Dual-wavelength photoacoustic remote sensing imaging system for non-contact absolute temperature measurement

Abstract

The invention relates to the technical field of photoacoustic imaging, and particularly provides a dual-wavelength photoacoustic remote sensing imaging system for non-contact absolute temperature measurement. The dual-wavelength photoacoustic remote sensing imaging system for non-contact absolute temperature measurement comprises a signal control assembly, an excitation light path assembly, a beam combination light path assembly and a scanning imaging assembly, and the signal control assembly comprises an editable logic gate array, control software and a remote sensing imaging subsystem. The excitation light path assembly, the detection light path assembly and the scanning imaging assembly are electrically connected with the signal control assembly and are controlled by signals sent by the signal control assembly; by means of the dual-wavelength photoacoustic remote sensing imaging system, high-spatial-resolution structural images / functional images of biological tissues can be obtained in a non-invasive and non-contact mode, the dual-wavelength photoacoustic remote sensing imaging system can be suitable for absolute temperature measurement of biological tissues such as open tissues and chronic tissue damage which are not suitable for coupling liquid, and the application range is widened.

Description

Technical Field

[0001] The invention relates to the technical field of photoacoustic imaging, and in particular provides a dual-wavelength photoacoustic remote sensing imaging system for contactless measurement of absolute temperature. Background Art

[0002] Photoacoustic imaging is an emerging imaging technology. In the medical field, photoacoustic imaging has attracted widespread attention due to its advantages of high resolution, deep penetration, simultaneous structural and functional imaging, and non-destructiveness. It can provide detailed information inside the tissue, such as vascular distribution, tumor boundaries, etc., without destroying the biological tissue. Photoacoustic imaging technology has rich optical absorption contrast and high spatial resolution. It can also be used for temperature detection by taking advantage of the linear correlation between the amplitude of the photoacoustic signal and the temperature in the range of 10 to 55°C, but it can only measure relative temperature. In addition, the traditional photoacoustic imaging system uses the principle of "light excitation and sound detection". In the process of collecting photoacoustic signals, coupling fluid is needed to reduce the attenuation of the signal from the tissue to the ultrasonic transducer. Therefore, it belongs to contact imaging and is limited in the detection of open tissues (such as eyes) and chronic tissue injuries (such as burns). At present, there is a lack of an imaging and temperature monitoring technology that can simultaneously have good spatiotemporal resolution and temperature sensitivity, and monitor absolute temperature distribution non-invasively. Summary of the invention

[0003] Based on this, it is necessary to provide a dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature to solve at least one technical problem in the background technology.

[0004] A dual-wavelength photoacoustic remote sensing imaging system for contactless measurement of absolute temperature comprises a signal control component, an excitation optical path component, a beam combining optical path component and a scanning imaging component. The signal control component comprises an editable logic gate array, control software and a remote sensing imaging subsystem. The excitation optical path component, the detection optical path component and the scanning imaging component are all electrically connected to the signal control component and controlled by a signal emitted by the signal control component. The excitation optical path component comprises a first pulse laser, a second pulse laser and a fiber-coupled SRS system. The first pulse laser and the second pulse laser are both used for emitting a short-wavelength pulse laser beam of 532 nm, wherein the pulse laser beam emitted by the first pulse laser is the first pulse laser beam, the pulse laser beam emitted by the second pulse laser is the second pulse laser beam, and the fiber-coupled SRS system is located on the optical path of the second pulse laser beam. The beam combining optical path component is located on the optical path of the first pulse laser beam. The scanning imaging component is located on the subsequent optical path of the first pulse laser beam after passing through the beam combining optical path component.

[0005] As a further improvement of the present invention, the beam combining optical path assembly includes a reflector, a first dichroic mirror, a beam expanding lens and a second dichroic mirror; the first dichroic mirror is located behind the reflector, the reflector reflects the first pulse laser beam emitted by the first pulse laser and guides it into the first dichroic mirror, the beam expanding lens is located behind the first dichroic mirror, the beam expanding lens is composed of two lenses with focal lengths of 25 mm and 50 mm respectively, and the second dichroic mirror is located behind the beam expanding lens.

[0006] As a further improvement of the present invention, the fiber-coupled SRS system includes a first converging lens at the input end, a single-mode polarization-maintaining fiber and a collimating lens at the output end. The single-mode polarization-maintaining fiber is located between the first converging lens and the collimating lens and the three are arranged in parallel. A bandpass filter is also arranged after the fiber-coupled SRS system. The second pulse laser beam emitted by the second pulse laser passes through the first converging lens, the single-mode polarization-maintaining fiber, the collimating lens and the bandpass filter in sequence. After the short-wavelength pulse laser beam passes through the single-mode polarization-maintaining fiber, a nonlinear stimulated Raman scattering effect occurs, generating multiple SRS peaks. After passing through the bandpass filter, a third pulse laser beam with a long wavelength of 558 nm is obtained. The third pulse laser beam is then injected into the first dichroic mirror. The third pulse laser beam and the first pulse laser beam are both multiplexed through the first dichroic mirror, and then the laser spot is expanded to twice the original through the beam expander lens, and then injected into the second dichroic mirror.

