Ultraviolet Photoacoustic Microscopy Imaging System with Large Depth of Focus and Imaging Method

Abstract

The present invention discloses an ultraviolet photoacoustic microscopy imaging system with a large depth of focus and an imaging method. The system includes a signal acquisition device and an imaging processing terminal. The signal acquisition device includes: an ultraviolet pulsed laser, a polarizer, a dimming glass slide, a filter, an optoacoustic lens, a moving platform, a groove, a medium, an ultrasonic transducer, an amplifier, and a data acquisition card. For the above-mentioned ultraviolet photoacoustic microscopy imaging system with a large depth of focus, circularly polarized light is obtained by modulating the photoacoustic excitation light through the polarizer and the dimming glass slide. The Gaussian beam is converted into a Bessel-like beam by the optoacoustic lens and focused on the sample. The volume expansion caused by the sample's absorption of the beam excites photoacoustic waves, which are conducted through the medium. The photoacoustic waves conducted through the medium are detected and imaged, thereby greatly expanding the optical focusing length and enabling the photoacoustic excitation light to have subcellular-level lateral resolution within a larger depth of focus range, thus greatly improving the imaging resolution of tissue pathological samples.

Description

Technical Field

[0001] The present invention relates to the technical field of optical microscopy imaging, and in particular, to an ultraviolet photoacoustic microscopy imaging system and an imaging method with a large depth of focus. Background Art

[0002] As is well known, tissue pathological examination is an important means of biomedical diagnosis. The process of conventional tissue pathological examination is mainly as follows: take a piece of diseased tissue, embed it in a paraffin block, cut it into thin slices, stain it with hematoxylin-eosin (H-E), observe it with a microscope, and finally make a pathological diagnosis. However, the time required for conventional tissue pathological examination is relatively long, usually 3-4 days, and it cannot make a diagnosis in a timely manner, etc.

[0003] Photoacoustic microscopy imaging is a booming biomedical imaging technology. Photoacoustic imaging can non-destructively observe biological tissues by detecting ultrasonic waves caused by the thermoelastic expansion after short-pulse laser irradiates biological tissues and the tissues absorb pulsed light. Due to many characteristics of photoacoustic imaging, it has the potential to be applied to tissue pathological imaging to replace the conventional method of observing hematoxylin-eosin stained tissue sections with a microscope.

[0004] Based on the rich imaging contrast mechanism of biological tissues, photoacoustic microscopy imaging is of great significance in revealing the pathological process of biological tissues. Photoacoustic imaging has many advantages compared with tissue pathological sections. First of all, in biological tissues, the acoustic scattering is more than 1000 times lower than the optical scattering, thus breaking through the limitation of optical scattering. At the same time, a photoacoustic microscope can image high-contrast biological structures from different dimensions. Moreover, different molecules absorb different wavelengths, which can reveal rich optical contrast information.

[0005] Xueding Wang et al. clearly measured the distribution of blood vessels in the mouse brain through a photoacoustic microscope, detected structures such as the intracranial cerebellum, hippocampus, and lateral ventricles of the mouse, and thus obtained image information on the parenchymal lesions of the mouse brain. Yating Wang et al. constructed a photoacoustic-ultrasonic dual-modal microscope to image the tumor-related vascular network and measure the thickness of melanoma, so as to diagnose and evaluate the in vivo detection of melanoma. However, the above-mentioned conventional photoacoustic pathological microscopy imaging technologies all have a short depth of focus and are not suitable for tissue pathological examination of thick samples, posing many challenges to clinical medical examinations.

[0006] The team from Huazhong University of Science and Technology introduced new optical imaging devices such as electro - controlled zoom lenses and imaging fiber bundles. By establishing a multi - scale photoacoustic microscopy imaging system with continuously adjustable resolution, multi - scale imaging of the blood microcirculation network was achieved. Utilizing the non - diffracting transmission characteristics and self - reconstruction properties of Bessel beams, a reflective large - depth - of - focus optical resolution photoacoustic microscopy imaging system was developed. However, this large - depth - of - focus photoacoustic imaging technology cannot operate in the ultraviolet band, so this method cannot be applied to tissue pathology detection.

