Limited-viewing-angle-corrected photoacoustic microscopy system based on three-beam interference excitation

Abstract

The present invention relates to the field of microscopic imaging technology, and in particular provides a limited-viewing-angle corrected photoacoustic microscopy imaging system based on three-beam interference excitation. The limited-viewing-angle corrected photoacoustic microscopy imaging system based on three-beam interference excitation includes a control circuit, a fixing component, a pulsed laser, a light field modulation component, an optical path lens component, an ultrasonic probe, and a three-dimensional scanning platform. The present invention utilizes a light field modulation component to modulate the excitation light field in the photoacoustic microscopy imaging system, and uses a striped light field formed by three-beam interference to excite a photoacoustic signal. Because the striped light field can effectively destroy the spatial coherence between ultrasonic wave sources excited by the photoacoustic effect, the limited-viewing-angle defect caused by coherent decomposition in the three-dimensional reconstructed image is eliminated without affecting system performance indicators such as imaging speed and imaging depth.

Description

Technical Field

[0001] The present invention relates to the field of microscopic imaging technology, and in particular provides a limited viewing angle correction photoacoustic microscopic imaging system based on three-beam interference excitation. Background Art

[0002] The biomedical microscopic imaging system is a comprehensive system that integrates multidisciplinary technologies such as optics, electronics, and computer science. As an emerging biomedical imaging system, the photoacoustic microscopic imaging system has been able to achieve deeper biological tissue imaging. Compared with other traditional imaging modalities, it has obvious advantages in deep human vascular imaging, especially melanoma tumor imaging.

[0003] However, photoacoustic microscopy has a systematic defect, namely, its limited viewing angle. In order to achieve high optical excitation efficiency and ultrasonic detection sensitivity, classical photoacoustic microscopy systems usually adopt a coaxial confocal optical excitation and acoustic detection mode. In the coaxial mode, the ultrasonic waves excited within the optical focal depth will cancel each other out during the propagation process due to interference, which is reflected in the "invisibility" of part of the sound source information along the optical axis in the imaging reconstruction. This phenomenon is called the limited viewing angle defect of the photoacoustic microscopy system. This defect makes it difficult for the photoacoustic microscopy system to restore the complete information of biological tissues with relatively uniform light absorption properties when used in such tissues. With the widespread application of photoacoustic microscopy systems, the limited viewing angle defect needs to be solved urgently. Existing solutions, such as oblique detection and the use of large numerical aperture objectives, have effectively eliminated the limited viewing angle defect, but these solutions have sacrificed system performance indicators such as imaging speed, imaging depth or system working distance, and there are many problems in practical applications. Summary of the Invention

[0004] Based on this, it is necessary to provide a limited viewing angle corrected photoacoustic microscopy system based on three-beam interference excitation to solve at least one technical problem in the background technology.

[0005] A limited-viewing-angle-corrected photoacoustic microscopy imaging system based on three-beam interference excitation comprises a control circuit, a fixed component, a pulsed laser, a light field modulation component, an optical path lens component, an ultrasonic probe, and a three-dimensional scanning platform. The control circuit comprises a control system and a driver, the control circuit comprising an editable logic gate array, and the driver is driven by an electrical signal converted from a control signal output by the control system. The pulsed laser is connected to the control circuit via a signal, and triggers the pulsed light source according to the control circuit to emit a high-energy, short-pulse-width pulsed laser beam. The light field modulation component comprises a spatial light modulator and a polarization optical path, the spatial light modulator being fixed to the fixed component, and the polarization optical path being arranged on the front optical path of the pulsed laser beam just after it is emitted from the pulsed laser. The optical path lens component is arranged perpendicularly to the fixed component and distributed on the optical path of the pulsed laser beam. The ultrasonic probe is located at the end of the optical path of the pulsed laser beam. The three-dimensional scanning platform comprises an x-scanning axis, a y-scanning axis, a z-scanning axis, and a sample placement area, the x-scanning axis, the y-scanning axis, and the z-scanning axis being arranged perpendicularly to each other, and the sample placement area being arranged at the end of a support rod extending from the middle of the z-scanning axis.

[0006] As a further improvement of the present invention, the fixed component includes a horizontal base plate and a vertical plate, the vertical plate is fixed on the horizontal base plate by two support rods; the pulse laser is fixed on the horizontal base plate by four support rods, the three-dimensional scanning platform is arranged on the horizontal base plate and adjacent to the vertical plate, and the spatial light modulator and the optical path lens assembly are both fixed on the vertical plate.

[0007] As a further improvement of the present invention, the spatial light modulator is an array-type light field modulation device. By loading a preset voltage on each pixel and combining it with the electro-optical effect, the phase of the incident light is changed. There are multiple pixel points in the spatial light modulator, and a specific phase distribution is loaded on these pixel points to modulate the initial phase of the light field of the spatial light modulator's output light. The spatial light modulator is loaded with the spectroscopic grating required by the system to generate three light beams.

[0008] As a further improvement of the present invention, the polarization optical path includes a polarizer, a polarization beam splitter, a quarter wave plate and an analyzer. The polarizer is arranged at the outlet of the pulse laser, the polarization beam splitter is arranged on a vertical plate and is located on the optical path of the pulse laser beam that is reflected and emitted straight upward, the quarter wave plate is located between the polarization beam splitter and the spatial light modulator, and the analyzer is located between the optical path lens components.

