Photoacoustic microscopy imaging device and imaging method based on photoacoustic confocal multi-depth convergence

Abstract

This invention discloses a photoacoustic microscopy imaging device and method based on photoacoustic confocal multi-depth convergence. The imaging device includes a laser emission module, a photoacoustic confocal multi-depth configuration module, and a system control and signal processing module. The photoacoustic confocal multi-depth configuration module enables the laser beam emitted from the laser emission module to form multiple optical focal points at different depths on the biological sample, exciting multi-source photoacoustic signals. The combination structure of the hollow transducer and the photoacoustic coupler allows all multiple photoacoustic signals to achieve photoacoustic confocalization, improving detection sensitivity and imaging signal-to-noise ratio. Furthermore, the device is compact, flexible in operation, and enhances its practicality in related fields. Multiple signals are independently reconstructed for imaging, and after focal information extraction and fusion, high-resolution and high-contrast imaging results are obtained, which can improve the depth of field of photoacoustic imaging and achieve high-sensitivity, uniform, and high-resolution imaging over a large depth range.

Description

Technical Field

[0001] This invention relates to the field of photoacoustic imaging technology and devices, specifically to a photoacoustic microscopy imaging device and imaging method based on photoacoustic confocal multi-depth convergence. Background Technology

[0002] Photoacoustic imaging combines the high contrast of optical imaging with the deep penetration of ultrasound imaging, enabling high-resolution, high-contrast imaging of deep tissues in living organisms. It can provide detailed information about the structure and function of biological tissues and shows great promise in the field of biomedical imaging.

[0003] The design of an optical imaging system mainly includes two parts: ultrasonic probe design and optical system design. The ultrasonic probe is typically optimized for a specific depth of focus, achieving the highest spatial resolution and signal-to-noise ratio (SNR) at the acoustic focal point. Outside the focal point, the ultrasonic beam spreads, causing a sharp decrease in both spatial resolution and SNR. In the optical system design, the size of the laser focusing spot also affects the imaging resolution. Smaller spot sizes result in higher resolution photoacoustic imaging, and coinciding with the acoustic focal point further improves detection sensitivity and SNR. Therefore, high-resolution photoacoustic imaging requires a high degree of flatness on the imaging surface.

[0004] However, when imaging actual biological samples, such as the mouse cerebral cortex, the imaging plane requires a certain height difference. A single grating scan cannot achieve focused imaging of structures at different heights, resulting in low imaging resolution. To address this issue, several rapid focusing and extended depth-of-focus imaging systems have been proposed. Patent application CN201810927962.X discloses a rapid focusing system and method for photoacoustic microscopy. This invention utilizes the sample signal position and image sharpness reflected in the photoacoustic B-mode scan image to continuously and automatically adjust the distance between the sample and the ultrasonic probe, achieving automatic and rapid adjustment of the sample onto the focal plane of the laser beam. However, its drawbacks include the need for iterative searching for the optimal focusing position, complex calculations, and slow imaging speed. Patent application CN202210694584.1 discloses a photoacoustic microscopy imaging system based on a high-speed focuser. This invention controls the displacement of a cemented doublet lens by moving a fast linear motor, thereby adjusting the focal position of the light beam and improving the signal-to-noise ratio and resolution of the image. However, a drawback is that it does not consider photoacoustic confocalization, which leads to a decrease in detection sensitivity when adjusting the focal position of the light beam. Patent application CN201910048137.7 discloses a photoacoustic endoscope device and imaging method based on Bessel optical extension of depth of focus. It can achieve high and uniform image resolution and contrast within a certain range, while improving detection sensitivity. However, a drawback is that artifacts generated by side lobes affect the resolution and the length of the depth of focus extension is limited. Summary of the Invention

[0005] The main objective of this invention is to overcome at least one of the shortcomings and deficiencies of existing technologies by proposing a photoacoustic microscopy imaging device based on photoacoustic confocal multi-depth convergence. This invention forms multiple photoacoustic confocal planes along the depth direction through a multi-channel configuration, eliminating the need for repeated adjustments to the focal plane position during the imaging process and thus eliminating positioning errors. When applied to the field of microscopic imaging of biological samples, it can maintain high-speed, high-resolution imaging within a certain depth range, resulting in more uniform image resolution and a higher signal-to-noise ratio.

