Method and device for measuring subcutaneous blood vessel parameters

Abstract

A method and device for measuring subcutaneous blood vessel parameters, wherein the measuring method includes irradiating the epidermis of the skin with multiple lasers of different pulse widths and simultaneously collecting temperature signals from the skin surface. A temperature distribution curve is drawn under each of the pulse width laser irradiations. Temperature peaks will appear on the temperature distribution curve. After the number of temperature peaks stabilizes, a stable temperature peak is obtained. The number of stable temperature peaks is the number of blood vessels, and the depth corresponding to the stable temperature peak is the depth of the center of the blood vessel. Furthermore, by obtaining and fitting different temperature peak information under different pulse width laser irradiations at the same depth, a fitting relationship is obtained; and then the diameter of the blood vessel is calculated based on the principle and definition of thermal relaxation. The measuring device includes a power supply, a display screen, a laser emitting component, a temperature collection component, and a control component. The control component is electrically connected to the power supply, the display screen, the laser emitting component, and the temperature collection component, and the control component controls the operation of the measuring device.

Description

Technical Field

[0001] The present invention relates to the field of blood vessel measurement, and in particular to a non-invasive subcutaneous blood vessel parameter measurement method and device. Background Art

[0002] Vascular skin diseases are abnormal aggregations of blood vessels in the skin or other parts of the body, appearing as red or purple masses. Hemangiomas are benign hamartomas formed from residual embryonic vascular cells and are generally clinically divided into three types: port-wine stains, simple hemangiomas, and cavernous hemangiomas. Based on the selective photothermal effect of biological tissue, laser therapy can selectively damage subcutaneous diseased blood vessels, maximally preserving normal tissue. It is currently the only effective clinical treatment for vascular skin diseases. However, at the same time, the crude, empirical clinical treatment technology of laser radiation has reached its "ceiling." Taking laser treatment of port-wine stains as an example, due to the lack of effective non-destructive detection methods for skin tissue structure and online monitoring of thermal damage to diseased blood vessels, current clinical treatment is mainly based on physician experience, and the complete cure rate has remained below 20% for nearly 10 years.

[0003] Skin tissue structure includes vascular parameters such as the number, depth, and diameter of subcutaneous blood vessels. Skin tissue structure is crucial for selecting parameters for laser treatment. Traditional pulsed photothermal radiation can achieve the goal of non-invasively measuring subcutaneous vascular parameters. This method works by first emitting a laser of a specific wavelength onto the skin surface. This laser energy is selectively absorbed by the diseased subcutaneous blood vessels, and the resulting heat is conducted to the skin surface through thermal conductivity. An infrared thermal imager is then used to capture the surface temperature signal. The value and variation trend of this temperature signal contain information about the temperature and tissue structure of the diseased blood vessels. Therefore, the structure and temperature of the subcutaneous blood vessels can be solved using the inverse thermal conductivity method.

[0004] Traditional pulsed photothermal radiation methods mainly use a single pulse width (the duration of a single laser irradiation) laser pulse to determine tissue structure. For example, Thomas et al. used a single pulse width of 0.1 ms laser to irradiate the skin, reconstructed the temperature distribution using the conjugate gradient method, and calculated the blood vessel diameter based on the temperature distribution using the full width at half maximum estimation method. (Related literature: Thomas, E, Milner, et al. Depth profiling of laser-heated chromophores in biological tissues by pulsed photothermal radiometry [J]. Journal of the Optical Society of America A, 1995, 12(7): 1479-1488.) For example, the algorithm of Wim et al. used a single pulse width of 3 ms laser to irradiate the skin, reconstructed the temperature distribution using a non-negative constraint combined with a truncated singular value inverse calculation algorithm, and calculated the blood vessel diameter based on the temperature distribution using the full width at half maximum estimation method. (Related literature: VERKRUYSSE W, MAJARON B, CHOI B, et al. Combining singular value decomposition and a non-negative constraint in a hybrid method for photothermal depth profiling[J]. Review ofScientific Instruments, 2005, 76(2):4301-1-4301-6-0.).

