A method for improving the depth of optical coherence tomography based on Mie scattering

Abstract

The present invention discloses a method for improving the depth of optical coherence tomography (OCT) based on Mie scattering: first, an OCT system simulation model based on a Monte Carlo ray tracing algorithm is established, and according to the wavelength of the OCT light source and the application scenario, the thickness of an optical film dispersed with forward scattering particles, the refractive index of the scattering particles and the medium, and the feasible range of the size and concentration of the scattering particles are calculated. Then, scattering particles that meet the requirements of the optimization design parameters of the simulation system are dispersed in the corresponding medium to prepare a scattering film that increases the photon collection rate of the OCT system. Then, when performing OCT detection, the prepared optical scattering film is placed between the optical probe and the object to be detected, which has the effect of improving the detection depth of OCT. The present invention realizes the detection depth gain of the OCT system by placing an optical film of a certain thickness dispersed with scattering particles of appropriate concentration and size with a specific refractive index between the optical probe and the object to be detected, or covering it on the surface of the object to be detected.

Description

Technical Field

[0001] The present invention belongs to the fields of optoelectronic technology and medicine, and particularly relates to a method for improving the depth of optical coherence tomography based on Mie scattering. Background Art

[0002] Optical Coherence Tomography (OCT) is a new imaging technology for imaging human tissue. Its principle of tissue detection is that the light beam from the sample arm is backscattered by the human tissue and returns with human tissue information, forming a coherent light field with the reference arm. By analyzing the coherent light field, the internal information of the human tissue can be obtained.

[0003] Human tissue can be regarded as a complex multi-layered highly scattering tissue. Different components in the tissue, such as cells, fat, and fibers, have different absorption and scattering characteristics. The size of these components is comparable to the incident light used by OCT, and the scattering that occurs is Mie scattering. From a macroscopic statistical point of view, the optical properties exhibited by each layer in the tissue are uniform, and can be simplified as a scattering layer model to describe the optical properties. At the same time, the concentration of each component is different in each layer, which determines that the scattering and absorption properties of each layer are different. For example, the epidermis, dermis, and blood vessels in the skin tissue have different optical properties. Furthermore, a scattering coefficient μ can be established based on the asymmetric factor g that characterizes the forward scattering of the scattering particles, the thickness of the scattering layer d, and the scattering absorption intensity. s and absorption coefficient μ a The scattering layer model.

[0004] Optical coherence tomography (OCT) technology offers an imaging depth exceeding that of traditional microscopic imaging techniques, while also boasting superior axial resolution to ultrasound imaging, providing a valuable supplement to the detection of human tissue information. In medical diagnosis, it can be used to detect tumor boundaries, eye structure, skin, blood vessels, and dental examinations, among other areas.

[0005] One of the main problems currently faced by traditional OCT systems is the imaging depth problem. The imaging depth of traditional OCT systems is currently on the order of several millimeters, which is a large gap compared to detection methods such as CT and ultrasound. How to obtain a larger imaging depth is a hot research topic in the field of OCT technology. Summary of the Invention

[0006] This invention creates an optical film dispersed with scattering particles of appropriate concentration and size. During OCT, this optical scattering film is placed between the optical probe and the object being detected, effectively increasing the OCT detection depth. This technology offers advantages such as being completely harmless to the human body, easy to operate, and low-cost. It can be widely applied in various OCT medical diagnostic applications.

[0007] The technical solution of the present invention is:

[0008] (1) According to the actual scenarios of optical coherence tomography (OCT) (OCT device wavelength, type of detected object), a scattering film based on Mie scattering is introduced into the optical path to improve the photon collection rate of the OCT system. First, the characteristics of the scattering film are simulated and designed. The scattering of the incident light when passing through the scattering film and the redistribution of the light field when the incident light from the detected object is backscattered and returned through the scattering film are comprehensively considered. The thickness of the optical film with dispersed forward scattering particles, the refractive index of the scattering particles and the medium, and the feasible range of the size and concentration of the scattering particles are calculated, so that the effect of the scattering film on improving the photon collection rate of the backscattered light returned from the detected object is greater than the scattering loss when the incident light passes through the scattering film.

[0009] (2) Based on the parameters obtained by the optimized design in step (1), scattering particles that meet the design requirements in step (1) are dispersed in the dielectric layer to prepare a scattering film that increases the photon collection rate of the OCT system.

[0010] (3) When performing OCT detection, the optical scattering film prepared in step (2) is placed between the optical probe and the object to be detected, thereby increasing the OCT detection depth.

