Photoacoustic microscopic imaging method and system

Abstract

The invention relates to a photoacoustic microscopic imaging method and system. The method comprises the following steps: arranging a sample at a specified position; the spatial light modulator loads a phase diagram corresponding to the Gaussian light, scanning is carried out at a set rate, and an imaging result is obtained; selecting a region of interest according to the imaging result, and performing axial modulation imaging in the region of interest; in the axial modulation imaging process, the spatial light modulator loads 2N + 1 phase diagrams corresponding to non-sinusoidal modulation functions of different phases in sequence; phases corresponding to the 2N + 1 phase diagrams are as follows: N is the number of modulation frequencies; and reconstruction is carried out based on 2N + 1 one-dimensional photoacoustic signals obtained through axial modulation imaging scanning, and the photoacoustic signals after bandwidth expansion are obtained. According to the invention, the bandwidth of the photoacoustic signal can be expanded to GHz, an axial high-resolution imaging result is obtained, the data volume is reduced, the imaging time is shortened, and the imaging speed is improved.

Description

A photoacoustic microscopy imaging method and system Technical Field

[0001] This invention relates to the field of biomedical imaging technology, and in particular to a photoacoustic microscopy imaging method and system. Background Technology

[0002] Biomedical imaging plays a crucial role in medical diagnosis and disease mechanism research. Photoacoustic imaging, as an emerging biomedical imaging technology, has broad application prospects and has become a hot research topic in the imaging field in recent years.

[0003] Optical-resolution photoacoustic microscopy (OR-PAM) is one of the main methods for photoacoustic imaging. It utilizes a focused laser beam to excite photoacoustic signals, and using high-NA objectives can achieve lateral resolution at the micrometer or even submicrometer scale, revealing the distribution of light absorption at the cellular and subcellular levels. For the detection portion of the excited photoacoustic signal, the photoacoustic spectrum induced by cellular and subcellular samples typically spans from hundreds of megahertz to gigahertz. Recovering the initial waveform of the photoacoustic signal generated by these samples requires an ultrasonic transducer with an ultra-wide bandwidth. However, most ultrasonic transducers have bandwidths in the range of several megahertz to tens of megahertz, making it difficult to recover the complete spectrum. This results in a lower axial resolution (typically <10 μm) compared to the lateral resolution of the OR-PAM system, leading to anisotropic three-dimensional imaging results that fail to reflect the true structure of biological tissues. Furthermore, the narrow detection bandwidth also limits the acquisition of information contained in the photoacoustic signal spectrum.

[0004] There are currently three main methods for achieving wide-bandwidth detection in OR-PAM: one is to use a traditional high-frequency piezoelectric transducer, another is an optical detection method, and the third is to use cosine structured light modulation.

[0005] High-frequency piezoelectric transducers improve the manufacturing process, creating thinner piezoelectric layers and thus achieving higher center frequencies and probe bandwidths. However, for piezoelectric ultrasonic transducers, high-frequency transducers and related hardware are typically expensive. Furthermore, for focused piezoelectric ultrasonic transducers, higher frequencies usually result in shorter focal lengths. At 1000 MHz, a typical transducer has a focal length of 80 μm, limiting the measurement range to at most a few cell monolayers. In contrast, a transducer with a center frequency of 10 MHz can be used to measure tissues several centimeters thick.

[0006] Common optical detection methods utilize microring resonators, which consist of a straight waveguide and a ring waveguide coupled together. Resonance occurs when the optical signal meets the basic resonance condition. Microring resonators made of soft polymer materials can serve as ultrasensitive detectors. Under the influence of sound waves, the sound pressure changes the refractive index of the microring resonator material, thus affecting the effective refractive index of the system and consequently altering the resonant mode of the microring resonator, causing a shift in its resonant wavelength. By measuring this shift, the change in demodulated voltage can be determined, and the sound pressure value can be further calculated. However, for ultrasonic transducers based on optical detection, the sensitivity is typically low, the manufacturing process is usually complex, and additional optical instruments are required, increasing the complexity of the system structure. Furthermore, due to the severe attenuation of high-frequency acoustic signals during propagation, it is difficult to achieve in-situ imaging when detecting GHz signals.