[0006] Another objective of this invention is to provide an imaging method using the aforementioned photoacoustic microscopy device. This invention is the first to apply photoacoustic confocal multi-depth aggregation to the field of photoacoustic microscopy. By extracting and fusing focal information from imaging results on different focal planes, high-resolution and efficient photoacoustic microscopy is achieved. Especially when performing microscopic imaging on non-planar biological samples, it can maintain uniform high resolution over a large depth range and has a high imaging signal-to-noise ratio.

[0007] To achieve the aforementioned primary objective, the present invention employs the following technical solution:

[0008] A photoacoustic microscopy imaging device based on photoacoustic confocal multi-depth convergence includes a laser emission module, a photoacoustic confocal multi-depth configuration module, and a system control and signal processing module;

[0009] The laser emitting module is used to generate multiple beams with different time delays;

[0010] The photoacoustic confocal multi-depth configuration module is used to convert the multi-beam into a multi-coaxial beam, forming multiple light focal points in the depth direction for illuminating the sample under test and generating multi-source photoacoustic signals.

[0011] Multi-source photoacoustic signals are transmitted to the system control and signal processing module for data processing, image reconstruction, and focus information extraction and fusion imaging. The system control and signal processing module is also responsible for controlling the laser triggering in the laser emission module.

[0012] Preferably, the laser emitting module includes a pulsed laser, a neutral density filter, an optical fiber coupler, and an optical fiber bundle arranged sequentially. The optical fiber bundle includes multiple optical fibers for outputting multiple beams with different time delays. During operation, the laser light is emitted from the pulsed laser, passes through the neutral density filter, and enters the optical fiber coupler. The neutral density filter is used to adjust the light intensity (the rotation axis of the filter is perpendicular to the optical path direction and is securely installed; the light intensity is adjusted by rotating the filter). One end of the optical fiber bundle is connected to the optical fiber coupler, which is used to adjust the output energy ratio of the optical fiber bundle. The other end is fixed at different height positions, outputting multiple beams.

[0013] Preferably, the pulsed laser outputs a laser with a wavelength of 532nm.

[0014] Preferably, the fiber bundle includes three optical fibers, and the fiber coupler adjusts the output energy of the three optical fibers in the fiber bundle proportionally, with the energy ratio of the fiber bundle being 37%:31%:32%.

[0015] Preferably, the system control and signal processing module includes an amplifier, a low-pass filter, and a host computer arranged sequentially. The signal received from the photoacoustic confocal multi-depth configuration module is input to the system control and signal processing module via the amplifier. The host computer is also used to control the pulsed laser. The received signal is amplified by the amplifier, filtered by the low-pass filter, and then stored in the host computer. The host computer performs signal processing, fusing the image through image reconstruction and focus information extraction to form an image.

[0016] Preferably, the fiber bundle includes n optical fibers for outputting n beams with different time delays;

[0017] The photoacoustic confocal multi-depth configuration module includes a reflecting prism, n cemented doublet lenses, n-1 cubic beam splitters, and a multi-channel photoacoustic signal receiver. The reflecting prism, n-1 cubic beam splitters, and multi-channel photoacoustic signal receiver are arranged sequentially, and the reflecting prism, n-1 cubic beam splitters, and n cemented doublet lenses are arranged one-to-one with each other. The output ends of the n optical fibers are arranged one-to-one with the n cemented doublet lenses.

[0018] Preferably, the multi-channel photoacoustic signal receiver includes a focusing lens, a prism group, a planar transducer, an acoustic lens, and n-1 hollow transducers. The focusing lens is located on the side wall of the prism group, the planar transducer is located on the top of the prism group, the bottom surface of the acoustic lens is curved, and the acoustic lens and n-1 hollow transducers are located below the prism group. The n-1 hollow transducers are nested together, and the acoustic lens is nested in the innermost hollow transducer.

