Polarized optical photoacoustic quantitative three-dimensional imaging method and system

Abstract

The application provides a kind of polarized optical-photoacoustic quantitative three-dimensional imaging method and system, it is related to data processing technical field, the method comprises: obtaining the anisotropic structure parameter of sample surface layer as verification benchmark;Based on photoacoustic effect, the polarized photoacoustic signal of deep sample is collected;Based on anisotropic light energy absorption theory model, the polarized photoacoustic signal data set is reconstructed to obtain the anisotropic structure reconstruction result of deep sample;Combined with the layered structure information obtained by optical imaging, the photoacoustic reconstruction result is verified and visualized correspondingly.The application realizes the comprehensive innovation of polarized photoacoustic imaging technology from theoretical model to system implementation, to solve the high-precision, high-specificity three-dimensional imaging problem of microstructure in deep living tissue.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of data processing, in particular to a polarization optical-photoacoustic quantitative three-dimensional imaging method and system. BACKGROUND

[0002] Photoacoustic imaging technology is a new biomedical imaging technology, which combines the high contrast of optical imaging and the deep penetration advantage of ultrasonic imaging. Its physical basis is the photoacoustic effect: when pulsed laser irradiates biological tissue, the tissue absorbs light energy and produces instantaneous thermal expansion, thereby exciting ultrasonic waves; by detecting these ultrasonic waves and using a reconstruction algorithm, the light absorption distribution image inside the tissue can be inverted. In the field of three-dimensional imaging, pure optical three-dimensional imaging technology (such as confocal microscope, structured light microscope) has high resolution, but due to the strong scattering of light in biological tissue, its effective imaging depth is usually limited, making it difficult to apply to in vivo research of deep tissues such as living brain nerves. Because the scattering of ultrasonic waves in biological tissue is much lower than the scattering of light, photoacoustic imaging can achieve imaging of several centimeters in depth and has great potential in living tissue detection.

[0003] However, the existing photoacoustic imaging technology has a fundamental limitation: its theoretical model is usually based on the simplified assumption that biological tissue is an optical isotropic medium. This assumption ignores the optical anisotropy caused by the microstructure of the tissue (such as nerve fibers, muscle fibers, collagen, etc.). In fact, the orientation of the microstructure will cause the medium to exhibit optical anisotropy, thereby introducing polarization-dependent absorption (such as dichroism) and changes in propagation characteristics (such as birefringence). The traditional isotropic model lacks a parameter that describes the relationship between the polarization state and the orientation of the microstructure, and cannot represent this polarization-dependent absorption, resulting in a deviation between the reconstructed light absorption distribution image and the real microstructure when imaging tissues with significant anisotropy, and the key microstructure information such as fiber orientation cannot be truly restored. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a polarization optical-photoacoustic quantitative three-dimensional imaging method and system, which realizes a comprehensive innovation of photoacoustic imaging technology from the theoretical model to the system implementation, to solve the problem of high-precision and high-specificity three-dimensional imaging of microstructure in deep living tissues.

[0005] To solve the above technical problems, the technical solutions of the present application are as follows:

[0006] In a first aspect, a polarization optical-photoacoustic quantitative three-dimensional imaging method is provided, the method comprising:

[0007] S1, obtaining an anisotropic structure parameter of a sample surface layer as a verification reference;

[0008] S2, based on the photoacoustic effect, collecting the polarized photoacoustic signal of the deep sample;

[0009] S3, based on the anisotropic light energy absorption theoretical model, reconstructing the polarized photoacoustic signal data set to obtain a reconstruction result;

[0010] S4, verifying and visualizing the reconstruction result by using the anisotropic structure parameters of the sample surface layer.

[0011] In a second aspect, a polarized optical-photoacoustic quantitative three-dimensional imaging system comprises:

[0012] A light source module is configured to provide pulsed excitation light and continuous excitation light.

[0013] A polarization modulation module is connected in optical path with the light source module and is configured to modulate the excitation light to generate linearly polarized light with different polarization directions.

[0014] A galvanometer scanning and illumination module is connected in optical path with the polarization modulation module and is configured to receive the linearly polarized light and selectively generate a vertical illumination or oblique illumination light beam by controlling the deflection state of the galvanometer.

[0015] A sample scanning module is configured to carry and move the sample.

[0016] A signal acquisition module comprises an optical detection unit configured to receive optical signals and a photoacoustic detection unit configured to receive photoacoustic signals.

[0017] A control and image reconstruction module is connected in control or data with the polarization modulation module, the galvanometer scanning and illumination module, the sample scanning module and the signal acquisition module, and is configured to coordinate the system timing and process data to reconstruct images.

[0018] In a third aspect, a computing device comprises:

[0019] One or more processors;

[0020] A storage device is configured to store one or more programs, when the one or more programs are executed by the one or more processors, so that the one or more processors implement the above method.

[0021] In a fourth aspect, a computer readable storage medium stores a program, when the program is executed by a processor, the above method is implemented.

[0022] The above scheme of the present application at least has the following beneficial effects:

[0023] The polarization photoacoustic three-dimensional imaging theory is established from the quantum electrodynamics level for the first time, the macroscopic absorption coefficient is associated with the microscopic electric transition dipole moment, and the dependence of polarization state on tissue structure is quantified through a dot product model, thereby breaking the limitation of the traditional isotropic model and laying a solid physical foundation for high specificity imaging.

[0024] By introducing a new data acquisition mode combining "oblique illumination" with "displacement stage point scanning", and using anisotropic model to constrain the reconstruction process, image artifacts and distortions caused by tissue anisotropy can be effectively corrected, thereby realizing high-fidelity and quantitative three-dimensional visualization of microstructures such as nerve fiber orientation at a penetration depth of several centimeters.

[0025] A dual-laser common-path design is adopted to realize seamless integration and fast switching of polarization optics and polarization photoacoustic dual-modality imaging. The system has compact structure and precise control, and through the unified scheduling of a single-chip microcomputer, the accuracy and reliability of data acquisition are ensured.

