CN108577806A - Viscoplasticity detecting system based on low frame per second laser speckle contrast imaging and method - Google Patents

Abstract

The invention discloses a viscoelasticity detection system and method based on low frame rate laser speckle contrast imaging. The laser beam collects multiple frames of laser speckle images with a lower frame rate and exposure time, and calculates the propagation speed of the aliasing wave, and calculates the propagation speed of the surface wave by using the relationship between the aliasing wave propagation speed and the surface wave propagation speed Speed, to obtain the elasticity and viscosity of the sample to be tested; the detection system includes an excitation subsystem and a laser speckle imaging subsystem. The present invention detects the surface wave excited by the orthogonal oscillation of the tested sample, and calculates the propagation velocity of the surface wave by using the aliased wave velocity collected at a low frame rate, thereby quantitatively solving the viscoelastic modulus of the tested sample, which is beneficial to Reduce the complexity and cost of detection; and adopt reflective laser speckle imaging, which is conducive to the convenience of actual detection.

Description

Viscoelasticity Detection System and Method Based on Low Frame Rate Laser Speckle Contrast Imaging

technical field

The invention relates to the technical field of viscoelasticity detection, in particular to a viscoelasticity detection system and method based on low frame rate laser speckle contrast imaging.

Background technique

The occurrence and development of diseases (such as atherosclerosis, skin tumors, etc.) will change the mechanical properties (such as elasticity and viscosity) of biological tissues. Biological tissue viscoelasticity measurement can be used to monitor the disease process and achieve the purpose of early diagnosis of disease.

The viscoelasticity measurement of biological tissue reflects the mechanical properties of biological tissue by measuring the strain of biological tissue under the action of stress, in which the stress is applied to the measured sample through an external excitation device, and the strain-related parameters can be imaged by laser speckle contrast method to measure. Laser speckle contrast imaging detects the motion of the measured object through the change of the speckle pattern under disturbance, and has been widely used in the detection of blood flow.

In optical imaging, the imaging field of view is small, generally ranging from a few millimeters to tens of millimeters, but the propagation speed of surface waves in biological soft tissues is generally 1m/s to 10m/s. So fast sampling rates are needed to track the propagation of surface waves. The sampling frame rate of laser speckle contrast imaging is related to the speed of the camera. The sampling frame rate of the camera is generally less than a few hundred frames per second, which cannot meet the high spatial resolution of tracking surface waves. At this stage, the sampling frame rate of the system is generally increased through expensive high-speed cameras, or different parts of the signal are time-divided through precise synchronization between acquisition and excitation, but both high-speed cameras and synchronous methods will increase System complexity and cost.

Contents of the invention

The purpose of the present invention is to overcome the above technical deficiencies, and propose a viscoelasticity detection system and method based on low frame rate laser speckle contrast imaging, which can obtain the viscoelasticity of the sample to be tested through low frame rate laser speckle contrast imaging. elasticity.

In order to achieve the above technical objectives, the technical solution of the present invention includes a viscoelasticity detection method based on low frame rate laser speckle contrast imaging, including the following steps:

S1. Carry out a certain frequency orthogonal oscillation excitation on the surface of the tested sample, and form a surface wave on the surface of the tested sample;

S2. Send out a laser beam irradiated on the surface of the tested sample, collect multi-frame laser speckle images of the tested sample during surface wave propagation at a lower frame rate and exposure time, and perform calculation processing on the multi-frame laser speckle images , to obtain the propagation velocity of the aliasing wave, calculate the propagation velocity of the surface wave by using the relationship between the aliasing wave propagation velocity and the surface wave propagation velocity, and obtain the elasticity and viscosity of the measured sample according to the propagation velocity of the surface wave.

At the same time, the present invention also provides a viscoelasticity detection system based on low frame rate laser speckle contrast imaging, which includes:

An excitation subsystem, which is used to excite the surface of the tested sample with a certain frequency of orthogonal oscillation, and form a surface wave on the surface of the tested sample;

The laser speckle imaging subsystem includes a laser for emitting a laser beam irradiated on the surface of the sample to be measured, and is used to collect multi-frame laser speckle images of the sample under test during surface wave propagation at a lower frame rate and exposure time. A camera for the speckle image, and a computer for calculating and processing the multi-frame laser speckle image, the computer obtains the propagation velocity of the aliasing wave, and calculates the propagation velocity of the surface wave by using the relationship between the aliasing wave propagation velocity and the surface wave propagation velocity Velocity, and obtain the elasticity and viscosity of the tested sample according to the propagation velocity of the surface wave.

