Integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device and imaging method

Abstract

The invention discloses an integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device, which comprises a light source assembly, a polarization assembly, a signal receiving assembly and a signal processing assembly, and is characterized in that the light source assembly is used for generating collimated pulse laser with different wavelengths, and the polarization assembly can enable the pulse laser with different wavelengths to generate a polarization state; the polarization angle of the light beam is changed, the signal receiving assembly can detect a photoacoustic signal after the polarized light irradiates a sample, the signal processing assembly is used for amplifying and collecting the photoacoustic signal, the multi-wavelength light source is adopted as an excitation light source, and the polarization assembly enables the laser of each wavelength to generate a polarization state; according to the multi-wavelength multi-frequency photoacoustic imaging system and the multi-wavelength multi-frequency photoacoustic imaging method, a plurality of ultrasonic transducers with different center frequencies are utilized to detect photoacoustic signals, so that polarized light acoustic imaging, multi-wavelength photoacoustic imaging and multi-frequency photoacoustic imaging can be combined, and the purpose of multi-angle and multi-parameter biomedical imaging is achieved.

Description

[0001] An integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device and imaging method Technical Field

[0002] The present invention belongs to the technical field of photoacoustic imaging, and more specifically relates to an integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device and an imaging method. Background Art

[0003] Photoacoustic imaging is a hybrid imaging technology based on the photoacoustic effect that has been developed in recent years and has attracted widespread attention in the biomedical field. The photoacoustic effect refers to the fact that when biological tissue is irradiated by a short-pulse laser, the tissue absorbs light energy and undergoes thermoelastic expansion, generating ultrasonic signals. However, different components in biological tissue have different light absorption coefficients, and it is difficult to image different components simultaneously using a single-wavelength photoacoustic imaging technology.

[0004] As a branch of photoacoustic imaging, photoacoustic tomography often uses a large spot to excite the sample, then uses an ultrasonic transducer to detect the photoacoustic signal at different spatial positions around the sample, and finally reconstructs the signal into an image reflecting the light absorption of biological tissue through a reconstruction algorithm. This imaging technology combines the advantages of rich optical contrast of optical imaging and high spatial resolution of ultrasonic imaging.

[0005] However, photoacoustic tomography usually treats the absorption coefficient of biological tissue as a scalar, while ignoring the anisotropy of biological tissue absorption. However, there are many tissues in the body whose optical absorption exhibits specific dichroism due to the orderly arrangement of molecules, which means that photons of different polarization states will experience different degrees of absorption when transmitted in the tissue. In photoacoustic tomography, the change of light absorption coefficient can be converted into the change of photoacoustic signal intensity. Therefore, polarization photoacoustic tomography combined with linearly polarized laser can enrich the ability of photoacoustic imaging to extract specific information in tissues.

[0006] In addition, in photoacoustic tomography, the frequency range of the photoacoustic signal generated is directly related to the size of the sample. The smaller the size, the higher the frequency of the photoacoustic signal, and the opposite is true for larger sizes. The detection bandwidth of the ultrasonic transducer is limited, which may lead to the loss of detection information. Summary of the invention

[0007] The main purpose of the present invention is to provide an integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device and imaging method, so as to detect various anisotropic signals of the sample, simultaneously image components with different light absorption coefficients and improve the detection bandwidth, so as to achieve the purpose of multi-angle and multi-parameter biomedical imaging.

[0008] To achieve the above object, the technical solution of the present invention is: An integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device comprises a light source component, a polarization component, a signal receiving component and a signal processing component; the light source component is used to generate collimated pulse lasers of different wavelengths, the light source component comprises a multi-wavelength light source that can emit pulse lasers according to the sample excitation spectrum and a beam expander that can make the light beam uniform; the polarization component can make the pulse lasers of different wavelengths produce polarization states and change the polarization angle of the light beam, the polarization component comprises a polarizer, a rotational deflection component and a concave lens that can expand the irradiation range of polarized light, the polarizer, the rotational deflection component and the concave lens are arranged in sequence The pulsed laser after emission is concentrically arranged; the signal receiving component can detect the photoacoustic signal after the sample is irradiated with polarized light, the signal receiving component includes a water tank that can accommodate the coupling medium and a plurality of ultrasonic transducers arranged in the water tank, a rotating component that can drive the ultrasonic transducer to rotate and scan is arranged above the water tank, and a base for fixing the sample is arranged in the water tank; the signal processing component is used to amplify and collect the photoacoustic signal, the signal processing component can reconstruct the collected photoacoustic signal to form a photoacoustic image, and the signal processing component includes a signal amplifier and a data acquisition card respectively connected to the output end of the signal amplifier.