[0026] The deep penetration capability of photoacoustic imaging and the specific recognition capability of polarization are combined to successfully apply to the fine structure imaging of deep tissues such as in vivo brain nerves, thereby solving the bottleneck problem of insufficient depth of pure optical imaging and lack of specificity of traditional photoacoustic imaging, and having broad application prospects in the fields of neuroscience and clinical diagnosis. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 FIG. 1 is a structural schematic diagram of a three-dimensional polarization photoacoustic-optical imaging device according to an embodiment of the present application;

[0028] Figure 2 FIG. 2 is a schematic diagram of a three-dimensional polarization photoacoustic-optical imaging method according to an embodiment of the present application.

[0029] 1-1, pulsed laser and continuous laser; 1-2, energy regulator and beam expander collimator set; 1-3, non-polarization beam splitter prism; 1-4, polarization beam splitter; 1-5, electro-optical modulator; 1-6, quarter-wave plate; 1-7, galvanometer; 1-8, objective lens; 1-9, high-precision three-axis displacement stage; 2-1, ultrasonic transducer; 2-2, filter; 2-3, amplifier; 2-4, data acquisition card; 3-1, single-chip microcomputer; 3-2, camera; 4-1, computer. DETAILED DESCRIPTION

[0030] Exemplary embodiments of the present disclosure will be described in greater detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be accurately conveyed to those skilled in the art.

[0031] In order to make the above objects, features and advantages of the present application more apparent, the following will combine the accompanying drawings to make a detailed description of the specific embodiments of the present application. Figures 1-2 The specific embodiments of the present application are described in detail.

[0032] The present application provides a polarized optical-photoacoustic quantitative three-dimensional imaging system and method, based on the system, quantitative three-dimensional imaging is realized, by fusing polarized optical measurement and photoacoustic imaging, an anisotropic light energy absorption model is established, and the model is used to constrain the photoacoustic three-dimensional reconstruction process, so that high-precision, quantitative three-dimensional imaging of deep tissues such as living brain nerves is realized.

[0033] The polarized optical-photoacoustic quantitative three-dimensional imaging system provided by the present application comprises: Figure 1 As shown in the figure, mainly includes: light source module, polarization modulation module, galvanometer scanning and oblique illumination module, sample scanning module, signal acquisition module and control and image reconstruction module.

[0034] Correspondingly, the polarized optical-photoacoustic quantitative three-dimensional imaging system comprises the following subsystems in sequence along the light path and signal flow direction:

[0035] Light source system: including pulse laser and continuous laser, respectively used for generating pulse excitation light required by polarized photoacoustic imaging and continuous excitation light required by polarized optical imaging.

[0036] Polarization modulation system: located behind the light source system, on the common light path. Including energy regulator, beam expander collimator, polarization beam splitter, electro-optic modulator and quarter-wave plate. Its function is to control the energy of the light beam from any wavelength laser, collimate, and through the combination of electro-optic modulator and wave plate, quickly and accurately generate linearly polarized light of different preset directions.

[0037] Galvanometer scanning and oblique illumination system: located behind the modulation system. Including galvanometer, lens group and objective lens. Its function is to accurately change the incident direction and focal spot position of the collimated polarized light beam by program controlling the deflection angle of the galvanometer, and then focusing through the objective lens, finally forming an oblique illumination spot with a controllable incident angle (relative to the sample normal) on the sample surface, so as to enhance the excitation specificity of specific microstructure.

[0038] Sample scanning system: including a high-precision displacement table that can be controlled to move in three dimensions, used for carrying and moving the sample. Its function is to realize point-by-point spatial coding by making the fixed oblique illumination spot traverse the sample to be measured area through the point scanning of the displacement table in the XY plane; through Z-axis movement, different thickness of samples can be adapted or multi-layer scanning can be carried out.

[0039] Signal acquisition system: including:

[0040] Optical signal acquisition unit: Composed of a scientific-grade camera, used to capture modulated optical images of the sample in polarization optical imaging mode.

[0041] Photoacoustic signal acquisition unit: It consists of an ultrasonic transducer, filter, amplifier and data acquisition card connected in sequence. It is used to receive, condition, amplify and digitize the photoacoustic signal generated by the sample in polarized photoacoustic imaging mode.

[0042] Control and image reconstruction system: This serves as the core of the entire system's control and processing. It includes a microcontroller and a computer.

[0043] The microcontroller acts as the lower-level machine, controlling and connecting with the electro-optic modulator, laser, galvanometer, displacement stage, and data acquisition card. It coordinates the timing of all hardware actions to achieve precise synchronization of polarization modulation, oblique illumination angle, point scanning position, and signal acquisition.

[0044] The computer, acting as the host computer, has built-in dedicated algorithm software to receive the acquired optical and photoacoustic data and perform image preprocessing, anisotropic parameter calculation, 3D image reconstruction based on the physical model, and bimodal result comparison as described above.

[0045] Furthermore, after passing through a polarization modulation system, the pulsed laser and the continuous laser share the subsequent galvanometer scanning, sample scanning, and signal acquisition optical paths, forming a highly efficient, compact, and spatially registered dual-mode common-path imaging system.

[0046] The specific implementation methods of each module are described in detail below with reference to the accompanying drawings.

[0047] The light source module includes two types of lasers (1-1) to meet the requirements of dual-modal imaging. A pulsed laser provides a pulsed excitation source for the polarized photoacoustic imaging mode. A continuous laser provides a continuous excitation source for the polarized optical imaging mode.

[0048] In the polarization modulation and beam combining module, the two laser paths are configured as follows:

[0049] L1 path (pulsed optical path): The beam from the pulsed laser passes sequentially through the energy regulator and the beam expander collimator assembly (1-2).

[0050] L2 path (continuous optical path): The beam from the continuous laser passes sequentially through the energy regulator and the beam expander collimator assembly (1-2).

[0051] After the two beams of light are combined at the non-polarizing beam splitter prism (NPBS, 1-3), they pass sequentially through the polarizing beam splitter (PBS, 1-4), the electro-optic modulator (EOM, 1-5), and the quarter-wave plate (QWP, 1-6) to generate high-quality linearly polarized light with different preset directions.

