Biological tissue viscoelasticity measuring system and method

Abstract

The invention relates to the technical field of medical imaging, in particular to a biological tissue viscoelasticity measuring system and method.The system comprises an exciting unit, a measuring unit and a processing unit, the exciting unit excites biological tissue elastic vibration to repeatedly induce elastic waves through target radiation force; the imaging unit is used for performing optical coherence tomography scanning on elastic waves of the biological tissues and acquiring tissue vibration space distribution data of the biological tissues at different moments through scanning; and the analysis unit is used for reconstructing an elastic wave propagation process according to the tissue vibration space distribution data at different time, analyzing a phase velocity dispersion parameter of the elastic wave based on the elastic wave propagation process, and calculating the viscoelasticity of the biological tissue according to the phase velocity dispersion parameter. Therefore, the problem that related technologies can only be used for evaluating the retina elasticity and cannot measure the visco-elasticity of the retina is solved.

Description

Technical Field

[0001] The present application relates to the field of medical imaging technology, and in particular to a biological tissue viscoelasticity measurement system and method. Background Art

[0002] Viscoelasticity is an important biomechanical property of biological tissues. The viscoelasticity measurement of biological tissues can not only evaluate the progression of diseases, but also contribute to the early diagnosis of diseases. Currently, the measurement of viscoelastic properties of tumor tissues and liver tissues based on ultrasound imaging has entered clinical trials. The viscoelasticity measurement of ophthalmic tissues is also very important. The retina is an important part of the eye, and in the early stages of certain retinal diseases (such as age-related macular degeneration), the biomechanical properties of the retina may change. Therefore, accurate measurement of retinal viscoelasticity helps in the diagnosis of ophthalmic diseases and is of great significance for clinical ophthalmic diagnosis and treatment.

[0003] Currently, there are several techniques that can be used to measure the viscoelastic properties of biological tissues. Traditional palpation can qualitatively assess the elasticity of superficial tissues such as the skin, but patients' eye tissues will feel uncomfortable when they are touched. MRE (Magnetic Resonance Elastography) has been used to measure the viscoelasticity of the liver. Compared with tissue biopsy, MRE can achieve non-invasive examination and can play a role in staging diagnosis of diseases such as fatty liver and liver fibrosis. Brillouin-Raman spectroscopy can analyze the viscoelastic properties of human biological fluids (blood, lymph, etc.). Related studies have been conducted to provide diagnostic information for the progression of chronic kidney disease. However, these methods are limited in their application scenarios and are difficult to apply to small tissues and organs, such as eye tissue. USE (Ultrasound Elastography) has been used to analyze the viscoelastic properties of the cornea. However, due to limited resolution, the application of the USE method in the field of ophthalmology is still challenging, and high-resolution viscoelastic distribution images of eye tissues cannot be obtained.

[0004] In OCT (Optical Coherence Tomography), the light beam on the reference arm of the low-coherence interferometer and the scattered light of the human eye to be tested on the sample arm interfere with each other. After Fourier transform, the scattering information of different depths of the tissue can be obtained. At present, optical coherence tomography is divided into frequency domain OCT, spectral domain OCT, etc. according to the type of light source used. Coherence tomography technology can be used to image the cornea and retina of the human eye. OCT-based OCE (Optical Coherence Elastography) has been used to evaluate the viscoelasticity of ocular tissue. OCE is a non-invasive imaging technology with high resolution and fast scanning speed. In OCE measurement, external excitation causes tissue vibration, and OCT is used to detect tissue vibration. Then, the viscoelasticity is determined by analyzing the vibration characteristics. OCE can be used to measure corneal elasticity by exciting the cornea with a piezoelectric sensor PZT (Lead Zirconate Titanate) or air pulse. However, this excitation method cannot penetrate the eye tissue and cause elastic vibration of the fundus retina, so it cannot excite fundus tissue such as the retina. The retina can be stimulated using ARF (Acoustic Radiation Force), but this method is only used to evaluate the elasticity of the retina and cannot measure the viscoelasticity of the retina. Summary of the invention

[0005] The present application provides a biological tissue viscoelasticity measurement system and method to solve the problem that the related technology can only be used to evaluate retinal elasticity but cannot measure retinal viscoelasticity.