[0007] Without changing the detector, cosine structured light modulation can extend the detection bandwidth of OR-PAM. By changing the phase map on the spatial light modulator (SLM), a series of structured light modulated beams of different frequencies are obtained near the focal plane of the objective lens. The resulting photoacoustic signal is then modulated, and combined with a super-resolution reconstruction algorithm, the detection bandwidth is extended. However, due to the large number of phase maps required for modulation, the process is slow and involves a large amount of data. Summary of the Invention

[0008] The first objective of this invention is to address the problems of slow speed and large data volume in cosine structured light modulation by providing a photoacoustic microscopy imaging method and system to reduce data volume, shorten imaging time, and improve imaging speed. The second objective of this invention is to improve the system structure and reduce limitations on application space.

[0009] To achieve the primary objective, the present invention provides the following technical solution:

[0010] A photoacoustic microscopy imaging method includes the following steps:

[0011] Arrange the samples in the designated locations;

[0012] A spatial light modulator loads a phase map corresponding to Gaussian light and scans it at a set rate to obtain an imaging result.

[0013] Based on the imaging results, a region of interest is selected, and axial modulation imaging is performed within that region. During axial modulation imaging, the spatial light modulator sequentially loads phase maps corresponding to 2N+1 different phase non-sinusoidal modulation functions. The non-sinusoidal structured light expression generated by the non-sinusoidal modulation functions, composed of multiple cosine components of different frequencies, is as follows: , , , , N represents the average intensity, fundamental spatial frequency, initial phase, modulation degree, and number of modulation frequencies of the non-sinusoidal structured light, respectively. ;

[0014] The photoacoustic signal with extended bandwidth is obtained by reconstructing 2N+1 one-dimensional photoacoustic signals obtained from axial modulation imaging scanning.

[0015] The process of reconstructing the 2N+1 one-dimensional photoacoustic signals obtained from axial modulation imaging scanning includes:

[0016] A system of linear equations is established based on 2N+1 one-dimensional photoacoustic signals. ,in η represents the thermal energy conversion efficiency. It is a vector composed of 2N+1 photoacoustic signals. It is the vector consisting of the one fundamental frequency component and 2N high-frequency components that need to be solved;

[0017] Solving this system of linear equations yields 2N+1 components. ;

[0018] Using the Fourier frequency shift property to analyze the 2N+1 components Modulation was performed to obtain results after modulation at different frequencies. , FFT and IFFT represent Fourier transform and inverse Fourier transform, respectively. , It is a translation The product of the axial light absorption coefficient distribution and the system frequency response. This represents the fundamental spatial frequency of non-sinusoidal structured light;

[0019] The result obtained by modulating different frequencies using a generalized Wiener filter Integration, that is ,in This is the final broadband spectrum. Let w be the nth-order frequency shift of the system's frequency response, and w be an empirical constant. Represents the apodization function;

[0020] right By performing an inverse Fourier transform, the photoacoustic signal with extended bandwidth can be obtained.

[0021] The present invention also provides a system for implementing the photoacoustic microscopy imaging method, including a structured light generation module, a scanning module, and a signal acquisition and processing module. The structured light generation module is used to generate a Gaussian beam and an axial structured beam. The scanning module is used to perform an initial scan based on the phase map corresponding to the Gaussian light speed and an axial modulation imaging scan based on the phase map corresponding to the axial structured beam. The signal acquisition and processing module is used to acquire 2N+1 one-dimensional photoacoustic signals obtained based on the axial modulation imaging scan and reconstruct them to obtain a photoacoustic signal with extended bandwidth.