[0052] In the galvanometer scanning and oblique illumination module, the modulated light beam is reflected by the galvanometer (1-7), passes through a lens group consisting of a scanning lens and a tube lens, is then deflected by a reflecting mirror, and is finally focused onto the sample by the objective lens (1-8). By programmably controlling the deflection of the galvanometer (1-7), oblique illumination required for photoacoustic imaging is achieved; by fixing the galvanometer at zero position, vertical illumination required for optical imaging is achieved.

[0053] The sample scanning module is equipped with a high-precision triaxial displacement stage (1-9) to support the sample and perform point scanning.

[0054] In the signal acquisition module, the optical signal acquisition unit consists of a camera (3-2); the photoacoustic signal acquisition unit consists of an ultrasonic transducer (2-1), a filter (2-2), an amplifier (2-3), and a data acquisition card (2-4) connected in sequence.

[0055] In the control and image reconstruction module, the control unit is based on a microcontroller (3-1) and is used for global timing synchronization; the reconstruction unit consists of a computer (4-1) and algorithm software and is used for data processing and image reconstruction.

[0056] Based on the aforementioned system, the imaging method of the present invention works in a dual-modal manner. Its core lies in transforming the anisotropic light energy absorption model from theory into an achievable imaging process, and using optical imaging results to provide experimental verification for the model.

[0057] The polarization optical three-dimensional imaging method provided by this invention includes the following steps:

[0058] S1, the sample is excited by monochromatic linearly polarized light with different polarization directions, and the original optical images under linearly polarized light with different polarization directions after being modulated by the sample are recorded.

[0059] Furthermore, in step S1:

[0060] S1.1, A continuous laser generates a broadband composite laser, and a single-wavelength continuous excitation light is obtained by using a specific filter;

[0061] S1.2, The galvanometer is fixed at the zero position by the control module to ensure that the beam is perpendicular to the sample;

[0062] S1.3 controls the electro-optic modulator to sequentially switch the polarization direction of the linearly polarized light from 10° to 360° at 10° intervals, and the polarizer, QWP, and analyzer rotate synchronously, locking their relative angles.

[0063] S1.4 Complete the image acquisition for all predetermined polarization directions to obtain a complete set of original polarization optical images containing information on different linear polarization directions.

[0064] S2, the original optical images of the sample under linearly polarized light in different linear polarization directions are registered to initially eliminate the image rigidity transformation error caused by mechanical operation and obtain the aligned primary optical image;

[0065] Furthermore, in step S2:

[0066] S2.1: Perform feature-based image registration on the acquired raw optical image sequence;

[0067] S2.2: Based on the matching results, solve for the rigid transformation parameters such as translation and rotation of each image to be registered relative to the reference image.

[0068] S2.3: Apply a nonlocal mean denoising algorithm to improve the image signal-to-noise ratio and obtain a spatially aligned secondary polarization optical image.

[0069] S3, perform Fourier series analysis on the secondary polarization optical image to reconstruct the structural optical image of the sample;

[0070] Furthermore, in step S3:

[0071] S3.1 At each pixel location, extract the corresponding light intensity value in the secondary optical image across all different polarization directions to form a discrete light intensity sequence. Using the least squares method or Fourier series analysis, the sequence is fitted to the formula:

[0072] ;

[0073] Where the coefficient and It is a second harmonic component, and the amplitude of its synthesis is... This reflects the degree of anisotropy of the structure at that point, while the orientation angle... This directly gives the direction of the principal axis of the structure.

[0074] S3.2, Calculate the anisotropic amplitude and principal axis orientation angle ;

[0075] The calculated structural parameter values ​​are mapped to grayscale or color information of image pixels, ultimately synthesizing a structural optical image that can intuitively characterize the microstructure of the sample. The orientation angle is then used to... The image is mapped to color to generate a structured optical image.

[0076] One embodiment of the present invention provides a polarization optical acoustic imaging method, which includes the following steps:

[0077] S1: Polarization field preparation and oblique illumination module.

[0078] The target wavelength, pulse width, and energy parameters of the pulsed laser are set and the laser is started to excite the sample. The control module drives the galvanometer (1-7) to deflect to a preset non-zero angle, so that the beam focused by the objective lens enters the sample at a specific tilt angle (i.e., oblique illumination). At the same time, the electro-optic modulator (1-5) is controlled to modulate the polarization direction of each laser pulse according to a preset sequence.

[0079] S2: Sample point scanning and photoacoustic signal acquisition module.

[0080] A high-precision displacement stage drives the sample to perform two-dimensional point scanning, allowing the oblique illumination spot to traverse the test area. At each scanning point and in each polarization direction, the ultrasonic transducer (2-1) receives the photoacoustic signal, which is then filtered, amplified, and digitally recorded by the data acquisition card (2-4).

[0081] Specifically, the dual-axis displacement stage is controlled to perform point scanning along the X and Y axes. After traversing one row of X-axis positions, the Y-axis coordinate is adjusted to enter the next row of traversal. After each positioning, a preset waiting time is maintained to obtain an effective depth signal. Photoacoustic signals are collected by an ultrasonic transducer, converted by a data acquisition device according to a preset timing sequence, and then transmitted to the computer by a microcontroller.

[0082] S3: Anisotropic model reconstruction, inversion of deep structure.

[0083] The LabVIEW reconstruction code on the computer processes the real-time acquired data and displays it dynamically in the image display window; after completing the full-area scan, the raw data is imported into MATLAB for image analysis.

[0084] Specifically, 3D reconstruction is performed based on the preprocessed data. First, a maximum projection image is generated using the depth time-series signal corresponding to the XY position to present the sample's depth structure, and then a complete 3D imaging is achieved. S4: 3D Visualization and Theoretical Verification

[0085] The three-dimensional initial pressure distribution reconstructed from S3.2 was obtained using volume rendering technology. The structured optical image (surface reference) obtained in S1.3 is converted into a visualized three-dimensional image. Spatial registration and quantitative comparison are performed between the structured optical image (surface reference) obtained in S1.3 and the photoacoustic three-dimensional image (deep inversion result) obtained in S4.1 to analyze the degree of agreement between the two in terms of microstructural orientation.