[0005] Traditional pulsed photothermal radiation methods suffer from significant errors and lack a scientific basis for measuring blood vessel diameter. This is primarily because a single laser pulse measurement method can only obtain a single temperature distribution. However, the temperature distribution of subcutaneous tissue is a dynamic process that is correlated with changes in pulse width. Therefore, the subcutaneous tissue structure estimated by a single laser pulse is also single and random, subject to significant errors, and unable to accurately capture the structure. Furthermore, during the measurement process, the signal response of the tissue surface after irradiation is very fast. Therefore, by the time the infrared thermal imager begins to collect the signal, the thermal radiation energy on the tissue surface has already dissipated to a certain extent. This results in a low thermal radiation signal captured by the infrared thermal imager, which increases the error in the final measurement. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention provides a method and device for measuring subcutaneous blood vessel parameters, which can accurately measure the parameters of subcutaneous blood vessels in a non-invasive manner.

[0007] To achieve the above-mentioned object, the present invention provides a method for measuring subcutaneous vascular parameters, characterized by comprising:

[0008] Irradiate the epidermis of the skin with multiple lasers of different pulse widths, collect temperature signals on the skin surface, and draw a temperature distribution curve reflecting the relationship between the depth and temperature of the subcutaneous tissue under each of the laser pulse width irradiations. A temperature peak will be generated on the temperature distribution curve:

[0009] irradiating the epidermis with multiple deep pulse width lasers until the number of temperature peaks in the temperature distribution curve is stable, and the temperature peaks are stable temperature peaks;

[0010] The epidermis is irradiated with lasers of multiple diameters and pulse widths to obtain temperature peak depths corresponding to the multiple temperature peaks. For each temperature peak depth, temperature peak information under irradiation with lasers of different diameters and pulse widths is collected, and the temperature peak with the highest temperature is obtained as the highest temperature peak. After fitting, a fitting relationship is obtained that reflects the relationship between the temperature peaks and the diameters and pulse widths. After the temperature of the highest temperature peak drops by a variable temperature, a thermal relaxation temperature is obtained.

[0011] Substituting the thermal relaxation temperature into the fitting equation to obtain the thermal relaxation pulse width;

[0012] The subcutaneous vascular parameters include:

[0013] The number of the blood vessels is the same as the number of the stable temperature peaks.

[0014] The depth of the blood vessel is the same as the depth corresponding to the stable temperature peak.

[0015] The diameter of the blood vessel is positively correlated with the thermal relaxation pulse width.

[0016] Furthermore, the pulse width of the deep pulse laser is greater than or equal to 5 ms and less than or equal to 20 ms.

[0017] Furthermore, the pulse width of the diameter pulse laser is less than 5 ms.

[0018] Furthermore, the pulse width of the deep pulse laser is greater than or equal to 5 ms and less than or equal to 20 ms; the pulse width of the diameter pulse laser is less than 5 ms.

[0019] Furthermore, the diameter of the blood vessel is proportional to the thermal relaxation pulse width.

[0020] Furthermore, the changing temperature is less than or equal to 50% of the temperature difference between the highest temperature peak and the temperature of the subcutaneous tissue before irradiation with the diameter pulse width laser.

[0021] Furthermore, the change temperature is 37% of the temperature difference between the highest temperature peak and the temperature of the subcutaneous tissue before irradiation with the diameter pulse width laser.

[0022] Furthermore, after each laser irradiation is completed, the pulse width of the laser can be changed only when the temperature signal of the skin surface returns to the level before the laser irradiation.

[0023] In addition, to achieve the above-mentioned purpose, the present invention also provides a device for measuring subcutaneous blood vessel parameters, comprising:

[0024] power supply,

[0025] Display screen, used to output results;

[0026] Laser emitting component, used for emitting lasers with different pulse widths;

[0027] A temperature collection component, used to collect temperature signals from the skin surface;

[0028] a control component electrically connected to the display screen, the laser emitting component, and the temperature collecting component;

[0029] The power supply supplies power to the device by connecting to the control component. The control component controls the laser emitting component to emit lasers with various pulse widths to irradiate the epidermis of the skin. After each irradiation is completed, the control component controls the temperature collecting component to collect the temperature signal of the skin surface and transmits the temperature signal to the control component; the control component processes the signal and outputs the obtained subcutaneous blood vessel parameters to the display screen.

[0030] The advantages of the present invention are:

[0031] 1. The measurement method of this invention avoids the serious difference in temperature distribution curves caused by different pulse widths in traditional measurement methods (single pulse width laser irradiation method), making the measurement results more stable and accurate. It also provides a scientific basis for the measurement of blood vessel diameter.

