Double-rotation zoom photoacoustic endoscope based on Moire superlens and imaging method

Abstract

The invention discloses a double-rotation zoom photoacoustic endoscope based on a Moire super lens and an imaging method. The endoscope comprises a host and a probe. The method comprises the following steps: generating a pulse laser signal and transmitting the pulse laser signal to a probe through a single-mode fiber; the first Moire superlens is driven to rotate around an optical axis to form a relative angle with the second superlens, and a focusing light field is output; the focused light field is deflected to target tissue, and an ultrasonic signal is generated; performing conversion processing on the ultrasonic signal to obtain a digital ultrasonic signal data stream; and in combination with the digital ultrasonic signal data stream and the spatial position information of the probe, performing image reconstruction through a time reversal algorithm to obtain a three-dimensional absorption coefficient distribution diagram. According to the invention, the focusing light field depth can be continuously adjusted and the photoacoustic signal excitation efficiency can be optimized, so that the imaging requirements of dynamically matching different tissue depths in real time can be met. The double-rotation zoom photoacoustic endoscope based on the Moire superlens and the imaging method can be widely applied to the technical field of photoacoustic endoscope imaging.

Description

Technical Field

[0001] The present invention relates to the field of photoacoustic endoscope imaging technology, and in particular to a double-rotation zoom photoacoustic endoscope based on a moiré superlens and an imaging method. Background Art

[0002] Photoacoustic endoscopy combines optical excitation with ultrasonic detection, achieving high-resolution imaging of biological tissues through the photoacoustic effect. This technology has important applications in minimally invasive diagnosis of narrow cavities such as the digestive tract and blood vessels. The focusing module of conventional photoacoustic endoscopes typically relies on mechanically driven axial movement of a lens or ultrasonic transducer to achieve focus adjustment. This mechanical focusing approach suffers from slow response speeds (on the order of seconds) and bulky size, making it difficult to meet the requirements for real-time imaging of dynamic tissues (such as pulsating blood vessel walls). Furthermore, long-term wear of the mechanical moving parts can lead to reduced accuracy, limiting the reliability and lifespan of the device. In recent years, metalenses (metalens) have been introduced into the field of photoacoustic imaging due to their ultrathin (subwavelength thickness) and lightweight properties. By precisely controlling the phase of light or sound waves through subwavelength structural units, they achieve efficient focusing. However, existing metalenses are mostly fixed-focal-length designs. Once manufactured, the focal position cannot be adjusted. Imaging at varying tissue depths (e.g., scanning from the mucosa to the muscularis) requires lens replacement or redesign of the metasurface structure, significantly increasing operational complexity and cost. In order to solve the problem of dynamic focus adjustment, existing attempts have been made to combine adjustable mechanisms with metalenses. For example, electromagnetic drive is used to change the resonance characteristics of the metasurface unit, or a microfluidic cavity is used to adjust the effective refractive index. However, these methods require the introduction of external drive components (such as electromagnets, pumps and valves), which leads to a significant increase in system complexity and volume, making it difficult to adapt to the miniaturization requirements of endoscopes (the probe diameter usually needs to be ≤3mm). In addition, mechanically coded metalenses achieve discrete focusing by rearranging the unit structure. Its adjustment process relies on physical displacement, which is prone to structural wear and cannot achieve continuous zoom. Summary of the Invention

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a dual-rotational zoom photoacoustic endoscope and imaging method based on a moiré superlens, which can continuously adjust the depth of the focused light field and optimize the excitation efficiency of the photoacoustic signal, thereby realizing real-time dynamic matching of imaging requirements at different tissue depths.

[0004] The first technical solution adopted by the present invention is: a dual-rotation zoom photoacoustic endoscope based on a moiré superlens, comprising a host and a probe, wherein the host and the probe are electrically connected, and the probe introduces a superlens beam focusing module, wherein:

[0005] The probe is used to obtain electrical signals from target tissue;

[0006] The host is used to perform preprocessing and visual display processing according to the electrical signal of the target tissue to obtain a three-dimensional absorption coefficient distribution map of the target tissue.

