CN112184879A - Imaging method and system for reflecting cavitation bubble size space-time distribution - Google Patents
Imaging method and system for reflecting cavitation bubble size space-time distribution Download PDFInfo
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Abstract
The invention discloses an imaging method and system for reflecting the space-time distribution of cavitation bubble sizes, the method extracts subharmonic signals of different orders from space two-dimensional radio frequency data, obtains three threshold value matrixes by utilizing data before cavitation bubble generation, obtains three signal intensity matrixes by utilizing data after cavitation bubble generation, performs noise reduction after comparing the three threshold value matrixes with the signal intensity matrixes, and performs color coding on the subharmonic signals of different orders to obtain an imaging graph of the space-time distribution of the cavitation bubble sizes. The method provided by the invention belongs to the field of active cavitation imaging, utilizes the extraction of subharmonic waves and combines a pulse inversion technology to further improve the sensitivity of cavitation bubble detection, can carry out real-time space imaging, approximately reflects the space distribution of cavitation bubble sizes and the change condition in time, can approximately reflect the position distribution of cavitation bubbles with different sizes in space and the approximate proportion of the cavitation bubbles in cavitation bubble groups, and is suitable for various occasions capable of generating cavitation bubbles.
Description
[ technical field ] A method for producing a semiconductor device
The invention belongs to the field of ultrasonic detection and imaging, and particularly relates to an imaging method and system for reflecting the space-time distribution of cavitation bubble sizes.
[ background of the invention ]
The ultrasonic cavitation effect refers to the dynamic process that micro gas nuclei existing in liquid form cavitation bubbles under the action of sound waves and vibrate, grow and collapse under the action of a sound field. Cavitation effects may be applied to High Intensity Focused Ultrasound (HIFU) therapy, to promote chemical reactions, to break up liquid suspensions, to make emulsions, to kill bacteria, and to ultrasonic cleaning. Different applications use different ultrasonic frequencies, and the size range of the generated cavitation bubbles is different. The size and distribution of cavitation bubble size are very closely related to the actual effect produced by the application.
In the High Intensity Focused Ultrasound (HIFU) treatment, the cavitation effect can obviously enhance the absorption of tissues to ultrasonic energy and improve the treatment efficiency. At the same time, however, some uncertainty can arise, as well as irregular "tadpole-like" damage to the tissue and unpredictable cell damage. The size and distribution of cavitation bubbles generated during HIFU therapy directly affect the degree of tissue damage and the distribution of the damage. However, the current means for monitoring cavitation in HIFU therapy in real time can only determine the existence of cavitation and the position of the overall cavitation, and there is no method for determining the distribution of cavitation bubble size; some current methods for measuring the size distribution of cavitation bubbles require a relatively long measuring time, and cannot reflect the distribution change condition of the cavitation bubbles in real time or the spatial distribution condition of the size of the cavitation bubbles.
The use of the nonlinear properties of cavitation bubbles is an important class of methods for detecting and imaging cavitation bubbles. At present, the main nonlinear method is to use the second harmonic or higher harmonic of cavitation bubbles, however, biological tissues or other objects with acoustic nonlinear characteristics can also generate the second harmonic and higher harmonic, which can generate background noise for imaging cavitation bubbles, and reduce the detection sensitivity of cavitation bubbles.
