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

Abstract

The application 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, 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 emitted by the signal control assembly; through the dual-wavelength photoacoustic remote sensing imaging system, high spatial resolution structure images / function images of biological tissues can be obtained in a non-invasive and non-contact manner, the absolute temperature of biological tissues, such as open tissues and chronic tissue damage, which are not suitable for coupling liquid, can be measured, and the application range is expanded.

Description

TECHNICAL FIELD

[0001] The application 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. BACKGROUND

[0002] Photoacoustic imaging technology is a new imaging technology, and in the medical field, the photoacoustic imaging technology is widely concerned due to its high resolution, thick penetration depth, simultaneous structural and functional imaging and non-invasive advantages. It can provide detailed information inside the tissue, such as blood vessel distribution, tumor boundary and the like without damaging the biological tissue. The photoacoustic imaging technology has rich optical absorption contrast and high spatial resolution, and the photoacoustic imaging technology can also be used for temperature detection by using the characteristic that the photoacoustic signal amplitude is linearly related to the temperature in the range of 10-55 DEG C, but it can only measure the relative temperature. In addition, the traditional photoacoustic imaging system utilizes the principle of 'light excitation and sound detection', and needs to use a coupling liquid to reduce the attenuation of the signal from the tissue to the ultrasonic transducer in the process of collecting the photoacoustic signal, so it belongs to the contact imaging and is limited in the detection of open tissues (such as the eye) and chronic tissue damage (such as burns). At present, there is a lack of an imaging and temperature monitoring technology which can simultaneously have good space-time resolution and temperature sensitivity and non-invasively monitor the absolute temperature distribution. SUMMARY

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

[0004] 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. 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 the signals emitted by the signal control assembly. The excitation light path assembly comprises a first pulsed laser, a second pulsed laser and a fiber-coupled SRS system. The first pulsed laser and the second pulsed laser are both used for emitting a 532 nm short-wavelength pulsed laser beam. The pulsed laser beam emitted by the first pulsed laser is a first pulsed laser beam, and the pulsed laser beam emitted by the second pulsed laser is a second pulsed laser beam. The fiber-coupled SRS system is located on the light path of the second pulsed laser beam. The beam combination light path assembly is located on the light path of the first pulsed laser beam. The scanning imaging assembly is located on the subsequent light path of the first pulsed laser beam after the beam combination light path assembly.

[0005] As a further improvement of the application, the beam combination optical assembly comprises a mirror, a first dichroic mirror, a beam expander lens and a second dichroic mirror; the first dichroic mirror is located behind the mirror, the mirror reflects the first pulsed laser beam emitted by the first pulsed laser into the first dichroic mirror, the beam expander lens is located behind the first dichroic mirror, the beam expander lens is composed of two lenses with focal lengths of 25mm and 50mm respectively, and the second dichroic mirror is located behind the beam expander lens.

[0006] As a further improvement of the application, the fiber-coupled SRS system comprises a first converging lens at the input end, a single-mode polarization-maintaining optical fiber and a collimating lens at the output end, the single-mode polarization-maintaining optical fiber is located between the first converging lens and the collimating lens and is arranged in parallel with the two, and the fiber-coupled SRS system is further provided with a band-pass filter, the second pulsed laser beam emitted by the second pulsed laser sequentially passes through the first converging lens, the single-mode polarization-maintaining optical fiber, the collimating lens and the band-pass filter, the short-wavelength pulsed laser beam undergoes nonlinear stimulated Raman scattering effect after passing through the single-mode polarization-maintaining optical fiber to generate multiple SRS peaks, and a third pulsed laser beam with a wavelength of 558nm is obtained after passing through the band-pass filter, the third pulsed laser beam further enters the first dichroic mirror, the third pulsed laser beam and the first pulsed laser beam both pass through the first dichroic mirror for optical path multiplexing, then the laser spot is expanded to twice the original size through the beam expander lens, and then the third pulsed laser beam further enters the second dichroic mirror.