[0007] Furthermore, the probe includes a metalens beam focusing module, an ultrasonic receiving module and a dual-axis rotation control unit, wherein the ultrasonic receiving module is located at the optical path output end of the metalens beam focusing module, and the dual-axis rotation control unit is electrically connected to the metalens beam focusing module, wherein:

[0008] The superlens beam focusing module is used to stimulate the target tissue with a pulsed laser signal to obtain an ultrasonic signal of the target tissue;

[0009] The ultrasonic receiving module is used to convert and process the ultrasonic signal of the target tissue to obtain the electrical signal of the target tissue;

[0010] The dual-axis rotation control unit is used to control the metalens beam focusing module to rotate around the optical axis.

[0011] Furthermore, the metalens beam focusing module includes a single-mode optical fiber, a first moiré metalens, a second moiré metalens and a reflector, the single-mode optical fiber is fixedly connected to the first moiré metalens through a fiber metalens connector, the first moiré metalens and the second moiré metalens are coaxially arranged, the second moiré metalens is located at the optical path output end of the first moiré metalens, and the reflector is located at the optical path output end of the second moiré metalens, wherein:

[0012] The single-mode optical fiber is used to obtain a pulsed laser signal and control the first moiré superlens to rotate synchronously;

[0013] The first moiré superlens is used to change the wavefront of the pulsed laser signal passing through the moiré superlens, and transmit the changed pulsed laser signal to the second moiré superlens, and form a relative angle with the second moiré superlens;

[0014] The second moiré superlens is used to change the phase superposition relationship between the second moiré superlens and the first moiré superlens through relative rotation, adjust the focus light field depth of the changed pulsed laser signal, and output a focused light field;

[0015] The reflector is used to deflect the focused light field to the target tissue, so that the target tissue is stimulated to generate an ultrasonic signal.

[0016] Furthermore, the first moiré superlens and the second moiré superlens are both axially adjustable-focus moiré superlenses, which are composed of a pair of phase-modulated serial metasurfaces, and the phase-modulated serial metasurfaces have a nanostructure, which includes a nanounit and a substrate.

[0017] Furthermore, the phase distribution between the pair of phase-modulated tandem metasurfaces is as follows in the polar coordinate (r, θ) system:

[0018]

[0019] In the above formula, λ represents the free space wavelength, F0 represents the reference focal length, round[·] represents the rounding operation, r represents the radial distance from a point on the metalens to the center of the lens, that is, the straight-line distance between the point and the center point, and θ represents the rotation angle of the point in the polar coordinate system relative to the reference direction (the initial direction of the x-axis). represents the phase distribution of the first moiré superlens, represents the phase distribution of the second moiré superlens.

[0020] Furthermore, the phase superposition relationship between the first moiré superlens and the second moiré superlens is as follows in the polar coordinate (r, θ) system:

[0021]

[0022] In the above formula, r represents the straight-line distance from a point on the metalens to the center of the lens, and θ represents the rotation angle of the point in the polar coordinate system relative to the reference direction (the initial direction of the x-axis). represents the phase distribution of the first moiré superlens, represents the phase distribution of the second moiré superlens, Represents the phase distribution of the moiré superlens after superposition.

[0023] Furthermore, the dual-axis rotation control unit includes a fiber optic rotation motor and a probe rotation motor, the fiber optic rotation motor is coaxially electrically connected to the single-mode optical fiber, the probe rotation motor is arranged at the rear end of the fiber optic rotation motor, and the probe rotation motor is electrically connected to the single-mode optical fiber through a magnetic coupling coupling, wherein:

[0024] The optical fiber rotation motor is used to drive the single-mode optical fiber to rotate around the optical axis;

[0025] The probe rotation motor is used to drive the probe to rotate around the optical axis.

[0026] Furthermore, the ultrasonic receiving module includes a light-transmitting reflective mirror, a photoacoustic window, and an ultrasonic transducer. The light-transmitting reflective mirror is arranged directly below the photoacoustic window by tilting at an angle of -45°. The ultrasonic transducer and the light-transmitting reflective mirror are coaxially arranged, wherein:

[0027] The light-transmitting reflective mirror is used to reflect ultrasonic signals;

[0028] The photoacoustic window is used to transmit the ultrasonic signal to the ultrasonic transducer;

[0029] The ultrasonic transducer is used to acquire ultrasonic signals and perform conversion processing to obtain electrical signals of target tissues.

