Method and device for measuring thermal conductivity of mammary tissue based on transient hot filament method

Abstract

The invention provides a mammary tissue thermal conductivity measuring method and device based on a transient hot filament method, and relates to the technical field of biological tissue thermal measurement. The method comprises the following steps: providing a mammary tissue sample, selecting a hot filament of which the effective length is smaller than that of the mammary tissue sample, and completely wrapping the mammary tissue sample with the hot filament; direct current is connected to the two ends of the hot wire, the change relation of the voltage at the two ends of the hot wire along with time is collected, and the change relation of the hot wire temperature along with time is obtained according to the linear relation of hot wire resistance and temperature; and based on a preset formula, obtaining the thermal conductivity of the mammary tissue sample according to the change relation of the hot filament temperature along with time. The thermal conductivity of the mammary tissue can be accurately measured, the requirement for accurately regulating and controlling the temperature is met, and parameter selection and scheme optimization are provided for photothermal therapy of the breast cancer.

Description

Technical Field

[0001] The present invention relates to the technical field of biological tissue thermal measurement, and in particular to a method and device for measuring the thermal conductivity of breast tissue based on a transient hot wire method. Background Art

[0002] Photothermal therapy (PTT) is a minimally invasive tumor treatment technology developed in recent years. It works by heating the diseased tissue with an external light source. Photothermal materials concentrated at the tumor site concentrate the light energy and convert it into heat. The tissue dissipates heat through accelerated blood flow and vasodilation. The increased temperature causes massive death in the localized diseased tissue or cancer cells, ultimately achieving therapeutic efficacy. PTT is also known as a "green therapy" because of its minimal side effects and pain.

[0003] The effectiveness of photothermal therapy depends largely on the type of cancer. Breast cancer is a relatively shallow primary disease. The breast is located superficially in the chest and has no intervening organs. The breast parenchyma lacks large blood vessels, making convective heat loss unlikely, making photothermal therapy easier to implement. Current research has demonstrated the feasibility of photothermal therapy for breast cancer.

[0004] During photothermal therapy, excessively high temperatures can cause irreversible damage to normal cells, while insufficient temperatures prevent the effective ablation of tumor cells in a short period of time, leading to a low tumor cure rate. Therefore, considering the need for precise temperature control in the clinical practice of photothermal therapy, measuring the thermal conductivity of breast tissue has both theoretical and practical significance: theoretically, it helps to fill in the relevant data on the thermal conductivity of breast tissue, promote the development of bioheat transfer theory, and provide a theoretical basis for the effective cure of breast cancer with photothermal therapy; in the clinical practice of photothermal therapy for breast cancer, it helps to achieve precise control of temperature distribution, reduce thermal damage to normal tissues, improve treatment efficacy, and promote the clinical application and transformation of photothermal therapy. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and device for measuring the thermal conductivity of breast tissue based on the transient hot wire method, which is used to solve the problems in the existing technology such as how to measure the thermal conductivity of breast tissue and meet the needs of precise temperature control. It can accurately measure the thermal conductivity of breast tissue, meet the needs of precise temperature control, and provide parameter selection and solution optimization for photothermal treatment of breast cancer.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for measuring the thermal conductivity of breast tissue based on a transient hot wire method, comprising: Step 1: providing a breast tissue sample, selecting a hot wire with an effective length shorter than the length of the breast tissue sample, and completely wrapping the breast tissue sample with the hot wire; Step 2: Apply direct current to both ends of the hot wire, collect the relationship between the voltage at both ends of the hot wire and time, and then obtain the relationship between the temperature of the hot wire and time based on the linear relationship between the resistance of the hot wire and the temperature; Step 3: Based on a preset formula and the relationship between the temperature of the hot wire and time, the thermal conductivity of the breast tissue sample is obtained.