[0007] As a further improvement of the application, the detection optical assembly further comprises a detection light source, a polarization beam splitter and a 1 / 4 wave plate, the detection light source is a superluminescent diode, which can emit a 1310nm incoherent detection light beam, the polarization beam splitter and the 1 / 4 wave plate are both located on the light path of the detection light beam emission direction and are arranged in parallel in the horizontal direction, the detection light beam first passes through the polarization beam splitter to generate a transmitted vertical linearly polarized light after being emitted, the linearly 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 enters the second dichroic mirror to be reflected and combined with the third pulsed laser beam and the first pulsed laser beam to become a combined beam, and then enters the scanning imaging assembly.

[0008] As a further improvement of the application, the scanning imaging assembly is arranged on the light path of the combined beam, and the scanning imaging assembly comprises a scanning galvanometer, an achromatic objective, a displacement platform, a heating box and an imaging sample, the achromatic objective is located behind the scanning galvanometer, the numerical aperture of the achromatic objective is 0.4 and the focal length is 25mm, the heating box is arranged on the displacement platform, and the imaging sample is placed on the heating box; the combined beam sequentially passes through the scanning galvanometer and the achromatic objective, and finally irradiates on the imaging sample to realize confocal on the imaging sample to complete the detection of photoacoustic signals, the scanning galvanometer can provide fast optical scanning in x and y directions, and the displacement platform provides mechanical scanning in z direction.

[0009] As a further improvement of the present application, under the photoacoustic effect, the probe light reflected back by the second dichroic mirror carries the information of the internal structure and characteristics of the imaging sample, becoming a reflected signal light beam, which is converted from circular polarization to horizontal polarization by the 1 / 4 wave plate, then enters the polarization beam splitter and is reflected at the interface, and the direction of the light path of the reflected signal light beam after passing through the polarization beam splitter is perpendicular to the emission direction of the probe light beam

[0010] As a further improvement of the present application, the signal collection assembly further comprises a long-pass filter, a second converging lens and a photodetector, which are sequentially arranged on the light path of the reflected signal light beam and are arranged in parallel with the polarization beam splitter, the reflected signal light beam enters the long-pass filter to suppress reflection, 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 application, the signal processing assembly further comprises a filter, an amplifier and a data acquisition card, the input end of the filter is connected with the output end of the photodetector, the input end of the amplifier is connected with the output end of the filter, the analog input port of the data acquisition card is connected with the output end of the amplifier, and the analog output port of the data acquisition card is connected with the signal control assembly, the signal received by the photodetector is transmitted to the filter, the filter removes unnecessary signal components, and then the signal is transmitted to the amplifier for amplification processing, and then the data is collected by the data acquisition card.

[0012] As a further improvement of the present application, the electronic thermometer is connected with the imaging sample at the detection end, and the signal output end of the electronic thermometer is connected with the signal control assembly, the signal control assembly outputs a high-frequency clock signal, the electronic thermometer reads the temperature of the imaging sample in real time, and at the same time, the signal control assembly is provided with a threshold temperature, the preset temperature increase range is 25-45 degrees Celsius, and when the reading value of the thermometer increases by 0.5 degrees Celsius, the signal control assembly outputs a control signal.

[0013] As a further improvement of the present application, when the electronic thermometer reaches the preset temperature point, the laser emission of the excitation light path assembly is triggered, and at each temperature point, the third pulsed laser beam and the first pulsed laser beam are emitted as excitation sources in turn for 20 ms, with an interval of 0.1 s, the data acquisition card completes data acquisition at a sampling rate of 250 MS / s, and 20 photoacoustic signals are collected at each preset temperature point, the average value is calculated to obtain the photoacoustic signal intensity of each temperature point under double wavelengths, and the system calibration curve and the temperature measurement data are obtained, and imaging is performed in the remote sensing imaging subsystem of the signal control assembly.

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

[0015] 1. In the photoacoustic imaging process, by precisely controlling the confocal of two different wavelength laser beams, it ensures that the excitation light energy can be accurately delivered and irradiated on the imaging tissue, thereby exciting the photoacoustic effect, making the refractive index of the imaging sample change, and through the detection of the light source, the light signals reflected from the imaging sample are carried by the reflected signal light beams and enter the photodetector after subsequent light beam reflection, which can be converted and processed.