[0009] In a specific embodiment of the present invention, the light source assembly further includes a reflector, and the beam expander and the reflector are both arranged on the optical path of the multi-wavelength light source.

[0010] In a specific embodiment of the present invention, a light hole is provided at the center of the deflection component, the polarizer is used to convert laser light into polarized light, the deflection component is used to change the polarization direction of the polarized light, and the concave lens is used to expand the irradiation range of the polarized light on the sample.

[0011] In a specific embodiment of the present invention, a clamping device is further provided on the deflection component, the polarizer can be fixed by the clamping device, and the polarizer and the deflection component are concentrically arranged.

[0012] In a specific embodiment of the present invention, the rotating assembly includes a rotating platform and an ultrasonic transducer clamping device, the ultrasonic transducer clamping device is provided with a plurality of transducer fixing holes, and a plurality of ultrasonic transducers can be respectively installed in the corresponding transducer fixing holes.

[0013] In a specific embodiment of the present invention, the signal processing component also includes a computer and a synchronization control component. The computer can convert the acquired signal into a photoacoustic image. The synchronization control component can achieve timing synchronization by respectively connecting to the multi-wavelength light source, the rotation component, the rotation component and the data acquisition card.

[0014] In a specific embodiment of the present invention, the following steps are included: 1) embedding the sample in agar or directly fixing the sample on the base, aligning the required imaging section of the sample with the plane where the acoustic foci of the ultrasonic transducers are located, adding coupling medium into the water tank to immerse the sample and the ultrasonic transducer; 2) According to the imaging requirements of the sample, the multi-wavelength light source is set to output the required wavelength laser; 3) Adjust the polarization component to adjust the laser polarization direction to the initial direction of 0°; 4) Rotate the ultrasonic transducers with different center frequencies around the sample to collect the photoacoustic signal generated by the sample. After the signal collection is completed, change the polarization direction of the laser through the polarization component to continue collecting the photoacoustic signal of the sample; 5) Processing the acquired photoacoustic signal by the computer to obtain a photoacoustic image.

[0015] In a specific embodiment of the present invention, the rotation method of the ultrasonic transducer in step 4) includes: the ultrasonic transducer first rotates around the sample for one circle to complete the acquisition of a cross-section signal of the sample. When acquiring the signal of the next image, the ultrasonic transducer rotates in the opposite direction for one circle, and the above steps are repeated until the imaging is completed.

[0016] In a specific embodiment of the present invention, the manner in which the polarization component in step 4) changes the polarization direction of the laser includes: after each signal acquisition is completed, the synchronization control component outputs a signal to the deflection component so that the polarizer rotates 15° and then continues signal acquisition for the next image. During the rotation of the deflection component, the ultrasonic transducer pauses rotation and stops signal acquisition.

[0017] In a specific embodiment of the present invention, the signal processing method in step 5) includes: reconstructing the photoacoustic signals collected by the plurality of ultrasonic transducers at each polarization angle into a photoacoustic image by using a filtered back projection algorithm.