[0007] To increase the optical focusing length, techniques such as using a cone prism or the Niebauer - Zernike light field modulation technique can be adopted to expand a Gaussian beam into a Bessel or Bessel - like beam, thereby increasing the optical depth of focus and improving the three - dimensional imaging quality. Although in this technical method, a digital micromirror device (DMD) or a spatial light modulator (SLM) is used for phase modulation, which can also expand the optical depth of focus. However, these devices are often difficult to be used to modulate the photoacoustic excitation beam in the ultraviolet band.

[0008] Optical - resolution photoacoustic microscopy (OR - PAM) can measure the optical absorption characteristics with micron - scale lateral resolution within biological tissues. Although photoacoustic microscopy technology has made great progress, there are still many deficiencies in this technology. Traditional photoacoustic microscopes all use Gaussian beams, and the imaging depth of focus is limited - only dozens of microns, which is difficult to meet the needs of observing thick tissue samples. For photoacoustic pathology imaging, the Gaussian beam commonly used in OR - PAM has a short depth of focus (DoF), and can only maintain micron - level lateral resolution within a limited depth range. In the defocused area, the photoacoustic imaging resolution deteriorates sharply, resulting in a serious reduction in image quality and being unable to accurately obtain the three - dimensional microscopic morphological structure characteristics of thick tissue samples, thus affecting the reliability of tissue pathology diagnosis. Therefore, the existing photoacoustic microscopy imaging technology has the problem of low imaging resolution when imaging samples. Summary of the Invention

[0009] The embodiments of the present invention provide a large - depth - of - focus ultraviolet photoacoustic microscopy imaging system and an imaging method, aiming to solve the problem of low imaging resolution existing in the existing photoacoustic microscopy imaging technology when imaging tissue pathology samples.

[0010] In a first aspect, an embodiment of the present invention provides an ultraviolet photoacoustic microscopy imaging system with a large depth of focus. The system includes a signal acquisition device and an imaging processing terminal. The signal acquisition device includes: an ultraviolet pulsed laser, a polarizer, a dimming glass slide, a filter, a photoacoustic lens, a moving platform, a groove, a medium, an ultrasonic transducer, an amplifier, and a data acquisition card. The polarizer is disposed downstream of the ultraviolet pulsed laser. The dimming glass slide is disposed downstream of the polarizer. The filter is disposed downstream of the dimming glass slide. The photoacoustic lens is disposed downstream of the filter. The groove is disposed on the moving platform to drive the groove to perform two-dimensional translation through the moving platform. A sample is placed in the groove, and the medium covers the sample. The beam output by the photoacoustic lens is focused and irradiates the sample, so that the volume expansion of the sample caused by absorbing the beam excites photoacoustic waves and conducts them through the medium. The beam output by the photoacoustic lens is a Bessel-like beam. The ultrasonic transducer is in contact with the medium to obtain the photoacoustic waves conducted by the medium through the ultrasonic transducer. The ultrasonic transducer is electrically connected to the data acquisition card through the amplifier, and the data acquisition card is electrically connected to the imaging processing terminal to output a digital photoacoustic signal to the imaging processing terminal. The imaging processing terminal processes the digital photoacoustic signals collected by the data acquisition card to obtain an imaging image of the sample.

[0011] In the ultraviolet photoacoustic microscopy imaging system with a large depth of focus, the dimming glass slide is a dimming glass slide with a phase plate.

[0012] In the ultraviolet photoacoustic microscopy imaging system with a large depth of focus, a confocal lens is disposed between the dimming glass slide and the filter. The confocal lens is composed of a first confocal lens and a second lens.

[0013] In the ultraviolet photoacoustic microscopy imaging system with a large depth of focus, the medium is physiological saline, distilled water, or deionized water.

[0014] In the ultraviolet photoacoustic microscopy imaging system with a large depth of focus, the groove is a transparent groove.