[0016] 2. The dual-wavelength photoacoustic remote sensing imaging system can realize non-invasive and non-contact acquisition of high spatial resolution structure images / function images of biological tissues, and can be applied to absolute temperature measurement of biological tissues such as open tissues and chronic tissue damage which are not suitable for coupling liquid, thereby expanding the application range.

[0017] 3. By measuring the correlation between the dual-wavelength photoacoustic signal change and the 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 in measuring the absolute temperature by using photoacoustic. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a three-dimensional schematic view of an embodiment of the present application;

[0019] Figure 2 is a three-dimensional schematic view of an embodiment of the present application; Figure 1 is a partial enlarged view of position A in FIG. 1;

[0020] Figure 3 is a flowchart of an embodiment of the present application;

[0021] Figure 4 is a timing diagram of a dual-pulse laser emission of an embodiment of the present application;

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

[0023] Figure 6 is a partial enlarged view of position A in FIG. 1; Figure 5

[0024] ​In the figure: 10, signal control assembly; 20, excitation light path assembly; 21, first pulsed laser; 210, first pulsed laser beam; 22, second pulsed laser; 220, second pulsed laser beam; 23, fiber-coupled SRS system; 231, first converging lens; 232, single-mode polarization-maintaining optical fiber; 233, collimating lens; 234, band-pass filter; 240, third pulsed laser beam; 30, beam-combining light path assembly; 31, reflecting mirror; 32, first dichroic mirror; 33, beam-expanding lens; 34, second dichroic mirror; 340, combined light beam; 40, scanning imaging assembly; 41, scanning galvanometer; 42, achromatic objective lens; 43, displacement platform; 44, heating box; 45, imaging sample; 50, probe light path assembly; 51, probe light source; 510, probe light beam; 52, polarization beam splitter; 520, reflected signal light beam; 53, 1 / 4 wave plate; 60, signal collection assembly; 61, long-pass filter; 62, second converging lens; 63, photodetector; 70, signal processing assembly; 71, filter; 72, amplifier; 73, data acquisition card; 80, electronic thermometer. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present application, a more full description of the present application will be made with reference to the accompanying drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present application can be more thoroughly and completely understood.

[0026] In the description of the present application, it should be noted that the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the present application is only for the purpose of describing specific embodiments and is not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0028] Please refer to Figures 1 to 6The application discloses a dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature, which comprises a signal control assembly 10, an excitation light path assembly 20, a beam combination light path assembly 30 and a scanning imaging assembly 40. The signal control assembly 10 comprises an editable logic gate array, control software and a remote sensing imaging subsystem. The excitation light path assembly 20, the detection light path assembly 40 and the scanning imaging assembly 50 are electrically connected with the signal control assembly 10 and are controlled by signals emitted by the signal control assembly 10. The excitation light path assembly 20 comprises a first pulsed laser 21, a second pulsed laser 22 and a fiber-coupled SRS system 23 (Stimulated Raman Scattering). The first pulsed laser 21 and the second pulsed laser 22 are used for emitting short-wavelength pulsed laser beams of 532 nm. The pulsed laser beam emitted by the first pulsed laser 21 is a first pulsed laser beam 210, the pulsed laser beam emitted by the second pulsed laser 22 is a second pulsed laser beam 220, and the fiber-coupled SRS system 23 is located on the light path of the second pulsed laser beam 220. The beam combination light path assembly 30 is located on the light path of the first pulsed laser beam 210. The scanning imaging assembly 40 is located on the subsequent light path of the first pulsed laser beam 210 after passing through the beam combination light path assembly 30.

[0029] The beam combination light path assembly 30 comprises a mirror 31, a first dichroic mirror 32, a beam expansion lens 33 and a second dichroic mirror 34. The first dichroic mirror 32 is located behind the mirror 31. The mirror 31 reflects the first pulsed laser beam 210 emitted by the first pulsed laser 21 into the first dichroic mirror 32. The beam expansion lens 33 is located behind the first dichroic mirror 32 and is composed of two lenses with focal lengths of 25 mm and 50 mm. The second dichroic mirror 34 is located behind the beam expansion lens 33.