[0011] The above-mentioned method for improving the depth of optical coherence tomography based on Mie scattering is based on the principle that after the light field passes through a scattering layer dispersed with forward-scattering particles, its intensity will be redistributed. In the present invention, for the OCT incident light (laser beam) with good collimation, some photons are scattered at large angles or even backscattered in the scattering layer and are lost; but at the same time, the scattering direction angle distribution of the backscattered light reflected back from the detection target position is random. At this time, the scattering layer has a converging effect on the backscattered light returning to the optical probe, which can improve the photon collection rate. Therefore, considering the incident light scattering loss and the return photon collection comprehensively, a scattering layer of a certain thickness with scattering particles of appropriate size and concentration is used, so that the increase ratio of the return photon collection rate is greater than the loss of the incident light, thereby improving the detection signal intensity and the detection distance. The principle diagram of the present invention is shown in FIG. Figure 1 shown.

[0012] The selection of parameters for an optical film containing dispersed scattering particles, taking into account both incident light scattering losses and return photon collection, involves an optimization problem. To address this, an OCT system simulation model based on a Monte Carlo ray tracing algorithm was developed. Simulations compared the number of photons collected by the OCT system with and without the addition of an optical scattering film to determine the optimal range for scattering film thickness, the refractive index of the scattering film medium and scattering particles, and the concentration and size of the scattering particles.

[0013] The main idea of ​​the OCT system simulation model used is to use the Henyey–Greenstein model of Mie scattering to determine the approximate scattering phase function by the asymmetric factor g, and then determine the probability of deflection in each direction during scattering. The probability of photons being scattered and absorbed is determined by the thickness d, scattering coefficient and absorption coefficient of the scattering layer. At the same time, the influence of the refractive index n of each layer on the reflection and refraction when passing through the layer is considered. Combined with the wavelength of the light source used by the OCT system and the application scenario, the asymmetric factor g, scattering layer thickness d, and scattering coefficient μ of the scattering layer required by the OCT system are calculated through the model. s , the range of refractive indices n0 and n1 of the scattering film medium and the scattering particles. The size of the scattering particles dispersed in the optical film can be further calculated by the asymmetric factor combined with the wavelength of the light source, and the concentration of the scattering particles can be calculated by the scattering coefficient.

[0014] In the OCT system simulation model described above, the Henyey-Greenstein (HG) model is used to determine the scattering angle of photons. The scattering particles are approximated as spheres, and the scattering phase function is approximated based on the asymmetry factor g to describe the angular scattering characteristics of the scattering particles:

[0015]

[0016] The above formula can be used to approximate the probability distribution of the propagation direction of particles in various direction angles after scattering.

[0017] The value of the asymmetry factor g is related to the integral of the analytical solution of the scattering phase function P(cosθ), and is further related to the size of the scattering particles. Its expression is as follows:

[0018]

[0019] Where: α is the scale factor of the particle α=2πr / λ, r is the particle radius, λ is the wavelength of light, Q sca is the particle scattering efficiency factor, is the Mie coefficient, which can be calculated according to Mie theory.

[0020]

[0021]

[0022] In the above formula, α is the scale factor of the particle α = 2πr / λ, and m is the refractive index of the scattering particle.

[0023]

[0024]

[0025] J n+1 / 2 (α) and They are the semi-odd order Bessel functions of the first kind and Hankel functions of the second kind respectively.

[0026] Combining the above formulas, we can establish a relationship between the asymmetry factor g, the light wavelength λ, the scattering particle refractive index m, and the size r. Given the wavelength and refractive index of the scattering particle, we can reverse-calculate the desired scattering particle size based on the desired asymmetry factor g.

[0027] In the above OCT system simulation model, the probability of photon scattering and absorption is determined by the thickness d of the scattering layer, the scattering coefficient μ s and absorption coefficient μ a Together, we determine that the probability of absorption or scattering follows the Lambert-Beer law, which is expressed as:

[0028]

[0029] Among them, μ t =μ a +μ s It can be seen that the probability of a photon being scattered or absorbed in the scattering layer is exponentially distributed. The longer the distance the photon moves in the scattering layer, the higher the probability of scattering. The maximum distance the photon moves in the scattering layer is related to the layer thickness and the scattering angle.

[0030] In addition, for the transparent non-absorbing scattering particles in the scattering film used, μ t =μ s , when the medium is approximately uniform, μ t =μ s =ε λ c,ε λ is a constant related to the material, and c is the molar concentration of the scattering particles. This establishes the corresponding relationship between the scattering coefficient and the concentration of the scattering particles.

[0031] Combining the two methods mentioned above for calculating the scattering angle and the probability of scattering, the specific process of the OCT system simulation algorithm is established:

[0032] 1. For each photon, the initial position and incident direction are randomly given according to the Gaussian beam distribution;

[0033] 2. The next step is to determine the distance the photon must travel to reach the next boundary based on the direction angle and current position;

[0034] 3. Determine whether the photon is scattered during this distance. If scattering occurs, the position and azimuth angle of the scattering will be randomly assigned by the probability distribution. Then, the distance the photon must travel to reach the next boundary is re-determined based on the new position and azimuth angle.