Compared with the prior art, the present invention detects the surface wave excited by the orthogonal oscillation of the tested sample, and calculates the propagation velocity of the surface wave by using the aliased wave velocity collected at a low frame rate, thereby quantitatively solving the viscosity of the tested sample. Elastic modulus, which is conducive to reducing the complexity and cost of detection; and the use of reflective laser speckle imaging, which is conducive to the convenience of actual detection.

Description of drawings

1 is a schematic diagram of the connection structure of the viscoelasticity detection system based on low frame rate laser speckle contrast imaging of the present invention;

Fig. 2 is the connection block diagram of computer of the present invention;

Fig. 3 is a flow chart of the viscoelastic detection method based on low frame rate laser speckle contrast imaging of the present invention;

Fig. 4 is a flow chart of laser speckle image operation processing in the present invention;

Fig. 5 is the calculation flowchart of the spatial distribution of the laser speckle contrast image of the present invention;

Fig. 6 is the flow chart of viscoelastic calculation of the present invention;

Fig. 7 is the spatial distribution map of the laser speckle contrast value of the 0.8% and 1.2% concentration agarose samples obtained by the low frame rate speckle contrast imaging at 10 frames per second under the continuous orthogonal excitation of 400.5Hz and its selected area Spatio-temporal distribution map;

Fig. 8 is the two-dimensional elastic diagram of the non-uniform phantom calculated by the viscoelasticity quantitative detection system of speckle contrast imaging at a low frame rate of 10 frames per second under continuous orthogonal excitation at 400.2 Hz.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

As shown in FIG. 1 , an embodiment of the present invention provides a viscoelasticity detection system 10 based on low frame rate laser speckle contrast imaging, which includes an excitation subsystem 11 and a laser speckle imaging subsystem 12 .

The excitation subsystem 11 is used to excite the surface of the tested sample 20 with a certain frequency of orthogonal oscillation, and form surface waves on the surface of the tested sample 20 .

Specifically, the excitation subsystem 11 includes a loudspeaker 111 and a loudspeaker driving device 112, the diaphragm of the loudspeaker 111 is in contact with the surface of the tested sample 20, and the loudspeaker driving device 112 is used to output a quadrature oscillation signal to drive the Loudspeaker 111, during its specific setting, loudspeaker 111 can be placed on the upper surface of the tested sample 20 through the bracket, and the vibrating diaphragm of the loudspeaker 111 is in light contact with the upper surface of the tested sample 20, and the loudspeaker driving device 112 can generate orthogonal oscillation The signal is used to drive the speaker 111 , which can cause the tested sample 20 to vibrate, and then form surface waves on the surface of the tested sample 20 . It should be noted that this embodiment is not limited to the above-mentioned manner of forming surface waves on the surface of the sample 20 to be tested.

The laser speckle imaging subsystem 12 includes a laser 121 for emitting a laser beam that irradiates the surface of the sample under test, and is used to collect multiple frames of the sample under test during surface wave propagation at a lower frame rate and exposure time A camera 122 for the laser speckle image, and a computer 123 for calculating and processing multiple frames of the laser speckle image, the computer 123 obtains the propagation velocity of the aliasing wave, and calculates it using the relationship between the aliasing wave propagation velocity and the surface wave propagation velocity The propagation velocity of the surface wave is obtained, and the elasticity and viscosity of the tested sample 20 are obtained according to the propagation velocity of the surface wave. This embodiment detects the surface wave excited by the orthogonal oscillation of the sample 20 under test, and calculates its propagation velocity by using the aliased wave collected at a low frame rate, so as to calculate the propagation velocity of the surface wave, thereby quantitatively solving the problem of the sample 20 under test. Viscoelastic modulus, which is beneficial to reduce the complexity and cost of detection.