[0018] One of the above technical solutions of the present invention has at least one of the following advantages or beneficial effects: The present invention adopts a multi-wavelength light source as an excitation light source, and uses a polarization component to make the lasers of each wavelength produce a polarization state, and uses a number of ultrasonic transducers with different center frequencies to detect photoacoustic signals, so that polarization photoacoustic imaging, multi-wavelength photoacoustic imaging and multi-frequency photoacoustic imaging can be combined. It can not only detect the anisotropic signal of the sample and image the components with different light absorption coefficients in the tissue separately, but also expand the detection bandwidth of the photoacoustic signal generated by the sample, thereby achieving the purpose of multi-angle and multi-parameter biomedical imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with the accompanying drawings and embodiments; Attached Figure 1 A structural block diagram of an embodiment of the present invention; Attached Figure 2 A flowchart of an embodiment of the present invention; Attached Figure 3 This is a graph showing the imaging capability of an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions from beginning to end. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0021] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0022] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0023] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more features.

[0024] In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the term "connection" should be understood in a broad sense. For example, it can be a fixed connection or a movable connection, a detachable connection or a non-detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, and it can be internal connection between two elements, indirect connection, or an interactive relationship between two elements.

[0025] The following disclosure provides many different embodiments or examples for implementing different solutions of the present invention.

[0026] See attached Figure 1 To Attachment Figure 3 As shown, an integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device includes a light source component 1, a polarization component 2, a signal receiving component 3 and a signal processing component 4.

[0027] In one embodiment of the present invention, the light source assembly 1 is used to generate collimated pulsed lasers of different wavelengths. The light source assembly 1 includes a multi-wavelength light source 11 that can emit pulsed lasers according to the sample excitation spectrum, a beam expander 12 that can homogenize the light beam, and a reflector 13. The multi-wavelength light source includes a pump laser and an optical parametric oscillator. The multi-wavelength light source is used to continuously and cyclically generate pulsed lasers of different wavelengths, wherein each pulse laser has a certain time interval, and the beam expander 12 and the reflector 13 are both arranged on the optical path of the multi-wavelength light source 11.

[0028] In one embodiment of the present invention, the output wavelength range of the multi-wavelength light source 11 is 650 nm-1064 nm, and 532 nm laser can be directly output through a pump laser, with a repetition frequency of 20 Hz, a pulse width of 7 ns, an energy density of 7 mj / cm², a spot diameter of 6 mm, and a magnification of 2 times by the beam expander 12. The multi-wavelength light source 11 continuously outputs pulsed lasers of different wavelengths in a cycle according to imaging requirements, and the time interval between two adjacent pulsed lasers of different wavelengths is 0.05 seconds. Then, the beam expander 12 expands and homogenizes the light beam to improve the quality of the light spot, and then reflects the light beam into the polarization component 2 through the reflector 13.

[0029] In one embodiment of the present invention, the polarization component 2 can make pulsed lasers of different wavelengths produce polarization states and change the polarization angle of the light beam. The polarization component 2 includes a polarizer 21, a deflection component 22 and a concave lens 23 that can expand the irradiation range of polarized light, which are arranged in sequence. The polarizer 21, the deflection component 22 and the concave lens 23 are concentrically arranged with the reflected pulsed laser.

[0030] In one embodiment of the present invention, a light-through hole is provided at the center of the deflection component 22, the polarizer 21 is used to convert laser light into polarized light, the deflection component 22 is used to change the polarization direction of the polarized light, the concave lens 23 is used to expand the irradiation range of the polarized light on the sample, and a clamping device is provided on the deflection component 22, the polarizer 21 can be fixed by the clamping device, and the polarizer 21 and the deflection component 22 are concentrically arranged.

[0031] In one embodiment of the present invention, the polarizer 21 is a polarizing plate, and the deflection component 22 drives a worm gear through a two-phase stepping motor to rotate the turntable. The focal length of the concave lens 23 is set to -150 mm. After the reflected light beam passes through the polarizing plate, it becomes polarized light. The polarizing plate can be rotated manually or electrically through the deflection component 22 to change the direction of the polarized light. After the polarized light passes through the light hole of the deflection component 22, the light spot is diffused by the concave lens 23 to further expand the diameter of the light spot, ensuring that the light beam can irradiate the entire sample. After the sample is irradiated by the light beam, a photoacoustic signal is generated.