[0019] Preferably, the multi-channel photoacoustic signal receiver further includes a linear displacement stage for adjusting the position of the multi-channel photoacoustic signal receiver.

[0020] Preferably, the system control and signal processing module is also responsible for controlling the laser trigger and the movement of the linear displacement stage in the laser emission module.

[0021] Preferably, the linear displacement stage includes three single-axis stepper motors and adopts open-loop control.

[0022] Preferably, the hollow transducer includes a hollow cylindrical backing layer and an annular high-frequency piezoelectric element, the annular high-frequency piezoelectric element being fitted onto the concave surface at the bottom of the hollow cylindrical backing layer.

[0023] Preferably, the hollow cylindrical backing layer is made of epoxy resin material, and the annular high-frequency piezoelectric element is made of PVDF material to focus and receive photoacoustic signals.

[0024] Preferably, the planar transducer is made of piezoelectric ceramic material and is bonded to the prism assembly with epoxy resin to receive photoacoustic signals passing through the acoustic lens.

[0025] Preferably, the fiber bundle includes three optical fibers. The photoacoustic confocal multi-depth configuration module is equipped with three cemented doublet lenses, defined as a first cemented doublet lens, a second cemented doublet lens, and a third cemented doublet lens, and two cubic beam splitters, defined as a first cubic beam splitter and a second cubic beam splitter. The multi-channel photoacoustic signal receiver is equipped with two hollow transducers, defined as a first hollow transducer and a second hollow transducer. The first beam of light exits from the optical fiber, passes through the first cemented doublet lens, is reflected by a reflecting prism, and then passes through the first and second cubic beam splitters to form a first coaxial beam. The second beam of light exits from the optical fiber... After entering the second cemented doublet lens, the third beam of light passes through the first and second cubic beam splitters to form a second coaxial beam. The third beam emerges from the optical fiber and enters the third cemented doublet lens, passing through the second cubic beam splitter to form a third coaxial beam. These three coaxial beams then pass through a focusing lens, a prism group, and an acoustic lens to form three focal points at different depths, illuminating the sample and generating photoacoustic signals. An acoustic lens is nested within a first hollow transducer, which in turn is nested within a second hollow transducer. The acoustic lens, the first hollow transducer, and the second hollow transducer focus on the three different focal points, achieving photoacoustic confocal focusing. The first and second hollow transducers focus and receive the photoacoustic signals, while the planar transducer uses the acoustic lens to receive the signals. After being received by the corresponding transducers, the photoacoustic signals are converted into three electrical signals.

[0026] Preferably, the reflecting prism is treated with a silver coating, and the average reflectivity is greater than 97%; the beam splitting ratio of the first cubic beam splitter is 50%:50%; and the beam splitting ratio of the second cubic beam splitter is 70%:30%.

[0027] Preferably, the prism assembly includes two prisms bonded together with UV-curable adhesive, wherein the lower prism is treated with an aluminum coating, and the acoustic lens, the first hollow transducer and the second hollow transducer are fixed to the prism assembly with epoxy resin.

[0028] Preferably, the radius of the arc surface of the acoustic lens is determined by the formula R = f(c g -c w ) / c g Sure.

[0029] Preferably, the host computer also controls the pulsed laser to emit laser pulses, collects data, and controls the movement of the linear displacement stage.

[0030] To achieve the second objective mentioned above, the present invention adopts the following technical solution:

[0031] The photoacoustic microscopy imaging method based on photoacoustic confocal multi-depth convergence includes the following steps:

[0032] A photoacoustic microscopy imaging method based on photoacoustic confocal multi-depth convergence, the method comprising the following steps:

[0033] Excitation: Multiple beams with different time delays are generated through the laser emission module;

[0034] Multiple beams enter the photoacoustic confocal multi-depth configuration module to form light focal points at different depths, which illuminate the sample under test and excite multi-source photoacoustic signals.

[0035] Data acquisition: The multi-source photoacoustic signal generated by the sample under test is detected by the hollow transducer and the planar transducer. The received photoacoustic signal is converted into multiple electrical signals for transmission, and after amplification and filtering, it is stored in the host computer.