[0006] The first aspect of the present application provides a biological tissue viscoelasticity measurement system, including: an excitation unit, which stimulates the elastic vibration of the biological tissue by target radiation force to repeatedly induce elastic waves; an imaging unit, which scans the elastic waves of the biological tissue by optical coherence tomography imaging, and collects spatial distribution data of tissue vibration of the biological tissue at different times through scanning; an analysis unit, which reconstructs the elastic wave propagation process according to the spatial distribution data of tissue vibration at different times, analyzes the phase velocity dispersion parameters of the elastic wave based on the elastic wave propagation process, and calculates the viscoelasticity of the biological tissue according to the phase velocity dispersion parameters.

[0007] Optionally, the phase velocity dispersion parameter includes wave velocities at different frequencies, and the wave velocity calculation formula is:

[0008]

[0009] Where, f is the selected frequency; D is the distance; is the phase change during shear wave propagation.

[0010] Optionally, calculating the viscoelasticity of biological tissue according to the phase velocity dispersion parameter includes: inputting the phase velocity dispersion parameter into a viscoelastic model, and the viscoelastic model outputs the viscoelasticity of the biological tissue, wherein the formula of the viscoelastic model is:

[0011]

[0012] Among them, ρ is the density of the medium; ω is the angular frequency of vibration; μ1 and μ2 are the shear elasticity and shear viscosity of the tissue, respectively.

[0013] Optionally, the vibration component parallel to the imaging beam or the vibration component perpendicular to the imaging beam at a certain moment can be analyzed, and the elastic wave propagation process can be reconstructed according to the elastic vibration spatiotemporal distribution data.

[0014] Optionally, the calculation formula for the vibration component parallel to the imaging beam is:

[0015]

[0016] Wherein, λ0 is the central wavelength of the OCT light source; n is the refractive index of the sample; For the i-th position at the depth position of the j-th A-line, calculate the phase shift generated between the same A-line at the two times t and t+τ, τ is the time interval between two A-lines, and the A-line is a single scan result performed by the OCT system along the depth direction at a specific lateral position.

[0017] The Doppler variance is used to detect the vibration component perpendicular to the imaging beam. The calculation formula of the Doppler variance is:

[0018]

[0019] Among them, F j,i and F j+1,i They are the OCT signals corresponding to time t and t+τ respectively.

[0020] Optionally, the imaging unit uses a target scanning mode to scan the biological tissue, wherein the target scanning mode includes a first mode scan and a second mode scan, the first mode scan refers to an imaging mode in which multiple processed signal lines along the depth direction that are spatially arranged side by side are combined into a two-dimensional plane and reflect the internal tomographic section of the biological tissue, and the second mode scan refers to multiple sampling at the same lateral position of the biological tissue, and the sampled signal lines are expanded in time sequence to form a one-dimensional time series imaging mode.

[0021] Optionally, it further includes: a laser light source, wherein a trigger signal of the laser light source synchronously controls the excitation unit and the imaging unit, so that during each scanning process of the imaging unit, the excitation unit is synchronously triggered to generate an excitation signal.

[0022] Optionally, the imaging unit is used for swept source optical coherence tomography or spectral domain optical coherence tomography.

[0023] Optionally, the excitation unit includes a function generator, an amplifier and a transducer, wherein the modulation signal generated by the function generator is amplified by the amplifier, and then the transducer generates an excitation signal of the target radiation force.

[0024] A second aspect of the present application provides a method for measuring the viscoelasticity of biological tissues, and the method is based on the biological tissue viscoelasticity measurement system of the first aspect for measurement, wherein the method includes the following steps: repeatedly inducing elastic waves by stimulating elastic vibrations of biological tissues through target radiation force; scanning the elastic waves of the biological tissues by optical coherence tomography, and collecting spatial distribution data of tissue vibrations of the biological tissues at different times through scanning; reconstructing the elastic wave propagation process according to the spatial distribution data of tissue vibrations at different times, analyzing the phase velocity dispersion parameters of the elastic waves based on the elastic wave propagation process, and calculating the viscoelasticity of the biological tissues according to the phase velocity dispersion parameters.