[0022] The generation module includes a light source, a first beam expander lens, a first collimating lens, a half-wave plate, a polarizing beam splitter, a beam splitter, a spatial light modulator, a second beam expander lens, an aperture, a second collimating lens, and an objective lens. The light beam emitted from the light source is expanded and collimated by the first beam expander lens and the first collimating lens, and then enters the spatial light modulator through the half-wave plate, the polarizing beam splitter, and the beam splitter. When the phase diagram is loaded onto the spatial light modulator, the higher-order diffracted beam propagates to the objective lens through the second beam expander lens, the aperture, and the second collimating lens in sequence.

[0023] The scanning module includes a biaxial galvanometer, a scanning lens, and a cylindrical lens. A Gaussian beam or an axial structure beam is incident on the objective lens and converged on the sample after passing through the biaxial galvanometer, the scanning lens, and the cylindrical lens.

[0024] The signal acquisition and processing module includes an optically transparent ultrasonic transducer, an amplifier, a data acquisition card, and a computer. The electrical signal obtained by the optically transparent ultrasonic transducer is amplified by the amplifier, acquired by the data acquisition card, and processed by the computer.

[0025] To achieve the second objective, the present invention provides the following technical solution:

[0026] The objective lens and the optically transparent ultrasonic transducer are located on the same side of the sample.

[0027] In the above scheme, the objective lens and the optically transparent ultrasonic transducer are located on the same side of the sample. Compared with the objective lens and the optically transparent ultrasonic transducer being located on opposite sides of the sample, they do not obstruct the sample and therefore do not limit the shape and size of the sample, thus avoiding the limitation of application space.

[0028] The optically transparent ultrasonic transducer includes a wafer, with electrode layers sputtered on both the upper and lower surfaces of the wafer. Each electrode layer has a brass ring at its edge, and the brass ring is connected to a BNC connector via a wire. The cavity in the middle of the brass ring on the upper surface of the wafer is filled with an epoxy resin layer, and an acoustic lens is disposed in the electrode layer on the lower surface of the wafer corresponding to the epoxy resin layer.

[0029] The optically transparent ultrasonic transducer with the above structure can directly transmit excitation light through the sensor, and its small size reduces the impact on the system structure.

[0030] It also includes a reflector, so that the light beam emitted from the second collimating lens is reflected by the reflector and then incident on the biaxial galvanometer.

[0031] In the above scheme, by setting a reflector to change the light path, space can be used more rationally, and a compact and miniaturized design can be achieved.

[0032] Compared with the prior art, the present invention has the following technical advantages:

[0033] 1. To address the limited detection bandwidth of traditional OR-PAM, a non-sinusoidal modulation function is constructed to excite the photoacoustic signal and then reconstruct it using a reconstruction algorithm. This greatly expands the signal bandwidth, with the limit depending only on the near-sub-nanometer objective axial resolution. In other words, this method can extend the signal bandwidth to GHz.

[0034] 2. Compared with the cosine structured light modulation method, the non-sinusoidal structured light used in this invention contains multiple frequency components and modulates multiple frequencies at once, reducing the number of phase maps that need to be loaded on the SLM during imaging from 3N to 2N+1, which greatly shortens the imaging time and reduces the amount of data.

[0035] 3. The device described in this invention utilizes a TUT to achieve a reflective structure, avoiding the limitations imposed by transmissive structures on sample shape and the selection and placement of system components, as well as their limited application scope. Simultaneously, the use of galvanometer scanning further enhances imaging speed, avoiding the long imaging time of mechanical scanning, enabling rapid three-dimensional high-resolution imaging of in vivo samples. Attached Figure Description

[0036] Figure 1 is a schematic diagram of the structure of a photoacoustic microscopy imaging system provided in an embodiment of the present invention.

[0037] Figure 2 is a schematic diagram of the structure of the optically transparent ultrasonic transducer in the embodiment.

[0038] Figure 3 is a flowchart of a photoacoustic microscopy imaging method provided in an embodiment of the present invention.

[0039] Figure 4 shows the waveforms of the reconstruction process. (a) and (b) show the spatial and frequency domain distributions of the non-sinusoidal modulation function, respectively. (c) and (d) show the corresponding spectral separation and fusion processes after the photoacoustic signal is excited by this structured light and reconstructed. Detailed Implementation

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0041] Please refer to Figure 1. This embodiment provides a photoacoustic microscopy imaging system, including a structured light generation module, a scanning module, and a signal acquisition and processing module.