[0036] Image reconstruction: The host computer performs individual reconstruction processing on the acquired multiple electrical signals, extracts and fuses the focus information of the multiple photoacoustic images obtained from the processing, and completes the high-resolution reconstruction of the photoacoustic images.

[0037] Preferably, the host computer emits laser pulses, collects data, and controls the movement of the linear displacement stage, using the movement of the linear displacement stage to achieve grating scanning and acquire full-area photoacoustic data.

[0038] Preferably, the step of extracting and fusing focus information from the multiple photoacoustic images obtained through processing includes:

[0039] Multiple photoacoustic images are converted into matrix data, and the focus information of the images is extracted;

[0040] Weighting of the winner-take-all strategy is performed based on the focus information of the image.

[0041] High-resolution and high-contrast photoacoustic images are obtained by weighted superposition and fusion.

[0042] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0043] (1) The present invention adopts photoacoustic confocal multi-depth aggregation method, which performs photoacoustic imaging with depth extension through multiple photoacoustic confoci in the depth direction. It can complete uniform high-resolution imaging over a large range in the depth direction without knowing the height change information of biological structures, and the imaging signal-to-noise ratio is high.

[0044] (2) The present invention adopts a multi-focus information extraction, fusion and reconstruction method, which has fast processing speed and high accuracy, and realizes high-speed and high-sensitivity detection.

[0045] (3) The photoacoustic microscopy imaging device provided by the present invention has a simple and compact structure, small size, flexible operation, no need to repeatedly adjust the focusing position, and high positioning accuracy. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the structure of the photoacoustic microscopy imaging device provided in an embodiment of the present invention;

[0047] Figure 2 This is a schematic diagram of the nested structure of the hollow transducer in an embodiment of the present invention;

[0048] Figure 3 This is a schematic diagram of the multi-focal information extraction, fusion, and reconstruction method in an embodiment of the present invention;

[0049] The system comprises: 1-Laser emitting module; 101-Pulsed laser; 102-Neutral density filter; 103-Fiber optic coupler; 104-Fiber optic bundle; 2-Photoacoustic confocal multi-depth configuration module; 201-First cemented doublet lens; 202-Second cemented doublet lens; 203-Third cemented doublet lens; 204-Reflecting prism; 205-First cubic beam splitter; 206-Second cubic beam splitter; 207-Focusing lens; 208-Prism group; 209-Acoustic lens; 210-Water tank; 211-First hollow transducer; 212-Second hollow transducer; 213-Planar transducer; 214-Linear displacement stage; 3-System control and signal processing module; 301-Amplifier; 302-Low-pass filter; 303-Host computer. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in further detail below with reference to the embodiments and accompanying drawings.

[0051] like Figure 1As shown, the present invention provides a photoacoustic microscopy imaging device based on photoacoustic confocal multi-depth aggregation, including a laser emission module 1, a photoacoustic confocal multi-depth configuration module 2, and a system control and signal processing module 3.

[0052] The laser emitting module 1 generates the multiple beams required by the system. After exiting the optical fiber, the multiple beams enter the photoacoustic confocal multi-depth configuration module 2. After passing through the focusing lens group and the reflecting prism or cube beam splitter, the multiple beams become multiple coaxial beams, forming multiple optical focal points in the depth direction to illuminate the sample under test and generate multi-source photoacoustic signals. The multi-channel photoacoustic signal receiver in the photoacoustic confocal multi-depth configuration module 2 achieves photoacoustic signal reception with high detection sensitivity through photoacoustic confocal configuration. The multi-channel photoacoustic signals (multi-source photoacoustic signals) are transmitted to the system control and signal processing module 3 for data processing, image reconstruction, and focal information extraction and fusion imaging. The system control and signal processing module 3 is also responsible for controlling the laser trigger in the laser emitting module 1 and the movement of the linear displacement stage in the photoacoustic confocal multi-depth configuration module 2.