[0030] Furthermore, the host includes a laser light source system, a probe scanning system, a data acquisition system, an image reconstruction system and a display system, wherein:

[0031] The laser light source system is used to generate a pulsed laser signal with adjustable wavelength;

[0032] The probe scanning system is used to acquire electrical signals of target tissues through a dual-axis rotation control unit;

[0033] The data acquisition system is used to acquire the electrical signal of the target tissue and perform signal preprocessing to obtain a digitized ultrasound signal data stream;

[0034] The image reconstruction system is used to combine the digitized ultrasound signal data stream with the spatial position information of the probe and perform image reconstruction using a time reversal algorithm to obtain a three-dimensional absorption coefficient distribution map of the target tissue;

[0035] The display system is used to visualize the three-dimensional absorption coefficient distribution map of the target tissue.

[0036] The second technical solution adopted by the present invention is: an imaging method of a dual-rotation zoom photoacoustic endoscope based on a moiré superlens, comprising the following steps:

[0037] Generates pulsed laser signal and transmits it to the probe via single-mode optical fiber;

[0038] The first moiré superlens is driven to rotate around the optical axis to form a relative angle with the second superlens. The axial depth of the focused light field is continuously adjusted through the moiré phase superposition effect to output a focused light field.

[0039] Deflecting the focused light field to the target tissue to stimulate the target tissue to generate an ultrasonic signal;

[0040] Converting and processing the ultrasonic signal generated by the target tissue to obtain a digital ultrasonic signal data stream;

[0041] The digitized ultrasound signal data stream is combined with the spatial position information of the probe, and the image is reconstructed through a time reversal algorithm to obtain a three-dimensional absorption coefficient distribution map of the target tissue.

[0042] The beneficial effects of the method and system of the present invention are as follows: the present invention introduces a superlens beam focusing module, and then continuously adjusts the axial depth of the focused light field through the Moiré phase superposition effect, outputs the focused light field, and the probe synchronously rotates radially to achieve lateral coverage. The superlens is directly driven to rotate by the optical fiber, which simplifies the mechanical structure, improves the focusing response speed, and adapts to the miniaturized endoscopic catheter, further deflects the focused light field to the target tissue, and stimulates the target tissue to generate an ultrasonic signal; the ultrasonic signal generated by the target tissue is converted and processed to obtain a digitized ultrasonic signal data stream, optimizes the photoacoustic signal excitation efficiency, and ensures the high sensitivity of the ultrasonic transducer to the echo signal. Finally, the digitized ultrasonic signal data stream is combined with the spatial position information of the probe, and the image is reconstructed through a time reversal algorithm to obtain a three-dimensional absorption coefficient distribution map of the target tissue, which can dynamically match the imaging requirements of different tissue depths in real time and is suitable for minimally invasive high-resolution photoacoustic imaging of narrow cavities such as the digestive tract and blood vessels. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the structural framework of the double-rotation zoom photoacoustic endoscope based on the moiré superlens of the present invention;

[0044] Figure 2 1. It is a schematic flow chart of the steps of an imaging method of a double-rotation zoom photoacoustic endoscope based on a moiré superlens according to the present invention;

[0045] Figure 3 Schematic diagram of the structure of the superlens beam focusing module and the ultrasonic receiving module provided by a specific embodiment of the present invention;

[0046] Figure 4 is a schematic diagram of the distribution of nano units and substrates provided by a specific embodiment of the present invention;

[0047] Figure 5 Schematic diagram of a dual-axis rotation focusing and probe integrated structure provided by a specific embodiment of the present invention;

[0048] Figure 6 1 is a side view schematic diagram of a moiré superlens structure provided by a specific embodiment of the present invention;

[0049] Figure 7 1 is a plan view of a moiré superlens provided by a specific embodiment of the present invention.

[0050] Figure numerals: 1. single-mode optical fiber; 2. optical fiber superlens connector; 3. first moiré superlens; 4. second moiré superlens; 5. reflector; 6. light-transmitting anti-acoustic mirror; 7. photoacoustic window; 8. ultrasonic transducer; 9. flexible sleeve; 10. nanounit; 11. substrate; 12. optical fiber rotation motor; 13. probe rotation motor; 14. ultrasonic signal transmission component. DETAILED DESCRIPTION

[0051] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The step numbers in the following embodiments are provided for ease of description only and do not limit the order of the steps. The order of execution of the steps in the embodiments can be adaptively adjusted based on the understanding of those skilled in the art.