The laser speckle imaging subsystem 12 of this embodiment is reflective imaging, that is, the laser 121 generates a laser beam that irradiates the surface of the sample 20 to be measured, and the camera 122 collects the laser speckle image during the surface wave propagation process. The camera of this embodiment 122 can be a CCD (Charge Coupled Device, Charge Coupled Device) camera or a CMOS (Complementary Metal Oxide Semiconductor, Complementary Metal Oxide Semiconductor) camera, and the camera 122 of this embodiment does not require a very high acquisition frame rate, generally tens of frames/ Seconds can meet the requirements, such as 10 frames per second, 20 frames per second, that is, expensive high-speed cameras are not needed to increase the acquisition frame rate to thousands or even tens of thousands. It should be noted that the lower frame rate mentioned above refers to the order of tens of frames per second, such as 10 frames per second and 20 frames per second, which is different from the existing technology that requires several hundred or several Thousands and tens of thousands of acquisition frame rates are in contrast.

Among them, the acquisition frame rate of the laser speckle image in this embodiment is lower than the frequency of the orthogonal oscillation excitation, for example, the frequency of the orthogonal oscillation excitation is 400HZ, and the acquisition frame rate is 20 frames per second, which is much lower than the Frequency of.

As shown in Figure 2, the computer 123 includes a laser speckle contrast calculation module 123a, a data preprocessing module 123b and a viscoelasticity calculation module 123c, wherein: the laser speckle contrast calculation module 123a is used to obtain a certain A frame of laser speckle image, using the contrast value corresponding to each pixel of the frame of laser speckle image to construct a two-dimensional spatial speckle contrast image, obtain a two-dimensional spatial speckle contrast image of each frame of laser speckle image, construct The three-dimensional spatial speckle contrast image is used to obtain the spatiotemporal distribution of the laser speckle contrast image; the data preprocessing module 123b is used to filter the spatiotemporal distribution of the laser speckle contrast image; the viscoelasticity calculation module 123c is used to process Calculate the propagation velocity of the aliasing wave from the space-time distribution of the laser speckle contrast image, and obtain the propagation velocity of the surface wave from the propagation velocity of the aliasing wave, change the frequency of the orthogonal oscillation excitation, and obtain the dispersion characteristics of the surface wave. And the viscosity and elasticity of the tested sample are solved by fitting according to the dispersion characteristic of the surface wave.

Specifically, the laser speckle contrast calculation module 123a in this embodiment includes a spatial speckle contrast calculation module, a two-dimensional image construction module, and a three-dimensional image construction module. The spatial speckle contrast calculation module is used to obtain a certain For a frame of laser speckle image, select a spatial window with a size of W×W on the frame of laser speckle image, then W×W pixels in the spatial window form a pixel set with a size of W ² , and calculate the spatial window The spatial speckle contrast C in the space; the two-dimensional image construction module is used to slide the spatial window, traverse the entire frame of the laser speckle image, obtain the contrast value C(x,y) corresponding to all pixels, and use each pixel The corresponding contrast value C(x, y) is the grayscale, and the two-dimensional spatial speckle contrast image is constructed; the three-dimensional image construction module is used to obtain the two-dimensional spatial speckle contrast image of the spatial window of each frame of the laser speckle image , to construct a three-dimensional spatial speckle contrast image to obtain the spatiotemporal distribution C(x,y,t) of the laser speckle contrast image, where x, y represent two-dimensional space, and t represents time.

The viscoelasticity calculation module 123c includes a surface wave velocity calculation module, an elastic distribution calculation module, a dispersion characteristic acquisition module, and a viscoelasticity calculation module. A calculation window of a fixed size is used to calculate the propagation velocity of the aliasing wave through the transit time of the aliasing wave propagation in the calculation window, slide the calculation window, traverse all the pixels of the image, obtain the two-dimensional spatial distribution of the aliasing wave propagation, and collect the The relationship between the superimposed wave propagation velocity and the surface wave propagation velocity is used to calculate the propagation velocity of the surface wave; the elastic distribution calculation module is used to calculate the elastic spatial distribution of the measured sample according to the propagation velocity of the surface wave; the dispersion characteristic acquisition module is used for Change the frequency of the orthogonal oscillation excitation to obtain the propagation velocity of the surface wave at different frequencies, that is, the dispersion characteristic of the surface wave; the viscoelastic calculation module is used to substitute the dispersion characteristic of the surface wave into the dispersion equation, and then it can be solved by fitting Viscosity and elasticity of the sample being tested.