[0007] As a further improvement of the present invention, it also includes a detection optical path component, which includes a detection light source, a polarization beam splitter and a 1 / 4 wave plate. The detection light source is a superluminescent diode that can emit a 1310nm incoherent detection light beam. The polarization beam splitter and the 1 / 4 wave plate are both located on the optical path in the emission direction of the detection light beam and are arranged in parallel in the horizontal direction. After the detection light beam is emitted, it first passes through the polarization beam splitter to generate a transmitted vertical linear polarized light. The linear polarized light is incident along the fast axis direction of the 1 / 4 wave plate to obtain circularly polarized light. Then the circularly polarized light is incident on the second dichroic mirror to be reflected and combined with the third pulse laser beam and the first pulse laser beam to become a combined beam, which is then incident on the scanning imaging component.

[0008] As a further improvement of the present invention, a scanning imaging component is arranged on the optical path of the combined light beam, and the scanning imaging component includes a scanning galvanometer, an achromatic objective lens, a displacement platform, a heating box and an imaging sample. The achromatic objective lens is located behind the scanning galvanometer, the numerical aperture of the achromatic objective lens is 0.4, and the focal length is 25 mm. The heating box is arranged on the displacement platform, and the imaging sample is placed on the heating box; the combined light beam passes through the scanning galvanometer and the achromatic objective lens in sequence, and finally irradiates the imaging sample, and confocalization is achieved on the imaging sample to complete the detection of the photoacoustic signal. The scanning galvanometer can provide fast optical scanning in both the x and y directions, and the displacement platform provides mechanical scanning in the z direction.

[0009] As a further improvement of the present invention, under the photoacoustic effect, the detection light reflected by the second dichroic mirror will carry the information of the internal structure and characteristics of the tissue of the imaging sample, and become a reflected signal light beam. The reflected signal light beam is converted from circular polarization to horizontal polarization through a 1 / 4 wave plate, and then enters the polarization beam splitter and reflects at the interface. The optical path direction of the reflected signal light beam after passing through the polarization beam splitter is perpendicular to the emission direction of the detection light beam.

[0010] As a further improvement of the present invention, it also includes a signal collection component, which includes a long-pass filter, a second converging lens and a photodetector. The long-pass filter, the second converging lens and the photodetector are arranged in sequence on the optical path of the reflected signal light beam and are all arranged parallel to the polarization beam splitter. The reflected signal light beam enters the long-pass filter to suppress reflection, and then enters the second converging lens to focus on the photodetector. The photodetector converts the received optical signal into an electrical signal, and then performs subsequent signal processing.

[0011] As a further improvement of the present invention, it also includes a signal processing component, which includes a filter, an amplifier and a data acquisition card. The input end of the filter is connected to the output end of the photodetector, the input end of the amplifier is connected to the output end of the filter, the analog input port of the data acquisition card is connected to the output end of the amplifier, and the analog output port of the data acquisition card is connected to the signal control component. The signal received by the photodetector is transmitted to the filter, and the unnecessary signal components are removed by the filter. The signal is then transmitted to the amplifier to amplify the signal, and then data is collected through the data acquisition card.

[0012] As a further improvement of the present invention, it also includes an electronic thermometer, the detection end of the electronic thermometer is connected to the imaging sample, the signal output end of the electronic thermometer is connected to the signal control component, the signal control component sends a high-frequency clock signal, the electronic thermometer will read the temperature of the imaging sample in real time, and at the same time, a threshold temperature is set for the signal control component, and the preset temperature increase range is 25-45 degrees Celsius. When the thermometer reads a value that increases by 0.5 degrees Celsius, the signal control component is triggered to output a control signal.

[0013] As a further improvement of the present invention, when the electronic thermometer reaches a preset temperature point, it will trigger the laser emission of the excitation optical path component. At each temperature point, the third pulse laser beam and the first pulse laser beam are emitted as excitation sources for 20ms in succession with an interval of 0.1s. The data acquisition card completes data acquisition at a sampling rate of 250MS / s, and collects 20 photoacoustic signals at each preset temperature point. After taking the average value, the photoacoustic signal intensity of each temperature point under dual wavelengths is calculated to obtain the system calibration curve and obtain the temperature measurement data, and imaging is performed in the remote sensing imaging subsystem of the signal control component.

[0014] The beneficial effects of the present invention are as follows:

[0015] 1. In the process of photoacoustic imaging, the co-focus of two laser beams of different wavelengths is precisely controlled to ensure that the excitation light energy can be accurately transmitted and irradiated onto the imaging tissue, thereby stimulating the photoacoustic effect, causing the refractive index of the imaging sample to change, and detecting the light signal reflected from the imaging sample through the detection light source. These light signals are carried by the reflected signal beam and enter the photodetector after subsequent beam reflection for signal conversion and processing.

[0016] 2. The dual-wavelength photoacoustic remote sensing imaging system can achieve non-invasive and non-contact acquisition of high spatial resolution structural images / functional images of biological tissues. It can be applied to absolute temperature measurement of biological tissues such as open tissues and chronic tissue damage that are not suitable for coupling fluids, thus expanding the scope of application.