[ summary of the invention ]
The invention aims to overcome the defects of the prior art and provide an imaging method and an imaging system for reflecting the space-time distribution of cavitation bubble sizes, which are used for solving the technical problems that the measurement time for determining the size distribution of cavitation bubbles is long, the space distribution condition of the cavitation bubble sizes is difficult to reflect, and the sensitivity is low when cavitation bubbles are detected by second harmonic waves or higher harmonic waves in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
an imaging method for reflecting the space-time distribution of cavitation bubble size,
filtering the spatial two-dimensional radio frequency data, extracting 1/2 subharmonic signals, 1/3 subharmonic signals and 1/4 subharmonic signals from the spatial two-dimensional radio frequency data, and converting the two-dimensional radio frequency data corresponding to the subharmonic signals into two-dimensional image data; acquiring three reference threshold matrixes from two-dimensional image data before cavitation bubble generation, and acquiring three signal intensity matrixes from the two-dimensional image data at each moment after cavitation bubble generation;
step 2, comparing a reference threshold matrix and a signal intensity matrix corresponding to 1/2-th harmonic signals for each moment of spatial two-dimensional radio frequency data, and setting the Colormap1 value of the 1/2-th harmonic signal occurrence position as 1 when the signal intensity in the intensity matrix is greater than the reference threshold in the reference threshold matrix, otherwise, setting the Colormap1 value as 0; comparing a reference threshold matrix and a signal intensity matrix corresponding to 1/3 subharmonic signals, and setting the value of the color coding Colormap2 at the occurrence position of the 1/3 subharmonic signals as 1 when the signal intensity is greater than the reference threshold value, otherwise, setting the value of the color coding Colormap as 0; comparing the reference threshold matrix and the signal intensity matrix corresponding to the 1/4 subharmonic signal, and setting the value of the color code Colormap3 at the position where the 1/4 subharmonic signal appears to be 1 when the signal intensity is greater than the reference threshold value, otherwise setting the value to be 0;
and 4, converting the three-dimensional matrix into actual imaging depth and transverse distance, and performing color display to obtain an imaging graph of the cavitation bubble size space-time distribution at each moment.
The invention is further improved in that:
preferably, in step 1, the spatial two-dimensional radio frequency data is pulse inversion summation, which is to sum echo signals of two ultrasound waveforms with the same shape and opposite phases.
Preferably, in step 1, the spatial two-dimensional radio frequency data is filtered by a butterworth filter, and a subharmonic signal of a set frequency is extracted.
Preferably, in step 1, each frame of two-dimensional radio frequency data is converted into two-dimensional image data by envelope detection.
Preferably, in step 2, before the three reference threshold matrices are compared with the signal strength matrix, the reference threshold matrices are modified by matrix coefficients N.
Preferably, the three reference threshold matrices are smoothed before being compared to the signal strength matrix.
Preferably, when two colors overlap in the image, it indicates that the size of the cavitation bubbles corresponding to the position in the image is between the sizes of the cavitation bubbles corresponding to the two types of subharmonic signals.
Preferably, when the three colors cross at a certain position in the image, the phenomenon that the cavitation bubbles break at the certain position in the image is represented.
Preferably, in the imaging graph, the shade of the color corresponding to each subharmonic represents the cavitation bubble signal intensity of the corresponding size.
An imaging system that reflects the spatiotemporal distribution of cavitation bubble size, comprising:
the acquisition module is used for acquiring space two-dimensional radio frequency data before cavitation bubbles are generated and space two-dimensional radio frequency data at each moment after the cavitation bubbles are generated;
the extraction module is used for extracting 1/2-order harmonic signals, 1/3-order harmonic signals and 1/4-order harmonic signals from the space two-dimensional radio frequency data, wherein the space two-dimensional radio frequency data before cavitation bubbles are generated form three reference threshold matrixes, and the space two-dimensional radio frequency data at each moment after the cavitation bubbles are generated form three signal intensity matrixes;
the comparison module is used for comparing the corresponding reference threshold matrix and the signal intensity matrix in each subharmonic signal and setting the color coding value of the position where each subharmonic signal appears according to the comparison result;
the compound module is used for carrying out product operation on the signal intensity matrix of each subharmonic at each moment and the corresponding color coding value of the subharmonic to obtain a new signal intensity matrix, and compounding the three new signal intensity matrices into a three-dimensional matrix;
and the imaging module is used for converting the three-dimensional matrix into actual imaging depth and transverse distance and carrying out color display to obtain an imaging graph of the cavitation bubble size space-time distribution at each moment.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses an imaging method for reflecting the space-time distribution of cavitation bubble sizes, which comprises the steps of firstly obtaining space two-dimensional radio frequency data after pulse inversion addition at different moments before and after cavitation bubble generation, extracting subharmonic signals (including 1/2,1/3 and 1/4 subharmonics) of different orders from the space two-dimensional radio frequency data so as to reflect cavitation bubbles of different sizes, obtaining three threshold matrixes by using the data before cavitation bubble generation, obtaining three signal intensity matrixes by using the data after cavitation bubble generation, carrying out color coding on the subharmonic signals of different orders after carrying out noise reduction after comparing the three threshold matrixes with the signal intensity matrixes, and carrying out component product operation on a color coding value and the signal intensity matrix so as to obtain an imaging graph of the space-time distribution of the cavitation bubble sizes. The method provided by the invention belongs to the field of active cavitation imaging, utilizes the extraction of subharmonic waves and combines a pulse inversion technology to further improve the sensitivity of cavitation bubble detection, can carry out real-time space imaging, approximately reflects the space distribution of cavitation bubble sizes and the change condition in time, can approximately reflect the position distribution of cavitation bubbles with different sizes in space and the approximate proportion of the cavitation bubbles in cavitation bubble groups, and is suitable for various occasions capable of generating cavitation bubbles. The invention can be applied to all occasions where cavitation bubbles are generated besides HIFU treatment, and only the proper ultrasonic frequency needs to be selected according to the actual application. In addition, compared with the existing single-first harmonic cavitation imaging method, the method can improve the detection sensitivity of cavitation bubbles on the whole.