[0052] First of all, it should be noted that the embodiment of the present invention deeply integrates the dynamic focusing mechanism of the moiré superlens with the needs of photoacoustic imaging. Through the relative rotation of the two-piece superlens (0°~360° continuously adjustable, angular resolution 0.1°), the moiré phase superposition effect is used to adjust the depth of the focused sound field in real time. At the same time, combined with the optical fiber direct drive technology, the focusing module is integrated into a micro-probe with a diameter of ≤2mm, avoiding the volume limitation of the traditional mechanical structure. Furthermore, the superlens unit adopts a nano-scale 3D printing process, combined with a water pressure-resistant packaging design, which can stably work in a high-frequency underwater ultrasonic environment (center frequency ≥5MHz), with a lateral resolution of less than 10μm, and the focusing response time is shortened to the millisecond level. Through the coordinated optimization of the optical path and the acoustic path (such as the design of a transparent reflective mirror), it is ensured that the excitation light penetrates the tissue efficiently and the ultrasonic echo signal is received with high sensitivity, providing a high-resolution, real-time dynamic minimally invasive diagnostic tool for scenarios such as early gastrointestinal cancer screening and vascular plaque imaging, effectively overcoming the key defects of the traditional photoacoustic endoscope focusing hysteresis and the complex structure of the existing adjustable superlens.

[0053] Reference Figure 1 The present invention provides a dual-rotation zoom photoacoustic endoscope based on a moiré superlens, comprising a host and a probe, wherein the host and the probe are electrically connected, and the probe introduces a superlens beam focusing module, wherein:

[0054] The probe is used to obtain electrical signals from target tissues, and the probe is also wrapped by a flexible sleeve 9;

[0055] Specifically, if Figure 3 As shown, the probe includes a metalens beam focusing module, an ultrasonic receiving module and a dual-axis rotation control unit. The ultrasonic receiving module is located at the optical path output end of the metalens beam focusing module. The dual-axis rotation control unit is electrically connected to the metalens beam focusing module, wherein:

[0056] The superlens beam focusing module is used to stimulate the target tissue with a pulsed laser signal to obtain an ultrasonic signal of the target tissue;

[0057] More specifically, the metalens beam focusing module includes a single-mode optical fiber 1, a first Moiré superlens 3, a second Moiré superlens 4 and a reflector 5. The single-mode optical fiber is fixedly connected to the first Moiré superlens through a fiber superlens connector 2. The first Moiré superlens and the second Moiré superlens are coaxially arranged. The second Moiré superlens is located at the optical path output end of the first Moiré superlens, and the reflector is located at the optical path output end of the second Moiré superlens. The single-mode optical fiber is used to obtain a pulsed laser signal and control the first Moiré superlens to rotate synchronously. The first Moiré superlens is used to change the light wave front of the pulsed laser signal passing through the Moiré superlens, transmit the changed pulsed laser signal to the second Moiré superlens, and form a relative angle with the second Moiré superlens. The second Moiré superlens is used to change the phase superposition relationship between the second Moiré superlens and the first Moiré superlens through relative rotation, adjust the focused light field depth of the changed pulsed laser signal, and output the focused light field. The reflector is used to deflect the focused light field to the target tissue, so that the target tissue is stimulated to generate an ultrasonic signal.

[0058] In some specific embodiments, a single-mode optical fiber serves as an excitation light transmission channel, extending along the axis of the probe and secured to the first moiré superlens at its distal end via a fiber superlens connector. Rotation of the optical fiber drives the first superlens to rotate synchronously about the optical axis. The first moiré superlens is located at the optical output end of the optical fiber, and its emitted light illuminates the surface of the second moiré superlens. The second moiré superlens is coaxially arranged with the first moiré superlens, and relative rotation alters the phase superposition relationship between the two superlenses, thereby continuously adjusting the depth of the focused light field. A reflector is used to deflect the focused light field toward the target tissue, thereby stimulating the target tissue to generate an ultrasonic signal. The focused light field is configured to pass through the ultrasonic signal transmission assembly.