[0017] 3. By measuring the correlation between the dual-wavelength photoacoustic signal changes and temperature, the system calibration curve is obtained, which can significantly reduce the error and improve the accuracy of the dual-wavelength photoacoustic remote sensing imaging system using photoacoustics to measure absolute temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a three-dimensional schematic diagram of an embodiment of the present invention;

[0019] Figure 2 for Figure 1 A partial enlarged view of the middle A;

[0020] Figure 3 A schematic diagram of a flow chart of an embodiment of the present invention;

[0021] Figure 4 A timing diagram of double-pulse laser emission according to an embodiment of the present invention;

[0022] Figure 5 This is a temperature measurement calculation principle diagram of a dual-wavelength photoacoustic remote sensing imaging system according to an embodiment of the present invention;

[0023] Figure 6 for Figure 5 Table explaining the meaning of some physical quantities.

[0024] In the figure: 10, signal control component; 20, excitation optical path component; 21, first pulse laser; 210, first pulse laser beam; 22, second pulse laser; 220, second pulse laser beam; 23, fiber-coupled SRS system; 231, first converging lens; 232, single-mode polarization-maintaining fiber; 233, collimating lens; 234, bandpass filter; 240, third pulse laser beam; 30, beam combining optical path component; 31, reflector; 32, first dichroic mirror; 33, beam expanding lens; 34, second dichroic mirror; 340, beam combining optical path component ; 40. Scanning imaging component; 41. Scanning galvanometer; 42. Achromatic objective lens; 43. Displacement platform; 44. Heating box; 45. Imaging sample; 50. Detection optical path component; 51. Detection light source; 510. Detection beam; 52. Polarization beam splitter; 520. Reflected signal beam; 53. 1 / 4 wave plate; 60. Signal collection component; 61. Long pass filter; 62. Second converging lens; 63. Photodetector; 70. Signal processing component; 71. Filter; 72. Amplifier; 73. Data acquisition card; 80. Electronic thermometer. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0026] In the description of the present invention, it should be noted that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0028] See also Figures 1 to 6A dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature comprises a signal control component 10, an excitation optical path component 20, a beam combining optical path component 30 and a scanning imaging component 40. The signal control component 10 comprises an editable logic gate array, control software and a remote sensing imaging subsystem. The excitation optical path component 20, the detection optical path component 40 and the scanning imaging component 50 are all electrically connected to the signal control component 10 and controlled by a signal emitted by the signal control component 10. The excitation optical path component 20 comprises a first pulse laser 21, a second pulse laser 22 and a fiber-coupled SRS system 23 (Stimulated Raman Scattering, stimulated Raman scattering), the first pulse laser 21 and the second pulse laser 22 are both used to emit a short-wavelength pulse laser beam of 532nm, wherein the pulse laser beam emitted by the first pulse laser 21 is a first pulse laser beam 210, and the pulse laser beam emitted by the second pulse laser 22 is a second pulse laser beam 220, and the fiber-coupled SRS system 23 is located on the optical path of the second pulse laser beam 220; the beam combining optical path component 30 is located on the optical path of the first pulse laser beam 210; and the scanning imaging component 40 is located on the subsequent optical path of the first pulse laser beam 210 after passing through the beam combining optical path component 30.

[0029] The beam combining optical path component 30 includes a reflector 31, a first dichroic mirror 32, a beam expander lens 33 and a second dichroic mirror 34; the first dichroic mirror 32 is located behind the reflector 31, and the reflector 31 reflects the first pulse laser beam 210 emitted by the first pulse laser 21 and guides it into the first dichroic mirror 32; the beam expander lens 33 is located behind the first dichroic mirror 32, and the beam expander lens 33 is composed of two lenses with focal lengths of 25 mm and 50 mm respectively; the second dichroic mirror 34 is located behind the beam expander lens 33.

[0030] In one embodiment, two lenses with focal lengths of 25 mm and 50 mm are selected to form a beam expansion lens 33 for beam expansion. On the one hand, the output first pulse laser beam 210 can be expanded twice, and its beam size is equivalent to the size of the objective lens entrance pupil, which will not cause energy waste. On the other hand, selecting a smaller focal length of 25 mm and 50 mm can shorten the optical path. Of course, lenses with focal lengths of 50 mm and 100 mm or other lenses with suitable focal lengths can also be selected according to actual application conditions.

[0031] The fiber-coupled SRS system 23 includes a first converging lens 231 at the input end, a single-mode polarization-maintaining fiber 232, and a collimating lens 233 at the output end. The single-mode polarization-maintaining fiber 232 is located between the first converging lens 231 and the collimating lens 233, and the three are arranged in parallel. A bandpass filter 234 is also arranged after the fiber-coupled SRS system 23. The second pulse laser beam 220 emitted by the second pulse laser 22 passes through the first converging lens 231, the single-mode polarization-maintaining fiber 232, the collimating lens 233, and the bandpass filter 234 in sequence. The short-wave After passing through the single-mode polarization-maintaining fiber 232, the long pulse laser beam 220 undergoes a nonlinear stimulated Raman scattering effect, generating multiple SRS peaks, and then passes through the bandpass filter 234 to obtain a third pulse laser beam 240 with a long wavelength of 558 nm. The third pulse laser beam 240 then enters the first dichroic mirror 32. The third pulse laser beam 240 and the first pulse laser beam 210 are both multiplexed through the first dichroic mirror 32, and then the laser spot is expanded to twice its original size through the beam expander lens 33, and then is emitted into the second dichroic mirror 34.

