Photoacoustic microscopic imaging system and method based on gradient needle-shaped light beam excitation

Abstract

The invention discloses a photoacoustic microscopic imaging system and method based on gradient needle-shaped light beam excitation, and the system comprises a water tank which is used for placing a sample, an ultrasonic transducer and a three-dimensional displacement platform are in communication connection with an upper computer, and the three-dimensional displacement platform is fixedly connected with the water tank; the laser outputs a laser beam, the polarization state of the laser beam is adjusted to be circular polarization through the polarization adjusting system, the 4F beam expanding system expands the circular polarization beam, the formed beam after beam expanding is reflected by the reflector and transmitted to the ultraviolet optical diffraction element, the beam after beam expanding is modulated by the ultraviolet optical diffraction element to form a gradient needle-shaped beam, and the gradient needle-shaped beam is transmitted to the laser. The ultrasonic transducer is used for detecting the ultrasonic signals and sending the detected ultrasonic signals to the upper computer, so that the upper computer completes image reconstruction based on the received ultrasonic signals. The photoacoustic microscopic imaging system has histological imaging capability with large focal depth and high depth resolution.

Description

Technical Field

[0001] The present invention relates to the field of photoacoustic microscopy imaging technology, and in particular, to a photoacoustic microscopy imaging system and method based on gradient needle-shaped beam excitation. Background Art

[0002] Histopathological examination is the gold standard for disease diagnosis. Its traditional method relies on tissue samples fixed with formalin and embedded in paraffin (FFPE). After micron-scale sectioning and hematoxylin-eosin (H&E) staining, cell and tissue structures are observed through a bright-field microscope. However, this process requires cumbersome steps such as fixation, embedding, sectioning, and staining, which take several hours to several days, and it is difficult to meet the real-time diagnosis needs such as rapid judgment of cancer margins during surgery. Although cryosectioning technology shortens the detection time to dozens of minutes through tissue freezing and rapid staining, it is prone to ice crystal artifacts or difficult sectioning in edematous tissues or hard tissues (such as cortical bone, calcified tumors), resulting in a decrease in diagnostic accuracy.

[0003] Microscopy imaging technology based on the photoacoustic effect provides a new path for non-invasive cell nucleus imaging: by utilizing the strong absorption characteristics of DNA / RNA in the ultraviolet band, ultrasonic signals are generated by laser excitation of tissues, enabling specific visualization of cell nuclei and avoiding the dependence on traditional staining. However, existing photoacoustic microscopy imaging technology faces two bottlenecks: 1. Limitations of depth of focus and surface adaptability: Conventional optical focusing systems have a short depth of focus. When imaging fresh thick tissues with irregular surfaces, it is easy to cause image blurring or information loss due to local defocus. Although some studies have expanded the depth of focus range through wavefront manipulation technology, its depth resolution is still determined by the ultrasonic transducer and has not been improved, and it is impossible to achieve depth-resolved imaging at the level of pathological sections (the thickness of the gold standard pathological section is about 7 µm); 2. Physical limitations of ultrasonic transducers: The bandwidth limitation of transducers restricts the sectioning ability of photoacoustic imaging to dozens of micrometers, making it difficult to distinguish fine deep structures, and there is a significant gap from the sectioning-level resolution required for pathological diagnosis.

[0004] Therefore, it is difficult for the existing technology to achieve rapid and accurate cell nucleus imaging of untreated thick tissue samples. Summary of the Invention

[0005] The purpose of the present invention is to provide a photoacoustic microscopy imaging system and method based on gradient needle-shaped beam excitation, aiming to solve the problem that it is difficult for the existing technology to achieve rapid and accurate cell nucleus imaging of untreated thick tissue samples.