[0042] The structured light generation module is mainly used to generate Gaussian beams and axial structured beams. The module includes a light source 1, a first beam expander 2, a first collimating lens 3, a half-wave plate 4, a polarizing beam splitter 5, a beam splitter 6, an SLM 7, a second beam expander 8, an aperture 9, a second collimating lens 10, and an objective lens 15. For example, the light source 1 is a pulsed laser with a wavelength of 532 nm, a pulse width of 400 ps, ​​and a repetition frequency of 100 kHz. After being expanded and collimated by the first beam expander 2 and the first collimating lens 3, the beam passes through the half-wave plate 4, the polarizing beam splitter 5, and the beam splitter 6 before being incident on the SLM 7. When the phase diagram is applied to the SLM 7, due to the grating structure of the SLM 7, the outgoing beam exhibits higher-order diffraction (the beam after passing through the SLM will be divided into multiple diffraction orders; higher-order diffraction has higher diffraction efficiency than lower-order diffraction, and the two are relative concepts). The aperture 9 blocks the lower-efficiency diffraction orders, allowing the higher-efficiency diffraction orders to propagate backward. By changing the phase diagram on the SLM7, a Gaussian beam or an axially structured beam can be generated near the back focal plane of objective lens 15.

[0043] The second beam expander 8 and the second collimating lens 10 form a beam expander and collimating system, which adjusts the size of the light spot to be suitable for incident on the dual-axis galvanometer 12. The second beam expander 8 also focuses the light emitted from the SLM7, which contains multiple diffraction orders, so that different diffraction orders can be easily separated at the aperture stop 9.

[0044] The scanning module is mainly used for initial scanning based on the phase map corresponding to the Gaussian speed of light, and for axial modulation imaging scanning based on the phase map corresponding to the axial structure beam. The scanning module includes a biaxial galvanometer 12, a scanning lens 13, and a tube lens 14. The Gaussian beam or axial structure beam, after passing through the biaxial galvanometer 12, scanning lens 13, and tube lens 14, is incident on the objective lens 15 and converged onto the sample 17. The sample 17 is excited by pulsed light to generate a photoacoustic signal, which is detected by the optically transparent ultrasonic transducer (TUT) 16 and converted into an electrical signal. The use of a biaxial galvanometer scanning method here can shorten signal acquisition time and improve imaging speed.

[0045] In the structure shown in Figure 1, the optically transparent ultrasonic transducer 16 and the objective lens 15 are located on the same side of the sample 17, forming a reflective structure with the sample 17, thus avoiding restrictions on the shape and size of the sample 17.

[0046] Referring to Figure 2, in order to achieve the reflection mode, in this embodiment, the optically transparent ultrasonic transducer 16 includes a wafer 22. Electrode layers 23 are sputtered on the upper and lower surfaces of the wafer 22. A brass ring 24 is provided on the edge of each electrode layer 23. The brass ring 24 is connected to a BNC connector 25 through a wire. The cavity in the middle of the brass ring 24 on the upper surface of the wafer 22 is filled with an epoxy resin layer 26. An acoustic lens is provided in the electrode layer 23 on the lower surface of the wafer 22 corresponding to the epoxy resin layer 26.

[0047] The fabrication process of the optically transparent ultrasonic transducer 16 is as follows: First, a 1cm × 1cm 36° Y-cut LiNbO3 wafer 22 with a thickness of 100μm is fabricated. Next, ITO with a thickness of approximately 108 nm is sputtered onto the upper and lower surfaces of the wafer 22 as electrode layers 23. Then, a brass ring 24 is attached to the edges of each electrode layer 23 using conductive silver paste for wire connection and fixation to the transducer assembly. The two wires fixed to the upper and lower brass rings 24 are connected to BNC connectors 25. Then, 0.2 g of degassed epoxy resin is poured into the interior 24 of the upper brass ring, and after curing, a 1 mm thick epoxy resin layer 26 is obtained. Finally, an acoustic lens 27 is attached to the outside of the lower electrode layer 23 using UV-curable adhesive; the acoustic lens 27 also serves as a matching layer.