[0032] In one embodiment, the main function of the first converging lens 231 at the input end of the fiber-coupled SRS system is to focus the incident second pulsed laser beam 220 into a smaller spatial range so as to be more effectively coupled into the optical fiber. By focusing, the energy density of the second pulsed laser beam 220 is increased, which is conducive to generating nonlinear effects in the optical fiber. The single-mode polarization-maintaining optical fiber 232 can keep the polarization state of light unchanged during transmission. When the second pulsed laser beam 220 passes through the single-mode polarization-maintaining optical fiber, a nonlinear stimulated Raman scattering (SRS) effect is induced. The SRS effect causes the light field to transfer part of its energy to the nonlinear medium, generating Stokes light with a frequency lower than the incident light, and forming multiple SRS peaks. The collimating lens 233 at the output end is used to collimate the second pulse laser beam 220 emitted from the optical fiber and convert it into a parallel beam. The beam then enters the bandpass filter 234. After passing through the bandpass filter in the bandpass filter 234, the bandpass filter can selectively allow light of a specific wavelength to pass through while blocking light of other wavelengths, and can screen out the third pulse laser beam 240 of 558nm from the multiple wavelengths generated by the SRS effect.

[0033] In one embodiment, the first dichroic mirror 32 is designed to have high reflectivity for the 558nm laser beam and high transmittance for the 532nm laser beam, that is, the 558nm third pulse laser beam 240 is reflected by the first dichroic mirror 32, and the 532nm first pulse laser beam 210 is projected by the first dichroic mirror 32, so that the 558nm third pulse laser beam 240 and the 532nm first pulse laser beam 210 can be merged into the same optical path, thereby realizing optical path multiplexing. It helps to reduce interference between laser beams and improve the overall performance of the system. Here, the precise separation and guidance of the two laser wavelengths is the basis for ensuring the accuracy of subsequent photoacoustic signal generation and detection.

[0034] In one embodiment, the beam expander lens 33 expands the combined laser spot of the third pulsed laser beam 240 and the first pulsed laser beam 210 to twice its original size, which can improve the stability of the beam during propagation and reduce the loss of the excitation beam and the difficulty of beam alignment.

[0035] In one embodiment, the length of the single-mode polarization-maintaining fiber 232 is selected to be 6 m, which is determined according to specific application requirements. Of course, it can also be other lengths. The length of the fiber will affect the generation and intensity of nonlinear effects in the SRS system. A longer fiber length helps to accumulate more nonlinear effects, but it will also introduce more loss and dispersion.

[0036] The dual-wavelength photoacoustic remote sensing imaging system for contactless measurement of absolute temperature also includes a detection optical path component 50, which includes a detection light source 51, a polarization beam splitter 52 and a 1 / 4 wave plate 53. The detection light source 51 is a superluminescent diode that can emit a 1310nm incoherent detection light beam 510. The polarization beam splitter 52 and the 1 / 4 wave plate 53 are both located on the optical path in the emission direction of the detection light beam 510 and are arranged in parallel in the horizontal direction. After the detection light beam 510 is emitted, it first passes through the polarization beam splitter 52 to generate a vertically transmitted linear polarized light. The linear polarized light is incident along the fast axis direction of the 1 / 4 wave plate 53 to obtain circularly polarized light. Then the circularly polarized light is incident on the second dichroic mirror 34 for reflection and combined with the third pulse laser beam 240 and the first pulse laser beam 210 to become a combined beam 340, which is then incident on the scanning imaging component 40.

[0037] In one embodiment, the second dichroic mirror 34 is designed to have high transmittance to 558nm and 532nm laser beams, and high reflectivity to 1310nm continuous beams, so most of the beam energy of the 558nm third pulse laser beam 240 and the 532nm first pulse laser beam 210 can pass through the second dichroic mirror 34, and the incoherent 1310nm detection beam 510 emitted by the detection light source 51 is reflected by the second dichroic mirror 34, ensuring the combination and separation of the excitation beam and the detection beam, so that the detection beam 510 can pass through the second dichroic mirror 34 with the third pulse laser beam 240 and the first pulse laser beam 210 to form a combined beam 340. The combination of the incoherent 1310nm beam and the laser beam can ensure that light of different wavelengths can accurately overlap at the target position, thereby improving the detection sensitivity.

[0038] In one embodiment, the selection of the first pulsed laser beam 210 with a short wavelength of 532 nm, the third pulsed laser beam 240 with a long wavelength of 558 nm, and the incoherent detection beam 510 with a wavelength of 1310 nm is suitable for the case where the biological tissue to be tested contains hemoglobin (such as for some vascular imaging), because hemoglobin has a high absorption degree for the selected wavelength range. However, in photoacoustic imaging, although different tissues will absorb certain wavelengths, corresponding light sources are required to better image different tissues. For example, ultraviolet light sources are used to image some cell nuclei. The selection of specific excitation beam wavelengths and detection beams of different wavelengths can be determined according to the characteristics of the biological tissue to be tested.

[0039] The scanning imaging component 40 is arranged on the optical path of the combined light beam 340. The scanning imaging component 40 includes a scanning galvanometer 41, an achromatic objective lens 42, a displacement platform 43, a heating box 44 and an imaging sample 45. The achromatic objective lens 42 is located behind the scanning galvanometer 41. The numerical aperture of the achromatic objective lens 42 is 0.4 and the focal length is 25 mm. The heating box 44 is arranged on the displacement platform 43, and the imaging sample 45 is placed on the heating box 44. The combined light beam 340 passes through the scanning galvanometer 41 and the achromatic objective lens 42 in sequence, and is finally irradiated on the imaging sample 45. Confocalization is achieved on the imaging sample 45 to complete the detection of the photoacoustic signal. The scanning galvanometer 41 can provide fast optical scanning in both the x and y directions, and the displacement platform 43 provides mechanical scanning in the z direction.