[0025] Therefore, this application includes the following beneficial effects:

[0026] The biological tissue viscoelasticity measurement system proposed in the embodiment of the present application utilizes the target radiation force to stimulate the elastic vibration of the biological tissue to repeatedly induce elastic waves through the excitation unit, and then uses the imaging unit to perform optical coherence tomography scanning on the elastic waves of the biological tissue, thereby obtaining the spatial distribution data of tissue vibration at different times of the biological tissue, and reconstructing the elastic wave propagation process by analyzing the spatial distribution data of tissue vibration at different times through the analysis unit, analyzing the phase velocity dispersion parameters of the elastic wave based on the elastic wave propagation process, and calculating the viscoelasticity of the biological tissue based on the phase velocity dispersion parameters, thereby realizing the viscoelasticity measurement of the living retina, achieving non-invasive detection, and achieving high-accuracy viscoelasticity measurement. Thus, the problem that the related technology can only be used to evaluate the elasticity of the retina but cannot measure the viscoelasticity of the retina is solved.

[0027] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0029] Figure 1 A schematic diagram of the structure of a biological tissue viscoelasticity measurement system provided according to an embodiment of the present application;

[0030] Figure 2 A flow chart of a biological tissue viscoelasticity measurement system provided according to one embodiment of the present application;

[0031] Figure 3 A structural diagram of a frequency sweep OCE system provided according to an embodiment of the present application;

[0032] Figure 4 A structural diagram of a spectral domain OCE system provided according to an embodiment of the present application;

[0033] Figure 5 A schematic diagram of a MB OCT data acquisition method provided according to an embodiment of the present application;

[0034] Figure 6 A flowchart of optical coherence elastography provided according to one embodiment of the present application;

[0035] Figure 7 The figure is a flow chart of a method for measuring viscoelasticity of biological tissue provided in accordance with an embodiment of the present application. DETAILED DESCRIPTION

[0036] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0037] The following describes the biological tissue viscoelasticity measurement system and method of the embodiment of the present application with reference to the accompanying drawings. In view of the problem that the related technology mentioned in the above background technology can only be used to evaluate the elasticity of the retina, but cannot measure the viscoelasticity of the retina, the present application provides a biological tissue viscoelasticity measurement system, in which an excitation unit uses the target radiation force to excite the elastic vibration of the biological tissue to repeatedly induce elastic waves, and then uses an imaging unit to scan the elastic waves of the biological tissue by optical coherence tomography to obtain the spatial distribution data of the tissue vibration at different times of the biological tissue, and reconstructs the elastic wave propagation process by analyzing the spatial distribution data of the tissue vibration at different times through the analysis unit, analyzes the phase velocity dispersion parameters of the elastic wave based on the elastic wave propagation process, and calculates the viscoelasticity of the biological tissue according to the phase velocity dispersion parameters, thereby realizing the viscoelasticity measurement of the living retina, achieving non-invasive detection, and achieving high-accuracy viscoelasticity measurement. Thus, the problem that the related technology can only be used to evaluate the elasticity of the retina, but cannot measure the viscoelasticity of the retina is solved.

[0038] Specifically, Figure 1 This is a structural example diagram of a biological tissue viscoelasticity measurement system provided in an embodiment of the present application.

[0039] like Figure 1 As shown, the biological tissue viscoelasticity measurement system 10 includes: an excitation unit 101 , an imaging unit 102 and an analysis unit 103 .

[0040] Among them, the excitation unit 101 excites the elastic vibration of the biological tissue through the target radiation force to repeatedly induce elastic waves; the imaging unit 102 scans the elastic waves of the biological tissue by optical coherence tomography, and collects the spatial distribution data of the tissue vibration of the biological tissue at different times through scanning; the analysis unit 103 reconstructs the elastic wave propagation process according to the spatial distribution data of the tissue vibration at different times, analyzes the phase velocity dispersion parameters of the elastic wave based on the elastic wave propagation process, and calculates the viscoelasticity of the biological tissue according to the phase velocity dispersion parameters.

[0041] It can be understood that the embodiment of the present application repeatedly applies radiation force through the excitation unit 101 to continuously cause elastic vibration of the biological tissue, thereby continuously generating new elastic waves, and then uses the imaging unit 102 to scan the generated elastic waves by optical coherence tomography, so as to collect the spatial distribution data of tissue vibration at different times of the biological tissue, and after obtaining the spatial distribution data of tissue vibration at different times of the biological tissue, the analysis unit 103 and the above data are used to reconstruct the elastic wave propagation process, analyze the phase velocity dispersion parameters of the elastic wave, and calculate the viscoelasticity of the biological tissue based on the phase velocity dispersion parameters.

[0042] In the embodiment of the present application, the phase velocity dispersion parameter includes wave velocities at different frequencies, and the wave velocity calculation formula is:

[0043]

[0044] Where, f is the selected frequency; D is the distance; is the phase change during shear wave propagation.