In order to facilitate the description of the specific detection process of the viscoelasticity detection system 10 based on low frame rate laser speckle contrast imaging in this embodiment, as shown in Figures 3 to 6, this embodiment provides a low frame rate laser speckle contrast imaging based The viscoelastic detection method of imaging, it comprises the steps:

S1. Carry out a certain frequency orthogonal oscillation excitation on the surface of the tested sample, and form a surface wave on the surface of the tested sample;

In this embodiment, surface waves can be formed on the surface of the sample to be tested through the above excitation subsystem, or surface waves can be formed on the surface of the sample to be tested in other ways.

S2. Send out a laser beam irradiated on the surface of the tested sample, collect multi-frame laser speckle images of the tested sample during surface wave propagation at a lower frame rate and exposure time, and perform calculation processing on the multi-frame laser speckle images , to obtain the propagation velocity of the aliasing wave, calculate the propagation velocity of the surface wave by using the relationship between the aliasing wave propagation velocity and the surface wave propagation velocity, and obtain the elasticity and viscosity of the measured sample according to the propagation velocity of the surface wave.

In this embodiment, the multi-frame laser speckle image is calculated and processed by a computer, and the above-mentioned calculation process includes:

S21. Obtain a certain frame of laser speckle image collected by the camera, construct a two-dimensional spatial speckle contrast image with the contrast value corresponding to each pixel of the frame of laser speckle image, and obtain the two-dimensional space of each frame of laser speckle image Spatial speckle contrast image, constructing a three-dimensional spatial speckle contrast image to obtain the spatiotemporal distribution of laser speckle contrast image;

The above step S21 is obtained by calculating the laser speckle contrast calculation module 123a of the computer, and the calculation process is as follows:

S211. Acquire a certain frame of laser speckle image collected by the camera, and select a spatial window with a size of W×W on the frame of laser speckle image, and W×W pixels in the spatial window form a pixel with a size of W ² Set, calculate the spatial speckle contrast C in the spatial window;

The formula for calculating the spatial speckle contrast ratio C is:

Among them, W is the size of the spatial window, and I _i represents the gray value of the i-th pixel in the W×W spatial window, is the average value of the gray levels of these W ² pixels;

In this embodiment, by calculating the spatial speckle contrast ratio C of the spatial window of a certain frame of laser speckle image, it can assign the pixel at the center position of the spatial window. It should be noted that the spatial window with a size of W×W should be smaller than the frame of the laser speckle image.

S212. Slide the space window, traverse the entire frame of the laser speckle image, obtain the contrast value C(x,y) corresponding to all pixels, and use the contrast value C(x,y) corresponding to each pixel as the gray level, Construct a two-dimensional spatial speckle contrast image;

The contrast value C(x, y) in this embodiment represents the contrast value corresponding to the x pixel on the abscissa and the y pixel on the ordinate on the frame of the laser speckle image.

S213. Obtain the two-dimensional spatial speckle contrast image of the spatial window of each frame of the laser speckle image, and construct the three-dimensional spatial speckle contrast image to obtain the spatiotemporal distribution C(x,y,t) of the laser speckle contrast image , where x and y represent two-dimensional space, and t represents time.

The spatiotemporal distribution C(x, y, t) of the laser speckle contrast image in this embodiment represents the contrast value corresponding to the x pixel on the abscissa and the y pixel on the ordinate on the frame of the laser speckle image at time t, that is, by The spatiotemporal distribution C(x, y, t) of the laser speckle contrast image can obtain the contrast value of any pixel in each frame of the laser speckle contrast image, which can describe the distribution of the laser speckle contrast value.