[0040] In one embodiment, a stepper motor is provided on the displacement platform 43, and the stepper motor is driven by the signal control component 10. An imaging sample 45 is placed on the displacement platform 43 to facilitate real-time adjustment of the imaging area and provide mechanical scanning of the imaging sample 45 in the z direction, while the scanning galvanometer 41 can provide fast optical scanning in both the x direction and the y direction. The combination of optical scanning and mechanical scanning is used to improve the three-dimensional point scanning and slicing imaging speed of the photoacoustic remote sensing imaging system.

[0041] In one embodiment, the selected achromatic objective lens 42 with a numerical aperture of 0.4 and a focal length of 25 mm has a high light collecting capability, which can not only correct chromatic aberration and spherical aberration, but also ensure that the light maintains a high focusing performance when passing through the objective lens, providing relatively high imaging resolution and contrast. Of course, the achromatic objective lens 42 with other numerical values ​​can also be selected according to the actual application.

[0042] Under the photoacoustic effect, the detection light beam 510 reflected back by the second dichroic mirror 34 will carry the information of the internal tissue structure and characteristics of the imaging sample 45, and become the reflected signal light beam 520. The reflected signal light beam 520 is converted from circular polarization to horizontal polarization through the 1 / 4 wave plate 53, and then enters the polarization beam splitter 52 and is reflected at the interface. The optical path direction of the reflected signal light beam 520 after passing through the polarization beam splitter 52 is perpendicular to the emission direction of the detection light beam 510.

[0043] The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature also includes a signal collection component 60, which includes a long-pass filter 61, a second converging lens 62 and a photodetector 63. The long-pass filter 61, the second converging lens 62 and the photodetector 63 are sequentially arranged on the optical path of the reflected signal light beam 520 and are all arranged parallel to the polarization beam splitter 52. The reflected signal light beam 520 is incident on the long-pass filter 54 to suppress reflection, and then is incident on the second converging lens 62 to focus on the photodetector 63. The photodetector 63 converts the received optical signal into an electrical signal, and then performs subsequent signal processing.

[0044] In one embodiment, the combined light beam 340 is confocused through the scanning galvanometer 41 and the achromatic objective lens 42, ensuring that the excitation light energy can be accurately transmitted and irradiated onto the imaging sample 45, thereby stimulating the photoacoustic effect, causing the refractive index of the imaging sample 45 to change, and detecting the light signals reflected from the imaging sample 45 through the detection light in the combined light beam 340. These light signals are carried by the reflected signal light beam 520 and enter the photodetector 63 after subsequent light beam reflection for signal conversion and processing.

[0045] The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature also includes a signal processing component 70, which includes a filter 71, an amplifier 72 and a data acquisition card 73. The input end of the filter 71 is connected to the output end of the photodetector 63, the input end of the amplifier 72 is connected to the output end of the filter 71, the analog input port of the data acquisition card 73 is connected to the output end of the amplifier 72, and the analog output port of the data acquisition card 73 is connected to the signal control component 10. The signal received by the photodetector 63 is transmitted to the filter 71, and the unnecessary signal components are removed by the filter 71. The signal is then transmitted to the amplifier 72 to amplify the signal, and then the data is collected by the data acquisition card 73.

[0046] The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature also includes an electronic thermometer 80. The detection end of the electronic thermometer 80 is connected to the imaging sample 45, and the signal output end of the electronic thermometer 80 is connected to the signal control component 10. The signal control component 10 sends a high-frequency clock signal. The electronic thermometer 80 will read the temperature of the imaging sample 45 in real time. At the same time, a threshold temperature is set for the signal control component 10, and the preset temperature increase range is 25-45 degrees Celsius. When the thermometer reading value increases by 0.5 degrees Celsius, the signal control component 10 is triggered to output a control signal.

[0047] like Figure 4 As shown, when the electronic thermometer 80 reaches the preset temperature point, it will trigger the laser emission of the excitation optical path component 20. At each temperature point, the third pulse laser beam 240 and the first pulse laser beam 210 are emitted as excitation sources for 20ms in succession with an interval of 0.1s. The data acquisition card 73 completes data acquisition at a sampling rate of 250MS / s, and collects 20 photoacoustic signals at each preset temperature point. After taking the average value, the photoacoustic signal intensity of each temperature point under dual wavelengths is calculated to obtain the system calibration curve and obtain the temperature measurement data, and imaging is performed in the remote sensing imaging subsystem of the signal control component 10.

[0048] In one embodiment, the data acquisition card 73 is set to complete the data collection at a sampling rate of 250MS / s, and 20 photoacoustic signals are collected at each preset temperature point. This is because by collecting multiple signals and averaging, a more stable signal value can be obtained, thereby improving the accuracy and reliability of signal processing. In the dual-wavelength photoacoustic signal detection system, the response characteristics of the system can be calibrated by measuring the photoacoustic signal intensity at different temperatures. The photoacoustic signal intensity calculated after collecting multiple signals and averaging can more accurately reflect the actual response of the system, thereby achieving effective calibration of the system. Of course, the sampling rate of the data acquisition card 73 and the number of photoacoustic signals collected at each preset temperature point can be adjusted according to demand under different conditions.