[0009] As a further improvement of the present invention, a beam expander is further provided on the outside of the pulse laser, and the beam expander is arranged after the polarizer. After the pulse laser beam is emitted from the pulse laser, it passes through the polarizer to adjust the polarization state of the laser beam, and then passes through the beam expander to adjust the beam spot diameter; the pulse laser beam emitted by the pulse laser passes through the polarizer to obtain S linear polarized light, and the S linear polarized light will be reflected by the polarization beam splitter, and then passes through a 1 / 4 wave plate whose fast axis forms an angle of degrees with the S polarization direction. At this time, the light is converted into left-handed / right-handed circularly polarized light, and then reflected by the spatial light modulator, resulting in half-wave loss, and obtaining right-handed / left-handed circularly polarized light, which is converted into P linear polarized light after passing through the 1 / 4 wave plate again, and is transmitted when passing through the polarization beam splitter and enters the subsequent optical path.

[0010] As a further improvement of the present invention, the optical path lens assembly includes a reflector group and a 4F system lens group, the 4F system lens group and the reflector group are both arranged on a vertical plate and spaced apart from each other, the reflector group includes a first reflector, a second reflector, a third reflector and a fourth reflector; the placement angles of the first reflector and the second reflector are both 45° clockwise, the placement angle of the third reflector is 135° clockwise, and the placement angle of the fourth reflector is 45° counterclockwise; the 4F system lens group is composed of multiple groups of 4F system lenses and a spatial filter, the multiple groups of 4F system lenses include a first lens group, a second lens group, a third lens group, a fourth lens group, a fifth lens group and a sixth lens group, and the spatial filter is arranged in the first Between the four reflectors and the third lens group, each group of 4F system lenses in the 4F system lens group is composed of two lenses with different focal lengths. The focal length ratio of the second lens group is smaller than the focal length ratio of the first lens group, the focal length ratio of the fourth lens group is smaller than the focal length ratio of the third lens group, and the focal length ratio of the sixth lens group is smaller than the focal length ratio of the fifth lens group. Multiple groups of 4F system lenses are used to successively reduce the changes in light spot shape caused by aberrations; the first lens group, the second lens group, the third lens group and the fourth lens group are lens groups with the same clear aperture size, and the fifth lens group and the sixth lens group are lens groups with the same clear aperture size, and the clear aperture is larger than that of the first lens group, the second lens group, the third lens group and the fourth lens group.

[0011] As a further improvement of the present invention, the light field modulation component, the reflector group and the 4F system lens group are staggered and spaced on the optical path of the pulsed laser beam. The pulsed laser beam passes through the polarizer, the beam expander, the first reflector, the polarization beam splitter, the quarter-wave plate, the spatial light modulator, the quarter-wave plate, the polarization beam splitter, the first lens group, the second reflector, the analyzer, the second lens group, the third reflector, the fourth reflector, the spatial filter, the third lens group, the fourth lens group, the fifth lens group and the sixth lens group in sequence, and then forms an interference pattern and is finally irradiated onto the sample.

[0012] As a further improvement of the present invention, the x-scanning axis, the y-scanning axis and the z-scanning axis all include a displacement platform and a stepper motor. The displacement platforms are slidably arranged on the x-scanning axis, the y-scanning axis and the z-scanning axis respectively. The three stepper motors are controlled by a control circuit and drive the movement of the displacement platforms on the x-scanning axis, the y-scanning axis and the z-scanning axis respectively. The x-scanning axis is fixedly arranged on the horizontal base plate, the y-scanning axis is arranged on the displacement platform of the x-scanning axis and is perpendicular to the x-scanning axis in the horizontal direction, and the z-scanning axis is arranged on the displacement platform of the y-scanning axis and is perpendicular to the y-scanning axis in the vertical direction. A support connecting the sample placement area and the z-scanning axis is provided. The other end of the support rod is fixed and perpendicular to the displacement platform on the z scanning axis. After each photoacoustic signal is generated and triggered, the stepper motor drives the displacement platform on the x scanning axis to move forward one step. After completing the preset number of steps, it drives the displacement platform on the y scanning axis to move forward one step. The displacement platforms on the x scanning axis and the y scanning axis perform step scanning in an "S"-shaped scanning path on the x and y planes. After completing the scan of one plane, it will return to the initial point. Then the stepper motor drives the displacement platform on the z scanning axis to move forward one step, and performs the above scanning on the new plane, repeating the three-dimensional scanning of the sample.

[0013] As a further improvement of the present invention, a sample and a detection end of an ultrasonic probe are placed in a sample placement area. The sample placement area uses a transparent water tank, which is more than half filled with clean water. The sample is placed at the bottom of the water tank, and the ultrasonic probe is an immersion ultrasonic probe. The center frequency of the ultrasonic probe is 25 MHz, and the angle between the 0th order and ±1st order diffraction lights of the three rays of the pulsed laser beam incident on the sample is between 20° and 40°.

[0014] As a further improvement of the present invention, a limited-view correction photoacoustic microscopy system based on three-beam interference excitation also includes an operational amplifier and a data acquisition card. The operational amplifier is connected to the output end of the ultrasonic probe to receive and amplify the ultrasonic signal output by it; the analog input port of the data acquisition card is connected to the output port of the operational amplifier, and the analog output port of the data acquisition card is connected to the control circuit; the data acquisition card is controlled by the control circuit, and the data transmission rate of the data acquisition card is 200Ms / s. After each photoacoustic signal is generated and triggered, the data acquisition card starts working after a preset time and collects a digital signal of a preset length. The collected photoacoustic signal is processed by a data processing algorithm to obtain a three-dimensional photoacoustic image of the sample; the control system also includes imaging software, and the imaging software provides a user interaction interface for setting system parameters, monitoring the imaging process, and displaying and storing imaging results.