[0059] In this embodiment, if Figure 4 As shown, the first moiré superlens and the second moiré superlens are both axially adjustable focus moiré superlenses, which are composed of a pair of phase-modulated serial metasurfaces, and the phase-modulated serial metasurfaces have a nanostructure, which includes a nanounit 10 and a substrate 11.

[0060] like Figure 6 Figure 2 shows a side view of a tunable moiré superlens, demonstrating its multilayer integrated design. The upper layer is the first moiré superlens, while the lower layer is the second moiré superlens, with the two mirror images arranged in a mirrored pattern. The monolithic moiré superlens substrate, shown in white, is composed of a silicon dioxide base. The nanopillars, shown in red, are composed of silicon nitride.

[0061] like Figure 7, which is a top view of a single piece of an adjustable moiré superlens, showing the distribution of nano-units 10 on the surface of the superlens.

[0062] The phase distribution between the pair of phase-modulated tandem metasurfaces is shown in the polar coordinate (r, θ) system as follows:

[0063]

[0064] In the above formula, λ represents the free space wavelength, F0 represents the reference focal length, round[·] represents the rounding operation, r represents the radial distance from a point on the metalens to the center of the lens, that is, the straight-line distance between the point and the center point, and θ represents the rotation angle of the point in the polar coordinate system relative to the reference direction (the initial direction of the x-axis). represents the phase distribution of the first moiré superlens, represents the phase distribution of the second moiré superlens.

[0065] The phase superposition relationship between the first moiré superlens and the second moiré superlens is as follows in the polar coordinate (r, θ) system:

[0066]

[0067] In the above formula, r represents the straight-line distance from a point on the metalens to the center of the lens, and θ represents the rotation angle of the point in the polar coordinate system relative to the reference direction (the initial direction of the x-axis). represents the phase distribution of the first moiré superlens, represents the phase distribution of the second moiré superlens, Represents the phase distribution of the moiré superlens after superposition.

[0068] In some specific embodiments, the moiré superlens includes a pair of series-connected transmission phase-based metasurfaces. The moiré superlens is an axially adjustable focus moiré superlens, which is composed of a pair of series-connected metasurfaces based on phase modulation. The transmission phase-based metasurface has a nanostructure; the nanostructure includes a nanounit and a substrate.

[0069] The ultrasonic receiving module is used to convert and process the ultrasonic signal of the target tissue to obtain the electrical signal of the target tissue;

[0070] More specifically, the ultrasonic receiving module includes a light-transmitting reflective mirror 6, a photoacoustic window 7 and an ultrasonic transducer 8. The light-transmitting reflective mirror is arranged directly below the photoacoustic window by tilting at an angle of -45°, and the ultrasonic transducer and the light-transmitting reflective mirror are coaxially arranged, wherein the light-transmitting reflective mirror is used to reflect ultrasonic signals; the photoacoustic window is used to transmit ultrasonic signals to the ultrasonic transducer; and the ultrasonic transducer is used to acquire ultrasonic signals and perform conversion processing to obtain electrical signals of the target tissue.

[0071] In some specific embodiments, the ultrasonic signal transmission component 14 includes a light-transmitting reflective mirror and a photoacoustic window. The light-transmitting reflective mirror is fixed at an inclination angle of -45° directly below the photoacoustic window, and is used to reflect the ultrasonic signal generated by the target tissue while allowing the excitation light to penetrate into the tissue; the ultrasonic transducer is coaxially arranged with the light-transmitting reflective mirror, and is used to receive the reflected ultrasonic signal and convert it into an electrical signal.

[0072] The dual-axis rotation control unit is used to control the metalens beam focusing module to rotate around the optical axis.

[0073] More specifically, the dual-axis rotation control unit includes a fiber optic rotation motor 12 and a probe rotation motor 13, the fiber optic rotation motor is coaxially electrically connected to the single-mode optical fiber, the probe rotation motor is arranged at the rear end of the fiber optic rotation motor, and the probe rotation motor is electrically connected to the single-mode optical fiber through a magnetic coupling coupling, wherein the fiber optic rotation motor is used to drive the single-mode optical fiber to rotate around the optical axis; the probe rotation motor is used to drive the probe to rotate around the optical axis.