[0049] In one embodiment, the electronic thermometer 80 is provided to calibrate the system before formally applying the dual-wavelength photoacoustic remote sensing imaging system for temperature measurement. A heating box 44 is provided to gradually heat up the imaging sample 45. The electronic thermometer 80 can measure the photoacoustic signal intensity of the imaging sample 45 at two wavelengths at different temperatures, so as to establish a relationship curve between the photoacoustic signal intensity of the imaging sample 45 and the actual temperature measured by the thermometer, which is used to calibrate the response characteristics of the system. By collecting multiple signals at different temperatures and calculating the photoacoustic signal intensity after taking the average value, a more stable signal value can be obtained, which can more accurately reflect the actual response of the system, thereby improving the accuracy and reliability of signal processing. The calibration calculation process is as follows: Figure 5 As shown, the specific calibration process is as follows:

[0050] ① Calculate the wavelength dependence and temperature dependence of the signal in photoacoustic temperature measurement, i.e., P(λ, T). Use the dual-wavelength photoacoustic temperature measurement system to calibrate the single-component graphite phantom for the first time. Perform regression analysis based on the recorded values ​​of the electronic thermometer and the photoacoustic signal intensity at the corresponding time to obtain the linear calibration coefficients A at the two wavelengths. * (λ) and 1 / (B(λ)μ a (λ)), thus obtaining a calibration factor of 1.

[0051] ② For the second calibration of in vitro tissue verification, in vitro tissue with similar biological tissue properties to the imaging sample 45 is generally selected for photoacoustic temperature measurement (for example, when imaging and measuring blood vessels, adipose tissue can be selected). A graduated spectrometer is used to measure the absorption coefficients of the graphite phantom and the in vitro tissue at the dual wavelengths of the system, and the system is calibrated for the second time, thereby obtaining a calibration factor 2.

[0052] ③ According to the dual-wavelength temperature measurement formula, combined with the calibration coefficient 1 and calibration coefficient 2 calculated in the previous steps, use the optimization algorithm (such as the least squares method) to obtain the system dual-wavelength temperature measurement value, that is, the absolute temperature value of the imaging sample 45 tissue we need to measure.

[0053] Figure 5 For the explanation of some physical quantities in the calculation formula, see Figure 6 As shown;

[0054] Among them, η is the thermal conversion efficiency. In photoacoustic temperature measurement, it is often assumed that the thermal conversion efficiency of the two wavelength acquisitions is equal, and the influence of wavelength and temperature on it is ignored;

[0055] The effect of wavelength on the thermoelastic parameter Γ of tissue is much greater than that on the absorption coefficient μ a The influence of temperature on Γ (such as the empirical formula in aqueous solution: Γ = 0.0043 + 0.0053T) is much smaller than the influence of temperature on μ a the extent of the impact;

[0056] The formula also includes F(z,μ eff ) item, the propagation (absorption and scattering) characteristics of lasers of different wavelengths in biological tissues are different, and the luminous flux of light of different wavelengths in tissues will also be different. Therefore, in the specific temperature measurement process, it is necessary to maintain the stability of the laser, use dual wavelengths and select two wavelengths with a small wavelength difference for calibration, which effectively reduces the influence of the effective attenuation coefficient on the luminous flux of the light focus.

[0057] In one embodiment, the temperature measured by the electronic thermometer is regarded as the true value of the absolute temperature, and the dual-wavelength calibration system is used to conduct a verification experiment on ex vivo tissues. The experimental results are compared with the single-wavelength temperature measurement system, which confirms that the temperature measurement error and accuracy of the dual-wavelength temperature measurement system are greatly improved (the error can be effectively reduced to below 0.1 degrees Celsius in the current experimental measurement, and the accuracy is twice that of the single-wavelength temperature measurement system). Its accuracy is much higher than the infrared temperature measurement technology currently used in medical treatment (±0.3 degrees Celsius). It is confirmed that the photoacoustic remote sensing dual-wavelength temperature measurement system can be used for absolute temperature measurement of living organisms, and can significantly reduce errors and improve temperature measurement accuracy.

[0058] In one embodiment, the dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature operates as follows:

[0059] (1) After the system is started, the excitation optical path component 20 and the detection light source 51 start to work, generating a stable dual-wavelength excitation light beam (i.e., the first pulse laser beam 210 and the third pulse laser beam 240) and a detection light beam 510.

[0060] (2) After the dual-wavelength excitation light beam and the detection light beam 510 are combined by the beam combining optical path component 30, they are focused by the scanning imaging component 40 and projected onto the imaging sample 45. The excitation light beam excites the photoacoustic effect on the imaging sample 45, and the detection light beam 510 detects the photoacoustic signal reflected from the imaging sample 45. These light signals enter the photodetector 63 after subsequent light beam reflection for signal conversion and processing.

[0061] (3) At this time, the photoacoustic signal generated by the imaging sample 45 absorbing the excitation light energy is carried by the reflected signal light beam 520 and is collected and transmitted to the photodetector 63 through reflection by the optical path system.