[0035] 4. When the photon reaches the boundary, the law of refraction determines the new direction of the photon's propagation. At the same time, the transmittance is used to determine whether the photon is reflected based on probability.

[0036] 5. Repeat steps 2 to 4 after entering the next scattering layer until the detection target depth is reached;

[0037] 6. At the target depth, photons need to be backscattered, and the direction angle of the photon movement after backscattering is given according to the probability distribution;

[0038] 7. Repeat steps 2 to 4 until the optical probe returns to the target and counts.

[0039] If a photon is determined to be uncollectable due to absorption or large-angle scattering between steps 8.1 and 7, the process will stop immediately and jump to step 1 to regenerate the photon.

[0040] 9. Track a sufficient number of photons and calculate the photon collection rate.

[0041] 10. Change the scattering film thickness d, scattering particle asymmetry factor g, and scattering coefficient μ s Parameters, repeat steps 1 to 9, and compare with the photon collection rate when no scattering film is added (also calculated by steps 1 to 9 of the above algorithm) to obtain the parameter range that improves the photon collection rate.

[0042] 11. The asymmetric factor combined with the wavelength of the light source can be used to calculate the refractive index n0 and n1 range of the scattering film medium and the scattering particles dispersed therein, as well as the size of the scattering particles. The scattering particle concentration can be calculated from the scattering coefficient, and the scattering film thickness, scattering particle size, and scattering particle concentration range that improves the photon collection rate can be obtained.

[0043] The OCT system simulation algorithm flow chart is as follows Figure 2 shown.

[0044] Based on the parameters optimized by the algorithm described above, scattering particles that meet the design requirements are dispersed in a dielectric layer to create a scattering film that increases the photon collection rate of the OCT system. During OCT detection, the prepared optical scattering film is placed between the optical probe and the object being detected, thereby increasing the OCT detection depth.

[0045] The preparation method of the scattering film is as follows: according to the parameters obtained by the optimized design in the simulation system, scattering particles and media that meet the refractive index design are selected; scattering particles and media with a specific ratio are weighed according to the concentration parameters obtained by the design; after mixing, they are fully stirred to make the scattering particles completely dispersed in the medium; degassing is then performed using a vacuum degassing machine; after degassing, it is spin-coated on a glass slide; and then placed in an oven for heating and curing, and finally a scattering film with a thickness of [0.1,3] (unit: mm) is prepared.

[0046] The scattering particle materials used for the scattering film can be silicon dioxide (refractive index 1.46@500nm), titanium dioxide (refractive index 2.35@500nm), aluminum oxide (refractive index 1.63@550nm), magnesium oxide (refractive index 1.70@500nm), zinc oxide (refractive index 2.0@500nm), zirconium oxide (refractive index 2.05@500nm), niobium oxide (refractive index 2.3@550nm), yttrium oxide (refractive index 1.8@50 The scattering particles in the scattering film can be selected from a variety of materials, including cerium oxide (refractive index 2.20 @ 550nm), cadmium selenide (refractive index 2.87 @ 900nm), aluminum antimonide (refractive index 3.3 @ 2000nm), cadmium telluride (refractive index 2.67 @ 10000nm), gallium arsenide (refractive index 3.3 @ 3000nm), indium phosphide (refractive index 3.45 @ 590nm), silicon (refractive index 1.47 @ 1550nm), and small bubbles (refractive index 1.0 @ 700-1700nm). One or more materials can be combined to form the scattering particles, adapting to various OCT application environments.

[0047] The dielectric material used for the scattering film can include flexible materials such as polyester (PET), polyimide (PI), polyvinyl alcohol (PVA), polyethylene naphthalate (PEN), or polydimethylsiloxane (PDMS). A combination of one or more materials can be selected to suit a variety of OCT applications.

[0048] When making the scattering film, a lens structure that has a converging effect on the corresponding wavelength can be added to further converge the emitted light and improve the imaging quality.

[0049] Fitting the scattering film tightly against the object being detected, or fitting the OCT probe tightly against the scattering film and the object being detected, can reduce the loss of light intensity in the air and further increase the imaging depth. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This schematic diagram shows the principle behind the method for enhancing optical coherence tomography imaging depth based on Mie scattering, as described in the present invention. (a) shows scattering losses during incident light, and (b) shows the improved collection rate of return photons. This method comprehensively considers both incident light scattering losses and return photon collection, establishing a simulation model to solve an optimization problem and selecting appropriate parameters for an optical film containing dispersed scattering particles to achieve an improved detection depth for the OCT system.