[0048] A common method for achieving reflection modes is to couple the excitation light with the acoustic wave using a combination mirror. However, this method is only suitable for objectives with long working distances, thus limiting the numerical aperture of the objective and preventing the achievement of high lateral resolution. Some research groups have developed annular or hollow ultrasonic transducers; however, the acoustic sensitivity and focusing ability of ultrasonic transducers are reduced due to the removal of their central portion. To overcome these drawbacks, this scheme introduces an optically transparent ultrasonic transducer that can directly transmit the excitation light through the sensor, while its small size reduces its impact on the system structure.

[0049] The structure shown in Figure 1 also includes a reflector 11. The light beam emitted from the lens 10 is first reflected by the reflector 11 before being incident on the dual-axis galvanometer 12. The purpose of this layout is to minimize the spatial structure of the entire system and achieve a compact design. If the spatial structure size is not a concern, the reflector 11 can be omitted, meaning that the reflector 11 is only an optional component.

[0050] The signal acquisition and processing module includes an optically transparent ultrasonic transducer 16, an amplifier 19, an acquisition card 20, and a computer 21. The electrical signal obtained by the optically transparent ultrasonic transducer 16 is amplified by the amplifier 19 and then acquired by the acquisition card 20 and processed by the computer 21.

[0051] Referring to Figure 3, the procedure for photoacoustic microscopy using the photoacoustic microscopy system shown in Figure 1 is as follows:

[0052] The sample 17 is attached to the bottom of the water tank 18. Deionized water is added to the water tank 18 to immerse the sample 17, the optically transparent ultrasonic transducer 16, and the front surface of the objective lens 15.

[0053] In order to select the imaging area, the SLM7 first loads the phase map corresponding to the Gaussian light, and then scans a larger area at a set rate;

[0054] Next, based on the imaging results, a region of interest is selected, and axial modulation imaging is performed within that region. The SLM sequentially loads phase maps corresponding to 2N+1 different non-sinusoidal modulation functions. The expression for the non-sinusoidal structured light generated by the non-sinusoidal modulation functions, consisting of multiple cosine components of different frequencies, is as follows: , , , , N represents the average intensity, fundamental spatial frequency, initial phase, modulation degree, and number of modulation frequencies of the non-sinusoidal structured light, respectively. The phases corresponding to the 2N+1 phase diagrams are respectively ;

[0055] After the scan is completed, the 2N+1 one-dimensional photoacoustic signals are saved in the computer 21 as bin files. The computer 21 reconstructs the photoacoustic signals based on the photoacoustic signals to obtain photoacoustic signals with extended bandwidth, thereby obtaining axial high-resolution imaging results.

[0056] The reconstruction process based on 2N+1 one-dimensional photoacoustic signals is as follows:

[0057] A system of linear equations is established based on 2N+1 one-dimensional photoacoustic signals. ,in , , , Let represent the average intensity, initial phase, and modulation index of the non-sinusoidal structured light, respectively; η represent the thermal energy conversion efficiency; and i is the imaginary unit. It is a vector composed of 2N+1 photoacoustic signals. It is the vector consisting of one fundamental frequency component and 2N high-frequency components that need to be solved. Here, high frequency and fundamental frequency are relative concepts.

[0058] Solving this system of linear equations yields 2N+1 components. .

[0059] By using the Fourier frequency shift property to modulate 2N+1 components, results with different frequency modulations can be obtained. , FFT and IFFT represent Fourier transform and inverse Fourier transform, respectively. , It is a translation The product of the axial light absorption coefficient distribution and the system frequency response. This represents the fundamental spatial frequency of non-sinusoidal structured light.