[0007] According to a method for measuring thermal conductivity of breast tissue based on a transient hot wire method provided by the present invention, in step 2, the hot wire is measured using a Wheatstone bridge method, and the specific process is as follows: There are two hot wires, each having different lengths but identical other parameters, and are respectively referred to as a long wire and a short wire; the breast tissue sample is completely wrapped with the long wire and the short wire; Provide hot wire measurement circuit, hot wire measurement circuit includes filament R L , short silk R S , adjustable resistor R J , fixed resistors of equal resistance R 1 and R 2. Data acquisition card and DC constant voltage source; filament R L The first end of the filament is connected to the first output end of the DC constant voltage source. R L The second end of the resistor is connected to R 1 first end, fixed value resistor R The second end of 1 is connected to the second output end of the DC constant voltage source; R S The first end of the adjustable resistor is connected to R J The first end of the adjustable resistor R J The second end of the resistor is connected to R 2. The first end, fixed value resistor R The second end of 2 is connected to the second output end of the DC constant voltage source; the data acquisition card is connected to the fixed value resistor R 1 first terminal and fixed value resistor R 2 first end; Adjusting the adjustable resistor R J , making ; Turn on the DC constant voltage source and collect the fixed resistance through the data acquisition card R 1 first terminal and fixed value resistor R 2, and then obtain the curve of the temperature of the heating wire changing with time based on the linear relationship curve between the resistance of the heating wire and the temperature.

[0008] According to a method for measuring thermal conductivity of breast tissue based on a transient hot wire method provided by the present invention, the voltage variation collected by the data acquisition card is:

[0009] Where, dR is the difference in resistance change between the long filament and the short filament, and U is the voltage of the DC constant voltage source; Therefore, the relationship between the temperature of the hot wire and time is:

[0010] in, , The temperature changes of the filaments and short filaments are equal, both are dT; Where dln t is the change in the natural logarithm of time t. According to a method for measuring thermal conductivity of breast tissue based on a transient hot wire method provided by the present invention, the preset formula is:

[0011] Where k is the thermal conductivity of the breast tissue sample; L cu is the effective length of the hot wire, which is equal to the difference in length between the long filament and the short filament. According to a method for measuring thermal conductivity of breast tissue based on a transient hot wire method provided by the present invention, the material of the hot wire is copper. According to a method for measuring thermal conductivity of breast tissue based on a transient hot wire method provided by the present invention, the ratio of the effective length of the hot wire to the hot wire diameter is greater than 25. According to a method for measuring thermal conductivity of breast tissue based on a transient hot wire method provided by the present invention, the output voltage of the DC constant voltage source is 1.2V~1.5V. According to a method for measuring thermal conductivity of breast tissue based on a transient hot wire method provided by the present invention, the model of the data acquisition card is NI USB-6003.

[0012] According to a method for measuring thermal conductivity of breast tissue based on a transient hot wire method provided by the present invention, a data acquisition card is connected to a computer and controlled by a data acquisition program on the computer.

[0013] In a second aspect, the present invention provides a breast tissue thermal conductivity measurement device based on a transient hot wire method, comprising: a processing unit for providing a breast tissue sample, selecting a hot wire having an effective length smaller than a length of the breast tissue sample, and completely wrapping the hot wire with the breast tissue sample; The acquisition unit is used to pass direct current to both ends of the hot wire, collect the change relationship between the voltage at both ends of the hot wire and time, and then obtain the change relationship between the temperature of the hot wire and time based on the linear relationship between the resistance of the hot wire and the temperature; The measuring unit is used to obtain the thermal conductivity of the breast tissue sample based on a preset formula and the relationship between the temperature of the hot wire and time.

[0014] The present invention has at least the following technical effects: 1. The present invention can eliminate the error caused by natural convection.

[0015] 2. The measurement speed of the present invention is very fast, and the water content of the breast tissue sample will not be affected by the long measurement time.