[0045] It can be understood that the embodiment of the present application can select the frequency, distance and phase change during the propagation of the shear wave, substitute it into the formula to calculate the wave velocity at different frequencies. The wave velocity varies with the frequency and depends on the viscoelastic properties of the medium. The detailed calculation method of the viscoelastic properties is as follows:

[0046] In an embodiment of the present application, the viscoelasticity of biological tissue is calculated according to the phase velocity dispersion parameter, including: inputting the phase velocity dispersion parameter into a viscoelastic model, and the viscoelastic model outputs the viscoelasticity of the biological tissue, wherein the formula of the viscoelastic model is:

[0047]

[0048] Among them, ρ is the density of the medium; ω is the angular frequency of vibration; μ1 and μ2 are the shear elasticity and shear viscosity of the tissue, respectively.

[0049] It can be understood that the embodiment of the present application constructs a viscoelastic model through the density of the medium, the angular frequency of vibration, the shear elasticity and shear viscosity of the tissue. When the viscosity of the sample cannot be ignored, the wave velocity can be obtained through the viscoelastic model.

[0050] In the embodiment of the present application, the excitation unit 101 includes a function generator, an amplifier and a transducer, wherein the modulation signal generated by the function generator is amplified by the amplifier, and then the transducer generates an excitation signal of the target radiation force.

[0051] Among them, the function generator can generate a modulated sine wave or square wave signal; the amplifier can increase the amplitude of the input signal; the transducer can convert one form of energy into another form of energy, such as converting an amplified electrical signal into mechanical vibration, i.e., sound waves.

[0052] It can be understood that the excitation unit 101 of the embodiment of the present application includes a function generator, an amplifier and a transducer. After the excitation unit 101 generates a modulation signal, an excitation signal of the target radiation force can be obtained after amplification by the amplifier and transduction by the transducer.

[0053] In the embodiment of the present application, the imaging unit 102 is used for swept source optical coherence tomography or spectral domain optical coherence tomography.

[0054] Among them, swept-source optical coherence tomography is a variant of OCT technology. It uses a swept-source laser as a light source, which can quickly change the wavelength of its emitted light within a certain range. The rapid modulation of the swept-source makes it possible to quickly obtain a series of information at different depths, thereby achieving high-speed imaging. Spectral-domain optical coherence tomography is another OCT technology that uses a broadband light source and sends the returned interference signal to a spectrometer for analysis, which can simultaneously obtain information over the entire depth range.

[0055] It is understandable that the imaging unit 102 of the embodiment of the present application can implement swept source optical coherence tomography or spectral domain optical coherence tomography according to specific imaging requirements and application scenarios to achieve the expected imaging effect.

[0056] In an embodiment of the present application, the imaging unit 102 uses a target scanning mode to scan biological tissue, wherein the target scanning mode includes a first mode scan and a second mode scan. The first mode scan refers to an imaging mode in which multiple processed signal lines along the depth direction that are spatially arranged side by side are combined into a two-dimensional plane and reflect the internal tomographic section of the biological tissue. The second mode scan refers to an imaging mode in which multiple samplings are performed at the same lateral position of the biological tissue, and the sampled signal lines are expanded in time sequence to form a one-dimensional time series.

[0057] Among them, the first mode scanning refers to combining multiple signal lines along the depth direction arranged side by side in space, namely A lines, into a two-dimensional plane image, which can reflect the internal section of the biological tissue, namely the cross-sectional image; the second mode scanning refers to multiple sampling at the same lateral position, and expanding the sampled signal lines in time sequence to form a one-dimensional time series imaging mode, which is mainly used to observe the changes of tissues over time, such as dynamic phenomena such as the propagation of shear waves.

[0058] It can be understood that the imaging unit 102 of the embodiment of the present application can perform two modes of scanning. The first mode of scanning can combine the A line into a two-dimensional plane image to reflect the internal section of the biological tissue; the second mode of scanning can perform multiple sampling at the same lateral position, and expand the sampled signal lines in time sequence to form a one-dimensional time series imaging mode, which can observe the changes of tissues over time, such as dynamic phenomena such as the propagation of shear waves.

[0059] In the embodiment of the present application, the analysis unit 103 is also used to analyze the vibration component parallel to the imaging beam or the vibration component perpendicular to the imaging beam at a certain moment, and reconstruct the elastic wave propagation process according to the elastic vibration spatiotemporal distribution data.