[0032] 2. The measuring device of the present invention integrates the functions of subcutaneous vascular parameter measurement and laser treatment, thereby improving the automation level of the measurement and treatment processes. While saving manpower and improving work efficiency, it can also effectively avoid the loss of thermal radiation energy caused by slow manual response during the measurement process. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the temperature distribution at the initial moment when the pulse laser is irradiated onto the multi-layer skin model.

[0034] Figure 2-Figure 11 Temperature distribution curves under laser irradiation with pulse widths of 20ms, 10ms, 5ms, 0.1ms, 0.2ms, 0.4ms, 0.6ms, 0.8ms, 1ms, and 1.2ms respectively.

[0035] Figure 12 Figure 2 is a graph showing the relationship between the peak central temperature and pulse width of three blood vessels.

[0036] Figure 13 Figure 3 is the fitted temperature peak pulse width diagram of three blood vessels.

[0037] Figure 14 This is a diagram showing the working principle of the subcutaneous blood vessel parameter measurement device of the present invention.

[0038] Figure 15 This is a comparison chart of the error in measuring blood vessel diameter using the method of the present invention and the error in measuring blood vessel diameter using the traditional calculation method.

[0039] Figure 16 The schematic diagram is used to reversely optimize the temperature distribution curve based on information such as blood vessel diameter and depth.

[0040] Figure 17 Comparison of temperature distribution curves optimized by reverse calculation under 0.1ms laser irradiation

[0041] Figure 18 Comparison of the error of the center temperature of blood vessels with different diameters DETAILED DESCRIPTION

[0042] The following is a detailed description of the technical means used by the present invention to achieve the intended purpose of the invention, with reference to the drawings and preferred embodiments of the present invention.

[0043] By irradiating the epidermis with a single pulse width laser and simultaneously collecting the temperature signal on the skin surface, a temperature distribution curve of the relationship between the depth of the subcutaneous tissue and the initial temperature can be drawn. The specific drawing principle is as follows:

[0044] The problem of solving the temperature distribution of subcutaneous blood vessels using pulsed photothermal radiation is an inverse problem of thermal conduction. Specifically, the blood vessels in the skin absorb light and generate heat that diffuses to the surface. The temperature distribution inside the skin is solved in reverse by collecting the temperature signal (the time evolution of the temperature near the skin surface).

[0045] More specifically, as Figure 1 The inverse heat conduction problem links the pulsed photothermal radiation signal ΔS(t) with the initial temperature distribution T(z, t=0), establishes an integral equation, and solves the unknown subcutaneous initial temperature distribution T(z, t=0) through the truncated singular value decomposition algorithm with a custom truncation parameter.

[0046] The specific establishment process is as follows:

[0047] According to the Green's function solution of the one-dimensional heat transfer problem, the temperature distribution ΔT(z,t) at any depth z and time t is:

[0048]

[0049] At any time t, the ideal pulsed photothermal radiation signal amplitude is proportional to the superposition of depth-dependent temperature variations:

[0050]

[0051] μ a —infrared absorption coefficient of the test material exposed at the detection wavelength,

[0052] C d —Proportional constant determined by the infrared detection system

[0053] Combining the two complementary formulas we can get:

[0054]

[0055] The simplified form is the first kind Fredholm integral equation:

[0056]

[0057] Since most first-kind Fredholm integral equations are ill-posed, that is, small perturbations (i.e., noise) in the measurement signal will cause large changes in the calculated solution estimate, regularization can alleviate the impact of the ill-posed estimation problem. The basic principle is: using the structure-related regularization component to enhance the cost function that is usually related to the data, and adding a smooth constraint to the input-output mapping established by the estimator to stabilize the solution. Truncated singular value decomposition (TSVD) is one of the regularization methods. The singular values ​​obtained by singular value decomposition (SVD) are non-negative and decrease in sequence. Generally, the singular values ​​after the kth tend to zero. Therefore, the principle of TSVD is to truncate the first k singular values ​​to avoid the amplification of the noise of high-frequency terms, and to restore the stability of the solution by sacrificing a certain amount of solution accuracy. Specifically, the system of linear equations obtained after discretizing the integral equation is:

[0058] ΔS(t)=KΔT

[0059] Perform singular value decomposition (SVD) on the kernel function:

[0060]

[0061] The core of the TSVD method is to determine the truncation parameter k. By setting a threshold for the singular values, the singular values ​​that are smaller than the threshold are truncated, so that the solution is stable while ensuring that the approximate solution is close enough to the true solution of the original problem.