[0006] In a first aspect, the present invention provides a photoacoustic microscopy imaging system based on gradient needle beam excitation. The system includes a laser, a polarization adjustment system, a 4F beam expander system, a mirror, an ultraviolet optical diffraction element, a water tank, an ultrasonic transducer, a host computer, and a three-dimensional displacement platform. The water tank is used to place a sample. Both the ultrasonic transducer and the three-dimensional displacement platform are communicatively connected to the host computer, and the three-dimensional displacement platform is fixedly connected to the water tank. The laser outputs a laser beam. The polarization state of the beam is adjusted to circular polarization by the polarization adjustment system. The 4F beam expander system expands the circularly polarized beam. The expanded beam is reflected by the mirror and transmitted to the ultraviolet optical diffraction element. The expanded beam is modulated by the ultraviolet optical diffraction element to form a gradient needle beam, which is focused on the sample to generate an ultrasonic signal. The ultrasonic transducer is used to detect the ultrasonic signal and send the detected ultrasonic signal to the host computer, so that the host computer completes image reconstruction based on the received ultrasonic signal.

[0007] Further, the polarization adjustment system includes a first wave plate, a polarization beam splitter, and a second wave plate. The laser beam is adjusted by the first wave plate, the polarization beam splitter, and the second wave plate in sequence to form a circularly polarized beam.

[0008] Further, the first wave plate is a half-wave plate, and the second wave plate is a quarter-wave plate.

[0009] Further, the 4F beam expander system includes a first lens and a second lens. The circularly polarized beam is expanded by the first lens and the second lens in sequence to form an expanded beam.

[0010] Further, an incident pinhole is provided between the first lens and the second lens for spatial filtering.

[0011] Further, the working wavelength of the ultraviolet optical diffraction element is selected according to the excitation spectrum peak of the target substance in the sample.

[0012] Further, the sample is located within the focal depth range of the gradient needle beam formed by the ultraviolet optical diffraction element.

[0013] Further, the water tank is filled with a coupling medium.

[0014] Further, the coupling medium is deionized water.

[0015] In a second aspect, the present invention also provides a photoacoustic microscopy imaging method based on gradient needle beam excitation, which is applied to the photoacoustic microscopy imaging system based on gradient needle beam excitation in the first aspect. The method includes: The laser outputs a laser beam, and the polarization state of the beam is adjusted to circular polarization by the polarization adjustment system; The 4F beam expander system expands the circularly polarized beam, and the expanded beam is reflected by the mirror and transmitted to the ultraviolet optical diffraction element; The expanded beam is modulated by the ultraviolet optical diffraction element to form a gradient needle-like beam, which is focused on the sample to generate an ultrasonic signal; The ultrasonic transducer is used to detect the ultrasonic signal and send the detected ultrasonic signal to the host computer, so that the host computer completes image reconstruction based on the received ultrasonic signal.