[0086] In terms of imaging theory derivation, the three-dimensional polarization optical-photoacoustic imaging theory involved in this invention includes a three-dimensional polarization optical reconstruction mathematical model and a three-dimensional polarization photoacoustic physical reconstruction model.

[0087] Physical scenario: The sample is fixed in place, while the polarizer (P), quarter-wave plate (QWP), and analyzer (A) rotate synchronously, with their relative angles locked: the polarizer and analyzer are always perpendicular (90° angle); the polarizer and the QWP transmission axis are always at 45°; the light propagation sequence is: incident light → polarizer (P) → QWP → sample (S) → analyzer (A).

[0088] The polarizer projects the incident light onto the β direction, forming linearly polarized light whose polarization direction rotates with β. Only light along this direction is allowed to pass through. The polarizer matrix is ​​as follows:

[0089] ;

[0090] The optical experiments used sample slices with a thickness of only a few hundred micrometers, which were pure birefringent materials. Dichroic absorption was not considered, and only a phase delay was generated. Coordinate system transformation (laboratory coordinate system ↔ sample principal axis coordinate system) was achieved through a rotation matrix, and the birefringence modulation matrix was a diagonal matrix. Combined with rotation matrix Sample matrix synthesis And simplify:

[0091]

[0092] Among them, the transmission axis of QWP rotates with β to The fast axis is along the transmission axis, and the slow axis is delayed relative to the fast axis. ( Its own principal axis matrix. Transformed by rotation matrix And simplify:

[0093] ;

[0094] further:

[0095] ;

[0096] The polarization direction of the analyzer rotates with β to β+90°, becoming perpendicular to the polarizer, and its matrix form is as follows:

[0097] ;

[0098] Therefore, according to the Jones matrix operation rule: the order of matrix multiplication is opposite to the direction of light propagation (matrix of the later-acting device × matrix of the earlier-acting device), that is, the emitted electric field: .

[0099] Polarizer output electric field Substitute and ,have to:

[0100] ;

[0101] QWP emitted electric field Substitute and Expand the calculation:

[0102] Further simplified to:

[0103] ;

[0104] Sample emitted electric field Substitute and ,use , , Simplifying, we finally get:

[0105] ;

[0106] Furthermore, The coefficients are:

[0107] ;

[0108] ;

[0109] Similarly, The coefficients are:

[0110] ;

[0111] ;

[0112] Analyzer output electric field Substitution and ,use , Further simplification, finally Both the real and imaginary parts are , Linear combinations of (in the following form, omitting complex constant factors and higher-order terms):

[0113] ;

[0114] in For containing δ and K are constants. The squares of the moduli of the two components are added together. Combine similar terms (DC terms, item, (The terms are superimposed separately) to obtain the standard modulation form of light intensity:

[0115] ;

[0116] The relationship between each coefficient and α and δ, where K is the background light intensity:

[0117] DC component: ;

[0118] Cosine coefficient: ;

[0119] Sine coefficient: .

[0120] Furthermore, the birefringence phase difference δ is solved.

[0121] Define the amplitude of the second harmonic synthesis: Substitute the coefficients into the relationship:

[0122] ;

[0123] because ,hour Combined with blank calibration K value (δ=0 after sample removal), ),have to:

[0124] ;

[0125] Furthermore, the direction of the optical axis α is determined.

[0126] Depend on , The ratio relationship:

[0127] ;

[0128] Summarized as follows:

[0129] ;

[0130] Because a patch slice of the hippocampus from an AD mouse brain with a thickness of 200 nm is used, it is approximately a purely birefringent sample. The positional order of the QWP and sample (whether it is "polarizer → sample → QWP → analyzer" or "polarizer → QWP → sample → analyzer") will affect the details of the coefficients in the light intensity formula, but will not affect the core logic (the light intensity remains a "DC + second harmonic" structure) and the feasibility of parameter extraction. Essentially, the different order of polarization state modulation leads to differences in mathematical expressions, but ultimately α and δ can be solved. (The difference in the order of QWP and sample only changes the quantitative values ​​of the phase modulation factor and light intensity coefficient, without destroying the core characteristics of "2β frequency harmonic modulation," and the final light intensity follows the same standard structure. This similarity stems from the essential constraint of polarization modulation under synchronous rotation, ensuring the uniformity of sample parameter solutions under different optical path configurations.)

[0131] Specifically, in step S1, an anisotropic material containing linear birefringence and linear dichroism is considered, and its principal axis coordinate system is set as follows ( ) and laboratory coordinate system ( The included angle is The electric field vector of the incident light in the laboratory coordinate system is expressed as:

[0132] ;

[0133] By rotation matrix Transform the electric field vector from the laboratory coordinate system to the material principal axis coordinate system:

[0134] ;

[0135] Where the rotation matrix The expression is:

[0136] ;

[0137] The time-domain electric field vector of a monochromatic plane electromagnetic wave propagating along the z-axis is:

[0138]

[0139] In the formula: , These represent the electric field amplitudes in the x and y directions, respectively. For wave number, Angular frequency ( (the frequency of light); , These are the initial phases of the electric field in the x and y directions, respectively; , These are the unit vectors for the x and y axes, respectively.

[0140] Simplified representation using complex form (retaining only frequency domain information, time domain factor) (can be ignored)

[0141] ;

[0142] In the formula , Let x be the complex amplitude of the electric field in the x and y directions, and y be the global phase factor. It does not affect the light intensity (the light intensity is independent of the phase), so the subsequent derivation can be omitted.

[0143] The polarizer outputs linearly polarized light in the x-direction. Its function is to project the polarization state of any incident light onto the x-axis direction. The matrix expression is as follows:

[0144] ;

[0145] If the initial electric field of the incident light is Then the output electric field of the polarizer is:

[0146] ;

[0147] In the formula Let x be the electric field component of the incident light in the x-direction, and then take... (Normalization processing), that is .

[0148] The birefringence effect of anisotropic materials causes a phase difference in the electric field components in the x and y directions. Its modulation matrix is ​​a diagonal matrix (when the principal axis coincides with the laboratory coordinate system):

[0149] ;

[0150] In the formula The birefringence phase difference is defined as:

[0151] ;

[0152] in, For material thickness, The difference in refractive index between the x and y directions of the material;

[0153] When the angle between the principal axis of the material and the x-axis of the laboratory is At this time, a rotation matrix is ​​required. Transform to the principal axis coordinate system; the material modulation matrix is ​​now:

[0154] ;

[0155] Where the rotation matrix Inverse matrix .