[0015] In the ultraviolet photoacoustic microscopy imaging system with a large depth of focus, the depth of the groove is 0.2 - 10 cm.

[0016] In the ultraviolet photoacoustic microscopy imaging system with a large depth of focus, the groove is a resin groove, a glass groove, or a quartz groove.

[0017] In another aspect, an embodiment of the present invention further provides a method for ultraviolet photoacoustic microscopy imaging with a large depth of focus. The method for ultraviolet photoacoustic microscopy imaging with a large depth of focus is applied to the above-mentioned ultraviolet photoacoustic microscopy imaging system with a large depth of focus. The method includes:

[0018] Control the output of the photoacoustic excitation light of the ultraviolet pulsed laser through the imaging processing terminal;

[0019] The photoacoustic excitation light is modulated into linearly polarized light by a polarizer and then modulated into circularly polarized light by a dimming glass slide; the circularly polarized light is left-handed circularly polarized light or right-handed circularly polarized light;

[0020] The circularly polarized light passes through a filter to filter out light outside the ultraviolet band and modulate the light energy to obtain a Gaussian beam;

[0021] The Gaussian beam is expanded into a Bessel-like beam by a photoacoustic lens and focused on the sample placed in the groove; the volume expansion of the sample caused by absorbing the beam excites photoacoustic waves and conducts them through the medium;

[0022] Receive the photoacoustic waves conducted by the medium through an ultrasonic transducer and output them to the amplifier for amplification to obtain an amplified signal;

[0023] The amplified signal is digitized by a data acquisition card to obtain a digitized photoacoustic signal;

[0024] The imaging processing terminal acquires the digitized photoacoustic signal and processes it to obtain the imaging image of the sample.

[0025] In the large depth-of-focus ultraviolet photoacoustic microscopy imaging method, the pulse width of the photoacoustic excitation light output by the ultraviolet pulsed laser is 10 nanoseconds to 800 nanoseconds.

[0026] In the large depth-of-focus ultraviolet photoacoustic microscopy imaging method, the wavelength of the photoacoustic excitation light output by the ultraviolet pulsed laser is 180 nanometers to 350 nanometers.

[0027] An embodiment of the present invention provides a large depth-of-focus ultraviolet photoacoustic microscopy imaging system and imaging method. The system includes a signal acquisition device and an imaging processing terminal. The signal acquisition device includes: an ultraviolet pulsed laser, a polarizer, a dimming glass slide, a filter, a photoacoustic lens, a moving platform, a groove, a medium, an ultrasonic transducer, an amplifier, and a data acquisition card. In the above large depth-of-focus ultraviolet photoacoustic microscopy imaging system, the photoacoustic excitation light is modulated into circularly polarized light through a polarizer and a dimming glass slide, the Gaussian beam is converted into a Bessel-like beam by a photoacoustic lens and focused on the sample, the volume expansion of the sample caused by absorbing the beam excites photoacoustic waves and conducts them through the medium, and the photoacoustic waves conducted through the medium are detected and imaged, thereby greatly expanding the optical focusing length, enabling the photoacoustic excitation light to have subcellular-level lateral resolution within a larger depth-of-focus range, greatly improving the resolution of imaging the sample, and thus improving the imaging quality. Description of the Drawings

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a schematic structural diagram of an ultraviolet photoacoustic microscopy imaging system with a large depth of focus provided by an embodiment of the present invention;

[0030] Figure 2 It is a schematic flow diagram of a method for ultraviolet photoacoustic microscopy imaging with a large depth of focus provided by an embodiment of the present invention;

[0031] Figure 3 It is a schematic diagram of the effect of an ultraviolet photoacoustic microscopy imaging system with a large depth of focus provided by an embodiment of the present invention;

[0032] Figure 4 It is a schematic diagram of the effect of an ultraviolet photoacoustic microscopy imaging system with a large depth of focus provided by an embodiment of the present invention;

[0033] Figure 5 It is a schematic diagram of the effect of an ultraviolet photoacoustic microscopy imaging system with a large depth of focus provided by an embodiment of the present invention;

[0034] Figure 6 It is a schematic diagram of the effect of an ultraviolet photoacoustic microscopy imaging system with a large depth of focus provided by an embodiment of the present invention. Detailed implementation manners

[0035] 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 some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0036] It should be understood that when used in this specification and the appended claims, the terms "comprises" and "comprising" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0037] 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.