[0062] Assume that δ is the singular value of the kernel function K, take the threshold as α, and k as the value that makes δ k The first integer ≤α, that is:

[0063] δ1≥δ2≥…δ k-1 ≥α≥δ k ≥δ r ≥0

[0064] The selection strategy of the truncation parameter k is flexible and diverse. The present invention designs a simple a priori selection method - the custom truncation parameter method, which is a statistically reasonable truncation parameter selection algorithm that can improve the versatility and reliability of parameter selection. The principle formula of the custom truncation parameter algorithm is:

[0065]

[0066] Where: k is the cutoff parameter; m is the total number of singular values; δp is the singular value, sorted in descending order; and σ is the percentage threshold (0 < σ ≤ 1). The principle is that the singular value number corresponding to the sum of the selected singular values ​​that just exceeds the percentage threshold is the cutoff parameter.

[0067] Based on the above principle, the initial temperature distribution of subcutaneous tissue is obtained, as shown in the attached figure. Figure 1 The temperature distribution curve at the initial moment T(z,t=0) is shown, where Curve 1 is the temperature distribution curve of the subcutaneous tissue in the depth direction under the irradiation of a wider pulse width, and Curve 2 is the temperature distribution curve of the subcutaneous tissue in the depth direction under the irradiation of a narrow pulse width. With the skin depth as the horizontal axis and the initial temperature as the vertical axis, the curve can be drawn as follows: Figure 2-11 The temperature distribution curve that reflects the relationship between the depth and temperature of the subcutaneous tissue is shown in Figure 2 As shown, a temperature peak can be obtained on the temperature distribution curve.

[0068] The method for measuring subcutaneous vascular parameters in this invention uses multiple laser pulse widths to irradiate the epidermis and collect temperature signals from the skin surface. The temperature distribution curve under each laser pulse width is plotted as follows:

[0069] Step a: Collect the temperature signal of the skin surface without laser irradiation, which is a zero pulse width temperature signal.

[0070] Step b: Use multiple deep pulse width lasers to irradiate the epidermis. Before each laser irradiation, wait until the temperature signal on the skin surface recovers to 0 pulse width temperature signal to avoid affecting the temperature signal acquisition during laser irradiation. During each laser irradiation, collect the temperature signal on the skin surface. According to the principle of solving the inverse problem of heat conduction, draw the following Figure 2When the number of temperature peaks in the temperature distribution curve shown in the figure reaches a stable level, the pulse width laser irradiation is stopped. At this time, the temperature peaks in the temperature distribution curve are stable temperature peaks. The number of stable temperature peaks is the number of subcutaneous blood vessels, and the depth corresponding to the stable temperature peak is the depth of the blood vessels.

[0071] Step c:

[0072] iUse multiple diameter pulse width laser to irradiate the epidermis. Before each laser irradiation, wait for the temperature signal on the skin surface to return to the zero pulse width temperature signal to avoid affecting the temperature signal acquisition during laser irradiation. During each laser irradiation, collect the temperature signal on the skin surface. According to the principle of solving the inverse problem of heat conduction, draw the following picture: Figure 5 The temperature distribution curve is shown.

[0073] ii Figure 5-11 As shown, due to the different diameter pulse widths, multiple temperature peaks will be generated at the same depth, and the depth corresponding to the temperature peak is the temperature peak depth; the temperature peak value at the same temperature peak depth can be drawn as shown below. Figure 12 The graph shown is the relationship between the peak temperature in the center of the blood vessel and the pulse width. In this graph, the horizontal axis is the pulse width, and the vertical axis represents the peak temperature in the center of the blood vessel under the corresponding pulse width. Different curves represent blood vessels at different depths. Each graph shows three blood vessels with diameters of 30μm, 50μm and 30μm respectively.