Furthermore, the pulse inversion technology and the subharmonic imaging technology are combined, fundamental wave signals can be eliminated, extraction of subharmonic signals is facilitated, and the detection capability of subharmonics is improved.
Furthermore, the filtering is carried out through a Butterworth filter, the extracted signal has good filtering effect, and the curve is flat.
Further, by modifying the reference threshold matrix, the tissue signal in the ultrasound image can be eliminated, and only the cavitation bubble signal is reserved.
Furthermore, the threshold matrix is smoothed, so that discontinuous parts of the image are reduced, and the image is not abrupt and is more continuous.
Furthermore, different colors in the image are overlapped, and the distribution condition and the number of cavitation bubbles corresponding to several types of subharmonic signals are fully reflected.
The invention also discloses an imaging system for reflecting the space-time distribution of cavitation bubble sizes, which reflects the space distribution condition of the cavitation bubble sizes and the change condition of the distribution in time through the acquisition module, the extraction module, the comparison module and the imaging module and is suitable for cavitation detection and imaging in the occasions where the cavitation bubbles are generated.
[ description of the drawings ]
FIG. 1 is a total flow of compound subharmonic cavitation imaging;
FIG. 2 is a schematic diagram of a combination of pulse inversion and subharmonic techniques;
FIG. 3 is a schematic diagram of a composite color coding;
FIG. 4 is an example of complex subharmonic cavitation imaging when the threshold values are not equal.
[ detailed description ] embodiments
The invention is described in further detail below with reference to the accompanying drawings:
in the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention; the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; furthermore, unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly and encompass, for example, both fixed and removable connections; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The invention provides an imaging method and system for reflecting cavitation bubble size space-time distribution by using a composite subharmonic by using a pulse inversion technology, a subharmonic imaging technology and a color coding composite display technology. After the cavitation bubbles are generated, the generated cavitation bubbles have cavitation bubbles at all positions of one frame picture in terms of space, and new cavitation bubbles are generated at all times in terms of time. Referring to fig. 1, the method specifically includes the following steps:
Step 1.1, obtain the reference threshold matrix
Referring to fig. 2, a pulse inversion transmission technology is adopted, two ultrasonic waveforms with the same shape and opposite phases are transmitted before cavitation bubbles are generated, echo signals are summed to obtain a frame of space two-dimensional radio frequency data after pulse inversion summation, and space image data is obtained after band-pass filtering and envelope detection are performed on the space two-dimensional radio frequency data before cavitation bubbles are generated. For each spatial position, a reference Threshold can be obtained for each subharmonic component, and three reference Threshold matrixes (Threshold1, Threshold2 and Threshold3) are formed and respectively correspond to 1/2 subharmonic, 1/3 subharmonic and 1/4 subharmonic.