[0016] 3. The present invention can measure biological tissues of smaller size. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] In the attached figure: Figure 1 This is a flow chart of the method for measuring thermal conductivity of breast tissue based on the transient hot wire method of the present invention; Figure 2 Schematic diagram of the structure of the method for measuring thermal conductivity of breast tissue based on the transient hot wire method of the present invention; Figure 3 This is a circuit diagram of the present invention using the Wheatstone bridge method to measure the hot wire; Figure 4 This is a schematic diagram of heat balance based on one-dimensional cylindrical coordinates of the present invention; Figure 5a and Figure 5b They are respectively a pressure difference-time relationship diagram and a pressure difference-logarithmic time relationship diagram of Example 1 of the present invention. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0020] The following will describe some embodiments of the present invention in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0021] The present invention provides a method for measuring the thermal conductivity of breast tissue based on the transient hot wire method. This method utilizes the transient thermal response characteristics of the heating wire and combines it with a data acquisition card to measure the pressure difference-time curve to calculate the thermal conductivity of breast tissue, with high measurement accuracy. Figure 1 and Figure 2 The method for measuring the thermal conductivity of breast tissue based on the transient hot wire method comprises the following steps: Step 1: providing a breast tissue sample, selecting a hot wire with an effective length shorter than the length of the breast tissue sample, and completely wrapping the breast tissue sample with the hot wire; Step 2: Apply direct current to both ends of the hot wire, collect the relationship between the voltage at both ends of the hot wire and time, and then obtain the relationship between the temperature of the hot wire and time based on the linear relationship between the resistance of the hot wire and the temperature; Step 3: Based on a preset formula and the relationship between the temperature of the hot wire and time, the thermal conductivity of the breast tissue sample is obtained.

[0022] Specifically, combined with the actual length of the breast tissue sample, the effective length of the hot wire selected in this embodiment is L cu = 1.5cm, radius r cu = 15.3 μm, and the breast tissue sample was completely wrapped with the hot wire to make a breast hot wire sample (i.e. Figure 2 The hot wire-sample portion of the sample is connected to the hot wire. A copper wire, which has a good temperature-resistance linear relationship and stable chemical properties, is used as the hot wire. The mammary gland-hot wire portion is connected to the circuit to measure the thermal conductivity of breast tissue. An adjustable DC constant voltage source is used to power the hot wire, ensuring stable output power and an output voltage between 1.2V and 1.5V. The ratio of the hot wire's effective length to its diameter is greater than 25.

[0023] In some embodiments, in step 2, the hot wire is measured using the Wheatstone bridge method, and the specific process is as follows: There are two hot wires, each having different lengths but identical other parameters, and are respectively referred to as a long wire and a short wire; the breast tissue sample is completely wrapped with the long wire and the short wire; Provide hot wire measurement circuit, hot wire measurement circuit includes filament R L , short silk R S , adjustable resistor R J , fixed resistors of equal resistance R 1 and R2. Data acquisition card and DC constant voltage source; filament R L The first end of the filament is connected to the first output end of the DC constant voltage source. R L The second end of the resistor is connected to R 1 first end, fixed value resistor R The second end of 1 is connected to the second output end of the DC constant voltage source; R S The first end of the adjustable resistor is connected to R J The first end of the adjustable resistor R J The second end of the resistor is connected to R 2. The first end, fixed value resistor R The second end of 2 is connected to the second output end of the DC constant voltage source; the data acquisition card is connected to the fixed value resistor R 1 first terminal and fixed value resistor R 2 first end; Adjusting the adjustable resistor R J , making ; Turn on the DC constant voltage source and collect the fixed resistance through the data acquisition card R 1 first terminal and fixed value resistor R 2, and then obtain the curve of the temperature of the heating wire changing with time based on the linear relationship curve between the resistance of the heating wire and the temperature.