[0030] In an embodiment, the beam expansion lens 33 is composed of two lenses with focal lengths of 25 mm and 50 mm. On the one hand, the first pulsed laser beam 210 can be expanded twice, and the size of the beam is comparable to the size of the objective lens entrance pupil, so that energy waste is avoided. On the other hand, the focal lengths of 25 mm and 50 mm are relatively small, so that the optical path can be shortened. Of course, according to actual application conditions, lenses with focal lengths of 50 mm and 100 mm or other suitable focal lengths can also be selected.

[0031] 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 arranged in parallel with the first converging lens 231 and the collimating lens 233, and the fiber-coupled SRS system 23 further comprises a band-pass filter 234. The second pulsed laser beam 220 emitted by the second pulsed laser 22 sequentially passes through the first converging lens 231, the single-mode polarization-maintaining optical fiber 232, the collimating lens 233, and the band-pass filter 234. After the short-wavelength pulsed laser beam 220 passes through the single-mode polarization-maintaining optical fiber 232, the nonlinear stimulated Raman scattering effect occurs, generating a plurality of SRS peaks. After passing through the band-pass filter 234, the third pulsed laser beam 240 with a wavelength of 558 nm is obtained. The third pulsed laser beam 240 further enters the first dichroic mirror 32. The third pulsed laser beam 240 and the first pulsed laser beam 210 both pass through the first dichroic mirror 32 for optical multiplexing. Then, the laser spot is expanded to twice the original size by the beam expander 33, and the third pulsed laser beam 240 further enters the second dichroic mirror 34.

[0032] In one embodiment, the first converging lens 231 at the input end of the fiber-coupled SRS system has the main function of focusing the incident second pulsed laser beam 220 into a smaller spatial range, so as to be more effectively coupled into the optical fiber. Through focusing, the energy density of the second pulsed laser beam 220 is increased, which is beneficial 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, the nonlinear stimulated Raman scattering (SRS) effect is induced. The SRS effect can cause the optical field to transfer part of the energy to the nonlinear medium, generate Stokes light with a lower frequency than the incident light, and form a plurality of SRS peaks. The collimating lens 233 at the output end has the function of collimating the second pulsed laser beam 220 emitted from the optical fiber, converting it into a parallel light beam. Then, the light beam enters the band-pass filter 234. After passing through the band-pass filter 234, the band-pass filter can selectively allow light of a specific wavelength to pass through while blocking light of other wavelengths. The band-pass filter can filter out the third pulsed laser beam 240 with a wavelength of 558 nm from the plurality of wavelengths generated by the SRS effect.

[0033] In one embodiment, the first dichroic mirror 32 is designed to have high reflectivity to the 558 nm laser beam and high transmissivity to the 532 nm laser beam, that is, the third pulsed laser beam 240 of 558 nm is reflected by the first dichroic mirror 32, and the first pulsed laser beam 210 of 532 nm is transmitted by the first dichroic mirror 32, so as to combine the third pulsed laser beam 240 of 558 nm and the first pulsed laser beam 210 of 532 nm into the same optical path, thereby realizing optical path multiplexing. It helps to reduce the interference between the laser beams and improve the overall performance of the system. The precise separation and guidance of the two laser wavelengths here are 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 the 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 optical fiber 232 is selected to be 6 m, which is determined according to the specific application requirements. Of course, it can also be other lengths. The length of the optical fiber will affect the generation and intensity of nonlinear effects in the SRS system. A longer optical fiber length helps to accumulate more nonlinear effects, but also introduces more loss and dispersion.

[0036] The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature also includes a detection optical path assembly 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, which can emit a 1310 nm incoherent detection beam 510. The polarization beam splitter 52 and the 1 / 4 wave plate 53 are both located on the optical path of the emission direction of the detection beam 510 and are arranged in parallel in the horizontal direction. After the detection beam 510 is emitted, it first passes through the polarization beam splitter 52 to produce a transmitted vertically polarized light. The linearly 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 into the second dichroic mirror 34 to be reflected and combined with the third pulsed laser beam 240 and the first pulsed laser beam 210 to become a combined beam 340, and then is incident into the scanning imaging assembly 40.