[0015] The beneficial effects of the present invention are as follows:

[0016] 1. The excitation light field in the photoacoustic microscopy system is modulated by a light field modulation component, and a stripe-shaped light field formed by three-beam interference is used to stimulate the photoacoustic signal. Since the stripe-shaped light field can effectively destroy the spatial coherence between the ultrasonic wave sources excited by the photoacoustic effect, the limited viewing angle defect caused by coherent decomposition in the 3D reconstructed image is eliminated without affecting system performance indicators such as imaging speed and imaging depth.

[0017] 2. Through the coordinated work of various components, high-resolution, wide-angle photoacoustic microscopy can be achieved, effectively eliminating the limited-angle system defect in the photoacoustic microscopy imaging system. Compared with the solution with a large numerical aperture objective lens, the three-beam interference solution is not affected by the numerical aperture of the optical path. As long as the three-beam angle is met, no matter what optical path is ultimately used, the purpose of eliminating the limited angle of view can be achieved. It can provide greater freedom in optical path design, and the system's working distance and imaging depth can be designed according to actual needs. It is compatible with a wide variety of lenses and has a wide range of applicable scenarios. It can effectively avoid damage to the bayonet mount and signal loss caused by the use of lenses that are too heavy or too long.

[0018] 3. Using grating diffraction's 0th and ±1st order light to generate a three-beam interference light field, with an ultrasound probe center frequency of 25MHz and a data acquisition card running at 200 Ms / s, testing shows that good visibility restoration can be achieved at angles between 20° and 40°. Ensuring the data acquisition card activates at the appropriate moment to capture the acoustic wave signals generated by the photoacoustic effect enables more efficient and accurate signal acquisition and data analysis, improving imaging quality and enhancing system performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. 1 is a perspective schematic diagram of an embodiment of the present invention.

[0020] Figure 2 It is a three-dimensional schematic diagram of another embodiment of the present invention.

[0021] Figure 3 Schematic diagram of polarization and reflection of a light beam in a polarization light path according to an embodiment of the present invention.

[0022] Figure 4 Schematic diagram of data collection timing in one embodiment of the present invention.

[0023] Figure 5 FIG. 4 is an imaging flow chart of an imaging system in one embodiment of the present invention.

[0024] In the figure: 10, control circuit; 11, control system; 20, fixing component; 21, horizontal base plate; 22, vertical plate; 30, pulse laser; 31, pulse laser beam; 32, beam expander; 40, light field modulation component; 41, spatial light modulator; 42, polarization light path; 421, polarizer; 422, polarization beam splitter; 423, 1 / 4 wave plate; 424, analyzer; 425, S linear polarized light; 426, left / right circularly polarized light; 427, right / left circularly polarized light; 428, P linear polarized light; 50, optical path lens component; 51, reflector group; 511, first reflector; 5 12. Second reflector; 513. Third reflector; 514. Fourth reflector; 52. 4F system lens group; 521. First lens group; 522. Second lens group; 523. Third lens group; 524. Fourth lens group; 525. Fifth lens group; 526. Sixth lens group; 53. Spatial filter; 60. Ultrasonic probe; 70. Three-dimensional scanning platform; 71. X-scanning axis; 72. Y-scanning axis; 73. Z-scanning axis; 74. Sample placement area; 740. Sample; 80. Operational amplifier; 90. Data acquisition card; 901. Acquisition delay time; 902. Digital signal acquisition length. DETAILED DESCRIPTION

[0025] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[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", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, 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 commonly understood by one skilled in the art to which this invention pertains. The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0028] See also Figures 1 to 5A limited-viewing-angle-corrected photoacoustic microscopy imaging system based on three-beam interference excitation includes a control circuit 10, a fixing component 20, a pulsed laser 30, a light field modulation component 40, an optical path lens component 50, an ultrasonic probe 60, and a three-dimensional scanning platform 70; the control circuit 10 includes a control system 11 and a driver, the control circuit 10 includes an editable logic gate array, and the driver is driven by an electrical signal converted from a control signal output by the control system 11; the pulsed laser 30 is connected to the control circuit 10 through a signal, and triggers a pulsed light source according to the control circuit 10 to emit a high-energy, short-pulse-width pulse laser beam 31; the light field modulation component 40 includes A spatial light modulator 41 and a polarization light path 42, wherein the spatial light modulator 41 is fixed on the fixed component 20, and the polarization light path 42 is arranged on the front optical path of the pulsed laser beam 31 just emitted from the pulsed laser 30; the optical path lens component 50 is arranged vertically on the fixed component 20 and is distributed on the optical path of the pulsed laser beam 31; the ultrasonic probe 60 is located at the end of the optical path of the pulsed laser beam 31; the three-dimensional scanning platform 70 includes an x-scanning axis 71, a y-scanning axis 72, a z-scanning axis 73 and a sample placement area 74, wherein the x-scanning axis 71, the y-scanning axis 72 and the z-scanning axis 73 are arranged vertically to each other, and the sample placement area 74 is arranged at the end of a support rod extending from the middle of the z-scanning axis 73.

[0029] In one embodiment, a pulsed laser 30 is used to emit a pulsed laser beam 31 for stimulating a photoacoustic signal. According to the relationship between the initial sound pressure P of the photoacoustic effect and the light flux F of the exciting light field, P is proportional to the first-order time derivative of F. Therefore, the pulse width of the pulsed laser 30 is relatively low to stimulate a higher initial sound pressure P, thereby obtaining a higher system signal-to-noise ratio; the pulsed laser 30 is controlled by a clock signal, and the rising edge of the clock signal triggers pulse emission.