[0016] The present invention discloses a photoacoustic microscopy imaging system and method based on the excitation of a gradient needle-like beam. The system includes a laser, a polarization adjustment system, a 4F beam expander system, a mirror, an ultraviolet optical diffraction element, a water tank, an ultrasonic transducer, a host computer, and a three-dimensional displacement platform. The water tank is used to place the sample. The ultrasonic transducer and the three-dimensional displacement platform are both communicatively connected to the host computer, and the three-dimensional displacement platform is fixedly connected to the water tank. The laser outputs a laser beam, and the polarization state of the beam is adjusted to circular polarization by the polarization adjustment system. The 4F beam expander system expands the circularly polarized beam, and the expanded beam is reflected by the mirror and transmitted to the ultraviolet optical diffraction element. The expanded beam is modulated by the ultraviolet optical diffraction element to form a gradient needle-like beam, which is focused on the sample to generate an ultrasonic signal. The ultrasonic transducer is used to detect the ultrasonic signal and send the detected ultrasonic signal to the host computer, so that the host computer completes image reconstruction based on the received ultrasonic signal. The above photoacoustic microscopy imaging system combines photoacoustic microscopy imaging technology and optical field control technology, breaks through the poor depth resolution caused by the bandwidth limitation of the ultrasonic transducer, and has the histological imaging ability of large focal depth and high depth resolution. Specifically, by manipulating the beam wavefront with an ultraviolet optical diffraction element, the amplitude of the photoacoustic signal excited by the cell nucleus is correlated with the depth position under the premise of large focal depth, and different amplitude photoacoustic signals generated by the gradient needle-like focus are decoded. While the focal depth is significantly expanded by more than ten times, the depth slicing ability is improved to ~8 µm. It can directly observe untreated thick tissue samples with uneven surfaces, and obtain slice-level depth-resolved histological images comparable to the gold standard without sectioning and labeling, providing new technical support for intraoperative pathological diagnosis. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 It is a schematic diagram of the photoacoustic microscopy imaging system provided by the embodiment of the present invention; Figure 2 It is a comparison diagram of the effects of a traditional objective depth resolution image and a large depth of focus depth resolution image; Figure 3 It is a schematic flow chart of the photoacoustic microscopy imaging method provided by the embodiment of the present invention; Among them, the reference numerals in the figure are as follows: 1. Laser; 2. First wave plate; 3. Polarizing beam splitter; 4. Second wave plate; 5. First lens; 6. Second lens; 7. Mirror; 8. Ultraviolet optical diffraction element; 9. Water tank; 10. Three-dimensional displacement platform; 11. Ultrasonic transducer; 12. Host computer; 13. Incident pinhole. Detailed implementation manners

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprise" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0021] It should also be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms.

[0022] It should be further understood that the term " / and" used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0023] Please refer to Figure 1 , Figure 1 It is a schematic diagram of the photoacoustic microscopy imaging system provided by the embodiment of the present invention. As Figure 1As shown in the figure, the present invention proposes a photoacoustic microscopy imaging system based on the excitation of a gradient needle-shaped beam. The system includes a laser 1, a polarization adjustment system, a 4F beam expander system, a mirror 7, an ultraviolet optical diffraction element 8, a water tank 9, an ultrasonic transducer 11, a host computer 12, and a three-dimensional displacement platform 10. The water tank 9 is used to place a sample. Both the ultrasonic transducer 11 and the three-dimensional displacement platform 10 are communicatively connected to the host computer 12, and the three-dimensional displacement platform 10 is fixedly connected to the water tank 9. The laser 1 outputs a laser beam, and the polarization adjustment system adjusts the polarization state of the beam to circular polarization. The 4F beam expander system expands the circularly polarized beam. The expanded beam is reflected by the mirror 7 and transmitted to the ultraviolet optical diffraction element 8. The expanded beam is modulated by the ultraviolet optical diffraction element 8 to form a gradient needle-shaped beam, which is focused on the sample to generate ultrasonic signals. The ultrasonic transducer 11 is used to detect the ultrasonic signals and send the detected ultrasonic signals to the host computer 12, so that the host computer 12 completes image reconstruction based on the received ultrasonic signals.

[0024] In this embodiment, the water tank 9 is used to place a sample. Both the ultrasonic transducer 11 and the three-dimensional displacement platform 10 are communicatively connected to the host computer 12, and the three-dimensional displacement platform 10 is fixedly connected to the water tank 9. The three-dimensional displacement platform 10 is used to drive the water tank 9 to move, and thus drive the sample to move. The present invention uses a laser 1 with a wavelength of 266 nm as the excitation light source. Its output laser beam is adjusted by the polarization adjustment system to circular polarization. The 4F beam expander system expands the circularly polarized beam. The expanded beam is reflected by the mirror 7 and transmitted to the ultraviolet optical diffraction element 8. The ultraviolet optical diffraction element 8 is used to adjust the wavefront of the expanded beam. The expanded beam is modulated by the ultraviolet optical diffraction element 8 to form a gradient needle-shaped beam, which is focused on the sample. Under the irradiation of the gradient needle-shaped beam, due to the transient thermoelastic effect and the photo-thermal effect, the sample generates ultrasonic waves at the focal point. The ultrasonic transducer 11 detects the generated ultrasonic signals and sends the detected ultrasonic signals to the host computer 12, so that the host computer 12 completes image reconstruction based on the received ultrasonic signals. The reconstructed image can reflect the specific morphology of the cell nucleus.