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

[0038] In one embodiment, the selection of the above-mentioned first pulsed laser beam 210 at 532 nm, the third pulsed laser beam 240 at 558 nm, and the incoherent probe light beam 510 at 1310 nm is suitable for the case where the biological tissue to be measured contains hemoglobin (such as some blood vessel imaging), because hemoglobin has a higher absorption to the selected wavelength range. However, in photoacoustic imaging, although different tissues will absorb certain wavelengths, better imaging of different tissues requires the use of corresponding light sources, such as imaging of some cell nuclei, which will utilize ultraviolet light sources. The selection of different wavelengths of excitation light beams and probe light beams can be determined according to the characteristics of the biological tissue to be measured.

[0039] The scanning imaging assembly 40 is arranged on the light path of the combined light 340, and the scanning imaging assembly 40 includes a scanning galvanometer 41, an achromatic objective 42, a displacement platform 43, a heating box 44, and an imaging sample 45. The achromatic objective 42 is located behind the scanning galvanometer 41, and has a numerical aperture of 0.4 and a focal length of 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 340 sequentially passes through the scanning galvanometer 41 and the achromatic objective 42, and finally irradiates on the imaging sample 45, so as to realize confocal imaging on the imaging sample 45 and complete the detection of photoacoustic signals. The scanning galvanometer 41 can provide fast optical scanning in the x direction and the y direction, and the displacement platform 43 can provide mechanical scanning in the z direction.

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

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

[0042] Under the photoacoustic effect, the detection light reflected back by the second dichroic mirror 34 carries the information of the internal structure and characteristics of the imaging sample 45, becoming a reflected signal light beam 520. The reflected signal light beam 520 passes through the 1 / 4 wave plate 53 and is converted from circular polarization to horizontal polarization. Then, the reflected signal light beam 520 enters the polarization beam splitter 52 and is reflected at the interface. After passing through the polarization beam splitter 52, the direction of the light path of the reflected signal light beam 520 is perpendicular to the direction of the outgoing light of the detection light beam 510.

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

[0044] In one embodiment, the combined light 340 passes through the scanning galvanometer 41 and the achromatic objective 42 to achieve confocal focusing, thereby ensuring that the excitation light energy can be accurately transmitted and irradiated onto the imaging sample 45, exciting the photoacoustic effect, changing the refractive index of the imaging sample 45, and detecting the light signal reflected from the imaging sample 45 by the detection light in the combined light 340. These light signals are carried by the reflected signal light beam 520 and enter the photodetector 63 after subsequent light beam reflection to be converted and processed.

[0045] The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature also includes a signal processing component 70. The signal processing component 70 includes a filter 71, an amplifier 72, and a data acquisition card 73. The input terminal of the filter 71 is connected to the output terminal of the photodetector 63, the input terminal of the amplifier 72 is connected to the output terminal of the filter 71, the analog input port of the data acquisition card 73 is connected to the output terminal 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, where unwanted signal components are removed. The signal is then amplified by the amplifier 72 and finally acquired 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 probe 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 emits a high-frequency clock signal, and 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, with a preset temperature rise range of 25-45 degrees Celsius. When the thermometer reading 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 the data acquisition at a sampling rate of 250MS / s and acquires 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. Imaging is then performed in the remote sensing imaging subsystem of the signal control component 10.

[0048] In one embodiment, the data acquisition card 73 is configured to acquire data at a sampling rate of 250 MS / s, and to acquire 20 photoacoustic signals at each preset temperature point. This is because by acquiring multiple signals and averaging them, a more stable signal value can be obtained, thereby improving the accuracy and reliability of signal processing. In a 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 acquiring multiple signals and averaging them 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 acquired at each preset temperature point can be adjusted according to requirements under different conditions.