[0030] The fixing assembly 20 includes a horizontal base plate 21 and a vertical plate 22. The vertical plate 22 is fixed on the horizontal base plate 21 by two support rods; the pulse laser 30 is fixed on the horizontal base plate 21 by four support rods, the three-dimensional scanning platform 70 is set on the horizontal base plate 21 and adjacent to the vertical plate 22, and the spatial light modulator 41 and the optical path lens assembly 50 are both fixed on the vertical plate 22.

[0031] The spatial light modulator 41 is an array-type light field modulation device that changes the phase of the incident light by applying a preset voltage to each pixel in combination with the electro-optical effect. There are multiple pixels in the spatial light modulator 41, and a specific phase distribution is applied to these pixels to modulate the initial phase of the light field of the light output from the spatial light modulator 41. The spectroscopic grating required by the system is loaded on the spatial light modulator 41 to generate three light beams.

[0032] In one embodiment, the use of the spatial light modulator 41 requires that the incident light be linearly polarized light with a polarization direction parallel to a specific direction. Therefore, a specific polarization light path 42 is required in the imaging system to function as the spatial light modulator.

[0033] The polarization light path 42 includes a polarizer 421, a polarization beam splitter 422, a quarter-wave plate 423 and an analyzer 424. The polarizer 421 is arranged at the exit of the pulse laser 30, the polarization beam splitter 422 is arranged on the vertical plate 22 and is located on the light path of the pulse laser beam 31 that is reflected and emitted straight upward. The quarter-wave plate 423 is located between the polarization beam splitter 422 and the spatial light modulator 41, and the analyzer 424 is located between the optical path lens assembly 40.

[0034] A beam expander 32 is also provided on the outside of the pulse laser 30. The beam expander 32 is arranged after the polarizer 421. After the pulse laser beam 31 is emitted from the pulse laser 30, it passes through the polarizer 421 to adjust the polarization state of the laser beam, and then passes through the beam expander 32 to adjust the beam spot diameter; the pulse laser beam 31 emitted by the pulse laser 30 passes through the polarizer 421 to obtain S linear polarized light 425, and the S linear polarized light 425 will be reflected by the polarization beam splitter 422, and then passes through a 1 / 4 wave plate 423 whose fast axis forms an angle of 45 degrees with the S polarization direction. At this time, the light is converted into left-handed / right-handed circularly polarized light 426, and then reflected by the spatial light modulator 41, resulting in half-wave loss, and obtaining right-handed / left-handed circularly polarized light 427, which passes through the 1 / 4 wave plate 423 again to be converted into P linear polarized light 428, and is transmitted when passing through the polarization beam splitter 422 and enters the subsequent optical path.

[0035] In one embodiment, the beam expander 32 is used to change the spot diameter of the beam incident on the spatial light modulator 41. This value affects the diffraction efficiency of the spatial light modulator 41 and the lateral resolution of the imaging system. If the grating constant loaded on the spatial light modulator 41 is constant, if the spot diameter is too small, the intensity difference between the 0th and ±1st order diffracted light emitted by the spatial light modulator 41 will be large, further affecting the generated fringe contrast. If the spot diameter is too large, it will affect the spot diameter of the three beams ultimately used to excite the photoacoustic signal, that is, the lateral resolution of the system.

[0036] In one embodiment, Figure 3As shown, when the S linear polarized light 425 is incident on the 1 / 4 wave plate 423 at an angle of 45 degrees, the light wave is decomposed into two components: one propagates along the fast axis (assuming it is at an angle of 45 degrees to the horizontal direction), and the other propagates along the slow axis (perpendicular to the fast axis). Due to the different light wave velocities on the fast axis and the slow axis, they will produce a phase difference of 2π after passing through the wave plate. Therefore, when these two components are recombined, they are no longer linearly polarized light, but become circularly polarized light. Whether it is left-handed circularly polarized light or right-handed circularly polarized light depends on the relative direction of the fast axis and the slow axis of the wave plate and the polarization direction of the incident light. After reflection from the spatial light modulator 41, the reflected light suffers a half-wave loss, which means that the phase of the reflected light changes by π relative to the incident light, resulting in a reversal of the direction of rotation of the circularly polarized light: left-handed circularly polarized light becomes right-handed circularly polarized light, and vice versa. The circularly polarized light, after being reflected and having its handedness reversed by the spatial light modulator, passes through the quarter-wave plate 423 again. Since the fast and slow axes of the wave plate remain unchanged, and the light wave is incident again at a 45-degree angle, it is once again decomposed into two components, each resulting in a phase difference of 2π after passing through the wave plate. However, since the handedness of the circularly polarized light has reversed, the recombined components are no longer circularly polarized light. Instead, they become P linearly polarized light 428, which is perpendicular to the original S linearly polarized light 425. Finally, the P linearly polarized light 428 is transmitted through the polarization beam splitter 422 and can then enter the subsequent optical path for further processing.