[0060] Finally, the results obtained by modulating different frequencies using a generalized Wiener filter. Integration, that is

[0061] ,in This is the final broadband spectrum. Let w be the nth-order frequency shift of the system's frequency response, and w be an empirical constant. This represents the apodization function, used to remove sidelobes and noise jitter caused by frequency discontinuities in edge regions. Finally, through... By performing an inverse Fourier transform, the photoacoustic signal with extended bandwidth can be obtained.

[0062] In a linear response PAM system, the detected one-dimensional photoacoustic signal PA can be expressed as: ,in For the axial point extension function of the system, It is the distribution of light energy along the z-axis. The light absorption coefficient distribution along the z-axis is given by η, where η represents the thermal energy conversion efficiency and ⊗ represents the convolution operation. In this invention, the illumination intensity along the z-axis is a non-sinusoidal structured light composed of multiple cosine components of different frequencies, denoted as... ,in , , , N represents the average intensity, fundamental spatial frequency, initial phase, modulation index, and number of modulation frequencies of the non-sinusoidal structured light, respectively. When illuminated with this non-sinusoidal structured light, there is... By performing a Fourier transform, the spectrum of the signal generated by the non-sinusoidal structured light illumination can be obtained. ,in This is the system frequency response. It is broken down into 2N+1 terms, defined as follows: ,in It can be seen that... It is a translation The product of the axial absorption coefficient distribution and the system frequency response indicates that, due to the modulation of the non-sinusoidal structured light, some high-frequency information is modulated into the low-frequency passband of the system. By reconstructing and restoring the high-frequency information within the low-frequency passband, the signal bandwidth can be extended to GHz.

[0063] In cosine structured light modulation, frequency component separation under a fundamental spatial frequency modulation requires three different phases of structured light illumination to obtain three one-dimensional photoacoustic signals. When modulating with N fundamental spatial frequencies, 3N one-dimensional photoacoustic signals are needed. Using SLM to obtain cosine structured light with different phases means that when modulating with N fundamental spatial frequencies, 3N phase maps need to be continuously loaded onto the SLM. When N is large, the number of phase maps required will also be large, which will lead to a longer imaging time and a larger data volume. However, this invention utilizes a multi-frequency optical modulation method, which contains multiple frequency components in the non-sinusoidal structured light used, which is equivalent to modulating multiple frequencies at once, without constantly changing the cosine structured light containing only a single frequency. Only 2N+1 one-dimensional photoacoustic signals with different phase modulations are needed to solve the linear equation system. Compared with the traditional cosine structured light modulation method, the number of phase maps is reduced by N-1. That is, when using SLM for modulation, only 2N+1 phase maps with different phases need to be continuously loaded, which greatly reduces the number of phase maps required, further shortens the imaging time, and reduces the data volume.

[0064] The main challenge of multi-frequency modulation lies in the generation of non-sinusoidal structured light. This invention constructs a non-sinusoidal function containing N modulation frequency components, and further constructs an SLM phase map corresponding to the axial structured light using this function. During modulation imaging, the SLM combined with the phase map achieves the purpose of expanding the bandwidth.

[0065] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A photoacoustic microscopy imaging method, characterized in that, The process includes the following steps: placing the sample at a designated location; loading a phase map corresponding to Gaussian light onto a spatial light modulator and scanning at a set rate to obtain an imaging result; selecting a region of interest based on the imaging result and performing axial modulation imaging on the region of interest; during axial modulation imaging, the spatial light modulator sequentially loads phase maps corresponding to 2N+1 different non-sinusoidal modulation functions; the non-sinusoidal structured light expression generated by the non-sinusoidal modulation function, composed of multiple cosine components of different frequencies, is as follows: ， 、 、 、 N represents the average intensity, fundamental spatial frequency, initial phase, modulation degree, and number of modulation frequencies of the non-sinusoidal structured light, respectively. ； The photoacoustic signal with extended bandwidth is obtained by reconstructing 2N+1 one-dimensional photoacoustic signals obtained from axial modulation imaging scanning.