[0053] The system control and signal processing module 3 includes an amplifier 301, a low-pass filter 302, and a host computer 303. The laser emission module 1 includes a pulsed laser 101, a neutral density filter 102, an optical fiber coupler 103, and an optical fiber bundle 104 arranged sequentially. Laser light is emitted from the pulsed laser 101, passes through the neutral density filter 102, and enters the optical fiber coupler 103. Multiple beams with different time delays are output through the optical fiber bundle 104 and enter the photoacoustic confocal multi-depth configuration module 2. The host computer 303 is connected to the pulsed laser 101. In one embodiment of the invention, the host computer 303 can control parameters such as the repetition frequency, output power, and wavelength of the pulsed laser 101. The output laser light undergoes intensity attenuation adjustment through the neutral density filter 102, enters the optical fiber coupler 103, and then enters the optical fiber bundle 104. The other ends of the optical fiber bundle 104 are fixed at different heights, and the length of each optical fiber in the bundle 104 is different, thereby outputting multiple beams with different time delays.

[0054] In one embodiment of the invention, the number of optical fibers in the fiber bundle 104 is three, meaning that three beams with different time delays are output through the fiber bundle 104. The following description is based on the output of three beams. It is understood that in other embodiments, the number of optical fibers in the fiber bundle 104 may be set to other values.

[0055] The photoacoustic confocal multi-depth configuration module 2 includes a first cemented doublet lens 201, a second cemented doublet lens 202, a third cemented doublet lens 203, a reflecting prism 204, a first cubic beam splitter 205, a second cubic beam splitter 206, and a multi-channel photoacoustic signal receiver. The reflecting prism 204, the first cubic beam splitter 205, the second cubic beam splitter 206, and the multi-channel photoacoustic signal receiver are arranged sequentially. The first cemented doublet lens 201 is positioned opposite to the reflecting prism 204, the second cemented doublet lens 202 is positioned opposite to the first cubic beam splitter 205, and the third cemented doublet lens 203 is positioned opposite to the second cubic beam splitter 206. The multi-channel photoacoustic signal receiver includes a planar transducer 213, a focusing lens 207, a prism group 208, an acoustic lens 209, and a first... The prism group 208 includes a hollow transducer 211, a second hollow transducer 212, and a linear displacement stage 214. A focusing lens 207 is located on the side wall of the prism group 208 and opposite to the second cubic beam splitter 206. A planar transducer 213 is located at the top of the prism group 208. An acoustic lens 209, a first hollow transducer 211, and a second hollow transducer 212 are located at the bottom of the prism group 208. The acoustic lens 209 is nested in the first hollow transducer 211, and the first hollow transducer 211 is nested in the second hollow transducer 212. The focusing positions of the acoustic lens 209, the first hollow transducer 211, and the second hollow transducer 212 coincide with the optical focal points at three different depths formed by the multi-beam array, achieving photoacoustic confocality. The linear displacement stage 214 is used to move the multi-channel photoacoustic signal receiver.

[0056] During operation, the first beam of light output from the fiber bundle 104 exits the fiber and passes through the first cemented doublet lens 201, is reflected by the reflecting prism 204, and then passes through the first cubic beam splitter 205 and the second cubic beam splitter 206 in sequence to form the first coaxial beam. The second beam of light exits the fiber and enters the second cemented doublet lens 202, and then passes through the first cubic beam splitter 205 and the second cubic beam splitter 206 in sequence to form the second coaxial beam. The third beam of light exits the fiber and enters the third cemented doublet lens 203, and then passes through the second cubic beam splitter 206 to form the third coaxial beam. Finally, the three coaxial beams pass through the focusing lens 207, the prism group 208, and the acoustic lens 209 in sequence to form three optical focal points (because the distance between the exit position of each beam of light and the height of the cemented doublet lens is different, the three optical focal points are located at different depths) and illuminate the sample under test, causing it to generate photoacoustic signals.

[0057] The optical focal point formed by the beam of the first cemented doublet lens 201 coincides with the focal position of the acoustic lens 209, the optical focal point formed by the beam of the second cemented doublet lens 202 coincides with the focal position of the first hollow transducer 211, and the optical focal point formed by the beam of the third cemented doublet lens 203 coincides with the focal position of the second hollow transducer 212, thereby achieving photoacoustic confocality and improving detection sensitivity.