[0037] The optical path lens assembly 50 includes a reflector group 51 and a 4F system lens group 52. The 4F system lens group 52 and the reflector group 51 are both arranged on the vertical plate 22 and spaced apart from each other. The reflector group 51 includes a first reflector 511, a second reflector 512, a third reflector 513 and a fourth reflector 514. The placement angles of the first reflector 511 and the second reflector 512 are both 45° clockwise, the placement angle of the third reflector 513 is 135° clockwise, and the placement angle of the fourth reflector 514 is 45° counterclockwise. The 4F system lens group 52 consists of multiple groups of 4F system lenses and a spatial filter 53. The multiple groups of 4F system lenses include a first lens group 521, a second lens group 522, a third lens group 523, a fourth lens group 524, a fifth lens group 525 and a sixth lens group 526. The spatial filter 53 is arranged on the fourth reflector. Between the lens 514 and the third lens group 523, each group of 4F system lenses in the 4F system lens group 52 is composed of two lenses with different focal lengths. The focal length ratio of the second lens group 522 is smaller than the focal length ratio of the first lens group 521, the focal length ratio of the fourth lens group 524 is smaller than the focal length ratio of the third lens group 523, and the focal length ratio of the sixth lens group 526 is smaller than the focal length ratio of the fifth lens group 525. The use of multiple groups of 4F system lenses gradually reduces the changes in the light spot shape caused by aberrations. The first lens group 521, the second lens group 522, the third lens group 523, and the fourth lens group 524 have the same optical aperture, while the fifth lens group 525 and the sixth lens group 526 have the same optical aperture and have a larger optical aperture than the first lens group 521, the second lens group 522, the third lens group 523, and the fourth lens group 524.

[0038] In one embodiment, the 4F system lens group 52 is an imaging configuration composed of two lenses with different focal lengths. The magnification of a 4F system lens group is determined by the ratio of the second lens' focal length f2 to the first lens' focal length f1, i.e., magnification A = f2 / f1. Multiple 4F system lens groups 52 can continuously reduce the incident light until it meets the imaging system's requirements. According to the Gaussian light imaging formula, the distance between each 4F system group cannot be too large to avoid the influence of the Gaussian light's divergence angle. The lenses of different focal lengths are arranged according to the sum of their focal lengths. In this case, the object-image relationship is related to the ratio of the two lens' focal lengths. Using multiple 4F system groups can gradually reduce the changes in light spot shape caused by aberrations. The 4F system also includes a spatial filter to block light from other diffraction orders, retaining only the 0th and ±1st order diffraction light.

[0039] In one embodiment, in order to provide a larger three-beam angle when the pulsed laser beam 31 approaches the sample, since the focal length of the lens is fixed, through the trigonometric relationship tan(theta)=D / f, (theta is the beam angle, f is the lens focal length, and D is the incident height), it can be seen that in order to achieve a larger angle, the incident height of the beams on both sides needs to be larger, so the fifth lens group 525 and the sixth lens group 526 use lens groups with larger clear apertures.

[0040] The light field modulation component 40, the reflective mirror group 51, and the 4F system lens group 52 are staggered and spaced on the optical path of the pulsed laser beam 31. The pulsed laser beam 31 passes through the polarizer 421, the beam expander 32, the first reflective mirror 511, the polarization beam splitter 322, the quarter-wave plate 423, the spatial light modulator 41, the quarter-wave plate 423, the polarization beam splitter 322, the first lens group 521, the second reflective mirror 512, the analyzer 324, the second lens group 522, the third reflective mirror 513, the fourth reflective mirror 514, the spatial filter 53, the third lens group 523, the fourth lens group 524, the fifth lens group 525, and the sixth lens group 526 in sequence, and then forms an interference pattern and is finally irradiated onto the sample.

[0041] In another embodiment of the present invention, Figure 2 As shown, the positions of the reflector group 51 and the 4F system lens group 52 can be changed according to the actual application conditions and requirements, and the positions and parameters of the lens groups and filters can be flexibly adjusted to obtain the best image processing effect.

[0042] The x-scanning axis 71, the y-scanning axis 72 and the z-scanning axis 73 all include a displacement platform and a stepper motor. The displacement platforms are slidably arranged on the x-scanning axis 71, the y-scanning axis 72 and the z-scanning axis 73 respectively. The three stepper motors are controlled by the control circuit 10 and drive the movement of the displacement platforms on the x-scanning axis 71, the y-scanning axis 72 and the z-scanning axis 73 respectively. The x-scanning axis 71 is fixedly arranged on the horizontal base plate 21, the y-scanning axis 72 is arranged on the displacement platform of the x-scanning axis 71 and is perpendicular to the x-scanning axis 71 in the horizontal direction, and the z-scanning axis 73 is arranged on the displacement platform of the y-scanning axis 72 and is perpendicular to the y-scanning axis 72 in the vertical direction. The sample placement area 74 is connected to the z-scanning axis 73. The other end of the support rod of the scanning axis 73 is fixed and perpendicularly arranged on the displacement platform on the z scanning axis 73. After each generation and triggering of the photoacoustic signal, the three-dimensional scanning platform 70 drives the displacement platform on the x scanning axis 71 to move forward one step. After completing the preset number of steps, it drives the displacement platform on the y scanning axis 72 to move forward one step. The displacement platforms on the x scanning axis 71 and the y scanning axis 72 perform step scanning in an "S"-shaped scanning path on the x and y planes. After completing the scanning of one plane, it will return to the initial point. Then the stepping motor drives the displacement platform on the z scanning axis 73 to move forward one step, and performs the above scanning on the new plane, repeating the three-dimensional scanning of the sample.

[0043] The sample 740 and the detection end of the ultrasonic probe 60 are placed in the sample placement area 74. The sample placement area 74 uses a transparent water tank that is more than half filled with clean water. The sample 740 is placed at the bottom of the water tank. The ultrasonic probe 60 is an immersion ultrasonic probe. The center frequency of the ultrasonic probe 60 is 25MHz, and the angle between the 0th order and ±1st order diffraction lights of the three light beams of the pulsed laser beam 31 incident on the sample is between 20° and 40°.