S22. Filtering the spatio-temporal distribution of the laser speckle contrast image;

The above step S22 can be processed through the data preprocessing module 123b of the computer, which specifically performs bandpass filtering and directional filtering on the spatiotemporal distribution of the laser speckle contrast image; specifically, it can be through spatial averaging, that is, in In the space domain, the spatial smoothing filter method is used to filter the speckle contrast imaging, and then through the band-pass filter, that is, in the time domain, each pixel in space is band-passed around the aliasing wave frequency according to the frequency of the aliasing wave Filtering; it can improve the signal-to-noise ratio through the above-mentioned filtering process, so as to facilitate the calculation of the propagation speed of the aliasing wave.

S23. Calculate the propagation velocity of the aliasing wave according to the time-space distribution of the filtered laser speckle contrast image, and obtain the propagation velocity of the surface wave from the propagation velocity of the aliasing wave, change the frequency of the orthogonal oscillation excitation, and obtain the surface wave The dispersion characteristics of the surface wave, and according to the dispersion characteristics of the surface wave, the viscosity and elasticity of the measured sample are solved.

Above-mentioned step S23 carries out computing processing by the viscoelasticity computing module 123c of computer, and its specific processing flow is as follows:

S231. Select a calculation window of a set size in the spatiotemporal distribution of the laser speckle contrast image, calculate the propagation speed of the aliasing wave through the transit time of the aliasing wave propagation in the calculation window, slide the calculation window, and traverse the entire image Pixel, obtain the two-dimensional spatial distribution of aliasing wave propagation, collect the relationship between aliasing wave propagation velocity and surface wave propagation velocity, and calculate the propagation velocity of surface wave;

For example, if the size of the calculation window is a×b, all the pixels in the calculation window can be averaged in the x direction to obtain the distribution of the speckle contrast value in the calculation window in the y-t direction, according to the propagation of the aliasing wave in the y direction The transit time of the aliasing wave is used to calculate the propagation velocity of the aliasing wave; sliding the calculation window and traversing the entire image can obtain the two-dimensional distribution of the aliasing wave propagation velocity, so as to realize the calculation of the propagation velocity of the surface wave through the propagation velocity of the aliasing wave, and the surface wave The formula for calculating the speed of propagation is as follows:

Among them, V _real is the propagation velocity of the surface wave, V _cal is the propagation velocity of the calculated aliasing wave, ω ₀ is the frequency of the orthogonal oscillation excitation, ω _s is the sampling frame rate of the laser speckle image, and round() means Rounding off to an integer, N is the integer after rounding.

S232. Calculate the spatial distribution of the elasticity of the measured sample according to the propagation velocity of the surface wave;

The spatial distribution of the elasticity of the tested sample in this embodiment is the shear elastic modulus or Young's modulus of the tested sample. The formula for calculating the shear modulus of elasticity of the sample is as follows:

G'≈ρ(1.05V _real ) ²

Among them, G' is the shear elastic modulus of the tested sample, ρ is the density of the tested sample, and V _real is the propagation velocity of the surface wave on the tested sample.

S233. Change the frequency of the orthogonal oscillation excitation to obtain the propagation speed of the surface wave at different frequencies, that is, the dispersion characteristic of the surface wave;

Specifically, by changing the frequency of the orthogonal oscillation excitation, it can measure the propagation speed of the surface wave at different frequencies, and then obtain the dispersion relationship of the surface wave.

S234. Substituting the dispersion characteristic of the surface wave into the dispersion equation, the viscosity and elasticity of the measured sample can be obtained by fitting.

Because the mechanical properties of biological tissues under low-frequency oscillation can generally be described by the Voigt model, the Voigt model is composed of a spring and a viscous pot connected in parallel, and the spring and viscous pot are ideal elastic and viscous bodies for model construction. For a viscoelastic solid whose upper surface is air, the relationship between the velocity Vs of the shear wave and the velocity V _real of the surface wave can be approximated as V _s /V _real ≈ 1.05, that is, the dispersion equation of the surface wave of the viscoelastic solid can be obtained by The following formula describes: .

Wherein, ω is the angular frequency of the surface wave, and the relationship between the frequency f is ω=2*πf; ρ is the density of the tested sample, μ ₁ is the elastic modulus of the tested sample, and μ ₂ is the measured sample Viscosity modulus.