[0051] Figure 2 This is a flow chart of the OCT system simulation algorithm described in the present invention.

[0052] Figure 3 This is an example of the calculation results of the OCT system simulation model described in the present invention. The x-axis and y-axis of the coordinate system are the asymmetry factor g and the scattering coefficient μ respectively.s The number of collected photons is represented by the z-axis coordinate when the light source wavelength is 800nm ​​and the film thickness is 1mm. The surface is the simulation result of the scene where the incident light enters the optical film from air (the average number of collected photons when no scattering layer is added is 1.92×10 4 ), it can be seen that the asymmetric factor g is in the range of [0.77, 0.81], and the scattering coefficient is in the range of [0.15, 0.30] (unit: mm -1 ), the corresponding scattering particle size is between [2.4,3.2] interval (unit: μm), and the concentration is between [0.04,0.10] interval (unit: g / cm 3 ), the acquisition signal intensity will gain, and the maximum imaging depth gain can reach 30%. DETAILED DESCRIPTION

[0053] The present invention will be further described below with reference to the accompanying drawings and implementation examples:

[0054] Example 1

[0055] For an OCT system using a light source with a wavelength in the range of [750, 1000] (unit: nm), scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of film thickness [0.5, 1.5] (unit: mm), so that the refractive index of the film medium material is between [1.0, 1.5], the difference in refractive index between the scattering particles and the medium is between [-0.5, 0.8], the size of the scattering particles is between [1.2, 3.2] (unit: μm), and the concentration is between [0.07, 0.08] (unit: g / cm 3 ), that is, the asymmetric factor g is in the interval [0.75, 0.81], and the scattering coefficient is in the interval [0.23, 0.25] (unit mm -1 When performing OCT, a thin film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to gain gain, thereby increasing the detection depth.

[0056] Example 2

[0057] For an OCT system using a light source with a wavelength of 800 nm, scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of film thickness [0.5, 1.5] (unit: mm), so that the refractive index of the film medium material is between [1.0, 1.5], the difference in refractive index between the scattering particles and the medium is between [-0.5, 0.8], the size of the scattering particles is between [0.8, 3.2] (unit: μm), and the concentration is between [0.06, 0.08] (unit: g / cm 3 ), that is, the asymmetric factor g is in the interval [0.70, 0.81], and the scattering coefficient is in the interval [0.20, 0.25] (unit mm -1When performing OCT, a thin film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to gain gain, thereby increasing the detection depth.

[0058] Example 3

[0059] For an OCT system using a light source with a wavelength of 800 nm, scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of a film thickness of 1 mm, so that the refractive index of the film medium material is between [1.0, 1.5], the difference in refractive index between the scattering particles and the medium is between [-0.5, 0.8], the size of the scattering particles is between [0.8, 3.2] (in μm), and the concentration is between [0.04, 0.10] (in g / cm 3 ), the corresponding asymmetric factor g is in the range of [0.70, 0.81], and the scattering coefficient is in the range of [0.15, 0.30] (unit: mm -1 ). When performing OCT, the thin film is covered on the surface of the object to be detected. The optical probe of the OCT system collects the signal intensity to gain gain, thereby achieving the purpose of increasing the detection depth. Under the conditions of light source wavelength of 800nm ​​and film thickness of 1mm, the maximum detection depth can be theoretically improved by 30%. The simulation results are as follows Figure 3 shown.

[0060] Example 4

[0061] For an OCT system using a light source with a wavelength of 840 nm, scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of a film thickness of 1 mm, so that the refractive index of the film medium is between [1.0, 1.5], the difference in refractive index between the scattering particles and the medium is between [-0.5, 0.8], the size of the scattering particles is between [0.9, 3.4] (in μm), and the concentration is between [0.04, 0.10] (in g / cm 3 ), the corresponding asymmetric factor g is in the range of [0.70, 0.81], and the scattering coefficient is in the range of [0.15, 0.30] (unit: mm -1 When performing OCT, a thin film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to gain gain, thereby increasing the detection depth.

[0062] Example 5

[0063] For an OCT system using a light source with a wavelength in the range of [1000, 1300] (unit: nm), scattering particles of appropriate concentration and size are dispersed in the optical film under the condition that the film thickness is in the range of [0.5, 1.5] (unit: mm), so that the refractive index of the film medium material is in the range of [1.0, 1.5], the difference in refractive index between the scattering particles and the medium is in the range of [-0.5, 0.8], the size of the scattering particles is in the range of [1.5, 4.5] (unit: μm), and the concentration is in the range of [0.06, 0.08] (unit: g / cm 3 ), that is, the asymmetric factor g is in the interval [0.75, 0.81], and the scattering coefficient is in the interval [0.15, 0.25] (unit mm -1 When performing OCT, a thin film is placed between the optical probe and the object being detected. The optical probe of the OCT system collects signal intensity to gain gain, thereby achieving the purpose of increasing the detection depth.