[0044] The limited-view correction photoacoustic microscopy imaging system based on three-beam interference excitation also includes an operational amplifier 80 and a data acquisition card 90. The operational amplifier 80 is connected to the output end of the ultrasonic probe 60 to receive and amplify the ultrasonic signal output by it; the analog input port of the data acquisition card 90 is connected to the output port of the operational amplifier 80, and the analog output port of the data acquisition card 90 is connected to the control circuit 10; the data acquisition card 90 is controlled by the control circuit 10, and the data transmission rate of the data acquisition card 90 is 200Ms / s. After each photoacoustic signal is generated and triggered, the data acquisition card 90 starts working after a preset time and collects a digital signal of a preset length. The collected photoacoustic signal is processed by a data processing algorithm to obtain a three-dimensional photoacoustic image of the sample; the control system 11 also includes imaging software, which provides a user interaction interface for setting system parameters, monitoring the imaging process, and displaying and storing imaging results.

[0045] In one embodiment, the pulse laser 30, the spatial light modulator 41, the ultrasonic probe 60, the three-dimensional scanning platform 70, the operational amplifier 80, and the data acquisition card 90 are all provided with drivers. When the imaging system is in use, the control system 11 is operated so that the control signal output by the control system 11 is transmitted to the driver. The driver then converts the different control signals into electrical signals to drive the various components in the imaging system to start functioning.

[0046] In one embodiment, the ultrasonic probe 60 receives the photoacoustic signal generated on the sample surface. Since the photoacoustic signal is relatively weak, it needs to be amplified by an operational amplifier 80. The received photoacoustic signal is amplified and preliminarily processed by the operational amplifier 80 for subsequent data acquisition and image reconstruction, and then transmitted to the control system 11.

[0047] In one embodiment, the data acquisition timing of the data acquisition card 90 is as follows: Figure 4 As shown, acquisition delay time 901 is determined by the imaging system circuit delay, optical path delay, and ultrasound propagation time. Digital signal acquisition length 902 is affected by the system focal depth. If the system focal depth is small, the initial acoustic pressure generated in the z-direction is distributed over a shorter length, and the resulting photoacoustic signal is also shorter. Therefore, digital signal length 902 does not need to be too long. Conversely, digital signal acquisition length 902 needs to be extended to ensure that data acquisition card 90 can begin operating at the appropriate time to capture the acoustic wave signal generated by the photoacoustic effect. This allows for more efficient and accurate signal acquisition and data analysis, improving imaging quality and enhancing system performance.

[0048] In one embodiment, the imaging flow chart of the imaging system is as follows: Figure 5 As shown, a programmable gate array (FPGA) provides a clock signal to control the imaging system. This signal's frequency is limited by the maximum scanning frequency of the 3D scanning platform 70 and the maximum repetition frequency of the pulsed laser beam 31. If these two values ​​are high, the clock signal can have a higher frequency, further improving the system's imaging speed. During this process, three-beam interference excitation and acoustic signal detection continue. The 3D scanning platform 70 scans the sample 740, and the data acquisition card 90 (i.e., DAQ) collects data, and then processes and amplifies the signal through the operational amplifier 80 (i.e., PA) simultaneously. Only when all pixels of the sample 740 have been scanned, acquired, and transmitted does the scanning platform terminate and return to its origin. This allows for precise control over the complete scanning of the sample 740.

[0049] In one embodiment, a sample is placed on a three-dimensional scanning platform and initially positioned and calibrated. The motion parameters of the three-dimensional scanning platform 70, such as scanning speed, step length, and scanning range, are set according to imaging requirements and sample characteristics. The pulse laser 30 emits three pulsed laser beams 31, which modulate the excitation light field in the photoacoustic microscopy imaging system through the light field modulation component 40. The striped light field formed by the interference of the three beams is used to excite the photoacoustic signal. After passing through the optical elements in the light field modulation component 40 and the optical path lens component 50, an interference pattern is formed. The interference pattern is irradiated on the sample 740, stimulating the photoacoustic effect in the sample 740 and generating an acoustic wave signal. The ultrasonic probe 60 receives the photoacoustic signal generated on the sample surface. Since the photoacoustic signal is relatively weak, an operational amplifier 80 is required to perform Amplification: The received photoacoustic signal is amplified and preliminarily processed by the operational amplifier 80 and transmitted to the data acquisition card 90 and the control circuit 10. Under the control of the control system 11, the three-dimensional scanning platform 70 starts to move the sample according to the preset scanning trajectory. During the scanning process, three-beam interference excitation and acoustic wave signal detection are continuously carried out to obtain photoacoustic signals of the sample 740 at different positions and depths. The collected photoacoustic signal is amplified and preliminarily processed by the operational amplifier 80, and then transmitted to the control system 11 for data processing algorithm processing to obtain a three-dimensional photoacoustic image of the sample 740. Since the set striped light field can effectively destroy the spatial coherence between the ultrasonic wave sources excited by the photoacoustic effect, the limited viewing angle defect caused by coherent decomposition in the three-dimensional reconstructed image is eliminated.

[0050] The present invention can achieve:

[0051] (1) The excitation light field in the photoacoustic microscopy imaging system is modulated by the light field modulation component 40, and the stripe light field formed by the interference of three light beams is used to excite the photoacoustic signal. Since the stripe light field can effectively destroy the spatial coherence between the ultrasonic wave sources excited by the photoacoustic effect, the limited viewing angle defect caused by coherent decomposition in the three-dimensional reconstructed image is eliminated without affecting the system performance indicators such as imaging speed and imaging depth.