[0032] In one embodiment of the present invention, the signal receiving component 3 can detect the photoacoustic signal after the sample is irradiated with polarized light. The signal receiving component 3 includes a water tank 31 that can accommodate a coupling medium and a plurality of ultrasonic transducers 32 arranged in the water tank 31. A rotating component 33 that can drive the ultrasonic transducer 32 to rotate and scan is provided above the water tank 31, and a base for fixing the sample is provided in the water tank 31.

[0033] In one embodiment of the present invention, the rotating assembly 33 includes a rotating platform and an ultrasonic transducer clamping device. The ultrasonic transducer clamping device is provided with a plurality of transducer fixing holes, and a plurality of ultrasonic transducers 32 can be respectively installed in the corresponding transducer fixing holes.

[0034] In one embodiment of the present invention, the rotating component 33 drives the worm gear through a two-phase stepping motor, thereby rotating the ultrasonic transducer clamping device fixed on the turntable, and a plurality of ultrasonic transducers 32 with different center frequencies are selected as focused ultrasonic transducers with center frequencies of 2.25 MHz and 5 MHz respectively. The coupling medium contained in the water tank 31 is deionized water. The ultrasonic transducer 32 rotates around the sample to receive the photoacoustic signal, and collects sequential signals every time it rotates 1°. Each image requires the ultrasonic transducer 32 to rotate around the sample once to collect 360 A-scan signals, and during the imaging process, the water needs to immerse the ultrasonic transducer 32 to couple the photoacoustic signal.

[0035] In one embodiment of the present invention, the signal processing component 4 is used to amplify and collect photoacoustic signals. The signal processing component 4 can reconstruct the collected photoacoustic signals to form photoacoustic images. The signal processing component 4 includes a signal amplifier 41, a data acquisition card 42 respectively connected to the output ends of the signal amplifier 41, a computer 43 and a synchronization control component 44.

[0036] In one embodiment of the present invention, the computer 43 can convert the acquired signal into a photoacoustic image, and the synchronization control component 44 can be connected to the multi-wavelength light source 11, the rotation component 22, the rotating component 33 and the data acquisition card 42 respectively, so as to achieve timing synchronization and control the multi-wavelength light source 11 to quickly switch the wavelength after emitting a pulsed laser.

[0037] In one embodiment of the present invention, the signal amplifier 41 uses two single-channel amplifiers with an amplification factor of 42 dB, the data acquisition card 42 uses an acquisition card with two acquisition channels and a sampling rate of 100 MHz, the computer 43 controls the system operation and signal acquisition through the labview program, and then post-processes the signal through the matlab program and reconstructs it into a photoacoustic image, the synchronization control component 44 uses FPGA, the signal amplifier 41 amplifies the signal detected by the ultrasonic transducer 32, and then the signal is collected by the data acquisition card 42, and then transmitted to the computer 43 to reconstruct it into an image.

[0038] In one embodiment of the present invention, the implementation steps of the imaging device include: The first step is to embed the sample in agar or fix the sample directly on the base, overlap the required imaging section of the sample with the plane where the acoustic focus of the ultrasonic transducers 32 is located, and add coupling medium into the water tank 31 to immerse the sample and the ultrasonic transducer 32; Step 2: According to the sample imaging requirements, the multi-wavelength light source 11 is set to output the required wavelength laser; Step 3: Adjust the polarization component 22 to adjust the laser polarization direction to the initial direction of 0°; Step 4: rotate a number of ultrasonic transducers 32 with different center frequencies around the sample to collect the photoacoustic signal generated by the sample. After the signal collection is completed, change the polarization direction of the laser through the polarization component 2 to continue collecting the sample photoacoustic signal; Step 5: Process the acquired photoacoustic signal through the computer 43 to obtain a photoacoustic image.

[0039] In one embodiment of the present invention, in the fourth step, the rotation method of the ultrasonic transducer 32 includes: the ultrasonic transducer 32 first rotates around the sample for one circle to complete the acquisition of a cross-section signal of the sample, and when acquiring the signal of the next image, the ultrasonic transducer 32 rotates in the opposite direction for one circle, and the above steps are repeated until the imaging is completed.