[0156] By simplifying using trigonometric identities, we finally obtain:

[0157] ;

[0158] Combining Euler's formula , Further simplified to:

[0159] ;

[0160] The analyzer outputs linearly polarized light in the y-direction. Its function is to project the polarization state of any incident light onto the x-axis direction. The matrix expression is as follows:

[0161] ;

[0162] This derivation adopts the concept of equivalent transformation: the physical scenario of "synchronous rotation of polarizer + QWP + analyzer and sample fixed" is equivalent to "the device system is fixed and the relative angle between the sample and the system changes with the rotation angle β". Therefore, the polarization modulation process is described by adjusting the rotation matrix of the sample (reflecting the change of the relative angle), and the physical essence is completely consistent with the actual scenario.

[0163] Therefore, for ease of understanding, the evolution chain is described as linearly polarized light (emission from polarizer) → QWP (linearly polarized light → circularly polarized light) → sample (circularly polarized light → elliptically polarized light, birefringence modulates phase difference δ) → analyzer (outputs light intensity after screening), and it is described in terms of rotating the sample. However, in actual experiments, the sample needs to be kept fixed on the displacement stage, and the cage structure "polarizer-QWP-analyzer" is rotated synchronously using a motor.

[0164] The core of the polarization modulation system is a series structure of "polarizer-QWP-material-analyzer". The overall transfer matrix of the polarization modulation system is the product of the matrices of each component, and the output electric field vector is... The transitive relationship can be represented as:

[0165]

[0166] In the formula: The x-direction linearly polarized electric field output by the polarizer; This is the polarization state conversion matrix (used to convert between linear polarization and other polarization states). This is the polarization modulation matrix for anisotropic materials (its core function is to introduce a birefringence phase difference δ). This is the projection matrix of the analyzer (here, the analyzer is along the y-axis, and only the y-direction polarization component is allowed to pass through).

[0167] The light intensity is the square of the electric field amplitude (ignoring the constant coefficient and only considering the relative light intensity), that is:

[0168] ;

[0169] in The emitted electric field vector The modulus (amplitude) needs to be solved through complex modulus operations.

[0170] Considering the analyzer angle Material principal axis angle The combined effect of the birefringence phase difference δ means that the magnitude of the emitted electric field component can be simplified through trigonometric identity transformations (the process is as follows):

[0171] ;

[0172] The formula utilizes the double-angle formula ( ) and Euler's formula ( Eliminating the complex exponent term transforms the expression into a real number form containing only trigonometric functions.

[0173] Squaring the electric field modulus, combined with , After simplifying the identity, we finally obtain the formula for the emitted light intensity:

[0174]

[0175] In the formula: The incident light intensity (polarizer output light intensity); The angle between the analyzer and the x-axis. The angle between the principal axis of the material and the x-axis; light intensity Follow Periodic changes, with a period of (because it contains) item).

[0176] To facilitate subsequent parameter fitting and inversion, equation (11) is further expanded into the standard harmonic form. Coefficients are defined as follows:

[0177] DC component: (Basic light intensity, independent of angle, reflects the average transmittance of the material).

[0178] Sine coefficient: ;

[0179] Cosine coefficient: ;

[0180] Substituting into equation (11) and expanding using trigonometric functions, we finally obtain:

[0181]

[0182] This form is a typical second-order harmonic function, containing only a DC component and second-order harmonic terms, and can be obtained through least-squares fitting of experimentally measured values. - The data can be directly inverted to obtain the birefringence phase difference δ and principal axis angle φ of the material, or it can be solved by discrete Fourier transform.

[0183] In the above process This represents the result when the sample rotates clockwise relative to the cage system. When rotating counter-clockwise, the expression should be: At this point, the formula for light intensity becomes The simplified result is Therefore, in other words, without distinguishing the sample rotation direction, the original light intensity formula is: When the sample is rotated clockwise, the substitution is carried over ( ),

[0184] Right now: ,

[0185] Expanding, we get: ;

[0186] Substitute ( ),Right now: ,

[0187] Expanding, we get: .

[0188] Finally, the optical parameters are calculated: birefringence phase difference: Spindle direction: .

[0189] The three-dimensional polarized photoacoustic physical reconstruction model involved in this invention is based on a rigorous photoacoustic imaging physical framework from microscopic quantum interactions to macroscopic signal generation, namely the multi-physics coupling theory of photoacoustic effects: from quantum leaps to ultrasonic emission. It explores a quantum mechanical description of the interaction between light and matter, with the core idea being to take the anisotropic energy level transitions induced by polarized light as the source of the entire process.

[0190] First, in photoacoustic experiments, a simplified engineering formula can be directly obtained through extensive data observation. This formula ignores complex physical details, retaining only the core relationship between "adjustable parameters" and "photoacoustic signal intensity," serving as the starting point for engineering applications. Its expression is:

[0191] (Equation 1.1)

[0192] In the formula, The intensity of the photoacoustic signal (in engineering, relative intensity is commonly used, such as the voltage amplitude of a detector). It is the light absorption coefficient; For Grueneisen coefficient; The photothermal conversion coefficient; This refers to luminous flux.

[0193] Equation 1.1 can explain the influence of "light intensity and sample characteristics" on the signal, but it cannot explain two key experimental phenomena:

[0194] (1) Polarization-dependent phenomenon: When light with different polarization directions (such as x-polarization and y-polarization) is excited into the same anisotropic sample (such as a crystal), the light flux will change. Although they are the same, the photoacoustic signal strengths still differ;

[0195] (2) Direct influence of electric field magnitude: luminous flux Essentially, it is a macroscopic manifestation of electric field energy flow density. However, the engineering formulas do not clearly define how the vector characteristics (magnitude + direction) of the electric field affect absorption.

