the time spectrum using the optical flow method. r (w m ,t n ) M×N For S e (w m ,t n ) M×N The relatively changing part is obtained by taking the moving portion D of the time spectrum of the signal to be processed relative to the time spectrum of the reference signal. M×N .

4. The adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering according to claim 3, characterized in that... The D M×N The calculation formula is: D M×N =S e (w,t n ) M×N -S r (w,t n ) M×N .

5. The adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering according to claim 1, characterized in that... The specific steps of step 3 are as follows: Step 3.1: Determine the threshold coefficient eff to decide whether the portion of the spectrum with a relative rate of change greater than the threshold coefficient is retained, and the portion with a relative rate of change less than the threshold coefficient is discarded; Step 3.2: Simultaneously add the spectral distribution factor Γ(w) of ultrasound ringing artifacts. m ): u0(t) is a ringing artifact; Step 3.3: The reference time spectrum S e (w m ,t n ) M×N Multiply by the threshold coefficient eff, and simultaneously add the spectral distribution factor Γ(w) m ), to determine the final comparison matrix M com (m,n): Step 3.4: Compare matrix M com (m,n) represents the moving portion D of the time spectrum of the signal to be processed relative to the time spectrum of the reference signal. M×N Compare them, and select D from them. M×N China-Belgium M com In a (m,n) pair, the larger element is set to 1, and the smaller element is set to 1. Setting the initial value to 0, we obtain the preliminary time-frequency filter A(m,n):

6. The adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering according to claim 1, characterized in that... The specific steps of step 4 are as follows: Step 41: Use the initially obtained time-frequency filter A(m,n) to perform time-frequency filtering on the time spectrum of the signal to be processed, and obtain the time-frequency filtered time spectrum S. result (w,t n ): S result (w m ,t n )=A(m,n)·S e (w m ,t n ) Step 42: Filter the time-frequency spectrum S after time-frequency filtering result (w,t n Perform an inverse time-frequency transformation to restore the time-domain signal and obtain an ultrasonic echo signal free of ultrasonic ringing artifacts.

7. The adaptive single-element endoscopic ultrasound ringing artifact removal method based on time-frequency analysis filtering according to claim 1, characterized in that... The specific steps of step 5 are as follows: Step 51: Perform ultrasound ringing artifact removal on all ultrasound data containing ultrasound echo signals to obtain ultrasound echo signals u free of ringing artifacts. clear num (t), this signal is the num-th among all A-line signals, and is superimposed and mixed with ultrasound data containing only ringing artifacts to simulate the actual ultrasound echo signal u. mix num (t); Step 52: Repeat the ultrasonic ringing artifact removal method to simulate the actual ultrasonic echo signal u. mix num (t) Perform ultrasonic ringing artifact removal to obtain the ultrasonic echo signal u after artifact removal. cleaned num (t), this signal is compared with the ultrasonic echo signal u that does not contain ringing artifacts. clear num The correlation coefficient of the signal (t) is calculated, and the filtering process is repeated. The correlation coefficient between the recovered ultrasound echo signal and the original ultrasound echo signal is optimized by adjusting the value of the threshold coefficient eff.

8. An adaptive single-element endoscopic ultrasonic ringing artifact removal device based on time-frequency analysis filtering, characterized in that... The device includes a memory and a processor, wherein: The memory stores computer programs; The processor is used to execute the computer program to implement the adaptive single-element endoscopic ultrasonic ringing artifact removal method based on time-frequency analysis filtering as described in any one of claims 1-7.

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