[0074] iii Figure 12 As shown in the figure, for the same blood vessel, the highest temperature peak is obtained as the highest temperature peak T, the temperature peak temperature corresponding to the diameter pulse width is selected, and the selected diameter pulse width and its corresponding temperature peak information are fitted, and the following is obtained: Figure 13 The shown figure shows the fitted peak temperature and pulse width diagram reflecting the relationship between the peak temperature and the diameter and pulse width, as well as the fitted relationship between the peak temperature and the diameter and pulse width. Each blood vessel corresponds to a curve and a fitted relationship.

[0075] iv According to the definition of thermal relaxation, the thermal relaxation temperature t of a blood vessel refers to the temperature of the blood vessel after the temperature of the blood vessel rises to the maximum temperature and then drops by a certain temperature during laser irradiation; the thermal relaxation time τ of a blood vessel refers to the time required from the start of laser irradiation to the temperature of the blood vessel rising to the maximum and then dropping to the thermal relaxation temperature.

[0076] In the present invention, the pulse width represents the duration of laser irradiation, and the peak temperature represents the initial temperature of the blood vessel under the pulse width irradiation. Since the pulse width time is in the order of milliseconds, the initial temperature can be regarded as the final temperature of the blood vessel under the pulse width irradiation; Figure 12As shown in the figure, within the diameter pulse width range, as the pulse width increases, that is, the laser irradiation time is prolonged, the temperature of the blood vessel first rises to a peak value and then decreases. Therefore, in the present invention, the thermal relaxation temperature t of the blood vessel can be regarded as the temperature after the highest temperature peak T drops by a certain temperature, and the thermal relaxation time τ of the blood vessel can be regarded as the pulse width corresponding to the thermal relaxation temperature t of the blood vessel, that is, the thermal relaxation pulse width τ'. Figure 13 The relationship shown in the figure allows the thermal relaxation time pulse width τ' of the three blood vessels to be calculated. Preferably, in the present invention, the changing temperature t is less than or equal to 50% of the temperature difference between the highest peak temperature T and the zero pulse width temperature signal. More preferably, the changing temperature t is 37% of the temperature difference between the highest peak temperature T and the zero pulse width temperature signal.

[0077] According to the principle of thermal relaxation, the thermal relaxation time τ of a blood vessel is positively correlated with the diameter d of the blood vessel. Furthermore, the thermal relaxation time τ of a blood vessel is proportional to the square of the diameter d of the blood vessel, that is: (α is the thermal diffusion coefficient of blood vessels = 1.3×10 -3 cm 2 / s); in the present invention, τ=τ', from which the diameter of the blood vessel can be solved.

[0078] In step b of the present invention, the pulse width of the deep pulse laser is preferably in the range of 5ms-20ms (including the end points). If the pulse width is too large, it will damage the skin; if the pulse width is too small, such as Figure 5-Figure 11 As shown, there will be other curve peaks that affect the judgment of the temperature peak.

[0079] In step c of the present invention, the pulse width range of the diameter pulse laser is preferably 0ms-5ms (excluding the end points), and more preferably 0ms-1.2ms (including the end point 1.2ms). Figure 12 As shown, when the pulse width is 0ms-1.2ms, the temperature peak temperature changes rapidly, which is conducive to solving the fitting temperature peak pulse width diagram and fitting relationship. In the present invention, there is no limit on the number of diameter pulse width lasers. The more the number, the more accurate the result.

[0080] In the present invention, the order of the above steps a, b and c is not limited, and as long as the corresponding results can be obtained, they are within the protection scope of the present invention.

[0081] The present invention also provides a device for non-invasively measuring subcutaneous blood vessel parameters using the above-mentioned measurement method. Figure 14 As shown, the device includes a power supply, a display screen, a laser emitting component, a temperature collection component, and a control component. The control component is electrically connected to the display screen, the laser emitting component, and the temperature collection component; the power supply is connected to the control component to supply power to the device.

[0082] The control unit can control the laser emitting device to emit lasers of varying pulse widths to irradiate the epidermis of the skin. After each emission, the control unit controls the temperature acquisition unit to acquire a temperature signal from the skin surface and transmit the temperature signal back to the control unit, which then processes the temperature signal and data. Furthermore, the control unit can control the laser emitting unit and the temperature acquisition unit to complete steps a, b, and c above, and output the number, depth, and diameter of subcutaneous blood vessels to a display screen.