[0196] The core issue lies in Equation 1.1 and Since these are all scalars, they cannot describe the degree of matching between the electric field direction and the sample's electronic transition direction, which is precisely the core of polarization dependence. Therefore, it is necessary to upgrade the scalar parameters to vector form to fill the gap in the microscopic physical mechanism.

[0197] To explain the polarization dependence, we need to trace back... The microscopic origin of light absorption is that electrons absorb photon energy and transition from the valence band to the conduction band. This process is directly related to the vector characteristics of the electric field.

[0198] First, when incident light irradiates a molecule or chromophore, the quantum transition of electrons from the ground state to the excited state is a resonant coupling between the electromagnetic wave and the electric and magnetic dipole transition moments of the molecule. For non-helical molecules or achiral chromophores irradiated with linearly polarized light, the interaction between the magnetic dipole moment and the electromagnetic wave is negligible; in this case, the light absorption of the chromophore is mainly contributed by the electric transition dipole moment.

[0199] The probability of an electron transition is determined by the "matching degree between the electric field vector and the electron transition dipole moment vector," derived using the Fermi golden rule. The Fermi golden rule is the core formula describing the probability of quantum transitions, and its general form is:

[0200] (Equation 2)

[0201] in, The Hamiltonian is the interaction between the light field and the electron. For the transition matrix elements, This represents the final state density.

[0202] The electric field of light is a transverse wave vector, and a complete description requires both its magnitude (amplitude) and direction (polarization):

[0203] (Equation 3)

[0204] In the formula, Let be the electric field amplitude vector, with a magnitude of The direction is determined by the polarization state; Let the wave vector of light satisfy the transverse wave property. ;

[0205] Specifically, the interaction energy between the electric field vector of the light field and the electron charge is expressed as:

[0206] (Equation 4)

[0207] Substituting into the electric field vector expression (Equation 3), and considering the monochromaticity of the light field, it can be simplified to:

[0208] (Equation 5)

[0209] In the formula, hc represents Hermitian conjugation, which physically corresponds to the photon emission process and can be focused on the first term during absorption.

[0210] Substituting the Hamiltonian into the matrix element expression, and utilizing the orthogonality of the Bloch function... (Conservation of momentum) gives:

[0211] ;

[0212] Define the transition dipole moment vector (Describing the directional characteristics of electronic transitions, inherent properties of the sample), then the matrix elements simplify to:

[0213] .

[0214] Substituting the matrix elements into the Fermi-Golden Rule and integrating over the final state energy (considering the continuous distribution of the density of states), we finally obtain the transition probabilities of the absorption process:

[0215] ;

[0216] in For band gap energy, This represents the density of states from the top of the valence band to the bottom of the conduction band, which is related to the band structure of the sample. The transition dipole moment vector. (Describe the directional characteristics of electronic transitions, inherent properties of the sample); transition probability (The square of the vector dot product reflects the degree of directional matching:) and The smaller the angle, the higher the transition probability.

[0217] Macroscopic absorption coefficient It is the integral sum of the transition probabilities of all electrons within a unit volume, i.e. ( (The product of the initial occupied number and the final empty number), combined with the differential form of the Lambert-Beer law, allows the macroscopic absorption coefficient to be upgraded from a scalar form to a vector form dependent on the polarization state of the incident light field, ultimately yielding the vector absorption coefficient:

[0218] ;

[0219] in: The constant term includes the angular frequency of light. Number density of absorption centers of the sample (e.g., macroscopic parameters) (Energy level broadening): Corrects the mathematical singularity of the ideal quantum model (the electronic energy levels in real solids have widths due to scattering / defects, rather than sharp peaks), so that the calculation results are consistent with experiments;

[0220] Physical meaning: The vector absorption coefficient simultaneously includes the magnitude of the electric field. ) and direction (with The angle between the two poles (the angle between the poles) has a perfect effect on the polarization-dependent phenomenon.

[0221] Engineering formulas assume an "ideal sample," but real solids exhibit three mechanisms that lead to energy level broadening (electron-phonon scattering, electron-electron scattering, and lattice defects), which need to be introduced. Correction (i.e., replacing the ideal Dirac delta function with the Lorentz function). (Eliminating the non-physical result of "infinite transition probability"); combining the thermoelastic model (conversion of thermal expansion to sound pressure), the vector absorption coefficient is... Substituting into the engineering formula, and supplementing with "sound propagation delay" and "solid elasticity parameters," we obtain the original physical formula for full vector sound pressure: integrating the vector absorption coefficient, thermoelastic conversion, and sound propagation delay, we finally obtain:

[0222] ;

[0223] Substitution The complete form (Equation 3), after expansion:

[0224] ;

[0225] In the formula, The electric field amplitude vector determines the polarization direction and intensity of light; The vector of the electronic transition dipole moment describes the directional characteristics of the transition; The Gruenisen coefficient quantifies the lattice anharmonicity (thermal-to-acoustic conversion efficiency). Photothermal conversion efficiency (ignoring losses such as fluorescence and scattering); The energy level broadening factor; The Dirac delta function characterizes the propagation delay (speed of sound) of the sound pressure pulse. Distance of transmission ); The bulk modulus of elasticity of a solid is a key elastic parameter that connects thermal expansion deformation with the generation of sound pressure.

[0226] In engineering, fixed elastic constants and time delays are usually ignored, and relative intensity is used instead of absolute sound pressure. This allows for engineering simplification of the full-vector sound pressure formula. Definition

[0227] ;

[0228] The full-vector sound pressure formula can be simplified in engineering. Therefore, the intensity of the photoacoustic signal generated after vector absorption by the sample absorber is:

[0229] (Equation 2.2)

[0230] in, The direction vector of molecules on the sample. Light absorption coefficient, For the Grueneisen coefficient, The photothermal conversion coefficient, This refers to luminous flux.

[0231] The full-vector formula does not negate the engineering formula, but rather supplements it with the effects of "polarization and real samples." Specific engineering applications can choose the appropriate formula based on their needs.