[0024] It should be noted that, in order to achieve efficient and accurate measurement of breast tissue thermal conductivity, the present invention uses the Wheatstone bridge method to measure the hot wire. The circuit diagram is as follows: Figure 3 At the same time, in order to reduce the error caused by heat transfer at the end of a single hot wire, the present invention uses two hot wires with the same parameters except for the length to perform the measurement, which are respectively recorded as the long wire and the short wire. The length difference between the long wire and the short wire is recorded as the effective length of the hot wire. L cu When the same current is passed through two hot wires, the two hot wires will produce the same end effect. At this time, the temperature difference between the two hot wires is equivalent to the temperature rise of a finite part of an infinitely long hot wire, thereby eliminating the end effect of the hot wire. The hot wire measurement circuit includes a long wire R L , short silk R S , adjustable resistor R J , fixed resistors of equal resistance R 1 and R 2. Data acquisition card and DC constant voltage source; filament R LThe first end of the filament is connected to the first output end of the DC constant voltage source. R L The second end of the resistor is connected to R 1 first end, fixed value resistor R The second end of 1 is connected to the second output end of the DC constant voltage source; R S The first end of the adjustable resistor is connected to R J The first end of the adjustable resistor R J The second end of the resistor is connected to R 2. The first end, fixed value resistor R The second end of 2 is connected to the second output end of the DC constant voltage source; the data acquisition card is connected to the fixed value resistor R 1 first terminal (node ​​a) and fixed value resistor R 2 first end (node ​​b). R J It can be a precision resistance box with adjustable resistance.

[0025] By placing the filament R L and short silk R S Designed in the two arms of the bridge, after power is turned on, the temperature changes due to heat transfer, resulting in changes in resistance. The resistance change of the hot wire is obtained according to the change in the voltage difference output in the bridge circuit. Based on the linear relationship between the resistance and temperature of the hot wire, the temperature change of the hot wire is obtained.

[0026] The heat transfer process between the line heat source (hot wire) and the breast tissue sample to be tested in the transient hot wire method can be approximately regarded as a heat balance process in one-dimensional cylindrical coordinates. Figure 4 middle, Represents any physical field, that is, the coordinate system used for calculation. Figure 4 The heat balance diagram of the transient heat conduction equation in one-dimensional cylindrical coordinates is established as: (1) in, T is the radius r The point at time t Temperature at time (K), α is the thermal diffusivity (m 2 / s).

[0027] The initial time line heat source and the temperature of the sample to be tested are both recorded as T 0, according to the corresponding initial conditions and boundary conditions: (2) (3) in, q is the constant heating power per unit length of the uniform line heat source (W / m), k is the thermal conductivity of the sample to be tested [W / (m·K)]. The solution of Equation (3) can be obtained by Laplace transform: (4) in E 1( x ) is the integral exponential function, defined as: (5) in γ = lnC = 0.577, which is Euler's constant.

[0028] When the line heat source is of radius r 0 cylinder, its surface temperature is uniform and r = r If the temperature of the sample to be tested at point 0 is the same, the surface temperature rise of the linear heat source is: (6) (7) in, r is the radius of the hot wire used in the measurement (m), α is the thermal diffusivity of the sample to be tested (m 2 / s). When r 0 is small enough, t When is long enough and the relationship between the two satisfies formula (7), the second-order expansion term in formula (6) can be omitted, and formula (6) can be simplified to obtain: (8) (9) (10) (11) Therefore, the thermal conductivity is obtained k The calculation expression is: (12) Before the measurement begins, input a small voltage value of 0.1 V to adjust the bridge to balance. Only when the voltage difference measured by the data acquisition card is 0 V before the measurement begins can the measured data be accurate. That is, the output voltage between points a and b is: (13) At this time, we have: (14) Then, the measurement voltage (1.2-1.5 V) is input to heat the long and short filaments. The output voltage change between points a and b is: (15) Where, dR is the difference in resistance change between the long filament and the short filament, and U is the voltage of the DC constant voltage source.

[0029] According to formula (15), the voltage difference change between points a and b can be converted into resistance change, thereby obtaining the change in temperature and time: (16) (17) (18) Where dT is the temperature change of the hot wire. Since a constant heating power per unit length is used, the temperature change of the long filament and the short filament is the same, both dT.