[0038] It should be further understood that the term "and / or" used in the specification and appended claims of the present invention refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0039] In this embodiment, please refer to Figure 1 , Figure 1 which is a schematic structural diagram of the ultraviolet photoacoustic microscopy imaging system with a large depth of focus provided by the embodiment of the present invention. As shown in the figure, the embodiment of the present invention provides an ultraviolet photoacoustic microscopy imaging system with a large depth of focus. The system includes a signal acquisition device and an imaging processing terminal 15. The signal acquisition device includes: an ultraviolet pulsed laser 1, a polarizer 2, a dimming glass slide 3, a filter 4, an optoacoustic lens 5, a moving platform 6, a groove 7, a medium 8, an ultrasonic transducer 9, an amplifier 11, and a data acquisition card 12. The polarizer 2 is arranged downstream of the ultraviolet pulsed laser 1. The dimming glass slide 3 is arranged downstream of the polarizer 2. The filter 4 is arranged downstream of the dimming glass slide 3. The optoacoustic lens 5 is arranged downstream of the filter 4. The groove 7 is arranged on the moving platform 6 to drive the groove 7 to perform two-dimensional translation through the moving platform 6. A sample 10 is placed in the groove 7, and the medium 8 covers the sample 10. The light beam output by the optoacoustic lens 5 is focused and irradiates the sample 10, so that the volume expansion of the sample 10 caused by absorbing the light beam excites photoacoustic waves and conducts them through the medium 8. The light beam output by the optoacoustic lens 5 is a Bessel-like beam. The ultrasonic transducer 9 is in contact with the medium 8 to obtain the photoacoustic waves conducted by the medium 8 through the ultrasonic transducer 9. The ultrasonic transducer 9 is electrically connected to the data acquisition card 12 through the amplifier 11, and the data acquisition card 12 is electrically connected to the imaging processing terminal 15 to output a digital photoacoustic signal to the imaging processing terminal 15, and the imaging processing terminal 15 processes the digital photoacoustic signal to obtain an imaging image of the sample.

[0040] The above ultraviolet photoacoustic microscopy imaging system with a large depth of focus uses an ultraviolet pulsed laser 1 as a light source to output photoacoustic excitation light in the ultraviolet band. Then, the photoacoustic excitation light is modulated into linearly polarized light by a polarizer 2 and then into circularly polarized light by a dimming glass slide 3. The dimming glass slide 3 is a dimming glass slide with a phase plate, which can be a quarter-wave plate. After being modulated by the dimming glass slide 3, the left-handed circularly polarized light or right-handed circularly polarized light required for the operation of the liquid crystal can be obtained. After the circularly polarized light is reflected by a mirror, the light outside the ultraviolet band is filtered by a filter 4, and the energy of the light is modulated to obtain a Gaussian beam. Then, after being collimated by a lens 13, it is reflected by a mirror and enters a photoacoustic lens 5. The photoacoustic lens 5 is a liquid crystal phase plate, and a corresponding modulation pattern is set on the liquid crystal phase plate. The optical phase distribution of the modulation pattern on the liquid crystal phase plate can be designed based on the extended Zernike algorithm. In addition, the material of the phase plate is not limited to liquid crystal, and other materials capable of performing phase modulation can also be used. The photoacoustic lens 5 can expand the incident Gaussian beam into a Bessel-like beam, and the photoacoustic lens 5 can replace the objective lens to focus the beam and irradiate it on a sample 10. The sample is placed in a groove 7, and the groove 7 is connected to a moving platform 6. The groove 7 can be driven by the moving platform 6 to perform two-dimensional translation, so that the focused Bessel-like beam scans the sample 10 in two directions of the X-axis and Y-axis. To achieve two-dimensional scanning of the sample 10, a galvanometer can also be used instead of the moving platform 6, and the scanning speed of the sample 10 can be greatly improved by the galvanometer. The sample 10 absorbs the energy of the Bessel-like beam, causing thermal volume expansion and emitting photoacoustic waves. The photoacoustic waves generated by the sample 10 are conducted through a medium 8 and received by an ultrasonic transducer 9. The ultrasonic transducer 9 transmits the received photoacoustic waves to an amplifier 11 for amplification to obtain an amplified signal. The amplified signal is transmitted to a data acquisition card 12 for digitization and storage. Each time the data acquisition card 12 sends a clock signal to an imaging processing terminal 15, ultrasonic data is acquired once. The imaging processing terminal 15 receives the digitized photoacoustic signal and processes it to obtain an imaging image of the sample 10, thereby accurately obtaining the physiological / pathological information of the sample tissue. The imaging image can be a two-dimensional image or a three-dimensional image reconstructed based on the digitized photoacoustic signal.