[0232] (1) Simple scenario: When the excitation source is natural light (without a fixed polarization direction) and the sample is an isotropic material (with no directional preference in the transition dipole moment), the polarization dependence can be ignored, and the photoacoustic signal intensity can be quickly estimated directly using the traditional engineering formula (Equation 1.1); (2) Complex scenario: When the excitation source is polarized light and the sample is anisotropic material (such as crystals or oriented biological tissues), the vector simplification formula (Equation 2.2) needs to be used for accurate calculation; or a polarization correction factor can be introduced into the traditional engineering formula. To simplify the calculation, the revised formula is as follows:

[0233] ;

[0234] in It is the absorption coefficient after polarization averaging. (when the directions are perfectly matched) Specifically, step S4 includes:

[0235] S41, its core item In and Representation;

[0236] S42, calculate the expansion of the squares of both and express it in matrix form.

[0237] Further, in step S41, for unit vector Used to describe the direction of observation, it can be represented by row vectors and column vectors respectively. The row vector form is shown in formula (Equation 3.1):

[0238] (Equation 3.1)

[0239] The column vector form is shown in formula (Equation 3.2):

[0240] (Equation 3.2)

[0241] in, Polar angle refers to the angle between the polar vectors and the unit vector. The angle between the z-axis and the z-axis has a range of values. ; The azimuth angle is a unit vector. The angle between the projection onto the xy-plane and the x-axis ranges from 0 to 1. .

[0242] Furthermore, regarding the incident photoelectric field vector It is perpendicular to the wave vector of the light wave. The specific method for constructing a vector at a specific angle within a plane is as follows:

[0243] In three-dimensional space, perpendicular to A plane can be traversed by two orthogonal unit vectors. and Zhang Cheng, the two correspond to the azimuth tangent and polar tangent respectively.

[0244] Azimuth direction base vector The expression for the tangential direction along the wave vector azimuth angle variation is:

[0245] (B.3)

[0246] Polar Angle Direction Base Vector The expression for the tangential direction along the polar angle variation of the wave vector is:

[0247] (B.4)

[0248] by As a reference direction, in the direction perpendicular to In-plane construction and The included angle is unit vector Utilizing the principle of orthogonal decomposition of two-dimensional plane vectors, through... and Linear combination implementation:

[0249] (B.5)

[0250] In the formula, and They are respectively exist and Projection coefficients in the direction.

[0251] Substituting equations (B.3) and (B.4) into equation (B.5), and expanding, we get... Cartesian coordinate components:

[0252] ;

[0253] Finally, perpendicular to the wave vector (polar angle) Azimuth ), and in relation to the reference direction The included angle is The length of the module is The vector, whose rectangular coordinates are ultimately expressed as:

[0254] ;

[0255] In step S42, the expansion of the square term and the derivation of variable separation are completed.

[0256] Known ,

[0257] make: , , ,but .

[0258] Expanding using the perfect square formula: ;

[0259] Further simplification yields:

[0260] ;

[0261] ;

[0262] ;

[0263] ;

[0264] ;

[0265] ;

[0266] Combining the results of the above expansions, we get The complete expression.

[0267] Observation reveals that each term can be decomposed into a single component containing only the wave source parameters. Factors containing only observation parameters The product of the factors of ), i.e.:

[0268] (Equation 3.4)

[0269] in, It contains only coefficients (vectors) The (each component) It contains only basis functions (vectors) The (each component) achieves variable separation.

[0270] Vectors M and V are crucial foundations for the subsequent derivation of the physical quantity PA; they are related to the wave source / polarization characteristics and the observation direction, respectively. It is an 11-dimensional column vector, and its expression is shown in (Equation 3.5):

[0271] (Equation 3.5)

[0272] vector Each component is about (wave vector polar angle) (Wave vector azimuth) A function of (electric field polarization angle), which includes trigonometric functions (such as...) , ), square terms, and product terms. As a scale parameter, its existence is to make the vector The dimensions of the vector conform to the requirements of actual physical scenarios. It is only related to the wave source / polarization characteristics, which means that for a specific wave source and polarization state, the vector It is a constant value.

[0273] vector Similarly, for an 11-dimensional column vector, its expression is shown in Equation 3.6:

[0274] (Equation 3.6)

[0275] vector Each component is only related to the observed parameters and The function includes a constant term and trigonometric functions (such as...). , ), product terms (such as ) and square terms (such as ). and vector Different, vector It is only related to the observation direction; when the observation direction changes, the vector... The situation will change accordingly.

[0276] Substituting matrices M and V into Equation 3.4, and then substituting the result into Equation 2.2, a new theoretical model is obtained, which uses the intensity of the photoacoustic signal generated by the interaction between the three-dimensional polarized incident light and the material structure as the supporting algorithm for the imaging system.

[0277] = ;

[0278] The invention relates to the theoretical work on polarized photoacoustic-optical three-dimensional imaging, which is based on the photoacoustic effect principle and polarized optics theory, constructing a complete theoretical system of polarized photoacoustic interaction. First, it clarifies the physical process of the interaction between polarized light and biological tissue: after polarized light is incident, different molecules in the tissue (such as the myelin sheath in nerve fibers) will absorb light with different polarization directions differently. This absorption difference is converted into polarization-related characteristics of the ultrasound signal through the photoacoustic effect. By establishing a physical model including parameters such as polarization angle, absorption coefficient, and ultrasound propagation speed, a quantitative relationship between the polarized photoacoustic signal characteristics and the tissue microstructure is derived, overcoming the limitation of traditional photoacoustic theory that ignores polarization information. Specifically, in the context of in vivo brain nerve imaging, by analyzing the influence of the angle between the incident angle θ of polarized light and the orientation of the nerve fiber on the light absorption efficiency, an expression for the photoacoustic signal amplitude A is derived: Where k is the system constant, I0 is the intensity of incident polarized light absorbed by the molecules, α(θ) is the tissue absorption coefficient related to the polarization angle, and β is the photoacoustic conversion efficiency of the tissue. This theory quantifies the correlation between polarization information and neural tissue structure for the first time, providing a theoretical basis for high-precision imaging.