[0052] (2) Through the coordinated work of various parts, high-resolution, wide-angle photoacoustic microscopy can be achieved, effectively eliminating the limited-angle system defects in the photoacoustic microscopy imaging system. Compared with the solution of large numerical aperture objective lens, the three-beam interference solution is not affected by the numerical aperture of the optical path. As long as the three-beam angle is met, no matter what optical path is finally used, the purpose of eliminating the limited angle of view can be achieved. It can provide greater freedom in optical path design. The working distance and imaging depth of the system can be designed according to actual needs. It is compatible with many types of lenses and has a wide range of applicable scenarios. It can effectively avoid the situation where the lens used is too heavy or too long and causes damage to the bayonet and signal loss.

[0053] (3) Using the 0th and ±1st order light diffracted by the grating to generate a three-beam interference light field, under the conditions of the ultrasound probe 60 having a center frequency of 25 MHz and the data acquisition card 90 operating at 200 Ms / s, the angle between the three beams was tested to be between 20° and 40°, achieving good visibility restoration. Ensuring that the data acquisition card 90 can start working at the appropriate time to capture the acoustic wave signal generated by the photoacoustic effect enables more efficient and accurate signal acquisition and data analysis, which is conducive to improving imaging quality and enhancing system performance.

[0054] The above-described embodiments merely represent several embodiments of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A limited-viewing-angle-corrected photoacoustic microscopy system based on three-beam interference excitation, characterized by: The invention comprises a control circuit (10), a fixing component (20), a pulse laser (30), a light field modulation component (40), an optical path lens component (50), an ultrasonic probe (60) and a three-dimensional scanning platform (70); the control circuit (10) comprises a control system (11) and a driver, the control circuit (10) comprises an editable logic gate array, and the driver is driven by an electrical signal converted from a control signal output by the control system (11); the pulse laser (30) is connected to the control circuit (10) through a signal, and triggers a pulse light source according to the control circuit (10) to emit a high-energy, short-pulse-width pulse laser beam (31); the light field modulation component (40) comprises a spatial light modulator (41) and a polarization optical path (42); the fixing component (20) comprises a horizontal bottom plate (21) and a vertical plate (22); the The vertical plate (22) is fixed on the horizontal bottom plate (21) through two support rods, and the polarized light path (42) is set on the front optical path of the pulse laser beam (31) just emitted from the pulse laser (30); the spatial light modulator (41) and the optical path lens assembly (50) are both fixed on the vertical plate (22) and distributed on the optical path of the pulse laser beam (31); the ultrasonic probe (60) is located at the end of the optical path of the pulse laser beam (31); the three-dimensional scanning platform (70) includes an x-scanning axis (71), a y-scanning axis (72), a z-scanning axis (73) and a sample placement area (74), the x-scanning axis (71), the y-scanning axis (72) and the z-scanning axis (73) are arranged perpendicular to each other, and the sample placement area (74) is set at the end of the support rod extending from the middle of the z-scanning axis (73); The spatial light modulator (41) is an array-type light field modulation device, which changes the phase of the incident light by loading a preset voltage on each pixel in combination with the electro-optical effect. There are multiple pixel points in the spatial light modulator (41), and specific phase distributions are loaded on these pixel points to modulate the initial phase of the light field of the light emitted by the spatial light modulator (41). The spatial light modulator (41) is loaded with the required system splitter grating to generate three light beams.

2. The limited viewing angle correction photoacoustic microscopy system based on three-beam interference excitation according to claim 1, characterized in that: The pulse laser (30) is fixedly mounted on the horizontal bottom plate (21) via four support rods, and the three-dimensional scanning platform (70) is mounted on the horizontal bottom plate (21) and adjacent to the vertical plate (22).

3. The limited viewing angle correction photoacoustic microscopy system based on three-beam interference excitation according to claim 1, characterized in that: The polarization light path (42) includes a polarizer (421), a polarization beam splitter (422), a quarter wave plate (423) and a polarizer (424), wherein the polarizer (421) is arranged at the exit of the pulse laser (30), the polarization beam splitter (422) is arranged on the vertical plate (22) and is located on the light path of the pulse laser beam (31) which is reflected and emitted straight upward, the quarter wave plate (423) is located between the polarization beam splitter (422) and the spatial light modulator (41), and the polarizer (424) is located between the light path lens components (50).

4. The limited viewing angle correction photoacoustic microscopy imaging system based on three-beam interference excitation according to claim 3, characterized in that: A beam expander (32) is further provided on the outside of the pulse laser (30). The beam expander (32) is provided after the polarizer (421). After the pulse laser beam (31) is emitted from the pulse laser (30), it passes through the polarizer (421) to adjust the polarization state of the laser beam, and then passes through the beam expander (32) to adjust the beam spot diameter. The pulse laser beam (31) emitted by the pulse laser (30) passes through the polarizer (421) to obtain S linear polarized light (425). The S linear polarized light (425) will be reflected after passing through the polarization beam splitter (422), and then pass through the 1 / 4 wave plate (423) whose fast axis forms an angle of 45 degrees with the S polarization direction. At this time, the light is converted into left-handed / right-handed circularly polarized light (426), and then reflected by the spatial light modulator (41), resulting in half-wave loss, and obtaining right-handed / left-handed circularly polarized light (427). After passing through the 1 / 4 wave plate (423) again, it is converted into P linear polarized light (428), and is transmitted when passing through the polarization beam splitter (422) and enters the subsequent optical path.