Step 1.2, obtaining a signal intensity matrix
Referring to fig. 2, after cavitation bubbles are generated, two ultrasonic waveforms with the same shape and opposite phases are transmitted by adopting a pulse inversion transmission technology, echo signals are summed, then subharmonic band-pass filtering is performed, spatial two-dimensional radio frequency data after pulse inversion summation of a frame are obtained at each moment, and data collected at different moments reflect the change condition of the cavitation bubbles in time. The time interval duration is set according to the requirement. In general ultrasonic imaging, broadband emission is generally adopted, and the signal pulse period is shorter and the axial resolution of images is better. However, broadband transmission can cause aliasing of the subharmonic signals in the echo with the fundamental signal in the frequency domain. The pulse inversion technology can eliminate fundamental wave signals, eliminate the interference of tissue or other reflected signals on cavitation bubble signals, enhance the detection of subharmonic signals and facilitate the improvement of the contrast of cavitation images.
For each frame of two-dimensional radio frequency data, 1/2,1/3 and 1/4 subharmonic signals are respectively extracted by adopting a Butterworth filter, and cavitation bubbles with different sizes are reflected by different subharmonics. After filtering, envelope detection is carried out on data corresponding to the subharmonic signals on each frame, and two-dimensional radio frequency data of each frame are changed into two-dimensional image data. The data obtained after cavitation bubble generation can respectively obtain three signal intensity matrixes at each moment.
The method can detect cavitation bubble signals with different sizes in a wider range by simultaneously extracting subharmonic components of different orders (1/2,1/3 and 1/4). This is because acoustic cavitation is generally a population effect that produces cavitated bubble populations with microbubbles of different sizes. Different sizes of cavitation bubbles have different resonant frequencies, and generate subharmonics of different orders. The sensitivity of cavitation imaging can be improved on the whole by detecting subharmonic components of different orders at the same time.
And 2, multiplying the reference threshold matrix obtained in the step 1 by a matrix coefficient N to obtain an actual threshold matrix (Th1, Th2 and Th3), removing noise signals of the signal Intensity matrix, and obtaining three new signal Intensity matrices (Intensity1, Intensity2 and Intensity3) at each moment.
In order to reduce the influence of background noise on the contrast of a cavitation image, a threshold value is set, before the threshold value is used, a reference threshold value matrix of three subharmonics is multiplied by a matrix coefficient N to serve as an actual threshold value matrix, the size of N can be manually adjusted according to actual conditions, the threshold value in the actual threshold value matrix is set based on radio frequency data obtained before cavitation bubbles are generated, and the three subharmonics correspond to the three actual threshold value matrices. Meanwhile, the threshold matrix can be further smoothed, that is, each pixel (matrix element) is taken as a center, a surrounding 3 × 3 area is taken as a smoothing window, and the average value of 9 pixels is assigned to the center pixel, so that the smoothed threshold matrix is obtained. Fig. 4 shows an example of cavitation imaging at different thresholds. The figure shows the B-mode image after cavitation and the complex subharmonic imaging results when the threshold coefficient N is set to 0, 1, 3, 5, respectively. When N is 0, it means that the threshold is not set. The images from top to bottom show that the HIFU irradiation power is gradually increased from small. Observing the composite subharmonic cavitation image when the threshold value is different, the tissue signal in the image is eliminated, and only the cavitation bubble signal is reserved. The cavitation bubble image generated at lower power has more noise signal. With the increase of the threshold coefficient N, the noise signals are gradually eliminated, but at the same time, some weak cavitation signals of the cavitation area are lost. Therefore, it is necessary to select an appropriate threshold value according to the actual application.
And step 3: the signal Intensity (Intensity1, Intensity2, Intensity3) and the Colormap (Colormap1, Colormap2, Colormap3) are multiplied by each component to obtain an Image (Intensity1, Colormap1, Intensity2, Colormap2, Intensity3, Colormap3), and the final Image is displayed in color. That is, the three new signal intensity matrixes are color-coded, the 1/2,1/3 and 1/4 subharmonic matrixes respectively correspond to green, blue and red, then the three monochromatic matrixes are compounded into a three-dimensional matrix, and each pixel point is displayed as color according to the value of three primary colors.