[0279] The three-dimensional polarized photoacoustic-optical imaging method provided by this invention involves scanning the sample surface with a galvanometer. At each scanning point on the sample surface, excitation light under different incident angles and polarization states is modulated to measure the photoacoustic / optical signal intensity under excitation light of different linear polarization states. An initial image of the sample surface structure is constructed using the signal intensity under excitation light of different linear polarization directions. Through preprocessing of the initial image, optical / photoacoustic reconstructed images under each linear polarization state are obtained. Compared to traditional polarized photoacoustic imaging, this invention can obtain polarized optical three-dimensional reconstruction results as a reference while sharing most of the optical path. This invention has the ability to measure the optical / photoacoustic signal intensity of samples under excitation light of different linear polarization directions within the same optical path. The device for implementing this method has a simple structure, is easy to use, and has great application prospects in the fields of bioimaging and detection of the surface structure and conformation of biological tissues.

[0280] Embodiments of the present invention also provide a computing device, including: a processor and a memory storing a computer program, wherein the computer program, when executed by the processor, performs the method described above. All implementations in the above method embodiments are applicable to this embodiment and can achieve the same technical effects.

[0281] Embodiments of the present invention also provide a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the method described above. All implementations in the above method embodiments are applicable to this embodiment and can achieve the same technical effects.

[0282] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polarized optical-photoacoustic quantitative three-dimensional imaging method, characterized by, The method comprises the following steps: S1, obtaining the anisotropy structure parameter of the sample surface layer as a verification reference, comprising: S1.1, sequentially exciting the sample by continuous laser with different linear polarization directions, and collecting the corresponding original optical image sequence; S1.2, performing image registration and denoising processing on the original optical image sequence to obtain spatially aligned secondary polarized optical images; S1.3, performing Fourier analysis on the secondary polarized optical images to obtain the anisotropy parameter and direction angle of the sample surface layer, thereby generating a structure optical image representing the microstructure; S2, based on the photoacoustic effect, collecting the polarized photoacoustic signal of the deep sample, comprising: S2.1, modulating the pulsed laser to produce a series of linearly polarized light with different preset directions, and controlling the linearly polarized light to be obliquely incident at a specific angle relative to the normal of the sample surface to form oblique illumination; S2.2, driving the sample to perform two-dimensional point scanning by a displacement table, so that the oblique illumination spot traverses the sample area to be measured; S2.3, at each scanning point and each polarization direction, collecting the photoacoustic signal generated by the sample, which is converted into a digital signal after processing, and finally obtaining a polarized photoacoustic signal dataset containing spatial position and polarization state information; S3, based on the anisotropic light energy absorption theoretical model, reconstructing the polarized photoacoustic signal dataset to obtain a reconstruction result, comprising: S3.1, constructing an anisotropic light energy absorption theoretical model, which characterizes the macroscopic absorption coefficient as the dot product relationship between the excitation light polarization state vector and the sample tissue structure feature vector; S3.2, coupling the anisotropic light energy absorption theoretical model as a physical constraint into the image reconstruction algorithm to solve the polarized photoacoustic signal dataset, and inversely calculating the three-dimensional initial pressure distribution of the deep sample representing the anisotropic microstructure, as the reconstruction result, comprising: S3.2a, the dot product relationship between the macroscopic absorption coefficient defined by the anisotropic light energy absorption theoretical model and the excitation light polarization state vector and the tissue structure feature vector is taken as a physical constraint condition; S3.2b, substituting the physical constraint condition into the improved filtered back-projection algorithm or iterative reconstruction algorithm to form a constraint reconstruction algorithm; S3.2c, using the constraint reconstruction algorithm to solve and calculate the polarized photoacoustic signal dataset, and inversely calculating the three-dimensional initial pressure distribution of the deep sample, which quantitatively represents the spatial orientation and absorption characteristics of the anisotropic microstructure, as the reconstruction result; S4, verifying and visualizing the reconstruction result using the anisotropic structure parameter of the sample surface layer, comprising: S4.1, performing three-dimensional visualization processing on the reconstruction result, i.e. the three-dimensional initial pressure distribution, using volume rendering technology to generate a photoacoustic three-dimensional image that can clearly present the deep fiber orientation; S4.2, spatially registering the structure optical image generated by S1.3 with the photoacoustic three-dimensional image generated by S4.1, and quantitatively comparing the microstructure orientation information of the two to verify the accuracy and effectiveness of the anisotropic light energy absorption theoretical model for deep structure inversion.

2. The polarized optical- photoacoustic quantitative three-dimensional imaging method according to claim 1, characterized in that, S2.3, at each scanning point and each polarization direction, collecting photoacoustic signals generated by the sample, converting the processed signals into digital signals, and finally obtaining a polarization photoacoustic signal data set containing spatial position and polarization state information, including: S2.3a, at each scanning point and each polarization direction, receiving original photoacoustic signals generated by the sample through an ultrasonic transducer; S2.3b, sequentially filtering and amplifying the original photoacoustic signals to obtain analog electrical signals after conditioning; S2.3c, converting the analog electrical signals into digital signals using a data acquisition card; S2.3d, arranging and storing the digital signals according to corresponding scanning point positions and polarization directions, and finally forming the polarization photoacoustic signal data set containing spatial position and polarization state information.

3. A polarized optical-photoacoustic quantitative three-dimensional imaging system for performing the method of any one of claims 1 to 2, characterized in that, Comprising: a light source module for providing pulsed excitation light and continuous excitation light; a polarization modulation module connected in optical path with the light source module, for modulating the excitation light to generate linearly polarized light of different polarization directions; a galvanometer scanning and illumination module connected in optical path with the polarization modulation module, for receiving the linearly polarized light and selectively generating a vertical illumination or oblique illumination beam by controlling the deflection state of the galvanometer; a sample scanning module for carrying and moving the sample; a signal acquisition module including an optical detection unit for receiving optical signals and a photoacoustic detection unit for receiving photoacoustic signals; a control and image reconstruction module connected with the polarization modulation module, the galvanometer scanning and illumination module, the sample scanning module and the signal acquisition module for coordinating system timing and processing data to reconstruct images.

4. A computing device, comprising: Comprising: one or more processors; a storage device for storing one or more programs, when the one or more programs are executed by the one or more processors, the one or more processors implement the method of any one of claims 1-2.

5. A computer readable storage medium, characterized in that, The computer readable storage medium stores a program which is executed by the processor to implement the method of any one of claims 1-2.

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