[0025] Preferably, the host computer 12 uses LABVIEW to control the movement of the three-dimensional displacement platform 10, thereby driving the sample to move. For thin tissue samples (~7um), a single scan in the XY axis can completely image the histological information of the sample. And because the beam is distributed in a gradient needle shape, for thick tissue samples, the depth information of the cell nucleus can be accurately obtained by capturing the difference in the amplitude of the photoacoustic signals of the cell nucleus at different depth positions.

[0026] The present invention combines photoacoustic microscopy technology and optical field modulation technology to design a photoacoustic microscopy imaging system based on gradient needle-shaped beam excitation. By using a customized ultraviolet optical diffraction element 8 to manipulate the wavefront of the excitation beam, it performs label-free and section-free histological imaging. By decoding the amplitude difference of the photoacoustic signals generated by the gradient needle-shaped focus, while significantly expanding the focal depth by more than ten times, the sectioning ability in the depth direction is increased to ~8 µm. Therefore, the present invention can obtain histological images with section-level depth resolution ability within a large focal depth range through a single scan by regulating the optical field distribution of the photoacoustic excitation beam. This method can image fresh tissue samples, realize the label-free, section-free, and accurate acquisition of nuclear information, avoid cumbersome sample preparation procedures, and obtain histological pathological images with subcellular resolution and section-level depth resolution ability within 20 minutes, providing rapid and accurate pathological diagnosis information for intraoperative margin assessment.

[0027] The present invention has been experimentally verified. The developed photoacoustic microscopy imaging system based on gradient needle-shaped beam excitation has achieved large focal depth and depth-resolved imaging on untreated thick mouse brain slice samples (with a thickness of ~3 mm). After verification by the hematoxylin and eosin (H&E) staining images of the samples, the nuclear and cytoplasmic information of the brain slices imaged by the system is well obtained and reliable. As Figure 2 shown, due to insufficient focal depth, the traditional objective lens image is defocused. The large focal depth image after optical field modulation has achieved the acquisition of complete histological images of the uneven sample surface and is highly similar to the "gold standard" H&E staining image, demonstrating the accuracy of imaging; for the depth-resolved image of the traditional objective lens, due to insufficient depth resolution, the cell nuclei at different positions cannot be accurately distinguished, and the image remains almost the same. In contrast, for the large focal depth depth-resolved image obtained based on gradient needle-shaped beam excitation, since the depth positions of the cell nuclei are accurately decoded from the photoacoustic signal amplitude, the depth resolution is improved, and the cell nuclei at different depth positions are well distinguished, realizing the non-destructive acquisition of section-level pathological information. (In (H&E) staining, hematoxylin dye binds to the DNA of the cell nucleus in the form of a nucleophilic dye, making the cell nucleus dark blue or purple; eosin dye stains the cytoplasm and extracellular matrix in the form of an acidic dye, making it pink.) Preferably, the ultrasonic transducer 11 is arranged directly above the water tank 9 to reduce the energy scattering in the sound beam propagation path.

[0028] Preferably, the present invention can also simultaneously collect images and perform depth-resolved imaging of the cell nucleus and cytoplasm by capturing synchronously excited fluorescence signals and based on confocal fluorescence imaging technology.

[0029] In one embodiment, as Figure 1As shown, the polarization adjustment system includes a first wave plate 2, a polarization beam splitter 3 and a second wave plate 4. The laser beam is adjusted by the first wave plate 2, the polarization beam splitter 3 and the second wave plate 4 in sequence to form a circularly polarized beam.

[0030] In this embodiment, the polarization adjustment system includes a first wave plate 2, a polarization beam splitter 3 and a second wave plate 4. The first wave plate 2 and the second wave plate 4 are both used to adjust the polarization state of the laser beam, so that the laser beam is adjusted by the first wave plate 2, the polarization beam splitter 3 and the second wave plate 4 in sequence to form a circularly polarized beam.