[0060] Among them, the vibration component of the elastic vibration parallel to the imaging beam refers to the propagation of internal elastic waves in the tissue after being stimulated; the vibration component perpendicular to the imaging beam refers to the vibration whose direction is perpendicular to the direction of the beam used in the imaging process. Both can be used to construct an image of the internal structure of the tissue and provide information about the tissue.

[0061] It can be understood that the analysis unit 103 of the embodiment of the present application can analyze and calculate the vibration component of the elastic vibration parallel to the imaging beam and the vibration component perpendicular to the imaging beam based on the spatial distribution data of tissue vibration at different times. The specific calculation method will be described in detail below and will not be repeated here. By obtaining the vibration component of the elastic vibration parallel to the imaging beam and the vibration component perpendicular to the imaging beam, the elastic wave propagation process can be reconstructed, thereby achieving the purpose of constructing an image of the internal structure of the tissue and providing information about the tissue.

[0062] In the embodiment of the present application, the calculation formula of the vibration component of the elastic vibration parallel to the imaging light beam is:

[0063]

[0064] Wherein, λ0 is the central wavelength of the OCT light source; n is the refractive index of the sample; For the i-th position at the depth position of the j-th A-line, calculate the phase shift generated between the same A-line at the two times t and t+τ, τ is the time interval between two A-lines, and the A-line is a single scan result performed by the OCT system along the depth direction at a specific lateral position.

[0065] The Doppler variance is used to detect vibrations perpendicular to the imaging beam. The Doppler variance is calculated as:

[0066]

[0067] Among them, F j,i and F j+1,u They are the OCT signals corresponding to time t and t+τ respectively.

[0068] It can be understood that the embodiment of the present application calculates the elastic vibration velocity by substituting the central wavelength of the light source, the refractive index of the sample, and the phase shift generated between the A lines into the calculation formula for the vibration component parallel to the imaging beam; and by substituting the corresponding OCT signal into the calculation formula for the Doppler variance, the Doppler variance is used to detect the vibration component perpendicular to the imaging beam.

[0069] In the embodiment of the present application, it also includes: a laser light source, wherein a trigger signal of the laser light source synchronously controls the excitation unit 101 and the imaging unit 102, so that during each scanning process of the imaging unit 102, the excitation unit 101 is synchronously triggered to generate an excitation signal.

[0070] It is understandable that the embodiment of the present application further includes a laser unit, and the trigger signal of the laser unit synchronously triggers the excitation unit 101 to generate an excitation signal during each scanning process of the imaging unit 102, thereby achieving synchronization between the two.

[0071] According to the biological tissue viscoelasticity measurement system proposed in the embodiment of the present application, an excitation unit utilizes target radiation force to excite elastic vibrations of biological tissues to repeatedly induce elastic waves, and then an imaging unit is used to perform optical coherence tomography scanning on the elastic waves of the biological tissues to obtain spatial distribution data of tissue vibrations at different times. The spatial distribution data of tissue vibrations at different times are analyzed by an analysis unit to reconstruct the elastic wave propagation process, the phase velocity dispersion parameters of the elastic waves are analyzed based on the elastic wave propagation process, and the viscoelasticity of the biological tissue is calculated based on the phase velocity dispersion parameters, thereby realizing the viscoelasticity measurement of the living retina, achieving non-invasive detection, and achieving high-accuracy viscoelasticity measurement.

[0072] The biological tissue viscoelasticity measurement system is further described below through a specific embodiment.

[0073] The usage process of this embodiment is as follows Figure 2As shown, it includes an acoustic radiation force excitation system 201, an optical coherence tomography system 202, a retinal tissue 203, an analysis system 204 and a viscoelasticity measurement 205.

[0074] OCE systems based on swept-frequency light sources such as Figure 3 As shown, the coupler divides the light emitted by the light source into a sample arm beam and a reference arm beam. Part of the light passes through the circulator and is focused on the retina, and the rest of the light passes through the delay line. The scattered light from the sample and the light from the delay line interfere in the coupler, and the interference signal is detected by a balanced photodetector. The acoustic radiation force excitation unit consists of a function generator, an amplifier, and an ultrasonic transducer. The modulated signal generated by the function generator is amplified and then generated by the focusing ring transducer to generate the acoustic radiation force. The central hole of the ring transducer allows the OCT beam to pass through.