Specifically, point-to-point comparison is respectively performed on each pixel in the threshold value matrixes Th1, Th2 and Th3 and the signal Intensity matrixes Intensity1, Intensity2 and Intensity3, when the signal Intensity is greater than the threshold value, the color code Colormap at the corresponding position is set to be 1, and otherwise, the color code Colormap is set to be 0; colormap1, Colormap2, Colormap3 correspond to green, blue and red, respectively; if all three components are 0, the display in the picture is black. The Colormap is a color vector, wherein Colormap1 corresponds to the green component of the color vector, Colormap2 corresponds to the blue component of the color vector, and Colormap3 corresponds to the red component of the color vector.
And are compounded into a three-dimensional matrix, and each three-dimensional matrix corresponds to an acquisition time.
The subharmonic signals of different orders are encoded with different colors and displayed in the same image according to the intensity variation, and the color encoding mode is as shown in fig. 3. In order to display the spatial distribution of cavitation bubbles detected by subharmonics of different orders in an image, 1/2 subharmonics, 1/3 subharmonics and 1/4 subharmonics are selected to perform composite subharmonic imaging, three colors of green, blue and red are respectively corresponding to 1/2 subharmonics, 1/3 subharmonics and 1/4 subharmonics and represent three different subharmonic signals to perform image display, and three subharmonic matrixes are respectively converted into three primary colors of color display by using a composite color coding method. The shade of the color represents the intensity of the signal and indicates the number of cavitation bubbles with the corresponding size of the subharmonic component to a certain extent, and the darker the color indicates that the greater the intensity of the signal, the greater the number of cavitation bubbles with the corresponding size. The appearance of the cross-overlapped part of the two colors in the image indicates that the subharmonic signals corresponding to the two colors are detected to be stronger, and the size of the corresponding cavitation bubble is between the two subharmonic components. If the crossed part of the three colors appears to be nearly white in the image, the detected three subharmonic signals are all stronger and similar to the existence of white noise, which reflects the rupture condition of cavitation bubbles to a certain extent (white noise is generated when the cavitation bubbles rupture). The sizes of the areas with different colors in the image approximately reflect the distribution situation of the cavitation bubbles with the sizes corresponding to the subharmonic signals with different orders, and the wider the distribution, the larger the area, the more the number of the distributed cavitation bubbles is.
The method encodes the subharmonic signals of different orders with different colors and displays the subharmonic signals in the same image, and the color encoding mode is as shown in figure 3. By means of the display mode, the general situation of the spatial distribution of cavitation bubbles with different sizes and the approximate proportion of each cavitation bubble in the cavitation bubble groups can be visually reflected in the same image. Meanwhile, the dynamic change of cavitation bubbles in time and space can be reflected because the cavitation imaging is carried out in real time.
And 4, step 4: the matrix is scaled to the actual imaging depth and lateral distance and displayed in color.
The invention mainly provides a cavitation imaging method using composite subharmonic waves to reflect the space distribution condition of cavitation bubble size and the change condition of distribution in time, and is suitable for cavitation detection and imaging in the cavitation bubble generation occasions. The method comprises the following steps: (1) by adopting a pulse reversal emission technology, obtaining a frame of space two-dimensional radio frequency data after pulse reversal addition at different moments before and after cavitation bubble generation, reflecting the change situation in time at different moments, respectively extracting different subharmonic signals (including 1/2,1/3 and 1/4 subharmonics) aiming at each frame of two-dimensional radio frequency data, reflecting cavitation bubbles with different sizes, obtaining three threshold value matrixes by using the data before cavitation bubble generation, obtaining three signal intensity matrixes by using the data after cavitation bubble generation, and obtaining corresponding three signal intensity matrixes at each moment; (2) after removing noise signals by using a threshold matrix, obtaining three new signal intensity matrixes at different moments; (3) carrying out color coding on the three matrixes, wherein 1/2,1/3 and 1/4 subharmonics respectively correspond to green, blue and red, and compounding the three matrixes into a three-dimensional matrix; (4) and finally, converting the three-dimensional matrix into the actual imaging depth and the actual lateral distance in proportion and displaying the images in color.