[0031] In one embodiment, if Figure 1 As shown, the first wave plate 2 is a half wave plate, and the second wave plate 4 is a quarter wave plate.

[0032] In this embodiment, the first wave plate 2 is a half wave plate, the second wave plate 4 is a quarter wave plate, and the laser beam is adjusted by the first wave plate 2, the polarization beam splitter 3 and the second wave plate 4 in sequence to form a circularly polarized beam.

[0033] In one embodiment, if Figure 1 As shown, the 4F beam expansion system includes a first lens 5 and a second lens 6. The circularly polarized light beam is expanded by the first lens 5 and the second lens 6 in sequence to form an expanded light beam.

[0034] In this embodiment, the 4F beam expansion system includes a first lens 5 and a second lens 6. The circularly polarized light beam is expanded sequentially by the first lens 5 and the second lens 6 to form an expanded light beam. By providing the first lens 5 and the second lens 6, the present invention reduces the beam divergence angle and improves the collimation.

[0035] In one embodiment, if Figure 1 As shown, an incident pinhole 13 is provided between the first lens 5 and the second lens 6 .

[0036] In this embodiment, an incident pinhole 13 is provided between the first lens 5 and the second lens 6 for spatial filtering.

[0037] In one embodiment, if Figure 1 As shown, the working wavelength of the ultraviolet optical diffraction element 8 is selected according to the excitation spectrum peak of the target substance in the sample.

[0038] In this embodiment, the ultraviolet optical diffraction element 8 is used to adjust the wavefront of the beam after beam expansion. The beam after beam expansion is modulated by the ultraviolet optical diffraction element 8 to form a gradient needle-shaped beam. The working wavelength of the ultraviolet optical diffraction element 8 is selected according to the excitation spectrum peak of the target substance in the sample. By using a customized ultraviolet optical diffraction element 8 to manipulate the beam wavefront, the present invention elongates the beam (ultraviolet photoacoustic excitation beam) axially, making the spot sizes at different axial positions remain almost the same and showing a gradient light intensity distribution along the optical axis direction. Under the irradiation of this gradient needle-shaped beam, since the cell nucleus is rich in DNA / RNA and has a strong light absorption coefficient, the amplitude of the photoacoustic signal excited is directly related to the light intensity, that is, there are differences in the amplitudes of the photoacoustic signals excited by the cell nuclei at different depth positions; because the light intensity of the gradient needle-shaped beam is distributed in a gradient manner and the light intensity at each depth is known, by correlating the light intensity with the specific depth position and quantitatively measuring the size of the photoacoustic signal, the accurate depth position information of the cell nucleus can be obtained from it. After acquisition and reconstruction, it can accurately reflect the morphology and spatial distribution of the cell nuclei in the tissue, providing a fast and reliable technical means for intraoperative pathological diagnosis.

[0039] In one embodiment, as Figure 1 shown, the sample is located within the depth of focus of the gradient needle-shaped beam formed by the ultraviolet optical diffraction element 8.

[0040] In this embodiment, the sample is placed at the bottom of the water tank 9 so that it is exactly at the focus of the ultraviolet optical diffraction element 8.

[0041] In one embodiment, as Figure 1 shown, the water tank 9 is filled with a coupling medium.

[0042] In this embodiment, the water tank 9 is filled with a coupling medium, and the coupling medium is deionized water. The system can be applied to a transmission detection scenario or a reflection detection scenario; in the transmission detection scenario (as Figure 1 shown), the sample is completely immersed in the coupling medium in the water tank, and the gradient needle-shaped beam penetrates the sample. The ultrasonic transducer 11 detects ultrasonic signals. At this time, the sound wave transmission direction and the light transmission direction are the same.