For biological soft tissues such as skin and mucous membrane, it is generally assumed that its density is close to that of water, which is 1000kg/m ³ , and the dispersion equation is described by parameters μ ₁ and μ ₂ , and ρ describes the relationship between surface wave propagation speed and frequency, so by The method of curve fitting can calculate elastic modulus μ ₁ and viscous modulus μ ₂ .

In order to further illustrate the advantages of the low frame rate laser speckle contrast imaging-based viscoelasticity detection system and method of this embodiment, a phantom test is now used for illustration.

The experimental object is a biological tissue phantom, which is made of agarose powder, fat emulsion and deionized water. This or similar phantom is widely used in the detection of biological tissue viscoelasticity. The biological tissue imitation made of agarose has rich elasticity, and the fat emulsion can change its scattering characteristics, so that the reduced scattering coefficient is consistent with the actual tissue. A semiconductor laser with a wavelength of 785nm is used as the light source to irradiate the biomimetic body, and the reflected light is collected through the imaging optical path, and a CCD camera is used to perform speckle imaging on the surface of the biomimetic body at a low frame rate, and through the low The frame-rate laser speckle contrast imaging viscoelasticity detection system acquires the original laser speckle image, calculates the value of the laser speckle contrast, calculates the propagation velocity of the aliased wave, and solves the propagation velocity of the surface wave. Calculate the shear elastic modulus of the tested sample through the propagation speed of the surface wave; further change the excitation frequency, calculate the dispersion curve of the surface wave propagation, bring it into the dispersion equation, and fit the elastic modulus μ of the measured sample ₁ and viscous modulus μ ₂ .

In this specific example, three concentrations of agarose analogs were used in the phantom experiment, and the mass proportions of agarose powder were 0.6%, 0.8% and 1.2% respectively; 1.6% fat emulsion was added to each sample solution. According to the nature of the agarose analog, the shear elastic modulus of the sample will increase when the mass specific gravity of the agarose increases.

As shown in Fig. 7(a), the spatial distribution of the laser speckle contrast can clearly see the propagation process of the surface wave for a 0.8% concentration agarose sample under the excitation of 400.5 Hz orthogonal continuous wave. In the spatial direction, due to the attenuation of the surface wave, the vibration amplitude becomes smaller, resulting in a larger laser speckle contrast value.

Figure 7(b) shows the distribution of the speckle contrast value in the y direction over time after all the pixel values in the black frame selection area in Figure 7(a) are superimposed and averaged along the x direction; as shown in Figure 7(b), we can see The aliasing wave oscillates at a frequency of 1 Hz, because the laser speckle contrast value is modulated by the surface wave excited by 400.5 Hz continuous orthogonal excitation, and will vibrate at a frequency of 801 Hz. Since the sampling frame rate is 10 frames per second, the aliasing wave The frequency is 1Hz; as time increases, the farther the surface wave propagates, and the relationship is almost linear; the slope represents the propagation speed of the surface wave under the excitation of 400.5Hz frequency.

Figure 7(c) shows the spatial distribution of the laser speckle contrast value of the 1.2% concentration agarose sample under 400.5Hz continuous wave excitation; comparing Figure 7(c) with Figure 7(a), it can be seen that the surface The wavelength of the wave on the 0.8% concentration sample is smaller than that of the 1.2% concentration sample, which means that the propagation velocity of the surface wave on the 0.8% concentration sample is lower than that on the 1.2% concentration sample.

Figure 7(d) shows the distribution of the speckle contrast value in the y direction along time after all the pixel values in the black frame selection area in Figure 7(c) are superimposed and averaged along the x direction; Figure 7(d) and Figure 7( b) In comparison, it can be seen that the slope of the straight line representing the position of the peak or trough in Figure 7(b) is smaller than that in Figure 7(d), which indicates that the propagation speed of the aliasing wave on the 0.8% concentration sample is less than 1.2% The speed of propagation on the concentration sample.