Design principle of the invention
The detection sensitivity of the cavitation bubbles can be greatly improved by using the principle that subharmonic signals can be generated uniquely by micro-bubbles, and subharmonic signals are hardly generated by biological tissues or other objects with acoustic nonlinear characteristics. Meanwhile, because the frequency of the subharmonic signal is lower, the acoustic attenuation of the subharmonic signal is much smaller than that of the second harmonic and the higher harmonic, so that the subharmonic signal can be used for cavitation imaging of deep tissues. At present, the application of subharmonic waves focuses on passive cavitation imaging of HIFU therapy, however, passive cavitation imaging can only detect cavitation bubbles generated by ultrasound, and cannot detect cavitation bubbles generated in other situations. Also, the axial resolution of passive cavitation imaging is low and can only be used for localized rather than true imaging.
Research shows that the equilibrium radius of the microbubbles is inversely proportional to the subharmonic frequency generated under nonlinear vibration of the microbubbles, and the relationship between the radius and the subharmonic frequency is as follows:
in the formula: ρ -liquid density; omega0-a transmission center frequency; r0-the microbubble equilibrium radius; n-order of subharmonic frequency; pA-hydrostatic pressure; gamma-adiabatic ideal gas constant; σ — gas-liquid contact surface tension.
As can be seen from the above formula, R0And ω0The ratio/n is inversely proportional, so large-sized cavitation bubbles are more likely to generate higher-order subharmonic components, and small-sized cavitation bubbles are more likely to generate lower-order subharmonic components.
Acoustic cavitation is generally a population effect that simultaneously produces a population of cavitation bubbles having microbubbles of different sizes, and the size distribution of the cavitation bubbles may be in a range. Cavitation bubbles of different sizes have different resonant frequencies and different degrees of difficulty in generating subharmonics of different orders, and the cavitation bubbles are more likely to generate subharmonic components close to the resonant frequencies of the cavitation bubbles. 1/2 th harmonic is typically used to detect cavitation bubbles, however cavitation bubbles that have a resonant frequency far from the subharmonic component are difficult to detect. The invention provides the method for simultaneously extracting subharmonic components of different orders (1/2,1/3 and 1/4) so as to detect cavitation bubble signals of different sizes in a larger range. Meanwhile, the subharmonic components of different orders reflect signals generated by cavitation bubbles of different sizes.
The method comprises the following steps: (1) by adopting a pulse reversal emission technology, obtaining a frame of space two-dimensional radio frequency data after pulse reversal addition at different moments before and after cavitation bubble generation, reflecting the change situation in time at different moments, respectively extracting different subharmonic signals (including 1/2,1/3 and 1/4 subharmonics) aiming at each frame of two-dimensional radio frequency data, reflecting cavitation bubbles with different sizes, obtaining three threshold value matrixes by using the data before cavitation bubble generation, obtaining three signal intensity matrixes by using the data after cavitation bubble generation, and obtaining corresponding three signal intensity matrixes at each moment; (2) after removing noise signals by using a threshold matrix, obtaining three new signal intensity matrixes at different moments; (3) carrying out color coding on the three matrixes, wherein 1/2,1/3 and 1/4 subharmonics respectively correspond to green, blue and red, and compounding the three matrixes into a three-dimensional matrix; (4) and finally, converting the three-dimensional matrix into the actual imaging depth and the actual lateral distance in proportion and displaying the images in color.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. An imaging method for reflecting the space-time distribution of cavitation bubble size is characterized in that,
step 1, acquiring space two-dimensional radio frequency data before cavitation bubbles are generated, and space two-dimensional radio frequency data at each moment after the cavitation bubbles are generated, wherein the space two-dimensional radio frequency data is space two-dimensional radio frequency data after pulse reverse summation;
filtering the spatial two-dimensional radio frequency data, extracting 1/2 subharmonic signals, 1/3 subharmonic signals and 1/4 subharmonic signals from the spatial two-dimensional radio frequency data, and converting the two-dimensional radio frequency data corresponding to the subharmonic signals into two-dimensional image data; acquiring three reference threshold matrixes from two-dimensional image data before cavitation bubble generation, and acquiring three signal intensity matrixes from the two-dimensional image data at each moment after cavitation bubble generation;
step 2, comparing a reference threshold matrix and a signal intensity matrix corresponding to 1/2-th harmonic signals for each moment of spatial two-dimensional radio frequency data, and setting the Colormap1 value of the 1/2-th harmonic signal occurrence position as 1 when the signal intensity in the intensity matrix is greater than the reference threshold in the reference threshold matrix, otherwise, setting the Colormap1 value as 0; comparing a reference threshold matrix and a signal intensity matrix corresponding to 1/3 subharmonic signals, and setting the value of the color coding Colormap2 at the occurrence position of the 1/3 subharmonic signals as 1 when the signal intensity is greater than the reference threshold value, otherwise, setting the value of the color coding Colormap as 0; comparing the reference threshold matrix and the signal intensity matrix corresponding to the 1/4 subharmonic signal, and setting the value of the color code Colormap3 at the position where the 1/4 subharmonic signal appears to be 1 when the signal intensity is greater than the reference threshold value, otherwise setting the value to be 0;
step 3, multiplying the signal intensity matrix of each subharmonic at each moment by the corresponding color code value to obtain a new signal intensity matrix, and compounding the three new signal intensity matrices into a three-dimensional matrix;
and 4, converting the three-dimensional matrix into actual imaging depth and transverse distance, and performing color display to obtain an imaging graph of the cavitation bubble size space-time distribution at each moment.