[0064] Example 6

[0065] For an OCT system using a light source with a wavelength of 1060 nm, scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of a film thickness of 1 mm, so that the refractive index of the film medium is between [1.0, 1.5], the difference in refractive index between the scattering particles and the medium is between [-0.5, 0.8], the size of the scattering particles is between [1.5, 3.2] (in μm), and the concentration is between [0.04, 0.10] (in g / cm 3 ), the corresponding asymmetric factor g is in the range of [0.70, 0.81], and the scattering coefficient is in the range of [0.15, 0.30] (unit: mm -1 When performing OCT, a thin film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to gain gain, thereby increasing the detection depth.

[0066] Example 7

[0067] For an OCT system using a light source with a wavelength in the range of [1300, 1700] (unit: nm), scattering particles of appropriate concentration and size are dispersed in the optical film under the condition that the film thickness is in the range of [0.5, 1.5] (unit: mm), so that the refractive index of the film medium material is in the range of [1.0, 1.5], the difference in refractive index between the scattering particles and the medium is in the range of [-0.5, 0.8], the size of the scattering particles is in the range of [1.8, 5.5] (unit: μm), and the concentration is in the range of [0.06, 0.08] (unit: g / cm 3 ), that is, the asymmetric factor g is in the interval [0.75, 0.81], and the scattering coefficient is in the interval [0.15, 0.25] (unit mm -1When performing OCT, a thin film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to gain gain, thereby increasing the detection depth.

[0068] Example 8

[0069] For an OCT system using a light source with a wavelength of 1300 nm, scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of a film thickness of 1 mm, so that the refractive index of the film medium is between [1.0, 1.5], the difference between the refractive index of the scattering particles and the medium is between [-0.5, 0.8], the size of the scattering particles is between [1.8, 3.9] (in μm), and the concentration is between [0.01, 0.08] (in g / cm 3 ), that is, the asymmetric factor g is in the interval [0.77, 0.81], and the scattering coefficient is in the interval [0.05, 0.25] (unit mm -1 When performing OCT, a thin film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to gain gain, thereby increasing the detection depth.

[0070] Example 9

[0071] For an OCT system using a light source with a wavelength of 1310 nm, scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of a film thickness of 1 mm, so that the refractive index of the film medium is between [1.0, 1.5], the difference between the refractive index of the scattering particles and the medium is between [-0.5, 0.8], the size of the scattering particles is between [1.8, 4.0] (in μm), and the concentration is between [0.01, 0.08] (in g / cm 3 ), that is, the asymmetric factor g is in the interval [0.77, 0.81], and the scattering coefficient is in the interval [0.05, 0.25] (unit mm -1 When performing OCT, a thin film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to gain gain, thereby increasing the detection depth.

[0072] Example 10

[0073] For an OCT system using a light source with a wavelength of 1550nm, scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of a film thickness of 1mm, so that the refractive index of the film medium material is between [1.0, 1.5], the difference between the refractive index of the scattering particles and the medium is between [-0.5, 0.8], the size of the scattering particles is between [4.5, 6.0] (unit: μm), and the concentration is between [0.01, 0.08] (unit: g / cm 3), that is, the asymmetric factor g is in the interval [0.77, 0.81], and the scattering coefficient is in the interval [0.05, 0.25] (unit mm -1 When performing OCT, a thin film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to gain gain, thereby increasing the detection depth.

[0074] Example 11

[0075] For OCT systems using an 800nm ​​wavelength light source, titanium dioxide (refractive index 2.35 at 500nm) is selected as the scattering layer particle. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). Titanium dioxide particles are weighed and mixed with the A / B adhesive at a ratio of [0.05, 0.2] g of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2.5] mm. During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0076] Example 12

[0077] For OCT systems using an 840nm wavelength light source, silica (refractive index 1.46 at 500nm) is used as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). To prepare the scattering layer, weigh the silica particles and mix them with the A / B adhesive at a ratio of [0.1, 0.5] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degasser. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2.5] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0078] Example 13

[0079] For OCT systems using an 800nm ​​wavelength light source, zinc oxide (refractive index 2.0 at 500nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). During preparation, zinc oxide particles are weighed and mixed with the A / B adhesive at a ratio of [0.05, 0.3] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2.5] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0080] Example 14

[0081] For OCT systems using an 850nm wavelength light source, zirconium oxide (refractive index 2.05 at 500nm) is used as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560 A / B adhesive (refractive index 1.4). During preparation, zirconium oxide particles are weighed and mixed with the A / B adhesive at a ratio of [0.05, 0.3] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degasser. After degassing, the film is spin-coated onto a glass slide and then heat-cured in an oven. The resulting scattering film has a thickness of [0.5, 2.5] (unit: mm). During OCT, the film is placed between the optical probe and the object being detected. The optical probe of the OCT system acquires signal intensity to achieve gain, thereby increasing the detection depth.