2. The photoacoustic microscopy imaging method according to claim 1, characterized in that, The process of reconstructing the 2N+1 one-dimensional photoacoustic signals obtained from axial modulation imaging scanning includes: establishing a system of linear equations based on the 2N+1 one-dimensional photoacoustic signals. ,in η represents the thermal energy conversion efficiency. It is a vector composed of 2N+1 photoacoustic signals. This corresponds to the vector consisting of one fundamental frequency component and 2N high-frequency components that need to be solved; solving this system of linear equations yields 2N+1 components. Using the Fourier frequency shift property to analyze the 2N+1 components Modulation was performed to obtain results after modulation at different frequencies. ， FFT and IFFT represent Fourier transform and inverse Fourier transform, respectively. ， It is a translation The product of the axial light absorption coefficient distribution and the system frequency response. Represents the fundamental spatial frequency of non-sinusoidal structured light; the result obtained by modulating different frequencies using a generalized Wiener filter. Integration, that is ,in This is the final broadband spectrum. Let w be the nth-order frequency shift of the system's frequency response, and w be an empirical constant. Represents the apodization function; for By performing an inverse Fourier transform, the photoacoustic signal with extended bandwidth can be obtained.

3. The photoacoustic microscopy imaging method according to claim 1, characterized in that, The process of placing the sample in a designated location includes: attaching the sample to the bottom of a water tank, adding deionized water to the water tank, and immersing the sample, the front surface of the optically transparent ultrasonic transducer, and the objective lens.

4. A system for implementing the photoacoustic microscopy imaging method of claim 1, characterized in that, The system includes a structured light generation module, a scanning module, and a signal acquisition and processing module. The structured light generation module is used to generate a Gaussian beam and an axial structured beam. The scanning module is used to perform an initial scan based on the phase map corresponding to the Gaussian light speed and an axial modulation imaging scan based on the phase map corresponding to the axial structured beam. The signal acquisition and processing module is used to acquire 2N+1 one-dimensional photoacoustic signals obtained based on the axial modulation imaging scan and reconstruct them to obtain a photoacoustic signal with extended bandwidth.

5. The system according to claim 4, characterized in that, The generation module includes a light source, a first beam expander lens, a first collimating lens, a half-wave plate, a polarizing beam splitter, a beam splitter, a spatial light modulator, a second beam expander lens, an aperture, a second collimating lens, and an objective lens. The light beam emitted from the light source is expanded and collimated by the first beam expander lens and the first collimating lens, and then enters the spatial light modulator through the half-wave plate, the polarizing beam splitter, and the beam splitter. When the phase diagram is loaded onto the spatial light modulator, the higher-order diffracted beam propagates to the objective lens through the second beam expander lens, the aperture, and the second collimating lens in sequence.

6. The system according to claim 5, characterized in that, The scanning module includes a biaxial galvanometer, a scanning lens, and a cylindrical lens. A Gaussian beam or an axial structure beam is incident on the objective lens and converged on the sample after passing through the biaxial galvanometer, the scanning lens, and the cylindrical lens.

7. The system according to claim 6, characterized in that, The signal acquisition and processing module includes an optically transparent ultrasonic transducer, an amplifier, a data acquisition card, and a computer. The electrical signal obtained by the optically transparent ultrasonic transducer is amplified by the amplifier, acquired by the data acquisition card, and processed by the computer.

8. The system according to claim 7, characterized in that, The objective lens and the optically transparent ultrasonic transducer are located on the same side of the sample.

9. The system according to claim 7, characterized in that, The optically transparent ultrasonic transducer includes a wafer, with electrode layers sputtered on both the upper and lower surfaces of the wafer. Each electrode layer has a brass ring at its edge, and the brass ring is connected to a BNC connector via a wire. The cavity in the middle of the brass ring on the upper surface of the wafer is filled with an epoxy resin layer, and an acoustic lens is disposed in the electrode layer on the lower surface of the wafer corresponding to the epoxy resin layer.

10. The system according to claim 6, characterized in that, It also includes a reflector, so that the light beam emitted from the second collimating lens is reflected by the reflector and then incident on the biaxial galvanometer.

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