[0058] In other embodiments, when the number of optical fibers in the fiber bundle 104 is other than the required number, it is necessary to adjust the number of optical fibers in the fiber bundle to match the required number of optical focal points. Accordingly, cubic beam splitters are added and the splitting ratio of each beam splitter is adjusted. The number of nested hollow transducers is also increased accordingly to ensure photoacoustic confocality at all times. For example, assuming the number of optical fibers in the fiber bundle 104 is n, the number of cemented doublet lenses is n, the number of cubic beam splitters is n-1, the number of hollow transducers is n-1, the reflecting prism and n-1 beam splitters are arranged sequentially, and the reflecting prism and n-1 beam splitters are arranged one-to-one with the corresponding cemented doublet lenses.

[0059] In one embodiment of the present invention, the energy ratio of the fiber bundle 104 is 37%:31%:32%, the reflecting prism 204 is treated with silver coating and has an average reflectivity greater than 97%, the splitting ratio of the first cubic beam splitter 205 is 50%:50%, and the splitting ratio of the second cubic beam splitter 206 is 70%:30%, thereby ensuring that the laser energy used to excite multi-source photoacoustic signals is basically consistent.

[0060] The first hollow transducer 211 and the second hollow transducer 212 directly focus on the received photoacoustic signal. The planar transducer 213 uses an acoustic lens 209 to focus and receive the photoacoustic signal. After being received by different transducers, the photoacoustic signal is converted into three electrical signals. These signals are then processed by an amplifier 301 and a low-pass filter 302 before being stored in a host computer 303. In one embodiment of the invention, the amplifier 301 amplifies the signal by 48dB, the cutoff frequency of the low-pass filter 302 is 70MHz, and the host computer 303 acquires the signal at a frequency of 200MHz with a sampling precision of 14 bits. The host computer 303 simultaneously controls a linear displacement stage to perform scanning motion. After the entire imaging area is scanned, signal processing and image reconstruction are performed in the host computer 303. The trigger signal for data acquisition is sent by the host computer 303.

[0061] Please see Figure 2In one embodiment of the present invention, the first hollow transducer 211 and the second hollow transducer 212 both include a hollow cylindrical backing layer 2111 and an annular high-frequency piezoelectric element 2112, with the annular high-frequency piezoelectric element 2112 attached to the concave surface at the bottom of the hollow cylindrical backing layer 2111. An acoustic lens 209 is nested in the central hole of a first hollow transducer 211, and the first hollow transducer 211 is nested in the central hole of a second hollow transducer 212. The bottom surface of the acoustic lens 209 is arc-shaped, and the upper surfaces of the acoustic lens 209, the first hollow transducer 211, and the second hollow transducer 212 are flush. The upper surfaces of the acoustic lens 209, the first hollow transducer 211, and the second hollow transducer 212 are fixedly connected to the prism assembly 208 with epoxy resin. The planar transducer 213 is bonded to the top of the prism assembly 208 with epoxy resin to receive photoacoustic signals passing through the acoustic lens 209. The focusing lens 207 is located on the side wall of the prism assembly 208.

[0062] In some embodiments of the present invention, the focal length of the acoustic lens 209 is 5.54 mm, the focal length of the first hollow transducer 211 is 5.79 mm, the focal length of the second hollow transducer 212 is 6.04 mm, the hollow cylindrical backing layer is made of epoxy resin, the annular high-frequency piezoelectric element is made of PVDF, and the planar transducer 213 is made of piezoelectric ceramic. The radius of curvature of the acoustic lens 209 is determined by the formula R = f(c g -c w ) / c g Let f be the focal length of the acoustic lens, and c be the focal length of the lens. g Let c be the sound velocity of the acoustic lens material. w The velocity of sound is the speed of sound in the coupling material.

[0063] In one embodiment of the present invention, the prism assembly 208 is obtained by bonding the inclined surfaces of two prisms together.