[0041] In the technical method of this embodiment, in response to a series of challenges faced by tissue pathological diagnosis, a microscopic imaging system based on ultraviolet light is provided. Photoacoustic excitation with a large optical depth of focus is achieved through a photoacoustic lens, and then a new type of ultraviolet photoacoustic microscope is constructed to realize label-free and rapid pathological observation of the three-dimensional microscopic morphological structure of thick tissue samples. This new technology has many capabilities such as a large optical depth of focus, subcellular lateral resolution, and label-free observation, and can realize "microscale, section-free, and label-free" observation of tissue pathological samples, providing new technical support for clinical medical detection.

[0042] Meanwhile, the imaging processing terminal 15 can be electrically connected to the mobile platform 6 and the ultraviolet pulsed laser 1; thereby, corresponding control parameters are input into the ultraviolet pulsed laser 1 through the imaging processing terminal 15 to control the ultraviolet pulsed laser 1 to generate optoacoustic excitation light with a specific wavelength and a specific pulse width; at the same time, corresponding movement parameters can be input into the mobile platform 6 through the imaging processing terminal to drive the groove 7 to move horizontally through the mobile platform 6. The imaging processing terminal 15 can be a terminal device such as a desktop computer, a laptop computer, or a tablet computer that can be used for data and image processing.

[0043] In a more specific embodiment, a confocal lens 14 is disposed between the dimming glass sheet 3 and the filter 4, and the confocal lens 14 is composed of a first confocal lens and a second confocal lens. To improve the imaging effect, a confocal lens 14 can also be disposed between the dimming glass sheet 3 and the filter 4. The circularly polarized light (left-handed circularly polarized light or right-handed circularly polarized light) emitted from the dimming glass sheet 3 is expanded through the 4F optical system formed by the confocal lens 14, and the expanded light beam is then transmitted to the filter 4 for filtering. The expansion can make the spot diameter of the circularly polarized light larger, thereby improving the filtering effect of the filter 4. Specifically, the detection light beam output by the dimming glass sheet 3 is not limited to left-handed polarized light. In actual application, right-handed circularly polarized light can also be used, and the specific rotation direction can be based on the corresponding characteristics of the liquid crystal.

[0044] In a more specific embodiment, the medium 8 is physiological saline, distilled water, or deionized water. In actual use, distilled water is preferably used as the medium 8, and deionized water is selected as the medium 8 in the optimal embodiment.

[0045] In a more specific embodiment, the groove 7 is a transparent groove. Specifically, the depth of the groove 7 is 0.2 - 10 cm. Among them, the groove 7 is a resin groove, a glass groove, or a quartz groove. Specifically, the groove 7 can be set as a transparent groove to increase the light transmittance of the groove 7. The depth of the groove 7 can also be reasonably set according to the actual use situation. The thickness of the medium 8 should be less than the depth of the groove 7 and adjusted according to the actual situation. By reasonably setting the thickness of the medium 8, the efficiency of the ultrasonic transducer 9 for receiving optoacoustic waves can be improved.