[0074] In some specific embodiments, Figure 5 As shown, the fiber optic rotation motor is coaxially connected to the single-mode optical fiber to drive the optical fiber to rotate around the optical axis; the probe rotation motor is arranged at the rear end of the fiber optic rotation motor and is connected to the optical fiber through a magnetic coupling coupling to drive the probe to rotate around the optical axis; wherein, the fiber optic rotation motor and the probe rotation motor are arranged orthogonally, and dual-axis synchronous motion is achieved through a closed-loop control circuit, covering three-dimensional scanning of the target area.

[0075] The host is used to perform preprocessing and visual display processing according to the electrical signal of the target tissue to obtain a three-dimensional absorption coefficient distribution map of the target tissue.

[0076] Specifically, the host includes a laser light source system, a probe scanning system, a data acquisition system, an image reconstruction system and a display system, wherein the laser light source system is used to generate a pulsed laser signal with adjustable wavelength; the probe scanning system is used to obtain the electrical signal of the target tissue through a dual-axis rotation control unit; the data acquisition system is used to obtain the electrical signal of the target tissue and perform signal preprocessing to obtain a digitized ultrasound signal data stream; the image reconstruction system is used to combine the digitized ultrasound signal data stream with the spatial position information of the probe, and perform image reconstruction through a time reversal algorithm to obtain a three-dimensional absorption coefficient distribution map of the target tissue; the display system is used to visualize the three-dimensional absorption coefficient distribution map of the target tissue.

[0077] The host analyzes the time delay, amplitude and spectral characteristics of the ultrasound signal and combines it with the spatial position information of the probe to reconstruct the absorption coefficient distribution map of the target tissue, thereby achieving micron-level resolution visualization of blood vessel wall stratification, tumor boundary identification and early lesions.

[0078] In some specific embodiments, the laser light source system is used to generate a pulsed laser with an adjustable wavelength (500-800 nm). The excitation light is transmitted to the probe's superlens beam focusing module via a single-mode optical fiber, stimulating the target tissue to produce a photoacoustic signal. The probe scanning system is electrically connected to the dual-axis rotation control unit to control the coordinated operation of the fiber rotation motor and the probe rotation motor. The fiber rotation motor drives the single-mode optical fiber around the optical axis, and the probe rotation motor drives the probe around the optical axis, achieving dual-degree-of-freedom scanning to cover the target area. The data acquisition system is connected to the ultrasonic transducer via a shielded signal cable, receives the electrical signal, and performs low-noise amplification, bandpass filtering, and analog-to-digital conversion to generate a digitized ultrasonic signal data stream. The image reconstruction system, based on a time reversal algorithm, combines the signal data output by the data acquisition system with the probe's spatial position information to reconstruct a three-dimensional absorption coefficient distribution map of the target tissue. Adaptive filtering and noise suppression techniques achieve micron-level imaging with a lateral resolution of ≤15μm and an axial resolution of ≤30μm. The display system receives the three-dimensional photoacoustic image data generated by the image reconstruction system and displays the tissue structure.

[0079] Reference Figure 2 , an imaging method of a dual-rotation zoom photoacoustic endoscope based on a moiré superlens, comprising:

[0080] S100, generating a pulsed laser signal and transmitting it to the probe via a single-mode optical fiber;

[0081] S200, driving the first moiré superlens to rotate around the optical axis to form a relative angle with the second superlens, continuously adjusting the axial depth of the focused light field through the moiré phase superposition effect, and outputting the focused light field;

[0082] S300, deflecting the focused light field to the target tissue to stimulate the target tissue to generate an ultrasonic signal;

[0083] S400, converting and processing the ultrasonic signal generated by the target tissue to obtain a digital ultrasonic signal data stream;

[0084] S500 , combining the digitized ultrasound signal data stream with the spatial position information of the probe, and performing image reconstruction through a time reversal algorithm to obtain a three-dimensional absorption coefficient distribution map of the target tissue.