By spatially selecting a calculation window of 40 pixels in the x direction and 60 pixels in the y direction, calculating the propagation velocity of the aliasing wave in the calculation window, sliding the calculation window, and traversing the entire image, the two-dimensional distribution of the aliasing wave in space can be obtained. The distribution of superimposed wave propagation velocity; through the relationship between the aliased wave propagation velocity and the surface wave propagation velocity, the two-dimensional distribution of the aliased wave propagation velocity can be converted into the surface wave propagation velocity, and the shear modulus and surface wave propagation The velocity relationship can be transformed into a two-dimensional elastic graph.

As shown in Figure 8, under the continuous orthogonal excitation of 400.2 Hz, the system samples at a speed of 10 frames per second, and the two-dimensional distribution of the shear elastic modulus of the non-uniform sample is obtained. The upper half of the non-uniform sample in the figure Part of the agarose sample with a concentration of 0.8%, and the lower part is an agarose sample with a concentration of 0.6%. It can be seen in the elastic graph that the boundary between the two concentration samples is very clear.

In order to verify the present invention, the shear elastic modulus of the phantom was also measured by a high frame rate method based on acquisition and excitation synchronization. The shear elastic moduli of 0.6%, 0.8% and 1.2% concentration samples measured based on the low frame rate speckle contrast imaging method are 1.79±0.05m/s, 2.83±0.07m/s and 4.93±0.31m/s, respectively s. The shear elastic moduli measured by the high frame rate method are 1.86±0.19m/s, 2.69±0.17m/s and 5.05±0.56m/s respectively. The obvious difference is that the viscoelasticity detection system and method based on low frame rate laser speckle contrast imaging in this embodiment can still accurately measure viscoelasticity on the basis of low frame rate speckle contrast imaging. The frame rate speckle contrast imaging avoids the need for expensive high-speed cameras and complex system synchronization requirements, which greatly simplifies the detection system and detection method, reduces the detection cost and facilitates the application.

The specific embodiments of the present invention described above do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (10)

1. a kind of viscoplasticity detection method based on low frame per second laser speckle contrast imaging, which is characterized in that include the following steps：

S1, the orthogonal vibratory stimulation that certain frequency is carried out to tested sample surface, and form surface wave on the surface of tested sample；

S2, the laser beam for being irradiated in tested sample surface is sent out, is existed with lower frame per second and time for exposure acquisition tested sample Multiframe laser speckle image during surface wave propagation carries out calculation process to multiframe laser speckle image, obtains aliasing wave Spread speed, the spread speed of surface wave, and root are calculated with aliasing velocity of wave propagation and surface wave propagation length velocity relation The elasticity and viscosity of tested sample are obtained according to the spread speed of surface wave.

2. viscoplasticity detection method according to claim 1, which is characterized in that the calculation process includes：

S21, a certain frame laser speckle image for obtaining camera acquisition, with the corresponding lining of each pixel of the frame laser speckle image Ratio structure two-dimensional space speckle contrasts image, and the two-dimensional space speckle for obtaining each frame laser speckle image contrasts image, structure It builds three dimensions speckle and contrasts image to obtain the spatial and temporal distributions that laser speckle contrasts image；

S22, the spatial and temporal distributions for contrasting image to laser speckle are filtered；

S23, the spatial and temporal distributions for contrasting image according to the laser speckle after being filtered calculate the spread speed of aliasing wave, and by mixing The spread speed of folded wave obtains the spread speed of surface wave, changes the frequency of orthogonal vibratory stimulation, and the frequency dispersion for obtaining surface wave is special Property, and the viscosity and elasticity for solving tested sample are fitted according to the Dispersion of surface wave.

3. viscoplasticity detection method according to claim 2, which is characterized in that step S21 includes：

S211, a certain frame laser speckle image for obtaining camera acquisition, it is W × W that size is chosen in the frame laser speckle image Spatial window, then it is W that W × W pixel in spatial window, which forms a size,²Set of pixels, calculate the spatial window Interior Space Speckle contrasts C；

S212, slide the spatial window, traverse the entire frame laser speckle image, obtain the corresponding lining ratio C of all pixels (x, Y), and respectively with the corresponding lining ratio C (x, y) of each pixel for gray scale, structure two-dimensional space speckle contrasts image；

S213, the spatial window for obtaining each frame laser speckle image two-dimensional space speckle contrast image, build three dimensions Speckle contrasts image to obtain the spatial and temporal distributions C (x, y, t) that laser speckle contrasts image, wherein x, y indicate two-dimensional space, t tables Show the time.