[0046] Compared with traditional photoacoustic microscopy techniques, the signal acquisition device in the above-mentioned ultraviolet photoacoustic microscopy system with large depth of focus has the following characteristics: 1. The depth of focus of conventional photoacoustic pathological microscopy techniques is short, while the liquid crystal phase modulation based on the photoacoustic lens can achieve photoacoustic excitation with a large optical depth of focus. 2. The photoacoustic lens therein has good lateral resolution (about 0.8 micrometers) in a large depth range, and can clearly observe subcellular structures such as cell nuclei. 3. The ultraviolet photoacoustic microscopy technique with large depth of focus can perform histopathological detection on thick samples, and has the advantages of integration and miniaturization, which is conducive to its application in clinical medical diagnosis.

[0047] In the embodiments of the present invention, the Bessel-like beam in the photoacoustic lens is analyzed. Figure 3 、 Figure 4 、 Figure 5 and Figure 6 are all schematic diagrams of the effects of the ultraviolet photoacoustic microscopy system with large depth of focus provided by the embodiments of the present invention. After analysis, the amplitude, phase, and intensity distribution of the Bessel-like beam in the photoacoustic lens are as shown in Figure 3 . Figure 3 Figure (a) in it is the amplitude distribution, Figure 3 Figure (b) in it is the phase distribution, Figure 3 Figure (c) in it is the intensity distribution; after analysis, the distribution of the light field in the photoacoustic lens is as shown in Figure 4 . After analysis, the lateral distribution (X-axis direction) curve of the focused light field of the photoacoustic lens is as shown in Figure 5 , and the axial distribution (Z-axis direction) curve of the focused light field of the photoacoustic lens is as shown in Figure 6 . Through the phase distribution of the photoacoustic lens, we can calculate the light field distribution of the beam, as shown in Figure 4 . Then, taking the lateral and axial cross-sections of the light field distribution respectively, as shown in Figure 5 and Figure 6 . Through Figure 5 and Figure 6 , it can be known that the photoacoustic lens stretches the beam into a Bessel-like beam with a lateral resolution of 0.85 μm, breaking through the diffraction limit, and the axial length is about 300 μm, which is 5-6 times that of a Gaussian beam, greatly improving the quality of the beam, thereby significantly improving the imaging resolution.

[0048] Please refer to Figure 2 . Figure 2 is a schematic flowchart of the method for the ultraviolet photoacoustic microscopy method with large depth of focus provided by the embodiments of the present invention. The embodiments of the present invention also provide a method for ultraviolet photoacoustic microscopy with large depth of focus. Among them, the method for ultraviolet photoacoustic microscopy with large depth of focus is applied to the above-mentioned ultraviolet photoacoustic microscopy system with large depth of focus, as shown in Figure 2 , and the method includes steps S110 - S170.

[0049] S110. Control the output of the photoacoustic excitation light of the ultraviolet pulsed laser through the imaging processing terminal;

[0050] Specifically, in this embodiment, the imaging processing terminal can be used to control the ultraviolet pulsed laser to output photoacoustic excitation light with a wavelength in the ultraviolet light band, where the wavelength of the photoacoustic excitation light is 180 nanometers to 350 nanometers. The imaging processing terminal can also be used to control the pulse width of the ultraviolet pulsed laser. For example, it can control the ultraviolet pulsed laser to generate photoacoustic excitation light with a nanosecond-level pulse width, such as the pulse width of the photoacoustic excitation light is 10 nanoseconds to 800 nanoseconds. For different tissue samples, photoacoustic excitation light with different wavelengths and different pulse widths can be used for imaging. For example, for a certain specific tissue sample, photoacoustic excitation light with a wavelength of 266 nm and a pulse width of 200 ns (nanoseconds) can be used. For different samples, the wavelength can be changed to maximize the absorption coefficient of the sample and generate the strongest photoacoustic signal.