[0049] In one embodiment, the electronic thermometer 80 is used to calibrate the dual-wavelength photoacoustic remote sensing imaging system before its formal application for temperature measurement. A heating chamber 44 is set up to gradually heat the imaging sample 45. The electronic thermometer 80 measures the photoacoustic signal intensity of the imaging sample 45 at two wavelengths at different temperatures, thereby establishing a curve relating the photoacoustic signal intensity of the imaging sample 45 to the actual temperature measured by the thermometer, which is used to calibrate the system's response characteristics. By acquiring multiple signals at different temperatures and averaging them to calculate the photoacoustic signal intensity, 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 thermometry, i.e., P(λ, T). Perform the first calibration on a single-component graphite phantom using a dual-wavelength photoacoustic thermometry system. Based on the recorded values ​​of the electronic thermometer and the photoacoustic signal intensity at the corresponding time, perform regression analysis to obtain the linear calibration coefficients A at the two wavelengths. * (λ) and 1 / (B(λ)μ a (λ)), thus obtaining the calibration coefficient 1.

[0051] ② For the second calibration of the ex vivo tissue verification, an ex vivo tissue with similar biological tissue properties to the imaging sample 45 is generally selected for photoacoustic thermometry (for example, when imaging and thermometry of blood vessels, adipose tissue can be selected). The absorption coefficients of the graphite phantom and the ex vivo tissue at the dual wavelengths of the system are measured using a scaled spectrometer to perform the second calibration of the system, thereby obtaining the calibration coefficient 2.

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

[0053] Figure 5 In the calculation formula, some physical quantities are explained in [the relevant section]. Figure 6 As shown;

[0054] Where η is the thermal conversion efficiency. In photoacoustic thermometry, 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 tissue thermoelastic parameter Γ is far greater than the effect of wavelength on the absorption coefficient μ. a The influence of temperature on Γ is much smaller than that on μ, while the influence of temperature on Γ (e.g., the empirical formula in aqueous solutions: Γ = 0.0043 + 0.0053T) is much smaller. a The degree of impact;

[0056] The formula also includes F(z,μ) eff The propagation (absorption and scattering) characteristics of lasers of different wavelengths in biological tissues vary, and the luminous flux of light of different wavelengths in tissues also differs. Therefore, in specific temperature measurement processes, it is necessary to maintain the stability of the laser. Using dual wavelengths and selecting two wavelengths with relatively small differences for calibration effectively reduces the impact of the effective attenuation coefficient on the luminous flux at the light focus.

[0057] In one embodiment, the temperature measured by the electronic thermometer is considered the true absolute temperature. A dual-wavelength calibration system is then used for verification experiments on ex vivo tissues. The experimental results are compared with those of a single-wavelength temperature measurement system, confirming that the dual-wavelength system significantly improves both measurement error and accuracy (currently, the error can be effectively reduced to below 0.1 degrees Celsius in experimental measurements, and the accuracy is twice that of the single-wavelength system). Its accuracy is far superior to the infrared temperature measurement technology currently used in medicine (±0.3 degrees Celsius). This demonstrates 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 measurement accuracy.

[0058] In one embodiment, the operation of a dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature is 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 beam (i.e., the first pulse laser beam 210 and the third pulse laser beam 240) and a detection beam 510.

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

[0061] (3) At this time, the photoacoustic signal generated by the imaging sample 45 after absorbing the excitation light energy is carried by the reflected signal beam 520 and collected and transmitted to the photodetector 63 through the reflection of 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 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 data to the signal control system 10, at which 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 comprehensively analyzes the temperature information and image data, generates measurement results, and outputs them to the user.

[0066] If the imaging sample 45 to be measured has not been measured in advance to obtain the calibration coefficient, a calibration process as described in the foregoing embodiments is required, a reasonable phantom and an ex vivo tissue are selected, steps (1) to (7) are repeated several times, the calibration coefficient of the imaging sample 45 to be measured is calculated, and then formal temperature measurement is performed; if the calibration coefficient of the imaging sample 45 to be measured is already available, steps (1) to (7) can be performed to complete the temperature measurement.