[0082] Example 15

[0083] For OCT systems using a 1060nm wavelength light source, zirconium oxide (refractive index 2.05 at 500nm) is used as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). During preparation, zirconium oxide particles are weighed and mixed with the A / B adhesive at a ratio of [0.05, 0.3] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degasser. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2.5] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0084] Example 16

[0085] For OCT systems using a 1300nm wavelength light source, yttrium oxide (refractive index 1.8 at 500nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). Yttrium oxide particles are weighed and mixed with the A / B adhesive at a ratio of [0.1, 0.3] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degasser. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0086] Example 17

[0087] For OCT systems using a 1310nm wavelength light source, magnesium oxide (refractive index 1.70 at 500nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). To prepare the scattering layer, weigh the magnesium oxide particles and mix them with the A / B adhesive at a ratio of [0.1, 0.3] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is placed between the optical probe and the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0088] Example 18

[0089] For OCT systems using a 1310nm wavelength light source, cadmium selenide (refractive index 2.87 at 900nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). To prepare the scattering layer, weigh the cadmium selenide particles and mix them with the A / B adhesive at a ratio of [0.05, 0.15] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles in the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0090] Example 19

[0091] For OCT systems using a 1490nm wavelength light source, niobium oxide (refractive index 2.3 at 550nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). During preparation, niobium oxide particles are weighed and mixed with the A / B adhesive at a ratio of [0.05, 0.2] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0092] Example 20

[0093] For OCT systems using a 1550nm wavelength light source, niobium oxide (refractive index 2.3 at 550nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). During preparation, niobium oxide particles are weighed and mixed with the A / B adhesive at a ratio of [0.05, 0.2] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0094] Example 21

[0095] For OCT systems using a 1550nm wavelength light source, silicon single crystals (refractive index 1.47 at 1550nm) are used as scattering particles in the scattering layer. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). During preparation, weighed silicon single crystal particles are mixed with the A / B adhesive at a ratio of [0.1, 0.3] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0096] Example 22

[0097] For OCT systems using a 1550nm wavelength light source, aluminum antimonide (refractive index 3.3 at 2000nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). During preparation, aluminum antimonide particles are weighed and mixed with the A / B adhesive at a ratio of [0.05, 0.15] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0098] Example 23

[0099] For OCT systems using a 1550nm wavelength light source, gallium arsenide (refractive index 3.3 at 3000nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). During preparation, weighed gallium arsenide particles are mixed with the A / B adhesive at a ratio of [0.05, 0.15] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0100] Example 24

[0101] For OCT systems using a 1650nm wavelength light source, cadmium selenide (refractive index 2.87 at 900nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). To prepare the scattering layer, weigh the cadmium selenide particles and mix them with the A / B adhesive at a ratio of [0.05, 0.15] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles in the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

[0102] Example 25

[0103] For OCT systems using a 1700nm wavelength light source, cadmium telluride (refractive index 2.67 at 10,000nm) is selected as the scattering layer particles. The scattering layer medium can be commercially available Dow Corning 6560A / B adhesive (refractive index 1.4). To prepare the scattering layer, weigh the cadmium telluride particles and mix them with the A / B adhesive at a ratio of [0.05, 0.15] (unit: g) of scattering particles per 100g of A / B adhesive. Stir thoroughly for 20 minutes to completely disperse the scattering particles throughout the A / B adhesive. Degassing is then performed using a vacuum degassing machine. After degassing, the film is spin-coated onto a glass slide and then cured in an oven. The resulting scattering film has a thickness of [0.5, 2] (unit: mm). During OCT, the film is applied to the surface of the object being detected. The optical probe of the OCT system collects signal intensity to achieve gain, thereby increasing the detection depth.