[0083] Furthermore, the control unit can establish a skin model, a light transmission model, a bioheat transfer model, and a thermal damage model based on the obtained skin vascular parameters, and simulate laser treatment processes with different parameters (including laser wavelength, frequency, and pulse width). Ultimately, the optimal laser treatment parameters are automatically selected and transmitted to the display screen. Simply by turning on the treatment switch on the display screen, the control unit controls the laser emitting device to treat the patient according to the optimal parameters.

[0084] The advantages of the method for measuring subcutaneous blood vessel parameters of the present invention are:

[0085] 1. The traditional single pulse width measurement method has different pulse width selections, and the shape of the obtained temperature distribution curve varies greatly, such as Figure 2-Figure 11 As shown, the number and location of temperature peaks obtained are inaccurate, resulting in inaccurate number and location of blood vessels. The method of the present invention uses multiple deep pulse width lasers to irradiate the epidermis until the temperature distribution curve stabilizes, and then obtains the number and depth of stable temperature peaks, thereby accurately obtaining the number and depth of blood vessels.

[0086] 2. The traditional single pulse width measurement method is to use the full width at half maximum (FWHM) of the temperature distribution curve, that is, to draw a straight line parallel to the horizontal axis through the midpoint of the vertical axis of the temperature peak, and the distance between the two points where this straight line intersects the curves on both sides of the peak is as follows: Figure 5 This method lacks scientific basis, and due to different pulse widths, the shapes of the temperature distribution curves obtained vary greatly, so the obtained blood vessel diameter is inaccurate.

[0087] The method of the present invention uses multiple temperature peaks after irradiation with multiple pulse widths to plot a fitted relationship between temperature peaks and pulse widths and solve a relationship equation. This avoids errors caused by large differences in temperature curves under different pulse widths and makes the calculation more accurate. It also introduces the definition and principles of thermal relaxation, associates the thermal relaxation pulse width with the thermal relaxation time, and converts the temperature peak of the blood vessel into the temperature of the vessel during laser irradiation. The thermal relaxation temperature is calculated, and the thermal relaxation pulse width is solved by fitting the relationship. The thermal relaxation time is then obtained, and ultimately the vessel diameter can be solved. This provides a scientific basis for the measurement of blood vessel diameter.

[0088] 3. The subcutaneous vascular parameter measurement device of the present invention can realize the automation of subcutaneous vascular measurement. The control device can control the skin measurement device to detect the skin surface in real time and automatically collect temperature data during laser irradiation, which reduces the response time and avoids the dissipation of thermal radiation energy when manually collecting temperature signals, making the measurement more accurate.

[0089] 4. The subcutaneous vascular parameter measurement device of the present invention can also optimize laser treatment parameters based on the acquired subcutaneous vascular parameters through a control system, and activate the laser emission device based on these parameters to further treat the skin. This achieves the technical effect of integrated measurement and treatment automation, saving time and manpower. It can also improve the cure rate of vascular skin diseases.

[0090] The following specific examples further illustrate and verify the technical means of the present invention:

[0091] Example 1

[0092] A multi-layered skin heat transfer model was established, consisting of the epidermis, vascular layer, and dermis. The vascular layer consisted of a single layer of blood vessels, whose diameter approximated the thickness of the vascular layer, consistent with the characteristics of actual vascular skin diseases. The three blood vessels in the model were labeled A, B, and C, with diameters of 30 μm, 50 μm, and 30 μm, respectively. Figure 2-Figure 11 The medium black rectangle represents the epidermal layer of the skin, and the light grey rectangle represents the vascular layer.

[0093] The subcutaneous blood vessel parameter measurement method of the present invention is used to simulate the measurement of the multi-layer skin heat transfer model:

[0094] like Figure 2-Figure 4 Temperature distribution curves were plotted for simulations of deep pulse widths of 20ms, 10ms, and 5ms. The graphs show that the temperature distribution curve stabilizes at 10ms and 5ms pulse widths, producing three stable temperature peaks. This indicates that three subcutaneous blood vessels are located at depths of 0.2mm, 0.31mm, and 0.42mm, respectively.

[0095] like Figure 5-Figure 11The temperature distribution curves drawn under the pulse width of 0.1ms, 0.2ms, 0.4ms, 0.6ms, 0.8ms, 1ms and 1.2ms are simulated respectively. Figure 12 The relationship diagram between the peak temperature and pulse width (including 5ms and 10ms pulse width) of the blood vessels is shown in the figure below. The fitting relationship between the peak temperature and pulse width of the three blood vessels can be fitted, as shown in the figure below. Figure 13 .