[0075] OCE systems based on the spectral domain are Figure 4 As shown, the system includes a spectral domain OCT imaging unit and an acoustic radiation force excitation unit, which can also achieve the purpose of measuring the viscoelasticity of biological tissues in this embodiment.

[0076] The OCT imaging unit and the ARF excitation unit are synchronized by the trigger signal of the laser light source. This embodiment uses the MB scanning mode to achieve the detection of elastic waves. The function generator and the scanning galvanometer are controlled by the trigger signal of the scanning light source. During the M scan, the OCT device records multiple A-line signals at each lateral position. After recording the signal multiple times, the light beam moves to the next lateral position, and each frame consists of multiple lateral positions. In each M scan, the acoustic radiation force is triggered once to achieve the effect of stimulating the retina.

[0077] The principle of the 0CT data acquisition method based on MB scanning adopted in this embodiment is as follows: Figure 5As shown. B scanning refers to combining multiple processed signal lines along the depth direction arranged side by side in space into a two-dimensional "anatomical image" (i.e., OCT B-mode image) that reflects the internal section of the object being tested. M scanning refers to multiple sampling at the same lateral position of the sample, and the sampled signal lines are expanded in time sequence to form a one-dimensional timing diagram (i.e., OCT M-mode image). In the process of repeated ultrasound induction of elastic waves, the OCT unit collects an M-mode timing diagram at each lateral position, and then reconstructs the M-mode timing diagrams at different lateral positions into a B-mode two-dimensional plane image that changes with time. In the MB scanning mode, each lateral position records N A-line scan data at different times (i.e., 1 M-mode scan), analyzes the change of phase with time at different depths of this lateral position, and thus analyzes the tissue vibration at this position. The ultrasonic transducer will continuously output the excitation signal between the nth to n+kth A-line scans, 1≤n≤n+k≤N. Afterwards, the scanning galvanometer controls the light beam to move to the next lateral position to repeat the above M-mode scanning and ultrasonic excitation steps. A complete B scan will continuously record L positions in the lateral direction. Depending on the scanning method, the A scan obtains one-dimensional information along the depth direction, the B scan can obtain a two-dimensional cross-sectional image, and the C scan can obtain a three-dimensional structural image.

[0078] The OCT system can detect vibrations of the retina. When optical coherence tomography is used to detect elastic vibrations, the Doppler phase method can be used to detect tissue vibrations, or methods such as signal decorrelation and signal variance can be used. Elastic waves are essentially the propagation of vibrations. A phase-sensitive Doppler optical coherence tomography method can be used to detect elastic vibrations parallel to the direction of the light beam. This embodiment uses a phase-sensitive Doppler optical coherence tomography method to detect elastic vibrations parallel to the direction of the light beam, as shown in FIG. Figure 6 As shown in Figure 2, the displacement (vibration) is detected by analyzing and comparing the phases between consecutive scanning signals, and the propagation of elastic waves is reconstructed through the propagation of vibration in space.

[0079] After obtaining the spatial distribution of tissue vibration at different times, the propagation process of elastic waves can be reconstructed. The principle of the Doppler optical coherence tomography method is to combine the Doppler principle with OCT and use phase-resolved Doppler OCT to extract phase information from the data collected by OCT. At the i-th position at the depth position of the j-th A-line, the phase shift between the same A-line at the two times t and t+τ is calculated. Where τ is the time interval between two A lines. The elastic vibration along the OCT beam direction is parallel to the imaging beam component V u,j (t) can be determined by the following formula:

[0080]

[0081] Where λ0 is the central wavelength of the OCT light source and n is the refractive index of the sample.

[0082] Phase-sensitive Doppler optical coherence tomography is sensitive to displacements parallel to the OCT beam, but cannot detect displacements perpendicular to the OCT beam. When orthogonal ARF excitation is used, the vibration of the lens is perpendicular to the OCT beam. Therefore, the OCT-based Doppler variance method is used to detect vibrations perpendicular to the OCT beam. On the jth A line, the depth position is the Doppler variance at the ith position. It can be determined from OCT data using the following equation:

[0083]

[0084] where F j,i and F j+1,i The OCT signals at time t and t+τ are respectively. The Doppler variance method is more sensitive to lateral vibration and will not be distorted by overall motion and phase wrapping, so data processing will be simpler and faster.