[0067] The present application can achieve:

[0068] 1. In the photoacoustic imaging process, the confocal of two laser beams with different wavelengths is accurately controlled to ensure that the excitation light energy can be accurately transmitted and irradiated onto the imaging sample 45, thereby exciting the photoacoustic effect, changing the refractive index of the imaging sample 45, and detecting the reflected light signal from the imaging sample 45 by the probe light in the combined light 340, which is carried by the reflected signal light beam 520 and enters the photodetector 63 after subsequent beam reflection to perform signal conversion and processing.

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

[0070] 3. To improve the accuracy of tissue absolute temperature measurement, two pulsed lasers with different wavelengths are used as photoacoustic excitation sources, and a synchronous trigger electronic thermometer is used to measure the correlation between the photoacoustic signal change and the temperature under two wavelengths in the phantom sample, to obtain the respective calibration system temperature measurement coefficient, to comprehensively analyze the temperature measurement results under two wavelengths, to establish a dual-wavelength temperature measurement formula through an optimization algorithm, to verify the accuracy of the formula in an ex vivo tissue sample, and to prove the potential of the dual-wavelength calibration temperature measurement system in the field of medical non-contact temperature measurement.

[0071] The above described embodiments only express several embodiments of the present application, which are described in more detail and in more detail, but cannot be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature, characterized by: The application relates to a remote sensing imaging system, which comprises a signal control component (10), an excitation light path component (20), a beam combining light path component (30), a scanning imaging component (40) and a detection light path component (50). The signal control component (10) comprises an editable logic gate array, control software and a remote sensing imaging subsystem. The excitation light path component (20), the detection light path component (50) and the scanning imaging component (40) are electrically connected with the signal control component (10) and are controlled by signals emitted by the signal control component (10). The excitation light path component (20) comprises a first pulse laser (21), a second pulse laser (22) and a fiber-coupled SRS system (23). The first pulse laser (21) and the second pulse laser (22) are used for emitting 532nm short-wavelength pulse laser beams. The pulse laser beam emitted by the first pulse laser (21) is a first pulse laser beam (210), 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 light path of the second pulse laser beam (220). The beam combining light path component (30) is located on the light path of the first pulse laser beam (210). The scanning imaging component (40) is located on the subsequent light path of the first pulse laser beam (210) after the beam combining light path component (30). The beam combining light path component (30) comprises a mirror (31), a first dichroic mirror (32), a beam expander lens (33) and a second dichroic mirror (34). 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 is arranged in parallel with the two lenses. A band-pass filter (234) is further arranged behind the fiber-coupled SRS system (23). The second pulse laser beam (220) emitted by the second pulse laser (22) sequentially passes through the first converging lens (231), the single-mode polarization maintaining optical fiber (232), the collimating lens (233) and the band-pass filter (234). After the short-wavelength pulse laser beam (220) passes through the single-mode polarization maintaining optical fiber (232), nonlinear stimulated Raman scattering effect occurs, a plurality of SRS peaks are generated, and a 558nm long-wavelength third pulse laser beam (240) is obtained after the beam passes through the band-pass filter (234). The third pulse laser beam (240) further enters the first dichroic mirror (32). The third pulse laser beam (240) and the first pulse laser beam (210) both pass through the first dichroic mirror (32) for light path multiplexing, then pass through the beam expander lens (33) to expand the laser spot to twice the original size, and further enter the second dichroic mirror (34). The probe light path assembly (50) comprises a probe light source (51), a polarization beam splitter (52) and a 1 / 4 wave plate (53), the probe light source (51) is a super radiation light emitting diode, capable of emitting a 1310nm incoherent probe light beam (510), the polarization beam splitter (52) and the 1 / 4 wave plate (53) are located on the light path of the probe light beam (510) and are arranged in parallel in the horizontal direction, the probe light beam (510) is first transmitted through the polarization beam splitter (52) to generate a transmitted vertical linearly polarized light, the linearly polarized light is incident along the fast axis direction of the 1 / 4 wave plate (53) to obtain a circularly polarized light, then the circularly polarized light is incident into the second dichroic mirror (34) to be reflected and combined with the third pulsed laser beam (240) and the first pulsed laser beam (210) to become a combined light (340), then the combined light (340) is incident into the scanning imaging assembly (40); The scanning imaging assembly (40) is arranged on the light path of the combined light (340), and the scanning imaging assembly (40) comprises a scanning galvanometer (41), an achromatic objective lens (42), a displacement platform (43), a heating box (44) and an imaging sample (45); Further comprising an electronic thermometer (80), the detection end of the electronic thermometer (80) is connected with the imaging sample (45), the signal output end of the electronic thermometer (80) is connected with the signal control assembly (10), the signal control assembly (10) outputs a high-frequency clock signal, the electronic thermometer (80) reads the temperature of the imaging sample (45) in real time, and at the same time, the signal control assembly (10) is provided with a threshold temperature, the preset temperature rising range is 25-45 degrees Celsius, and when the thermometer reading value increases by 0.5 degrees Celsius, the signal control assembly (10) is triggered to output a control signal.

2. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 1, characterized in that: The first dichroic mirror (32) is located behind the reflector (31), the reflector (31) reflects the first pulsed laser beam (210) emitted by the first pulsed laser (21) into the first dichroic mirror (32), the beam expander lens (33) is located behind the first dichroic mirror (32), the beam expander lens (33) is composed of two lenses with focal lengths of 25mm and 50mm respectively, and the second dichroic mirror (34) is located behind the beam expander 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 achromatic objective (42) is located behind the scanning galvanometer (41), the numerical aperture of the achromatic objective (42) is 0.4, the focal length is 25mm, 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 beam (340) sequentially passes through the scanning galvanometer (41) and the achromatic objective (42), and finally irradiates on the imaging sample (45), so that the confocal is realized on the imaging sample (45) to complete the detection of the photoacoustic signal, and the scanning galvanometer (41) can provide fast optical scanning in x direction and y direction, and the displacement platform (43) provides mechanical scanning in z direction.

4. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature of claim 1, wherein: Under the photoacoustic effect, the detection light reflected back by the second dichroic mirror (34) carries the information of the internal structure and characteristics of the imaging sample (45) to become a reflected signal light beam (520), the reflected signal light beam (520) is converted from circular polarization to horizontal polarization by the 1 / 4 wave plate (53), then enters the polarization beam splitter (52) and is reflected at the interface, and the direction of the light path of the reflected signal light beam (520) after passing through the polarization beam splitter (52) is perpendicular to the direction of the outgoing direction of the detection light beam (510).

5. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 4, characterized in that: Further comprising a signal collection assembly (60), the signal collection assembly (60) comprises 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 light path of the reflected signal light beam (520) and are arranged in parallel with the polarization beam splitter (52), the reflected signal light beam (520) enters the long-pass filter (61) to suppress reflection, then enters the second converging lens (62) to focus on the photodetector (63), and the photodetector (63) converts the received optical signal into an electrical signal for subsequent signal processing.

6. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 5, characterized in that: Further comprising a signal processing assembly (70), the signal processing assembly (70) comprises a filter (71), an amplifier (72) and a data acquisition card (73), the input end of the filter (71) is connected with the output end of the photodetector (63), the input end of the amplifier (72) is connected with the output end of the filter (71), the analog input port of the data acquisition card (73) is connected with the output end of the amplifier (72), and the analog output port of the data acquisition card (73) is connected with the signal control assembly (10), the signal received by the photodetector (63) is transmitted to the filter (71), the filter (71) removes unnecessary signal components, and then the signal is conducted to the amplifier (72) for amplification processing, and then data is collected through the data acquisition card (73).

7. The dual-wavelength photoacoustic remote sensing imaging system for non-contact measurement of absolute temperature according to claim 6, characterized in that: The electronic thermometer (80) reaches the preset temperature point will trigger the laser emission of the excitation light path component (20), and each temperature point is 20 ms as the excitation source, and the interval is 0.1 s. The data acquisition card (73) completes the data acquisition at a sampling rate of 250 MS / 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 double wavelengths is calculated, so as to obtain the system calibration curve and derive the temperature measurement data, and imaging is carried out in the remote sensing imaging subsystem of the signal control component (10).

Images