[0040] In one embodiment of the present invention, in the fourth step, the polarization component 2 changes the polarization direction of the laser in the following manner: after each signal acquisition is completed, the synchronization control component 44 outputs a signal to the deflection component 22, so that the polarizer 21 rotates 15° and then continues the signal acquisition of the next image. During the rotation of the deflection component 22, the ultrasonic transducer 32 pauses rotation and stops signal acquisition.

[0041] In one embodiment of the present invention, in the fifth step, the signal processing method includes: reconstructing the photoacoustic signals collected by the plurality of ultrasonic transducers 32 at each polarization angle into a photoacoustic image by using a filtered back projection algorithm.

[0042] In one embodiment of the present invention, polyvinyl alcohol (PVA) and polyvinyl chloride (PVC) are imaged, as shown in the attached figure. Figure 3 (a) shows the ability of the imaging device to extract the anisotropic information of the sample. Among them, polyvinyl alcohol has strong anisotropy, while polyvinyl chloride is isotropic. Figure 3 (a) From left to right are the optical photos of polyvinyl alcohol and polyvinyl chloride, the photoacoustic imaging results at different polarization angles, and the original signals extracted from the photoacoustic images at different polarization angles. It can be seen that for polyvinyl alcohol with strong anisotropy, the intensity change of its photoacoustic signal first decreases and then increases due to the change in the polarization angle of the polarization light, and the signal intensity change is similar to that of the cosine signal. For isotropic polyvinyl chloride, its signal intensity remains basically unchanged and is independent of the laser polarization angle.

[0043] As attached Figure 3 As shown in (b), the "A" and "Z" models composed of black tape are imaged by ultrasonic transducers 32 with center frequencies of 2.25 MHz and 5 MHz respectively, indicating the difference in imaging effects of ultrasonic transducers 32 with different center frequencies.

[0044] Attached Figure 3 (b) From left to right are the optical photograph of the sample, the imaging result of the ultrasonic transducer with a center frequency of 2.25MHz, and the imaging result of the ultrasonic transducer with a center frequency of 5MHz. When the ultrasonic transducer with a center frequency of 2.25MHz is used for imaging, the sample has a clearer outline and a better overall shape. When the ultrasonic transducer with a center frequency of 5MHz is used for imaging, the sample signal distribution is more uniform, and the traces of the interlacing between the black tapes that make up the letters can be observed. The imaging results fully prove that when the ultrasonic transducer with a lower center frequency is used for imaging, the macroscopic information of the sample is better, and when the ultrasonic transducer with a higher center frequency is used for imaging, the sample has richer imaging details.

[0045] As attached Figure 3 As shown in (c), methylene blue, ICG and mouse blood were imaged at wavelengths of 532nm, 670nm and 780nm, respectively, proving the system's ability to perform multi-wavelength photoacoustic tomography. Methylene blue, ICG and mouse blood have large light absorption coefficients at wavelengths of 670nm, 780nm and 532nm, respectively. The imaging results show that the three samples have better imaging contrast at the corresponding wavelengths, which is consistent with the theory. The imaging results show that the imaging device is capable of multi-wavelength photoacoustic tomography and provides high-contrast images for components with different light absorption coefficients.

[0046] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. An integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device, characterized in that: It comprises a light source component (1), a polarization component (2), a signal receiving component (3) and a signal processing component (4); The light source assembly (1) is used to generate collimated pulsed lasers of different wavelengths, and the light source assembly (1) comprises a multi-wavelength light source (11) capable of emitting pulsed lasers according to a sample excitation spectrum, and a beam expander (12) capable of homogenizing the light beam; The polarization component (2) can cause pulsed lasers of different wavelengths to generate polarization states and change the polarization angle of the light beam. The polarization component (2) comprises a polarizer (21), a deflection component (22), and a concave lens (23) that can expand the irradiation range of polarized light, which are arranged in sequence. The polarizer (21), the deflection component (22), and the concave lens (23) are arranged concentrically with the reflected pulsed laser. The signal receiving component (3) can detect photoacoustic signals after the sample is irradiated with polarized light. The signal receiving component (3) comprises a water tank (31) capable of accommodating a coupling medium and a plurality of ultrasonic transducers (32) arranged in the water tank (31). A rotating component (33) capable of driving the ultrasonic transducers (32) to rotate and scan is arranged above the water tank (31). A base for fixing the sample is arranged in the water tank (31); The signal processing component (4) is used to amplify and collect photoacoustic signals. The signal processing component (4) can reconstruct the collected photoacoustic signals to form photoacoustic images. The signal processing component (4) comprises a signal amplifier (41) and a data acquisition card (42) respectively connected to the output end of the signal amplifier (41).