[0096] Furthermore, taking blood vessel B as an example, the measured 0 pulse width temperature signal is 37.1°C, and the highest temperature peak T is read as the change temperature of 49.91. Then the change temperature is (49.91-37.1)*37%=4.7397°C, and the thermal relaxation temperature is 49.91-4.7397=45.1703°C. Substituting the thermal relaxation temperature into Figure 12 The fitting relationship (45.1703=49.786e-0.093x) is used to obtain the thermal relaxation pulse width τ'=1.046ms. Then the thermal relaxation pulse width is input into the thermal relaxation formula to solve for the blood vessel diameter d=46.6μm, which has an error of only 6.8% compared with the actual blood vessel diameter.

[0097] In the same way, the diameter of blood vessel A was calculated to be 39.4 μm, with an error of 31.3%; the diameter of blood vessel C was calculated to be 39.3 μm, with an error of 31%.

[0098] Example 2:

[0099] A multilayer skin heat transfer model with blood vessel diameters of 30 μm, 35 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, and 100 μm was established in the same manner as in Example 1. The blood vessel diameters were simulated and measured using the method of the present invention and the traditional method, and the error values ​​were calculated. The results were plotted as shown in the figure. Figure 15 The error comparison diagram of the blood vessel diameter calculation, wherein the curve where the triangle is located represents the method of the present invention, the curve where the square is located represents the algorithm of Thomas et al., and the curve where the circle is located represents the algorithm of Wim et al.

[0100] As attached Figure 15 As shown, the traditional single-laser pulse irradiation method has a larger overall calculation error than the method of the present invention, regardless of whether a pulse width as short as 0.1ms or a relatively long pulse width of 3ms is used. This error is also increased when the vessel diameter is too small or too large. The method proposed in this project only has a larger error when measuring vessels with a smaller diameter (less than 40μm), but this error is still much smaller than that of the traditional method.

[0101] Example 3

[0102] Based on the information of blood vessel diameter, depth, etc., the temperature distribution curve of the present invention can be optimized by reverse deduction. The optimization principle is as follows: Figure 16 As shown: The dotted line is the temperature distribution calculated by the inverse problem, and the temperature distribution curve is reconstructed by inverse deduction through information such as blood vessel diameter and depth, while the solid line is the simulated temperature distribution curve of the skin temperature curve heat transfer model calculated by the forward problem of heat transfer after laser irradiation. According to the research of Anderson R et al. (Anderson RR, Parrish J A. Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation [J]. Science, 1983, 220 (4596): 524-527.), the thickness of the tissue layer, that is, the blood vessel diameter d, is defined as the time when each temperature peak decays to half on both sides (i.e. Figure 16 In addition, the half-peak temperature values ​​of the dotted line and the solid line in the figure basically coincide with each other. Therefore, after measuring the diameter d of the blood vessel and the depth z of the blood vessel center, the depth z of the blood vessel center is found in the abscissa of the temperature distribution curve, and the width of d / 2 is extended to the left and right sides with z as the center, and the temperature distribution curve reconstructed by reverse deduction is obtained. Figure 16 The intersection of the dotted line in the figure is the temperature value approximately corresponding to the half-peak temperature, and then the peak temperature value can be calculated. Then, the temperature distribution curve can be optimized by reverse deduction based on the calculated peak temperature value, the half-peak temperature value, and the minimum values ​​on both sides of the dotted temperature peak, a total of 5 temperature points.

[0103] Figure 17 This is a temperature distribution curve optimized using the above-mentioned inverse optimization method: the solid line is the skin temperature curve calculated by the forward heat transfer problem after laser irradiation, which is the standard curve; the circular dotted line is the temperature distribution curve obtained by inverse calculation based on the vascular parameters measured using the method of the present application; the triangular dotted line is the temperature distribution curve obtained by inverse calculation based on the vascular parameters measured using the algorithm of Thomas et al. under single pulse width 0.1ms laser irradiation.