[0043] The embodiment of the present invention also provides a photoacoustic microscopy imaging method based on the excitation of a gradient needle-shaped beam. The method is applied to the above-mentioned photoacoustic microscopy imaging system based on the excitation of a gradient needle-shaped beam. As Figure 3 shown, the method includes steps S110 - S140: S110. The laser outputs a laser beam, and the polarization adjustment system adjusts the polarization state of the beam to circular polarization; S120. The 4F beam expander expands the circularly polarized light beam, and the expanded light beam is reflected by the mirror and transmitted to the ultraviolet optical diffraction element; S130. The expanded light beam is modulated by the ultraviolet optical diffraction element to form a gradient needle-shaped light beam, which is focused on the sample to generate ultrasonic signals; S140. The ultrasonic transducer is used to detect ultrasonic signals and send the detected ultrasonic signals to the host computer, so that the host computer completes image reconstruction based on the received ultrasonic signals.

[0044] In this embodiment, the laser outputs a laser beam, and the polarization adjustment system adjusts the polarization state of the light beam to circular polarization. The 4F beam expander expands the circularly polarized light beam, and the expanded light beam is reflected by the mirror and transmitted to the ultraviolet optical diffraction element. The ultraviolet optical diffraction element is used to adjust the wavefront of the expanded light beam. The expanded light beam is modulated by the ultraviolet optical diffraction element to form a gradient needle-shaped light beam, which is focused on the sample. Under the irradiation of the gradient needle-shaped light beam, due to the transient thermoelastic effect and photo-thermal effect, ultrasonic waves are generated at the focal point of the sample. The ultrasonic transducer detects the generated ultrasonic signals and sends the detected ultrasonic signals to the host computer, so that the host computer completes image reconstruction based on the received ultrasonic signals. The reconstructed image can reflect the specific morphology of the cell nucleus. By manipulating the wavefront of the light beam with the ultraviolet optical diffraction element, the present invention correlates the amplitude of the photoacoustic signal excited by the cell nucleus with the depth position under the premise of a large depth of focus, decodes the different amplitude photoacoustic signals generated by the gradient needle-shaped focal point, while significantly expanding the depth of focus by more than ten times, the depth slicing ability is improved to ~8 µm, and the untreated thick tissue sample with uneven surface can be directly observed. Under the premise of avoiding sectioning and without labeling, a section-level depth-resolved histological image comparable to the gold standard is obtained, providing new technical support for intraoperative pathological diagnosis.

[0045] The present invention discloses a photoacoustic microscopy imaging system and method based on gradient needle beam excitation. The system includes a laser, a polarization adjustment system, a 4F beam expander system, a mirror, an ultraviolet optical diffraction element, a water tank, an ultrasonic transducer, a host computer, and a three-dimensional displacement platform. The water tank is used to place a sample. Both the ultrasonic transducer and the three-dimensional displacement platform are communicatively connected to the host computer, and the three-dimensional displacement platform is fixedly connected to the water tank. The laser outputs a laser beam, and the polarization adjustment system adjusts the polarization state of the beam to circular polarization. The 4F beam expander system expands the circularly polarized beam, and the expanded beam is reflected by the mirror and transmitted to the ultraviolet optical diffraction element. The expanded beam is modulated by the ultraviolet optical diffraction element to form a gradient needle beam, which is focused on the sample to generate ultrasonic signals. The ultrasonic transducer is used to detect the ultrasonic signals and send the detected ultrasonic signals to the host computer, so that the host computer completes image reconstruction based on the received ultrasonic signals. The above-mentioned photoacoustic microscopy imaging system combines photoacoustic microscopy imaging technology and optical field control technology, breaks through the poor depth resolution caused by the bandwidth limitation of the ultrasonic transducer, and has the histological imaging ability with a large depth of focus and high depth resolution. Specifically, by manipulating the beam wavefront with an ultraviolet optical diffraction element, the amplitude of the photoacoustic signal excited by the cell nucleus is correlated with the depth position under the premise of a large depth of focus, and different amplitude photoacoustic signals generated by the gradient needle focus are decoded. While the depth of focus is significantly expanded by more than ten times, the depth slicing ability is improved to ~8 µm. It can directly observe untreated thick tissue samples with uneven surfaces and obtain slice-level depth-resolved histological images comparable to the gold standard without sectioning and labeling, providing new technical support for intraoperative pathological diagnosis.