[0051] S120. Modulate the photoacoustic excitation light into linearly polarized light through a polarizer and then into circularly polarized light through a dimming glass slide; the circularly polarized light is left-handed circularly polarized light or right-handed circularly polarized light.

[0052] The light beam output after being modulated by the dimming glass slide can be left-handed circularly polarized light or right-handed circularly polarized light, which depends on the liquid crystal characteristics of the liquid crystal phase plate configured on the dimming glass slide in the specific application process.

[0053] S130. Filter out the light outside the ultraviolet band through a filter and modulate the light energy of the circularly polarized light to obtain a Gaussian beam.

[0054] S140. Expand the Gaussian beam into a Bessel-like beam through a photoacoustic lens and focus it on the sample placed in the groove; the volume expansion of the sample caused by absorbing the light beam excites photoacoustic waves and conducts them through the medium.

[0055] Specifically, the medium can be selected from any one of normal saline, distilled water or deionized water.

[0056] S150. Receive the photoacoustic waves conducted by the medium through an ultrasonic transducer and output them to the amplifier for amplification to obtain an amplified signal.

[0057] S160. Digitize the amplified signal through a data acquisition card to obtain a digitized photoacoustic signal.

[0058] S170. The imaging processing terminal acquires the digitized photoacoustic signal and processes it to obtain the imaging image of the sample.

[0059] The ultraviolet photoacoustic microscopy imaging method with large depth of focus in this embodiment is applicable to constructing an ultraviolet photoacoustic microscopy imaging system by using a photoacoustic lens modulated in the ultraviolet band. Through this technical method, the technical bottleneck that digital micromirror devices (DMD) or spatial light modulator (SLM) cannot work in this band is overcome. The photoacoustic lens in the above imaging system modulates a Gaussian beam into a Bessel-like beam, realizing focusing with a large optical depth of focus and having subcellular-level lateral resolution within a larger depth range. Facing the major demand of tissue pathology photoacoustic imaging in clinical medicine, a large-depth-of-focus ultraviolet photoacoustic microscope is constructed, making the imaging device miniaturized and simplified, thus providing a new technical means suitable for "label-free and section-free" pathological observation of thick tissue samples. The large-depth-of-focus ultraviolet photoacoustic microscopy imaging system constructed based on the above technical method is suitable for observing thick tissue samples, can excite photoacoustic signals of tissues at a larger depth, while ensuring subcellular-level lateral resolution, and realizes "label-free and section-free" imaging of the three-dimensional microscopic structure of tissue samples.

[0060] In the embodiment of the present invention, there is provided a large-depth-of-focus ultraviolet photoacoustic microscopy imaging system and an imaging method. The system includes a signal acquisition device and an imaging processing terminal. The signal acquisition device includes: an ultraviolet pulsed laser, a polarizer, a dimming glass slide, a filter, a photoacoustic lens, a moving platform, a groove, a medium, an ultrasonic transducer, an amplifier, and a data acquisition card. In the above large-depth-of-focus ultraviolet photoacoustic microscopy imaging system, circularly polarized light is obtained by modulating the photoacoustic excitation light through the polarizer and the dimming glass slide. The Gaussian beam is converted into a Bessel-like beam by the photoacoustic lens and focused on the sample. The volume expansion of the sample caused by absorbing the beam excites photoacoustic waves, which are conducted through the medium. The photoacoustic waves conducted through the medium are detected and imaged, thereby greatly expanding the optical focusing length, enabling the photoacoustic excitation light to have subcellular-level lateral resolution within a larger depth of focus, greatly improving the resolution of imaging the sample, and thus improving the imaging quality.

[0061] As mentioned above, the above is only the specific implementation manner 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 shall be subject to the protection scope of the claims.