5. The limited viewing angle correction photoacoustic microscopy system based on three-beam interference excitation according to claim 4, characterized in that: The optical path lens assembly (50) comprises a reflector group (51) and a 4F system lens group (52). The 4F system lens group (52) and the reflector group (51) are both arranged on the vertical plate (22) and spaced apart from each other. The reflector group (51) comprises a first reflector (511), a second reflector (512), a third reflector (513) and a fourth reflector (514). The placement angles of the first reflector (511) and the second reflector (512) are both 45° clockwise, and the placement angle of the third reflector (513) is 45° clockwise. The placement angle of the reflecting mirror (513) is 135° clockwise, and the placement angle of the fourth reflecting mirror (514) is 45° counterclockwise; the 4F system lens group (52) is composed of multiple groups of 4F system lenses and a spatial filter (53), and the multiple groups of 4F system lenses include a first lens group (521), a second lens group (522), a third lens group (523), a fourth lens group (524), a fifth lens group (525) and a sixth lens group (526), ​​and the spatial filter (53) is arranged on the fourth reflecting mirror (514). Between the projection lens (514) and the third lens group (523), each group of 4F system lenses in the 4F system lens group (52) is composed of two lenses with different focal lengths, the focal length ratio of the second lens group (522) is smaller than the focal length ratio of the first lens group (521), the focal length ratio of the fourth lens group (524) is smaller than the focal length ratio of the third lens group (523), and the focal length ratio of the sixth lens group (526) is smaller than the focal length ratio of the fifth lens group (525). Multiple groups of 4F system lenses are used in sequence. Reduce the change of light spot shape caused by aberration; the first lens group (521), the second lens group (522), the third lens group (523) and the fourth lens group (524) are lens groups with the same light aperture size, and the fifth lens group (525) and the sixth lens group (526) are lens groups with the same light aperture size, and the light aperture is larger than that of the first lens group (521), the second lens group (522), the third lens group (523) and the fourth lens group (524).

6. The limited viewing angle correction photoacoustic microscopy system based on three-beam interference excitation according to claim 5, characterized in that: The light field modulation component (40), the reflector group (51) and the 4F system lens group (52) are staggered and spaced on the optical path of the pulsed laser beam (31). The pulsed laser beam (31) passes through the polarizer (421), the beam expander (32), the first reflector (511), the polarization beam splitter (422), the 1 / 4 wave plate (423), the spatial light modulator (41), the 1 / 4 wave plate (423), the polarization beam splitter (422), the first lens group (521), the second reflector (512), the analyzer (424), the second lens group (522), the third reflector (513), the fourth reflector (514), the spatial filter (53), the third lens group (523), the fourth lens group (524), the fifth lens group (525) and the sixth lens group (526) in sequence, and then forms an interference pattern and is finally irradiated on the sample.

7. The limited viewing angle correction photoacoustic microscopy system based on three-beam interference excitation according to claim 6, characterized in that: The x-scan axis (71), the y-scan axis (72) and the z-scan axis (73) all include a displacement platform and a stepper motor. The displacement platforms are slidably arranged on the x-scan axis (71), the y-scan axis (72) and the z-scan axis (73), respectively. The three stepper motors are controlled by the control circuit (10) and respectively drive the movement of the displacement platforms on the x-scan axis (71), the y-scan axis (72) and the z-scan axis (73); the x-scan axis (71) is fixedly arranged on the horizontal base plate (21), the y-scan axis (72) is arranged on the displacement platform of the x-scan axis (71) and is perpendicular to the x-scan axis (71) in the horizontal direction, and the z-scan axis (73) is arranged on the displacement platform on the y-scan axis (72) and is perpendicular to the y-scan axis (72) in the horizontal direction. The sample placement area (74) is vertical; the other end of the support rod connecting the sample placement area (74) and the z scanning axis (73) is fixed and vertically arranged on the displacement platform on the z scanning axis (73); after each generation and triggering of the photoacoustic signal, the stepper motor drives the displacement platform on the x scanning axis (71) to move forward one step; after completing the preset number of steps, the displacement platform on the y scanning axis (72) is driven to move forward one step; the displacement platforms on the x scanning axis (71) and the y scanning axis (72) perform step scanning in an "S"-shaped scanning path in the x and y planes; after completing the scanning of one plane, they return to the initial point; then the stepper motor drives the displacement platform on the z scanning axis (73) to move forward one step; the above scanning is performed on the new plane, and the three-dimensional scanning of the sample is repeated.

8. The limited viewing angle correction photoacoustic microscopy system based on three-beam interference excitation according to claim 7, characterized in that: The sample placement area (74) contains a sample (740) and a detection end of the ultrasonic probe (60). The sample placement area (74) is a transparent water tank, which is more than half filled with clean water. The sample (740) is placed at the bottom of the water tank. The ultrasonic probe (60) is a water immersion ultrasonic probe. The center frequency of the ultrasonic probe (60) is 25 MHz. The angle between the 0th order and ±1st order diffraction lights of the three rays of the pulsed laser beam (31) incident on the sample is between 20° and 40°.

9. The limited viewing angle correction photoacoustic microscopy system based on three-beam interference excitation according to claim 8, characterized in that: The system further comprises an operational amplifier (80) and a data acquisition card (90), wherein the operational amplifier (80) is connected to the output end of the ultrasonic probe (60) to receive and amplify the ultrasonic signal outputted by the ultrasonic probe; the analog input port of the data acquisition card (90) is connected to the output port of the operational amplifier (80), and the analog output port of the data acquisition card (90) is connected to the control circuit (10); the data acquisition card (90) is controlled by the control circuit (10), and the data transmission rate of the data acquisition card (90) is 200 Ms / s. After each generation and triggering of a photoacoustic signal, the data acquisition card (90) starts working after a preset time and acquires a digital signal of a preset length. The acquired photoacoustic signal is processed by a data processing algorithm to obtain a three-dimensional photoacoustic image of the sample; the control system (11) further comprises imaging software, wherein the imaging software provides a user interaction interface for setting system parameters, monitoring the imaging process, and displaying and storing imaging results.

Images