[0046] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A photoacoustic microscopy imaging system based on the excitation of gradient needle-shaped light beams, characterized in that The system includes a laser, a polarization adjustment system, a 4F beam expander system, a mirror, an ultraviolet optical diffraction element, a water tank, an ultrasonic transducer, a host computer, and a three-dimensional displacement platform. The water tank is used to place a sample. Both the ultrasonic transducer and the three-dimensional displacement platform are communicatively connected to the host computer. The three-dimensional displacement platform is fixedly connected to the water tank; The laser outputs a laser beam. The polarization adjustment system adjusts the polarization state of the beam to circular polarization. The 4F beam expander system expands the circularly polarized beam, and the expanded beam formed is reflected by the mirror and transmitted to the ultraviolet optical diffraction element. The expanded beam is modulated by the ultraviolet optical diffraction element to form a gradient needle-shaped beam, and is focused on the sample to generate an ultrasonic signal. The ultrasonic transducer is used to detect the ultrasonic signal and send the detected ultrasonic signal to the host computer, so that the host computer completes image reconstruction based on the received ultrasonic signal.

2. The photoacoustic microscopy imaging system based on gradient needle beam excitation according to claim 1, wherein The polarization adjustment system includes a first wave plate, a polarization beam splitter, and a second wave plate. The laser beam is adjusted by the first wave plate, the polarization beam splitter, and the second wave plate in sequence to form a circularly polarized beam.

3. The photoacoustic microscopy imaging system based on gradient needle beam excitation according to claim 2, wherein The first wave plate is a half-wave plate, and the second wave plate is a quarter-wave plate.

4. The photoacoustic microscopy imaging system based on gradient needle beam excitation according to claim 1, wherein The 4F beam expander system includes a first lens and a second lens. The circularly polarized beam is expanded by the first lens and the second lens in sequence to form an expanded beam.

5. The photoacoustic microscopy imaging system based on gradient needle-shaped beam excitation according to claim 4, wherein An incident pinhole is arranged between the first lens and the second lens for spatial filtering.

6. The photoacoustic microscopy imaging system based on gradient needle-shaped beam excitation according to claim 1, wherein The operating wavelength of the ultraviolet optical diffraction element is selected according to the excitation spectrum peak value of the target substance in the sample.

7. The photoacoustic microscopy imaging system based on gradient needle-shaped beam excitation according to claim 1, wherein The sample is located within the focal depth range of the gradient needle-shaped beam formed by the ultraviolet optical diffraction element.

8. The photoacoustic microscopy imaging system based on gradient needle-shaped beam excitation according to claim 1, wherein The water tank is filled with a coupling medium.

9. The photoacoustic microscopy imaging system based on gradient needle-shaped beam excitation according to claim 8, wherein The coupling medium is deionized water.

10. A photoacoustic microscopy imaging method based on gradient needle beam excitation, which is applied to the photoacoustic microscopy imaging system based on gradient needle beam excitation described in any one of claims 1-9, and is characterized in that, The method includes: The laser outputs a laser beam. The polarization adjustment system adjusts the polarization state of the beam to circular polarization; The 4F beam expander system expands the circularly polarized beam, and the expanded beam formed is reflected by the mirror and transmitted to the ultraviolet optical diffraction element; The expanded beam is modulated by the ultraviolet optical diffraction element to form a gradient needle-shaped beam, and is focused on the sample to generate an ultrasonic signal; The ultrasonic transducer is used to detect the ultrasonic signal and send the detected ultrasonic signal to the host computer, so that the host computer completes image reconstruction based on the received ultrasonic signal.

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