2. An imaging method for reflecting the spatio-temporal distribution of cavitation bubble size according to claim 1, characterized in that, in step 1, the spatial two-dimensional radio frequency data is pulse reversal summation, which is to sum the echo signals of two ultrasound waveforms with the same shape and opposite phase.
3. The imaging method for reflecting the spatiotemporal distribution of cavitation bubble sizes as claimed in claim 1, wherein in step 1, the spatial two-dimensional radio frequency data is filtered by a Butterworth filter to extract a subharmonic signal with a set frequency.
4. An imaging method for reflecting the spatiotemporal distribution of cavitation bubble size according to claim 1, characterized in that, in step 1, each frame of two-dimensional radio frequency data is converted into two-dimensional image data by envelope detection.
5. An imaging method for reflecting the spatiotemporal distribution of cavitation bubble sizes according to claim 1, characterized in that in step 2, the three reference threshold matrices are modified by matrix coefficients N before being compared with the signal strength matrix.
6. An imaging method reflecting the spatio-temporal distribution of cavitation bubble sizes as claimed in claim 1, characterized in that the three reference threshold matrices are smoothed before being compared with the signal strength matrix.
7. An imaging method according to claim 1, wherein when two colors overlap in the image, the size of the corresponding cavitation bubble at the position in the image is between the sizes of the corresponding cavitation bubbles of the two types of subharmonic signals.
8. An imaging method according to claim 1, wherein the phenomenon of cavitation bubble collapse at a certain position in the image is indicated when three colors intersect at the certain position in the image.
9. An imaging method according to claim 1, wherein the intensity of the cavitation bubble signal in the corresponding size is represented by the shade of the color corresponding to each subharmonic in the imaging map.
10. An imaging system that reflects the spatiotemporal distribution of cavitation bubble size, comprising:
the acquisition module is used for acquiring space two-dimensional radio frequency data before cavitation bubbles are generated and space two-dimensional radio frequency data at each moment after the cavitation bubbles are generated;
the extraction module is used for extracting 1/2-order harmonic signals, 1/3-order harmonic signals and 1/4-order harmonic signals from the space two-dimensional radio frequency data, wherein the space two-dimensional radio frequency data before cavitation bubbles are generated form three reference threshold matrixes, and the space two-dimensional radio frequency data at each moment after the cavitation bubbles are generated form three signal intensity matrixes;
the comparison module is used for comparing the corresponding reference threshold matrix and the signal intensity matrix in each subharmonic signal and setting the color coding value of the position where each subharmonic signal appears according to the comparison result;
the compound module is used for carrying out product operation on the signal intensity matrix of each subharmonic at each moment and the corresponding color coding value of the subharmonic to obtain a new signal intensity matrix, and compounding the three new signal intensity matrices into a three-dimensional matrix;
and the imaging module is used for converting the three-dimensional matrix into actual imaging depth and transverse distance and carrying out color display to obtain an imaging graph of the cavitation bubble size space-time distribution at each moment.
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| HUIZHONG，ET AL.: "Pulse inversion based multi-subharmonic composite cavitation imaging", 《IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM》 * |
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