[0030] Therefore, when a DC constant voltage source is used as the input, the input power is: (19) Then the thermal conductivity calculation formula (12) is transformed into: (20) The thermal conductivity of breast tissue is theoretically derived as follows: (twenty one) Specifically, after multiple power-on measurements of the same sample, the measurement results are averaged to reduce the fluctuations caused by noise interference on the data and ensure the accuracy of the experimental results. d Δ U out with dln t After the relationship curve is obtained, the slope is obtained by least square fitting, and the data is put into formula (21) to calculate the thermal conductivity of breast tissue.

[0031] The measurement process requires recording the voltage signals at points A and B over time, requiring high accuracy and stability. This places high demands on the data acquisition device's sampling frequency and accuracy. The NI USB-6003 acquisition card is a multi-function I / O device that combines multiple channels with high precision, capable of acquiring data up to 1000 times per second, meeting these measurement requirements. To ensure synchronization between powering the operating circuit and data acquisition during the measurement process, the traditional manual switch operation inevitably introduces a time lag. Using relays to control the circuit would complicate the simple circuit and increase noise interference. Therefore, the data acquisition card is connected to a computer-controlled data acquisition program. During the measurement process, the data acquisition program is first launched on the computer, followed by power. A non-zero voltage value is sufficient as the starting point for the acquired data. This facilitates operation while ensuring the integrity of the recorded data, facilitating accurate measurement results.

[0032] It should be noted that breast tissue exfoliation and measurement were performed at room temperature (25°C) throughout the measurement process. Studies on the temperature dependence of thermal conductivity of meats such as pork, beef, and lamb within the -25°C to 65°C temperature range have shown that the temperature dependence of non-frozen tissue is very low, less than 0.2% / °C. Studies on the temperature dependence of pig liver thermal conductivity have shown minimal variation within the 10°C to 70°C temperature range, less than 0.25% / °C. Therefore, it can be assumed that within the therapeutic temperature range achieved by photothermal therapy, the thermal conductivity of breast tissue varies very little with temperature. Thermal conductivity measurements at 25°C can be used to approximate the thermal conductivity within the photothermal therapy temperature range (actual human breast tissue) in correlation analyses.

[0033] In order to verify the measurement effect of the present invention, a specific embodiment of the present invention is introduced below.

[0034] Example 1 1. Select deionized water standard sample as the sample to be tested for verification.

[0035] 2. Obtain the pressure difference-time data from the data acquisition card and draw the following Figure 5a The pressure difference and time relationship diagram shown in the figure shows that the natural logarithm of the pressure difference-time (logarithmic time) corresponding to this process has good linearity, as shown in the figure below. Figure 5b shown.

[0036] 3. For example Figure 5b The data in the equation are fitted with the least squares method to obtain the corresponding straight line and its slope. Substituting the slope obtained by fitting into formula (21), the thermal conductivity can be calculated.

[0037] Example 2 1. Select fresh lean pork and fat pork as biological tissue samples for calibration measurement.

[0038] 2. Based on the actual length of the lean pork sample, make the lean pork hot wire sample.

[0039] 3. Use an adjustable DC voltage and current source to energize the heating wire to ensure stable output power.

[0040] 4. Use the computer-controlled NI USB-6003 acquisition card to collect data and calculate thermal conductivity.

[0041] The thermal conductivities obtained in the above two specific embodiments are shown in Table 1.

[0042] Table 1. Thermal conductivity [W / (m·K)]

[0043] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the embodiments disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and variations can be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for measuring the thermal conductivity of breast tissue based on the transient hot wire method, characterized in that: include: Step 1: providing a breast tissue sample, selecting a hot wire with an effective length shorter than the length of the breast tissue sample, and completely wrapping the breast tissue sample with the hot wire; Step 2: applying direct current to both ends of the hot wire, collecting the relationship between the voltage at both ends of the hot wire and time, and then obtaining the relationship between the temperature of the hot wire and time based on the linear relationship between the resistance of the hot wire and the temperature; Step 3: Based on a preset formula and the relationship between the temperature of the hot wire and time, the thermal conductivity of the breast tissue sample is obtained.