[0104] Select a blood vessel at a depth of 0.3 mm and change the diameter of the blood vessel. Figure 17 The peak temperature of blood vessels of different diameters at a depth of 0.3 mm was obtained. Taking the peak temperature of the simulated temperature distribution curve as the standard value, the error between the peak temperature of the algorithm of Thomas et al. and the peak temperature of the method of this application and the standard value was calculated, as shown in the figure. Figure 18 shown. Figure 18 The square dotted line in the middle represents the algorithm of Thomas et al., and the circle dotted line represents the method of this application.

[0105] Depend on Figure 17 and Figure 18 As shown, the temperature distribution curve calculated by inversely calculating the vascular parameters measured by the method of the present application is closer to the standard curve than the temperature distribution curve calculated by inversely calculating the vascular parameters using the algorithm of Thomas et al., and no matter how the vascular diameter changes, the error value of the temperature peak calculated by inversely calculating the vascular parameters measured by the method of the present application is low and relatively stable.

[0106] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for measuring subcutaneous vascular parameters, characterized in that: include: Irradiate the epidermis of the skin with multiple lasers of different pulse widths, collect temperature signals on the skin surface, and draw a temperature distribution curve reflecting the relationship between the depth and temperature of the subcutaneous tissue under each of the laser pulse width irradiations. A temperature peak will be generated on the temperature distribution curve: irradiating the epidermis with multiple deep pulse width lasers until the number of temperature peaks in the temperature distribution curve is stable, and the temperature peaks are stable temperature peaks; The epidermis is irradiated with lasers of multiple diameters and pulse widths to obtain temperature peak depths corresponding to the multiple temperature peaks. For each temperature peak depth, temperature peak information under irradiation with lasers of different diameters and pulse widths is collected, and the temperature peak with the highest temperature is obtained as the highest temperature peak. After fitting, a fitting relationship is obtained that reflects the relationship between the temperature peaks and the diameters and pulse widths. After the temperature of the highest temperature peak drops by a variable temperature, a thermal relaxation temperature is obtained. Substituting the thermal relaxation temperature into the fitting equation to obtain the thermal relaxation pulse width; The subcutaneous vascular parameters include: The number of the blood vessels is the same as the number of the stable temperature peaks. The depth of the blood vessel is the same as the depth corresponding to the stable temperature peak. The diameter of the blood vessel is positively correlated with the thermal relaxation pulse width.

2. The method for measuring subcutaneous blood vessel parameters according to claim 1, wherein: The pulse width of the deep pulse laser is greater than or equal to 5 ms and less than or equal to 20 ms.

3. The method for measuring subcutaneous blood vessel parameters according to claim 1, wherein: The pulse width of the diameter pulse laser is less than 5 ms.

4. The method for measuring subcutaneous blood vessel parameters according to claim 1, wherein: The pulse width of the deep pulse laser is greater than or equal to 5 ms and less than or equal to 20 ms; the pulse width of the diameter pulse laser is less than 5 ms.

5. The method for measuring subcutaneous blood vessel parameters according to claim 4, characterized in that: The diameter of the blood vessel is proportional to the thermal relaxation pulse width.

6. The measuring method according to any one of claims 1 to 5, characterized in that The change temperature is less than or equal to 50% of the temperature difference between the highest temperature peak and the temperature of the subcutaneous tissue before irradiation with the diameter pulse width laser.

7. The measuring method according to claim 6, characterized in that The change temperature is 37% of the temperature difference between the highest temperature peak and the temperature of the subcutaneous tissue before irradiation with the diameter pulse width laser.

8. The method for measuring subcutaneous blood vessel parameters according to claim 7, characterized in that: After each laser irradiation is completed, the pulse width of the laser can be changed only when the temperature signal of the skin surface returns to the level before the laser irradiation.

9. A device for measuring subcutaneous blood vessel parameters using the measurement method according to any one of claims 1 to 8, characterized in that: include: power supply, Display screen, used to output results; Laser emitting component, used for emitting lasers with different pulse widths; A temperature collection component, used to collect temperature signals from the skin surface; a control component electrically connected to the display screen, the laser emitting component, and the temperature collecting component; The power supply supplies power to the device by connecting to the control component. The control component controls the laser emitting component to emit lasers with various pulse widths to irradiate the epidermis of the skin. After each irradiation is completed, the control component controls the temperature collecting component to collect the temperature signal of the skin surface and transmits the temperature signal to the control component; the control component processes the signal and outputs the obtained subcutaneous blood vessel parameters to the display screen.

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