[0085] By analyzing the propagation of elastic waves, the propagation velocity c of elastic waves in the retina can be measured. s , as shown in formula (3)

[0086]

[0087] Where f is the selected frequency, D is the distance, is the phase change during shear wave propagation. The shear wave velocity varies with frequency and depends on the viscoelastic properties of the medium. For the viscoelastic measurement of the retina, we use a viscoelastic model based on elastic wave dispersion, which is obtained by formula (4).

[0088]

[0089] Where ρ is the density of the medium, ω is the angular frequency of vibration, μ1 and μ2 are the shear elasticity and shear viscosity of the tissue, respectively.

[0090] The MB scanning mode of the OCT system is used to detect the vibration of the retina and obtain the OCT B-scan image. The phase velocity changes at different frequencies. The displacement-time image obtained by OCT is subjected to fast Fourier transform, and the phase velocity c of each frequency is calculated according to formula (3): s In determining the phase velocity c s Then, the viscoelasticity of the model is solved according to formula (4). If there are more than 2 phase velocities c s , when solving the two parameters μ1 and μ2, the least squares method can be used.

[0091] Next, the biological tissue viscoelasticity measurement method proposed in the embodiment of the present application is described with reference to the accompanying drawings.

[0092] Figure 7 is a flow chart of a method for measuring viscoelasticity of biological tissue according to an embodiment of the present application, such as Figure 7 As shown, the biological tissue viscoelasticity measurement method comprises the following steps:

[0093] In step S401, elastic waves are repeatedly induced by stimulating elastic vibration of biological tissue through target radiation force.

[0094] It is understandable that when the target radiation force acts on biological tissue, the tissue will undergo elastic vibration and induce elastic waves. The embodiment of the present application stimulates the elastic vibration of biological tissue by the target radiation force to repeatedly induce elastic waves to obtain more data.

[0095] In step S402, optical coherence tomography is performed on the elastic waves of the biological tissue to collect spatial distribution data of tissue vibration at different times through scanning.

[0096] The optical coherence tomography scanning of elastic waves of biological tissue is performed by an imaging unit.

[0097] It can be understood that the embodiment of the present application uses an imaging unit to scan the elastic waves of biological tissues by optical coherence tomography, collects spatial distribution data of tissue vibration of biological tissues at different times, and uses the above data for subsequent analysis.

[0098] In step S403, the elastic wave propagation process is reconstructed according to the spatial distribution data of tissue vibration at different times, the phase velocity dispersion parameters of the elastic wave are analyzed based on the elastic wave propagation process, and the viscoelasticity of the biological tissue is calculated according to the phase velocity dispersion parameters.

[0099] Among them, the elastic wave propagation process is reconstructed according to the spatial distribution data of tissue vibration at different times through the analysis unit.

[0100] It can be understood that the embodiment of the present application reconstructs the spatial distribution data of tissue vibration collected at different times through the analysis unit to obtain the elastic wave propagation process. The phase velocity dispersion parameters of the elastic wave and the viscoelasticity of the biological tissue can be calculated through the elastic wave propagation process, thereby realizing the viscoelasticity measurement of the living retina, achieving non-invasive detection, and achieving high-accuracy viscoelasticity measurement.

[0101] It should be noted that the above explanations of the embodiment of the biological tissue viscoelasticity measurement system are also applicable to the biological tissue viscoelasticity measurement method of this embodiment, and will not be repeated here.

[0102] According to the biological tissue viscoelasticity measurement method proposed in the embodiment of the present application, elastic waves are repeatedly induced by stimulating elastic vibrations of biological tissues through target radiation force, and optical coherence tomography is performed on the elastic waves to collect spatial distribution data of tissue vibrations of biological tissues at different times. The elastic wave propagation process is reconstructed according to the above data, and the phase velocity dispersion parameters of the elastic waves are analyzed based on the elastic wave propagation process. The viscoelasticity of the biological tissue is calculated based on the phase velocity dispersion parameters, thereby realizing the viscoelasticity measurement of the living retina, achieving non-invasive detection, and achieving high-accuracy viscoelasticity measurement.

[0103] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0104] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, "N" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0105] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or N executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0106] It should be understood that the various parts of the present application can be implemented in hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, the steps or methods can be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array, a field programmable gate array, etc.

[0107] A person of ordinary skill in the art may understand that all or part of the steps carried by the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the above-mentioned program may be stored in a computer-readable storage medium, which, when executed, includes one of the steps of the method embodiment or a combination thereof.