[0062] (4) The photodetector 63 receives the photoacoustic signal and converts it into an electrical signal.

[0063] (5) The filter 71 and the amplifier 72 amplify and filter the electrical signal and transmit it to the data acquisition card 73 for digital processing.

[0064] (6) The data acquisition card 73 transmits the data to the signal control system 10. At this time, the remote sensing imaging subsystem inside the signal control system 10 images the imaging sample 45 to obtain a surface temperature distribution image.

[0065] (7) The system conducts a comprehensive analysis of the temperature information and image data, generates measurement results, and outputs them to the user.

[0066] Among them, if the calibration coefficient of the imaging sample 45 to be measured is not measured in advance, it is necessary to perform the calibration process described in the above embodiment, select a reasonable phantom and an ex vivo tissue, repeat steps (1) to (7) several times, calculate the calibration coefficient of the imaging sample 45 to be measured, and then perform formal temperature measurement; if the calibration coefficient of the imaging sample 45 to be measured is already available, the temperature measurement can be completed by executing steps (1) to (7).

[0067] The present invention can achieve:

[0068] 1. During the photoacoustic imaging process, the co-focusing of two laser beams of different wavelengths is precisely controlled to ensure that the excitation light energy can be accurately transmitted and irradiated onto the imaging sample 45, thereby stimulating the photoacoustic effect, causing the refractive index of the imaging sample 45 to change, and the light signal reflected from the imaging sample 45 is detected by the detection light in the combined light beam 340. These light signals are carried by the reflected signal light beam 520 and enter the photodetector 63 after subsequent light beam reflection for signal conversion and processing.

[0069] 2. The dual-wavelength photoacoustic remote sensing imaging system can achieve non-invasive and non-contact acquisition of high spatial resolution structural images / functional images of biological tissues. It can be applied to absolute temperature measurement of biological tissues such as open tissues and chronic tissue damage that are not suitable for coupling fluids, thus expanding the scope of application.

[0070] 3. In order to improve the accuracy of tissue absolute temperature measurement, two pulsed lasers with different wavelengths were used as photoacoustic excitation sources, and a synchronously triggered electronic thermometer was used to measure the correlation between the photoacoustic signal changes and temperature at two wavelengths in the phantom sample, respectively, to obtain the respective calibration system temperature measurement coefficients. The temperature measurement results at the two wavelengths were combined, and a dual-wavelength temperature measurement formula was established through an optimization algorithm. The accuracy of the formula was verified in in vitro tissue samples, demonstrating the potential of the dual-wavelength calibration temperature measurement system in the field of medical non-contact temperature measurement.

[0071] The above-mentioned embodiments only express several embodiments of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature, characterized in that: The invention comprises a signal control component (10), an excitation optical path component (20), a beam combining optical path component (30) and a scanning imaging component (40), wherein the signal control component (10) comprises an editable logic gate array, control software and a remote sensing imaging subsystem, the excitation optical path component (20), the detection optical path component (40) and the scanning imaging component (50) are all electrically connected to the signal control component (10) and are controlled by a signal emitted by the signal control component (10); the excitation optical path component (20) comprises a first pulse laser (21), a second pulse laser (22) and a fiber-coupled SRS system (23), wherein the first pulse laser (21 ) and the second pulse laser (22) are both used to emit a short-wavelength pulse laser beam of 532 nm, wherein the pulse laser beam emitted by the first pulse laser (21) is a first pulse laser beam (210), and the pulse laser beam emitted by the second pulse laser (22) is a second pulse laser beam (220), the fiber-coupled SRS system (23) is located on the optical path of the second pulse laser beam (220); the beam combining optical path component (30) is located on the optical path of the first pulse laser beam (210); and the scanning imaging component (40) is located on the subsequent optical path of the first pulse laser beam (210) after passing through the beam combining optical path component (30).

2. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 1, characterized in that: The beam combining optical path component (30) comprises a reflecting mirror (31), a first dichroic mirror (32), a beam expanding lens (33) and a second dichroic mirror (34); the first dichroic mirror (32) is located behind the reflecting mirror (31); the reflecting mirror (31) reflects the first pulse laser beam (210) emitted by the first pulse laser (21) and guides it into the first dichroic mirror (32); the beam expanding lens (33) is located behind the first dichroic mirror (32); the beam expanding lens (33) is composed of two lenses with focal lengths of 25 mm and 50 mm respectively; and the second dichroic mirror (34) is located behind the beam expanding lens (33).

3. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 1, characterized in that: The fiber-coupled SRS system (23) comprises a first converging lens (231) at the input end, a single-mode polarization-maintaining optical fiber (232) and a collimating lens (233) at the output end. The single-mode polarization-maintaining optical fiber (232) is located between the first converging lens (231) and the collimating lens (233), and the three are arranged in parallel. A bandpass filter (234) is also arranged behind the fiber-coupled SRS system (23). The second pulse laser beam (220) emitted by the second pulse laser (22) passes through the first converging lens (231), the single-mode polarization-maintaining optical fiber (232), the collimating lens (233) and the bandpass filter (234) in sequence. ), the short-wavelength pulsed laser beam (220) undergoes a nonlinear stimulated Raman scattering effect after passing through the single-mode polarization-maintaining optical fiber (232), generating a plurality of SRS peaks, and then passes through the bandpass filter (234) to obtain a third pulsed laser beam (240) with a long wavelength of 558 nm, and the third pulsed laser beam (240) is then injected into the first dichroic mirror (32), and the third pulsed laser beam (240) and the first pulsed laser beam (210) are both optically multiplexed through the first dichroic mirror (32), and then the laser spot is expanded to twice its original size through the beam expansion lens (33), and then injected into the second dichroic mirror (34).

4. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 1, characterized in that: The invention also comprises a detection optical path component (50), wherein the detection optical path component (50) comprises a detection light source (51), a polarization beam splitter (52) and a quarter wave plate (53). The detection light source (51) is a superluminescent diode capable of emitting a 1310 nm incoherent detection light beam (510). The polarization beam splitter (52) and the quarter wave plate (53) are both located on an optical path in the emission direction of the detection light beam (510) and are arranged in parallel in a horizontal direction. After the detection light beam (510) is emitted, it first passes through the polarization beam splitter (52) to generate a vertically transmitted linear polarized light. The linear polarized light is incident along the fast axis direction of the quarter wave plate (53) to obtain a circularly polarized light. Then, the circularly polarized light is incident on the second dichroic mirror (34) to be reflected and combined with the third pulse laser beam (240) and the first pulse laser beam (210) to form a combined light (340), which is then incident on the scanning imaging component (40).

5. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 4, characterized in that: The scanning imaging component (40) is arranged on the optical path of the combined light beam (340), and the scanning imaging component (40) comprises a scanning galvanometer (41), an achromatic objective lens (42), a displacement platform (43), a heating box (44) and an imaging sample (45). The achromatic objective lens (42) is located behind the scanning galvanometer (41), and the numerical aperture of the achromatic objective lens (42) is 0.4 and the focal length is 25 mm. The heating box (44) is arranged on the displacement platform (43), and the imaging sample (45) is placed on the heating box (44). The combined light beam (340) passes through the scanning galvanometer (41) and the achromatic objective lens (42) in sequence, and finally irradiates the imaging sample (45), and confocalization is achieved on the imaging sample (45) to complete the detection of the photoacoustic signal. The scanning galvanometer (41) can provide fast optical scanning in both the x direction and the y direction, and the displacement platform (43) provides mechanical scanning in the z direction.

6. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 4, characterized in that: Under the photoacoustic effect, the detection light beam (510) reflected back by the second dichroic mirror (34) carries information about the internal structure and characteristics of the tissue of the imaging sample (45) and becomes a reflected signal light beam (520). The reflected signal light beam (520) is converted from circular polarization to horizontal polarization by the quarter wave plate (53), and then enters the polarization beam splitter (52) and is reflected at the interface. The optical path direction of the reflected signal light beam (520) after passing through the polarization beam splitter (52) is perpendicular to the emission direction of the detection light beam (510).

7. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 1, characterized in that: It also includes a signal collection component (60), which includes a long-pass filter (61), a second converging lens (62) and a photodetector (63). The long-pass filter (61), the second converging lens (62) and the photodetector (63) are sequentially arranged on the optical path of the reflected signal light beam (520) and are all arranged parallel to the polarization beam splitter (52). The reflected signal light beam (520) is incident on the long-pass filter (54) to suppress reflection, and then is incident on the second converging lens (62) to focus on the photodetector (63). The photodetector (63) converts the received optical signal into an electrical signal, and then performs subsequent signal processing.

8. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 1, characterized in that: The device also comprises a signal processing component (70), wherein the signal processing component (70) comprises a filter (71), an amplifier (72) and a data acquisition card (73); the input end of the filter (71) is connected to the output end of the photodetector (63); the input end of the amplifier (72) is connected to the output end of the filter (71); the analog input port of the data acquisition card (73) is connected to the output end of the amplifier (72); the analog output port of the data acquisition card (73) is connected to the signal control component (10); the signal received by the photodetector (63) is transmitted to the filter (71); the signal is processed by the filter (71) to remove unnecessary signal components; the signal is then transmitted to the amplifier (72) to amplify the signal; and data is collected by the data acquisition card (73).

9. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 1, characterized in that: The electronic thermometer (80) is also included. The detection end of the electronic thermometer (80) is connected to the imaging sample (45). The signal output end of the electronic thermometer (80) is connected to the signal control component (10). The signal control component (10) sends a high-frequency clock signal. The electronic thermometer (80) reads the temperature of the imaging sample (45) in real time. At the same time, a threshold temperature is set for the signal control component (10). The preset temperature increase range is 25-45 degrees Celsius. When the value read by the thermometer increases by 0.5 degrees Celsius, the signal control component (10) is triggered to output a control signal.

10. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 9, characterized in that: When the electronic thermometer (80) reaches a preset temperature point, it will trigger the laser emission of the excitation optical path component (20). At each temperature point, the third pulse laser beam (240) and the first pulse laser beam (210) are successively emitted as excitation sources for 20ms, with an interval of 0.1s. The data acquisition card (73) completes data acquisition at a sampling rate of 250MS / s, and collects 20 photoacoustic signals at each preset temperature point. After taking the average value, the photoacoustic signal intensity of each temperature point under dual wavelengths is calculated to obtain a system calibration curve and obtain temperature measurement data, and imaging is performed in the remote sensing imaging subsystem of the signal control component (10).

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