4. viscoplasticity detection method according to claim 3, which is characterized in that Space Speckle contrasts C's in step S211 Calculation formula is：

Wherein, W is the size of spatial window, I_iThe gray value of ith pixel in the spatial window of the W × W is represented,For this W²The average value of a pixel grey scale.

5. viscoplasticity detection method according to claim 3, which is characterized in that step S23 includes：

S231, the calculating window being sized is chosen in the spatial and temporal distributions that laser speckle contrasts image, calculating in window by mixed The transition time that folded wave is propagated calculates the spread speed of aliasing wave, slides calculation window, traverses whole pixels of image, mixed The two-dimensional space distribution that folded wave is propagated, acquires the relationship between aliasing velocity of wave propagation and surface wave propagation speed, gauging surface The spread speed of wave；

S232, the elastic spatial distribution that tested sample is calculated according to the spread speed of surface wave；

S233, the frequency for changing orthogonal vibratory stimulation obtain the spread speed of different frequency following table surface wave, the i.e. frequency dispersion of surface wave Characteristic；

S234, the Dispersion of surface wave is substituted into dispersion equation, you can fitting solves the viscosity and elasticity of tested sample.

6. viscoplasticity detection method according to claim 5, which is characterized in that the spread speed of surface wave in step S231 Calculation formula be：

Wherein, V_realFor the spread speed of surface wave, V_calFor the spread speed for the aliasing wave being calculated, ω₀For orthogonal oscillation The frequency of excitation, ω_sFor the sampling frame per second of laser speckle image, round () indicates that round, N are whole after rounding Number.

7. viscoplasticity detection method according to claim 6, which is characterized in that dispersion equation is in step S234：

Wherein, ω is the angular frequency of surface wave, and the relationship between frequency f is ω=2* π f；ρ is the density of tested sample, μ₁For The elasticity modulus of tested sample, μ₂For the viscous modulus of tested sample.

8. a kind of viscoplasticity detecting system based on low frame per second laser speckle contrast imaging, which is characterized in that including：

Subsystem is encouraged, is used to carry out tested sample surface the orthogonal vibratory stimulation of certain frequency, and in tested sample Surface forms surface wave；

Laser speckle imaging subsystems comprising the laser for sending out the laser beam for being irradiated in tested sample surface is used In the phase of the multiframe laser speckle image with lower frame per second and time for exposure acquisition tested sample during surface wave propagation Machine, and the computer for carrying out calculation process to multiframe laser speckle image, the computer obtain the propagation speed of aliasing wave The spread speed of surface wave is calculated with aliasing velocity of wave propagation and surface wave propagation length velocity relation for degree, and according to surface wave Spread speed obtain tested sample elasticity and viscosity.

9. viscoplasticity detecting system according to claim 8, which is characterized in that the excitation subsystem include loud speaker and The vibrating diaphragm of speaker driving apparatus, the loud speaker is contacted with the surface of tested sample, and the speaker driving apparatus is used In output quadrature oscillator signal to drive the loud speaker.

10. viscoplasticity detecting system according to claim 9, which is characterized in that the computer includes：

Laser speckle contrasts computing module, is used to obtain a certain frame laser speckle image of camera acquisition, is dissipated with the frame laser The corresponding value structure two-dimensional space speckle that contrasts of each pixel of spot image contrasts image, obtains each frame laser speckle image Two-dimensional space speckle contrasts image, and structure three dimensions speckle contrasts image to obtain the when space division that laser speckle contrasts image Cloth；

Data preprocessing module, the spatial and temporal distributions for being used to contrast laser speckle image are filtered；

Viscoplasticity computing module, the spatial and temporal distributions for being used to contrast according to the laser speckle after being filtered image calculate aliasing wave Spread speed, and by the spread speed of aliasing wave obtain surface wave spread speed, change the frequency of orthogonal vibratory stimulation, obtain The Dispersion of surface wave is taken, and solves the viscosity and elasticity of tested sample according to the fitting of the Dispersion of surface wave.