[0085] In some specific embodiments, a pulsed laser is transmitted to the probe via a single-mode optical fiber, driving the first moiré superlens to rotate around the optical axis, forming a relative angle θ with the second superlens, and continuously adjusting the axial depth of the focused light field through the moiré phase superposition effect. The probe synchronously rotates radially to achieve lateral coverage, and the focused light field is deflected to the target tissue by a reflector, stimulating a photoacoustic signal. The ultrasonic signal is reflected by a transparent reflective mirror (-45° inclination) to a coaxial ultrasonic transducer, converted into an electrical signal, and the tissue absorption coefficient distribution map is reconstructed using a time reversal algorithm.

[0086] In summary, the embodiment of the present invention includes an optical fiber, a first moiré superlens, a second moiré superlens, a reflector, a semi-transparent reflector, an ultrasonic transducer, and a dual-axis rotation control unit. The moiré superlens is composed of two superlenses. By rotating one of the superlenses, the relative angle between the two superlenses is changed, thereby changing the wavefront of the light wave passing through the moiré superlens, thereby achieving continuous adjustment of the focus. The first moiré superlens is connected to the optical fiber, and the rotation of the optical fiber drives the rotation of the moiré superlens. The reflector and the semi-transparent reflector cooperate to guide the excitation light path, optimize the excitation efficiency of the photoacoustic signal, and ensure the high sensitivity of the ultrasonic transducer to the echo signal. The present invention directly drives the rotation of the superlens through the optical fiber, simplifies the mechanical structure, improves the focusing response speed, adapts to the miniaturized endoscopic catheter, can dynamically match the imaging requirements of different tissue depths in real time, and is suitable for minimally invasive high-resolution photoacoustic imaging of narrow cavities such as the digestive tract and blood vessels.

[0087] The contents of the above method embodiments are all applicable to the present system embodiments. The functions specifically implemented by the present system embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0088] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A dual-rotation zoom photoacoustic endoscope based on a moiré superlens, characterized in that: The system comprises a host and a probe, wherein the host and the probe are electrically connected, and the probe introduces a super lens beam focusing module, wherein: The probe is used to obtain electrical signals from target tissue; The host is used to perform preprocessing and visual display processing according to the electrical signal of the target tissue to obtain a three-dimensional absorption coefficient distribution map of the target tissue.

2. The dual-rotation zoom photoacoustic endoscope based on the moiré superlens according to claim 1, characterized in that: The probe includes a metalens beam focusing module, an ultrasonic receiving module and a dual-axis rotation control unit. The ultrasonic receiving module is located at the optical path output end of the metalens beam focusing module. The dual-axis rotation control unit is electrically connected to the metalens beam focusing module, wherein: The superlens beam focusing module is used to stimulate the target tissue with a pulsed laser signal to obtain an ultrasonic signal of the target tissue; The ultrasonic receiving module is used to convert and process the ultrasonic signal of the target tissue to obtain the electrical signal of the target tissue; The dual-axis rotation control unit is used to control the metalens beam focusing module to rotate around the optical axis.

3. The double-rotation zoom photoacoustic endoscope based on the moiré superlens according to claim 2, characterized in that: The metalens beam focusing module includes a single-mode optical fiber, a first moiré metalens, a second moiré metalens and a reflector. The single-mode optical fiber is fixedly connected to the first moiré metalens through a fiber metalens connector. The first moiré metalens and the second moiré metalens are coaxially arranged. The second moiré metalens is located at the optical path output end of the first moiré metalens. The reflector is located at the optical path output end of the second moiré metalens, wherein: The single-mode optical fiber is used to obtain a pulsed laser signal and control the first moiré superlens to rotate synchronously; The first moiré superlens is used to change the wavefront of the pulsed laser signal passing through the moiré superlens, and transmit the changed pulsed laser signal to the second moiré superlens, and form a relative angle with the second moiré superlens; The second moiré superlens is used to change the phase superposition relationship between the second moiré superlens and the first moiré superlens through relative rotation, adjust the focus light field depth of the changed pulsed laser signal, and output a focused light field; The reflector is used to deflect the focused light field to the target tissue, so that the target tissue is stimulated to generate an ultrasonic signal.

4. The double-rotation zoom photoacoustic endoscope based on the moiré superlens according to claim 3 is characterized in that: The first moiré superlens and the second moiré superlens are both axially adjustable focus moiré superlenses, which are composed of a pair of phase-modulated serial metasurfaces, and the phase-modulated serial metasurfaces have a nanostructure, which includes a nanounit and a substrate.