[0064] In one embodiment of the present invention, a photoacoustic microscopy imaging method based on photoacoustic confocal multi-depth aggregation is also provided, comprising the following steps:

[0065] (1) Fix the biological sample in the water tank 210, start the photoacoustic confocal multi-depth polymerization photoacoustic microscopy imaging device, and the pulse laser 101 emits a short pulse laser of 532nm to form three light focal points in the depth direction of the biological sample.

[0066] (2) The host computer 303 controls the linear displacement stage to perform grating scanning. The photoacoustic signal generated by the excitation is received by two hollow transducers and a planar transducer and converted into three electrical signals. Then, the signal is transmitted to the amplifier 301 and the filter 302 through the acquisition signal line. After the signal is amplified and filtered, it is transmitted to the host computer 301 for storage and processing.

[0067] (3) The host computer 303 independently programs and reconstructs the three signals, and uses existing photoacoustic signal processing methods to process the data to obtain three photoacoustic signal images.

[0068] (4) The three photoacoustic signal reconstructed images are converted into matrix data I1, I2, I3. The focus information of the images is extracted using the focus extraction function F. GLV get:

[0069]

[0070] Where u is the average gray level of the image, N is the number of pixels in the two-dimensional neighborhood window, and I (x,y) For the matrix data used to reconstruct the image, x is the column index of the matrix data and y is the row index of the matrix data.

[0071] Based on the results of extracting focus information Weighting for a winner-takes-all strategy, such as... Then k1(x,y)=1, k2(x,y)=0, k3(x,y)=0, where k is the weight matrix; finally, the high-resolution and high-contrast photoacoustic image PI is obtained by weight superposition and fusion, and the fusion process is as follows: Figure 2 As shown.

[0072]

[0073] The apparatus and method provided in the foregoing embodiments of the present invention can improve the depth of field of photoacoustic imaging, achieve high-sensitivity uniform high-resolution imaging over a large depth range, and have a high imaging signal-to-noise ratio. They are highly adaptable to biological samples with different complex structures and can be widely used in the field of biomedical imaging.

[0074] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A photoacoustic microscopy imaging device based on photoacoustic confocal multi-depth convergence, characterized in that, Includes a laser emission module, a photoacoustic confocal multi-depth configuration module, and a system control and signal processing module; The laser emitting module is used to generate multiple beams with different time delays; The photoacoustic confocal multi-depth configuration module is used to convert the multi-beam into a multi-coaxial beam, forming multiple light focal points in the depth direction for illuminating the sample under test and generating multi-source photoacoustic signals. Multi-source photoacoustic signals are transmitted to the system control and signal processing module for data processing, image reconstruction, and focus information extraction and fusion imaging. The system control and signal processing module is also used to control the laser triggering in the laser emission module. The laser emitting module (1) includes a pulsed laser (101), a neutral density filter (102), an optical fiber coupler (103), and an optical fiber bundle (104) arranged in sequence. The system control and signal processing module (3) includes an amplifier (301), a low-pass filter (302) and a host computer (303) arranged in sequence; the signal received from the photoacoustic confocal multi-depth configuration module is input into the low-pass filter (302) through the amplifier (301), and the host computer (303) is also used to control the pulsed laser (101). The fiber bundle (104) includes n optical fibers for outputting n beams with different time delays; The photoacoustic confocal multi-depth configuration module (2) includes a reflecting prism, n cemented doublet lenses, n-1 cubic beam splitters, and a multi-channel photoacoustic signal receiver. The reflecting prism, n-1 cubic beam splitters, and multi-channel photoacoustic signal receiver are arranged sequentially. The reflecting prism and n-1 cubic beam splitters have n optical elements and n cemented doublet lenses arranged one-to-one, and the output ends of n optical fibers are arranged one-to-one with the n cemented doublet lenses. Where n≥2; The multi-channel photoacoustic signal receiver includes a focusing lens (207), a prism group (208), a planar transducer (213), an acoustic lens (209), and n-1 hollow transducers. The focusing lens (207) is located on the side wall of the prism group (208), the planar transducer (213) is located on the top of the prism group (208), the bottom surface of the acoustic lens (209) is curved, and the acoustic lens (209) and n-1 hollow transducers are located below the prism group (208). The n-1 hollow transducers are nested together, and the acoustic lens (209) is nested in the innermost hollow transducer.