Claims

1. A method for improving the depth of optical coherence tomography based on Mie scattering, characterized in that: The following steps are involved: (1) According to the actual scenario of optical coherence tomography (OCT), a scattering film based on Mie scattering is introduced into the optical path to improve the photon collection rate of the OCT system. First, the characteristics of the scattering film are simulated and designed, and the scattering of the OCT system when the incident light passes through the scattering film and the redistribution of the light field when the detected object is backscattered and returned through the scattering film are comprehensively considered. The thickness of the optical film dispersed with forward scattering particles, the refractive index of the scattering particles and the medium, and the effective range of the size and concentration of the scattering particles are calculated, so that the scattering film can improve the photon collection rate of the backscattered light returned from the detected object more than the scattering loss when the incident light passes through the scattering film; (2) according to the parameters optimized and designed in step (1), dispersing scattering particles that meet the design requirements in step (1) in the dielectric layer to prepare a scattering film that increases the photon collection rate of the OCT system; (3) When performing OCT detection, the optical scattering film prepared in step (2) is placed between the optical probe and the object to be detected, thereby improving the OCT detection depth; The calculation requirements for the various parameters of the scattering film used in step (1) are used to establish an OCT system simulation model based on the Monte Carlo ray tracing algorithm. The implementation scheme is to use the Henyey–Greenstein model of Mie scattering to determine the approximate scattering phase function P by the asymmetric factor g. HG (θ,g), and then determine the probability of deflection in each direction during scattering. The probability of photons being scattered and absorbed is determined by the thickness d of the scattering layer, the scattering coefficient and the absorption coefficient. At the same time, the influence of the refractive index n of each layer on the reflection and refraction when passing through the layer is considered. Combined with the wavelength of the light source used by the OCT system and the application scenario, the asymmetric factor g, the scattering layer thickness d, and the scattering coefficient μ of the scattering layer required by the OCT system are calculated through the model. s , the range of refractive indices n0 and n1 of the scattering film medium and the scattering particles, and further infer the size of the scattering particles dispersed in the optical film by combining the asymmetric factor with the wavelength of the light source, and infer the concentration of the scattering particles by the scattering coefficient. The specific algorithm flow includes the following steps: (I) For each photon, the initial position and incident direction are first randomly given according to the Gaussian beam distribution; (II) The next step is to determine the distance the photon must travel to reach the next boundary based on the direction angle and the current position; (III) Determine whether the photon is scattered during this distance. If scattering occurs, the position and azimuth angle of the scattering will be randomly assigned by probability distribution, and then the distance the photon must travel to reach the next boundary will be re-determined based on the new position and azimuth angle; (IV) When the photon reaches the boundary, the law of refraction determines the new direction of the photon propagation, and based on the transmittance, the probability of whether the photon is reflected is determined; (V) after entering the next scattering layer, repeating steps (II) to (IV) until the detection target depth is reached; (VI) The effective photons that can be collected by the probe must come from the backscattering of photons at the target depth, and the direction angle of the photon movement after backscattering is given according to the probability distribution; (VII) repeating steps (II) to (IV) until returning to the optical probe, and counting; (VIII) If the photon is determined to be unable to be collected due to absorption or large-angle scattering between steps (I) and (VII), the process will stop immediately and jump to step (I) to regenerate the photon; (IX) tracking a sufficient number of photons and calculating the photon collection rate; (X) Change the scattering film thickness d, the scattering particle asymmetry factor g, and the scattering coefficient μ s Parameters, repeating steps (I) to (IX), comparing the photon collection rate with that without adding the scattering film, and obtaining the parameter range that improves the photon collection rate; (XI) The refractive index range n0 and n1 of the scattering film medium and the scattering particles dispersed therein, and the size of the scattering particles are calculated from the asymmetric factor combined with the wavelength of the light source. The concentration of the scattering particles is calculated from the scattering coefficient, and the scattering film thickness, scattering particle size, and scattering particle concentration range that improves the photon collection rate are obtained.

2. The method for improving the depth of optical coherence tomography based on Mie scattering according to claim 1, characterized in that: For an OCT system using a light source with a wavelength in the range of [750nm, 1000nm], scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of film thickness [0.5mm, 1.5mm], so that the refractive index of the film medium material is between [1.0, 1.5], the difference between the refractive index of the scattering particles and the medium is between [-0.5, 0.8], the size of the scattering particles is between [1.2μm, 3.2μm], and the concentration is between [0.07g / cm 3 ,0.08g / cm 3 ] interval, that is, the asymmetric factor g is in the interval [0.75,0.81], and the scattering coefficient is between [0.23mm -1 ,0.25mm -1 ] interval, when performing OCT, a thin film is covered on the surface of the object to be detected, and the optical probe of the OCT system collects signal intensity to obtain gain, thereby achieving the purpose of increasing the detection depth.