5. The dual-rotation zoom photoacoustic endoscope based on the moiré superlens according to claim 4, characterized in that: The phase distribution between the pair of phase-modulated tandem metasurfaces is shown in the polar coordinate (r, θ) system as follows: In the above formula, λ represents the free space wavelength, F0 represents the reference focal length, round[·] represents the rounding operation, r represents the radial distance from a point on the metalens to the center of the lens, that is, the straight-line distance between the point and the center point, and θ represents the rotation angle of the point in the polar coordinate system relative to the reference direction (the initial direction of the x-axis). represents the phase distribution of the first moiré superlens, represents the phase distribution of the second moiré superlens.

6. The dual-rotation zoom photoacoustic endoscope based on the moiré superlens according to claim 5, characterized in that: The phase superposition relationship between the first moiré superlens and the second moiré superlens is as follows in the polar coordinate (r, θ) system: In the above formula, r represents the straight-line distance from a point on the metalens to the center of the lens, and θ represents the rotation angle of the point in the polar coordinate system relative to the reference direction (the initial direction of the x-axis). represents the phase distribution of the first moiré superlens, represents the phase distribution of the second moiré superlens, Represents the phase distribution of the moiré superlens after superposition.

7. The dual-rotation zoom photoacoustic endoscope based on the moiré superlens according to claim 6, characterized in that: The dual-axis rotation control unit includes an optical fiber rotation motor and a probe rotation motor, wherein the optical fiber rotation motor is coaxially electrically connected to the single-mode optical fiber, and the probe rotation motor is arranged at the rear end of the optical fiber rotation motor, and the probe rotation motor is electrically connected to the single-mode optical fiber through a magnetic coupling coupling, wherein: The optical fiber rotation motor is used to drive the single-mode optical fiber to rotate around the optical axis; The probe rotation motor is used to drive the probe to rotate around the optical axis.

8. The dual-rotation zoom photoacoustic endoscope based on the moiré superlens according to claim 7, characterized in that: The ultrasonic receiving module includes a light-transmitting reflective mirror, a photoacoustic window, and an ultrasonic transducer. The light-transmitting reflective mirror is arranged directly below the photoacoustic window at an angle of -45°. The ultrasonic transducer and the light-transmitting reflective mirror are coaxially arranged, wherein: The light-transmitting reflective mirror is used to reflect ultrasonic signals; The photoacoustic window is used to transmit the ultrasonic signal to the ultrasonic transducer; The ultrasonic transducer is used to acquire ultrasonic signals and perform conversion processing to obtain electrical signals of target tissues.

9. The double-rotation zoom photoacoustic endoscope based on the moiré superlens according to claim 8, characterized in that: The host includes a laser light source system, a probe scanning system, a data acquisition system, an image reconstruction system and a display system, wherein: The laser light source system is used to generate a pulsed laser signal with adjustable wavelength; The probe scanning system is used to acquire electrical signals of target tissues through a dual-axis rotation control unit; The data acquisition system is used to acquire the electrical signal of the target tissue and perform signal preprocessing to obtain a digitized ultrasound signal data stream; The image reconstruction system is used to combine the digitized ultrasound signal data stream with the spatial position information of the probe and perform image reconstruction using a time reversal algorithm to obtain a three-dimensional absorption coefficient distribution map of the target tissue; The display system is used to visualize the three-dimensional absorption coefficient distribution map of the target tissue.

10. An imaging method for a dual-rotation zoom photoacoustic endoscope based on a moiré superlens, characterized in that: The following steps are involved: Generate a pulsed laser signal and transmit it to the probe via a single-mode optical fiber; The first moiré superlens is driven to rotate around the optical axis to form a relative angle with the second superlens. The axial depth of the focused light field is continuously adjusted through the moiré phase superposition effect to output a focused light field. Deflecting the focused light field to the target tissue to stimulate the target tissue to generate an ultrasonic signal; Converting and processing the ultrasonic signal generated by the target tissue to obtain a digital ultrasonic signal data stream; The digitized ultrasound signal data stream is combined with the spatial position information of the probe, and the image is reconstructed through a time reversal algorithm to obtain a three-dimensional absorption coefficient distribution map of the target tissue.

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