2. The integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device according to claim 1, characterized in that: The light source assembly (1) further comprises a reflector (13), and the beam expander (12) and the reflector (13) are both arranged on the optical path of the multi-wavelength light source (11).

3. The integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device according to claim 1, characterized in that: The center of the deflection component (22) is provided with a light-through hole, the polarizer (21) is used to convert laser light into polarized light, the deflection component (22) is used to change the polarization direction of the polarized light, and the concave lens (23) is used to expand the irradiation range of the polarized light on the sample.

4. The integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device according to claim 3, characterized in that: The deflection component (22) is also provided with a clamping device, and the polarizer (21) can be fixed by means of the clamping device; the polarizer (21) and the deflection component (22) are arranged concentrically.

5. The integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device according to claim 1, characterized in that: The rotating assembly (33) comprises a rotating platform and an ultrasonic transducer clamping device, wherein the ultrasonic transducer clamping device is provided with a plurality of transducer fixing holes, and a plurality of the ultrasonic transducers (32) can be respectively installed in the corresponding transducer fixing holes.

6. The integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device according to claim 1, characterized in that: The signal processing component (4) further comprises a computer (43) and a synchronization control component (44). The computer (43) can convert the acquired signal into a photoacoustic image. The synchronization control component (44) can achieve timing synchronization by being connected to the multi-wavelength light source (11), the rotational deflection component (22), the rotating component (33) and the data acquisition card (42) respectively.

7. The integrated polarization, multi-wavelength and multi-frequency photoacoustic tomography device according to claim 6, characterized in that: The steps include: 1) embedding the sample in agar or directly fixing the sample on the base, aligning the required imaging section of the sample with the plane where the acoustic focus of the ultrasonic transducers (32) is located, and adding a coupling medium into the water tank (31) to immerse the sample and the ultrasonic transducers (32); 2) According to the imaging requirements of the sample, the multi-wavelength light source (11) is set to output laser light of the required wavelength; 3) adjusting the polarization component (22) to adjust the polarization direction of the laser to an initial direction of 0°; 4) rotating a plurality of ultrasonic transducers (32) with different center frequencies around a sample to collect photoacoustic signals generated by the sample, and after signal collection is completed, changing the polarization direction of the laser through the polarization component (2) to continue collecting the photoacoustic signals of the sample; 5) Processing the acquired photoacoustic signal by the computer (43) to obtain a photoacoustic image.

8. The imaging step according to claim 7, characterized in that: The rotation method of the ultrasonic transducer (32) in step 4) includes: the ultrasonic transducer (32) first rotates around the sample for one circle to complete the acquisition of a cross-section signal of the sample, and when acquiring the signal of the next image, the ultrasonic transducer (32) rotates in the opposite direction for one circle, and the above steps are repeated until the imaging is completed.

9. The imaging step according to claim 7, characterized in that: The manner in which the polarization component (2) changes the polarization direction of the laser in step 4) includes: after each signal acquisition is completed, the synchronous control component (44) outputs a signal to the deflection component (22) so that the polarizer (21) rotates 15° before continuing to acquire the signal of the next image; during the rotation of the deflection component (22), the ultrasonic transducer (32) pauses its rotation and stops signal acquisition.

10. The imaging step according to claim 7, characterized in that: The signal processing method in step 5) includes: reconstructing the photoacoustic signals collected by the plurality of ultrasonic transducers (32) at each polarization angle into a photoacoustic image through a filtered back projection algorithm.

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