2. The photoacoustic microscopy imaging device based on photoacoustic confocal multi-depth convergence according to claim 1, characterized in that, The multi-channel photoacoustic signal receiver also includes a linear displacement stage (214) for adjusting the position of the multi-channel photoacoustic signal receiver.

3. The photoacoustic microscopy imaging device based on photoacoustic confocal multi-depth convergence according to claim 1, characterized in that, The hollow transducer includes a hollow cylindrical backing layer and an annular high-frequency piezoelectric element, which is attached to the concave surface at the bottom of the hollow cylindrical backing layer.

4. A photoacoustic microscopy imaging device based on photoacoustic confocal multi-depth convergence according to any one of claims 1-3, characterized in that, The fiber bundle (104) includes three optical fibers. The photoacoustic confocal multi-depth configuration module (2) is equipped with three cemented doublet lenses, defined as the first cemented doublet lens (201), the second cemented doublet lens (202), and the third cemented doublet lens (203), and two cubic beam splitters, defined as the first cubic beam splitter (205) and the second cubic beam splitter (206). The multi-channel photoacoustic signal receiver is equipped with two hollow transducers, defined as the first hollow transducer (211) and the second hollow transducer (212). The first beam of light exits from the optical fiber and passes through the first cemented doublet lens (201), is reflected by the reflecting prism (204), and then passes through the first cubic beam splitter (205) and the second cubic beam splitter (206) to form the first coaxial beam. The second beam of light exits from the optical fiber and enters the second cemented doublet lens (202), and then passes through the first cubic beam splitter (205) and the second cubic beam splitter (206) to form the second coaxial beam. After exiting the optical fiber, the three beams of light enter the third doublet lens (203), and after passing through the second cubic beam splitter (206), they form the third coaxial beam. The three coaxial beams finally pass through the focusing lens (207), the prism group (208), and the acoustic lens (209) to form three light focal points at different depths. These light focal points can illuminate the sample under test, causing it to generate photoacoustic signals. The acoustic lens (209) is nested in the first hollow transducer (211). In the second hollow transducer (212), the focusing positions of the acoustic lens (209), the first hollow transducer (211), and the second hollow transducer (212) coincide with the optical focal points at three different depths, achieving photoacoustic confocality. The first hollow transducer (211) and the second hollow transducer (212) focus to receive photoacoustic signals, and the planar transducer (213) uses the acoustic lens (209) to receive photoacoustic signals. After being received by different transducers, the photoacoustic signals are converted into three electrical signals.

5. A photoacoustic microscopy imaging method based on photoacoustic confocal multi-depth convergence, characterized in that, Using the apparatus of claim 1, the method includes the steps of: Multiple beams with different time delays are generated by the laser emission module; Multiple beams enter the photoacoustic confocal multi-depth configuration module (2) to form light focal points at different depths, which illuminate the sample to be tested and excite multi-source photoacoustic signals; The multi-source photoacoustic signal generated by the sample under test is detected by the hollow transducer and the planar transducer. The received photoacoustic signal is converted into multiple electrical signals for transmission to the system control and signal processing module. The system control and signal processing module reconstructs the acquired multiple electrical signals individually, extracts and fuses the focus information of the multiple photoacoustic images obtained through processing, and completes the high-resolution reconstruction of the photoacoustic images.

6. The photoacoustic microscopy imaging method based on photoacoustic confocal multi-depth convergence according to claim 5, characterized in that, The step of extracting and fusing focus information from the multiple photoacoustic images obtained through processing includes: Multiple photoacoustic images are converted into matrix data, and the focus information of the images is extracted; Weighting of the winner-take-all strategy is performed based on the focus information of the image. High-resolution and high-contrast photoacoustic images are obtained by weighted superposition and fusion.

Images