[0108] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A biological tissue viscoelasticity measurement system, characterized in that: include: An excitation unit, which excites elastic vibration of biological tissue through target radiation force to repeatedly induce elastic waves; An imaging unit, which performs optical coherence tomography scanning on the elastic waves of the biological tissue, and collects spatial distribution data of tissue vibration of the biological tissue at different times through scanning; The analysis unit reconstructs the elastic wave propagation process according to the spatial distribution data of tissue vibration at different times, analyzes the phase velocity dispersion parameters of the elastic wave based on the elastic wave propagation process, and calculates the viscoelasticity of the biological tissue according to the phase velocity dispersion parameters.

2. The biological tissue viscoelasticity measurement system according to claim 1, characterized in that: The phase velocity dispersion parameter includes wave velocities at different frequencies, and the wave velocity calculation formula is: Where, f is the selected frequency; D is the distance; is the phase change during shear wave propagation.

3. The biological tissue viscoelasticity measurement system according to claim 2, characterized in that: The step of calculating the viscoelasticity of the biological tissue according to the phase velocity dispersion parameter comprises: The phase velocity dispersion parameter is input into a viscoelastic model, and the viscoelastic model outputs the viscoelasticity of the biological tissue, wherein the formula of the viscoelastic model is: Among them, ρ is the density of the medium; ω is the angular frequency of vibration; μ1 and μ2 are the shear elasticity and shear viscosity of the tissue, respectively.

4. The biological tissue viscoelasticity measurement system according to claim 1, characterized in that: The analysis unit may also analyze a vibration component parallel to the imaging light beam or a vibration component perpendicular to the imaging light beam at a certain moment, and reconstruct the elastic wave propagation process according to the elastic vibration spatiotemporal distribution data.

5. The biological tissue viscoelasticity measurement system according to claim 4, characterized in that: The calculation formula of the vibration component parallel to the imaging beam is: Wherein, λ0 is the central wavelength of the OCT light source; n is the refractive index of the sample; For the i-th position at the depth position of the j-th A-line, calculate the phase shift between the same A-line at two times t and t+τ, τ is the time interval between two A-lines, and the A-line is a single scan result along the depth direction at the lateral position of the OCT system; The Doppler variance is used to detect the vibration component perpendicular to the imaging beam. The calculation formula of the Doppler variance is: Among them, F j,i and F j+1,i They are the OCT signals corresponding to time t and t+τ respectively.

6. The biological tissue viscoelasticity measurement system according to claim 1, characterized in that: The imaging unit scans the biological tissue using a target scanning mode, wherein the target scanning mode includes a first mode scan and a second mode scan, wherein the first mode scan refers to an imaging mode in which a plurality of processed signal lines arranged side by side in space along the depth direction are combined into a two-dimensional plane and reflect the internal tomographic section of the biological tissue, and the second mode scan refers to an imaging mode in which multiple samplings are performed at the same lateral position of the biological tissue, and the sampled signal lines are expanded in time sequence to form a one-dimensional time series.

7. The biological tissue viscoelasticity measurement system according to claim 6, characterized in that: Also includes: A laser light source, wherein a trigger signal of the laser light source synchronously controls the excitation unit and the imaging unit, so that during each scanning process of the imaging unit, the excitation unit is synchronously triggered to generate an excitation signal.

8. The biological tissue viscoelasticity measurement system according to claim 1, characterized in that: The imaging unit is used for swept-source optical coherence tomography or spectral-domain optical coherence tomography.

9. The biological tissue viscoelasticity measurement system according to claim 1, characterized in that: The excitation unit includes a function generator, an amplifier and a transducer, wherein the modulation signal generated by the function generator is amplified by the amplifier, and then the transducer generates an excitation signal of the target radiation force.

10. A method for measuring viscoelasticity of biological tissue, characterized in that: The method is based on the biological tissue viscoelasticity measurement system according to any one of claims 1 to 9 for measurement, wherein the method comprises the following steps: The elastic waves are repeatedly induced by stimulating elastic vibration of biological tissues through target radiation force; Scanning the elastic waves of the biological tissue by optical coherence tomography to collect spatial distribution data of tissue vibration of the biological tissue at different times through scanning; The elastic wave propagation process is reconstructed according to the spatial distribution data of tissue vibration at different times, the phase velocity dispersion parameters of the elastic wave are analyzed based on the elastic wave propagation process, and the viscoelasticity of the biological tissue is calculated according to the phase velocity dispersion parameters.

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