Claims

1. An ultraviolet photoacoustic microscopy imaging system with a large depth of focus, characterized in that The system includes a signal acquisition device and an imaging processing terminal. The signal acquisition device includes: an ultraviolet pulsed laser, a polarizer, a dimming glass slide, a filter, an optoacoustic lens, a moving platform, a groove, a medium, an ultrasonic transducer, an amplifier, and a data acquisition card; The polarizer is arranged downstream of the ultraviolet pulsed laser, the dimming glass slide is arranged downstream of the polarizer, the filter is arranged downstream of the dimming glass slide, and the optoacoustic lens is arranged downstream of the filter; The groove is arranged on the moving platform to drive the groove to perform two-dimensional translation through the moving platform; a sample is placed in the groove, and the medium covers the sample; The light beam output by the optoacoustic lens is focused and irradiated on the sample, so that the volume expansion of the sample caused by absorbing the light beam excites an optoacoustic wave and conducts it through the medium; the light beam output by the optoacoustic lens is a Bessel-like beam; The ultrasonic transducer is in contact with the medium to obtain the optoacoustic wave conducted by the medium through the ultrasonic transducer; The ultrasonic transducer is electrically connected to the data acquisition card through the amplifier, and the data acquisition card is electrically connected to the imaging processing terminal to output a digital optoacoustic signal to the imaging processing terminal, and the imaging processing terminal processes the digital optoacoustic signal collected by the data acquisition card to obtain an imaging image of the sample.

2. The ultraviolet photoacoustic microscopy imaging system with a large depth of focus according to claim 1, characterized in that, The dimming glass slide is a dimming glass slide with a phase plate.

3. The ultraviolet photoacoustic microscopy imaging system with a large depth of focus according to claim 1 or 2, characterized in that, A confocal lens is arranged between the dimming glass slide and the filter, and the confocal lens is composed of a first lens and a second lens that are confocal.

4. The ultraviolet photoacoustic microscopy imaging system with a large depth of focus according to claim 1, wherein The medium is normal saline, distilled water or deionized water.

5. The ultraviolet photoacoustic microscopy imaging system with a large depth of focus according to claim 1, characterized in that, The groove is a transparent groove.

6. The ultraviolet photoacoustic microscopy imaging system with a large depth of focus according to claim 5, wherein The depth of the groove is 0.2 - 10 cm.

7. The ultraviolet photoacoustic microscopy imaging system with a large depth of focus according to claim 5 or 6, characterized in that, The groove is a resin groove, a glass groove or a quartz groove.

8. An ultraviolet photoacoustic microscopy imaging method with a large depth of focus, characterized in that, The ultraviolet optoacoustic microscopy imaging method with large depth of focus is applied to the ultraviolet optoacoustic microscopy imaging system according to any one of claims 1 - 7. The method includes: Controlling the ultraviolet pulsed laser to output optoacoustic excitation light through the imaging processing terminal; The optoacoustic excitation light is modulated into linearly polarized light by the polarizer and modulated into circularly polarized light by the dimming glass slide; the circularly polarized light is left-handed circularly polarized light or right-handed circularly polarized light; The circularly polarized light passes through the filter to filter out light outside the ultraviolet band and modulate the light energy to obtain a Gaussian beam; The Gaussian beam is expanded into a Bessel-like beam by the optoacoustic lens and focused and irradiated on the sample placed in the groove; the volume expansion of the sample caused by absorbing the light beam excites an optoacoustic wave and conducts it through the medium; Receiving the optoacoustic wave conducted by the medium through the ultrasonic transducer and outputting it to the amplifier for amplification to obtain an amplified signal; The amplified signal is digitized by the data acquisition card to obtain a digital optoacoustic signal; The imaging processing terminal acquires the digital optoacoustic signal and processes it to obtain an imaging image of the sample.

9. The method for ultraviolet photoacoustic microscopy imaging with a large depth of focus according to claim 8, wherein The pulse width of the optoacoustic excitation light output by the ultraviolet pulsed laser is 10 nanoseconds to 800 nanoseconds.

10. The ultraviolet photoacoustic microscopy imaging method with a large depth of focus according to claim 8, characterized in that, The wavelength of the optoacoustic excitation light output by the ultraviolet pulsed laser is 180 nanometers to 350 nanometers.

Images