2. The method for measuring thermal conductivity of breast tissue based on the transient hot wire method according to claim 1, characterized in that: In step 2, the Wheatstone bridge method is used to measure the hot wire, and the specific process is as follows: There are two hot wires, which have different lengths but the same other parameters, and are respectively recorded as long wire and short wire; the breast tissue sample is completely wrapped with the long wire and the short wire; A hot wire measurement circuit is provided, the hot wire measurement circuit including a filament R L , short silk R S , adjustable resistor R J , fixed resistors of equal resistance R 1 and R 2. Data acquisition card and DC constant voltage source; filament R L The first end of the filament is connected to the first output end of the DC constant voltage source. R L The second end of the resistor is connected to R 1 first end, fixed value resistor R The second end of 1 is connected to the second output end of the DC constant voltage source; R S The first end of the adjustable resistor is connected to R J The first end of the adjustable resistor R J The second end of the resistor is connected to R 2. The first end, fixed value resistor R The second end of 2 is connected to the second output end of the DC constant voltage source; the data acquisition card is connected to the fixed value resistor R 1 first terminal and fixed value resistor R 2 first end; Adjusting the adjustable resistor R J , making ; Turn on the DC constant voltage source and collect the fixed resistance through the data acquisition card R 1 first terminal and fixed value resistor R 2, and then obtain the curve of the temperature of the heating wire changing with time based on the linear relationship curve between the resistance of the heating wire and the temperature.

3. The method for measuring thermal conductivity of breast tissue based on the transient hot wire method according to claim 2, characterized in that: The voltage variation collected by the data acquisition card is: Where, dR is the difference in resistance change between the long filament and the short filament, and U is the voltage of the DC constant voltage source; Therefore, the relationship between the temperature of the hot wire and time is: in, , The temperature changes of the filaments and short filaments are equal, both are dT; Where dln t is the change in the natural logarithm of time t.

4. The method for measuring thermal conductivity of breast tissue based on the transient hot wire method according to claim 3, characterized in that: The preset formula is: Where k is the thermal conductivity of the breast tissue sample; L cu is the effective length of the hot wire, which is equal to the difference in length between the long filament and the short filament.

5. The method for measuring thermal conductivity of breast tissue based on the transient hot wire method according to claim 1, characterized in that: The material of the heating wire is copper.

6. The method for measuring thermal conductivity of breast tissue based on the transient hot wire method according to claim 1, characterized in that: The ratio of the effective length of the hot wire to the hot wire diameter is greater than 25.

7. The method for measuring thermal conductivity of breast tissue based on the transient hot wire method according to claim 2, characterized in that: The output voltage of the DC constant voltage source is 1.2V~1.5V.

8. The method for measuring thermal conductivity of breast tissue based on the transient hot wire method according to claim 2, characterized in that: The model of the data acquisition card is NI USB-6003.

9. The method for measuring thermal conductivity of breast tissue based on the transient hot wire method according to claim 2, characterized in that: The data acquisition card is connected to a computer and is controlled by a data acquisition program on the computer.

10. A breast tissue thermal conductivity measurement device based on a transient hot wire method, characterized in that: include: a processing unit, configured to provide a breast tissue sample, select a hot wire having an effective length smaller than a length of the breast tissue sample, and completely wrap the hot wire with the breast tissue sample; A collection unit is used to pass direct current to both ends of the hot wire, collect the relationship between the voltage at both ends of the hot wire and time, and then obtain the relationship between the temperature of the hot wire and time based on the linear relationship between the resistance of the hot wire and the temperature; The measuring unit is used to obtain the thermal conductivity of the breast tissue sample based on a preset formula and the relationship between the temperature of the hot wire and time.

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