3. The method for improving the depth of optical coherence tomography based on Mie scattering according to claim 1, characterized in that: For an OCT system using a light source with a wavelength in the range of [1000nm, 1300nm], scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of film thickness in the range of [0.5mm, 1.5mm], so that the refractive index of the film medium material is in the range of [1.0, 1.5], the difference between the refractive index of the scattering particles and the medium is in the range of [-0.5, 0.8], the size of the scattering particles is in the range of [1.5μm, 4.5μm], and the concentration is in the range of [0.06g / cm 3 ,0.08g / cm 3 ] interval, that is, the asymmetric factor g is in the interval [0.75,0.81], and the scattering coefficient is between [0.15mm -1 ,0.25mm -1 ] interval, when performing OCT, the film is placed between the optical probe and the object to be detected, and the optical probe of the OCT system collects signal intensity to obtain gain, thereby achieving the purpose of increasing the detection depth.

4. The method for improving the depth of optical coherence tomography based on Mie scattering according to claim 1, characterized in that: For an OCT system using a light source with a wavelength in the range of [1300nm, 1700nm], scattering particles of appropriate concentration and size are dispersed in the optical film under the condition of film thickness in the range of [0.5mm, 1.5mm], so that the refractive index of the film medium material is in the range of [1.0, 1.5], the difference between the refractive index of the scattering particles and the medium is in the range of [-0.5, 0.8], the size of the scattering particles is in the range of [1.8μm, 5.5μm], and the concentration is in the range of [0.06g / cm 3 ,0.08g / cm 3 ] interval, that is, the asymmetric factor g is in the interval [0.75,0.81], and the scattering coefficient is between [0.15mm -1 ,0.25mm -1 ] interval, when performing OCT, a thin film is covered on the surface of the object to be detected, and the optical probe of the OCT system collects signal intensity to obtain gain, thereby achieving the purpose of increasing the detection depth.

5. The method for improving the depth of optical coherence tomography based on Mie scattering according to claim 1, characterized in that: In step (2), the scattering particle materials used for the scattering film include silicon dioxide with a refractive index of 1.46@500nm, titanium dioxide with a refractive index of 2.35@500nm, aluminum oxide with a refractive index of 1.63@550nm, magnesium oxide with a refractive index of 1.70@500nm, zinc oxide with a refractive index of 2.0@500nm, zirconium oxide with a refractive index of 2.05@500nm, niobium oxide with a refractive index of 2.3@550nm, yttrium oxide with a refractive index of 1.8@500nm, and tantalum with a refractive index of 2.20@550nm. nm cerium oxide, cadmium selenide with a refractive index of 2.87@900nm, aluminum antimonide with a refractive index of 3.3@2000nm, cadmium telluride with a refractive index of 2.67@10000nm, gallium arsenide with a refractive index of 3.3@3000nm, indium phosphide with a refractive index of 3.45@590nm, silicon with a refractive index of 1.47@1550nm, and small bubbles with a refractive index of 1.0@700-1700nm. One or more of the above materials can be selected as scattering particles of the scattering film to adapt to various OCT application environments.

6. The method for improving the depth of optical coherence tomography based on Mie scattering according to claim 1, characterized in that: In step (2), the dielectric material used for the scattering film uses flexible materials such as polyester PET, polyimide PI, polyvinyl alcohol PVA, polyethylene naphthalate PEN or dimethylsiloxane PDMS. One or more of the above materials are selected as the dielectric material of the scattering film to adapt to various OCT application environments.

7. The method for improving the depth of optical coherence tomography based on Mie scattering according to claim 1, characterized in that: In step (2), the preparation method is: for an OCT system using a light source with a wavelength of 1550nm, a silicon single crystal with a refractive index of 1.47@1550nm is selected as a scattering particle of the scattering layer, and the scattering layer medium adopts Dow Corning 6560A / B glue with a refractive index of 1.4 directly purchased. When preparing, the silicon single crystal particles are weighed and mixed with the A / B glue, and the ratio is [0.1g, 0.3g] of scattering particles per 100g of A / B glue. The mixture is stirred for 20 minutes to completely disperse the scattering particles in the A / B glue, and then a vacuum degassing machine is used for degassing. After degassing, the mixture is spin-coated on a glass slide, and then placed in an oven for heating and curing. Finally, a scattering film with a thickness of [0.5mm, 2mm] is prepared. When performing OCT, the film is covered on the surface of the object to be detected, and the optical probe of the OCT system collects the signal intensity to obtain gain, thereby achieving the purpose of improving the detection depth.

8. The method for improving the depth of optical coherence tomography based on Mie scattering according to claim 1, characterized in that: In step (2), when the scattering film is manufactured, a lens structure having a convergence effect on the corresponding wavelength is added to further converge the emitted light, thereby improving the imaging quality.

9. The method for improving the depth of optical coherence tomography based on Mie scattering according to claim 1, characterized in that: In step (3), the scattering film and the object to be detected are closely attached, or the OCT probe, the scattering film and the object to be detected are closely attached, so as to reduce the loss of light intensity in the air and further improve the imaging depth.

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