CN114699045B - Portable photoacoustic microscopic imaging system and method based on scanning galvanometer - Google Patents

Abstract

The invention discloses a portable photoacoustic microscopic imaging system based on a scanning galvanometer, which comprises a laser part, a micro-mirror part and a signal processing part, wherein the laser part is used for generating laser, collimating an optical path and focusing a light beam; the micro-mirror part reflects the incident laser to different positions on the surface of the biological tissue by utilizing the axial movement or deflection of the MEMS scanning galvanometer; the signal processing part is used for judging the working state of the system and carrying out three-dimensional reconstruction on biological tissues, the laser part comprises a laser, a lens, an optical fiber coupler, an optical fiber, a spectroscope and a light-transmitting anti-sound mirror, and the micro mirror part comprises an MEMS scanning vibrating mirror and a function generator. The MEMS scanning galvanometer technology is applied to a laser point-by-point scanning process in optical resolution photoacoustic microscopy imaging, so that the volume of photoacoustic microscopy imaging equipment is reduced, the imaging speed and the scanning precision are improved, and the rapid high-resolution photoacoustic microscopy imaging suitable for multiple scenes is realized.

Description

A portable photoacoustic microscopy imaging system and imaging method based on scanning galvanometer

technical field

The invention relates to the technical field of photoacoustic imaging, in particular to a portable photoacoustic microscopic imaging system and imaging method based on a scanning galvanometer.

Background technique

Photoacoustic Imaging (PAI) is a non-ionizing, non-invasive biomedical imaging technology that has emerged in recent years. This technology uses short-pulse laser to irradiate the surface of biological tissue, and the biological tissue emits photo-induced ultrasonic signals, and then undergoes a series of signal processing to realize the reconstruction of the three-dimensional shape of biological tissue. PAI has high contrast comparable to optical imaging and high penetration depth of ultrasound imaging, and can also realize three-dimensional imaging of biological tissues.

Photoacoustic microscopy (PAM) is a branch of photoacoustic imaging, which can achieve submicron resolution, and can be divided into optical resolution photoacoustic microscopy (OR-PAM) and acoustic resolution Acoustic resolution photoacoustic microscopy (AR-PAM), in which OR-PAM has higher resolution than AR-PAM, but its imaging depth is smaller.

Since the 1990s, optical MEMS devices have been greatly developed. At present, a large number of optical device products are inseparable from MEMS scanning mirrors, such as: microlenses, gratings, bio-optical detection systems, etc. MEMS scanning mirrors are a kind of spatial distribution of incident light that uses micro-drivers to control the translation or rotation of the mirror surface. modulator.

Photoacoustic microscopy imaging uses point-by-point scanning to obtain high resolution. Since the resolution achieved by optical scanning is higher than that of acoustic scanning, when the imaging system pursues imaging resolution, optical resolution photoacoustic microscopy ( OR-PAM). The existing mature optical resolution photoacoustic microscopy imaging system often uses motor-driven laser head to realize point-by-point scanning of laser; traditional OR-PAM system mainly involves laser adjustment part and signal receiving part; laser adjustment part includes optical path collimation Focusing with the beam to achieve the purpose of acting on a point on the surface of biological tissue; the signal processing part includes signal processing circuits commonly used in measurement and control circuits such as ultrasonic transducers and filter amplifiers.

MEMS scanning mirror is an important optical device, which is mainly used in optical communication, radar, optical scanning and other fields. It has the characteristics of small size, low cost, fast response and high integration. Different, MEMS scanning mirrors are mainly divided into electrostatic type, piezoelectric type, electromagnetic type and electrothermal type. Among them, the electrostatic type cannot achieve continuous rotation well; the piezoelectric type has a simple process but consumes a lot of power; the electromagnetic type also has The problem of large power consumption; the electrothermal type can achieve low power consumption and large displacement.

Traditional photoacoustic microscopy systems mostly use stepping motors for scanning, which face problems such as low scanning speed, poor scanning accuracy, and large equipment volume. High-performance photoacoustic microscopy imaging devices are expensive and not easy to carry, which greatly limits Application scenarios of photoacoustic microscopy imaging equipment.

Contents of the invention

Based on the technical problems existing in the background technology, the present invention proposes a portable photoacoustic microscopic imaging system and imaging method based on scanning galvanometers.

A portable photoacoustic microscopic imaging system based on a scanning galvanometer proposed by the present invention includes a laser part, a micromirror part, and a signal processing part. The laser part is used for generating laser light, collimating optical paths, and focusing beams; The mirror part uses the axial movement or deflection of the MEMS scanning galvanometer to reflect the incident laser light to different positions on the surface of the biological tissue; the signal processing part is used to judge the working state of the system and perform three-dimensional reconstruction of the biological tissue, and the laser part includes Laser, lens, fiber optic coupler, optical fiber, beam splitter, light-transmitting acoustic mirror, the micromirror part includes MEMS scanning vibrating mirror, function generator, MEMS scanning vibrating mirror includes four electrothermal brakes and a mirror, the function The generator receives the instructions sent by the computer and generates a driving signal to act on the MEMS scanning galvanometer. The signal processing part includes a photoelectric sensor, an ultrasonic transducer, a data collector, a filter, and an amplifier. The photoelectric sensor receives the The laser light reflected by the beam splitter, the ultrasonic transducer is used to receive the photoinduced ultrasonic signal reflected by the light-transmitting acoustic mirror, the ultrasonic transducer is a piezoelectric ultrasonic transducer, four electrothermal brakes Evenly distributed around the lens, the electrothermal brake adopts a double-chip design, using thermal resistance and two materials with large differences in thermal expansion coefficients to realize the conversion of electrical energy to thermal energy and then to mechanical energy. The thermal resistance is placed in the thermal expansion coefficient. Between the two materials, three materials are laminated to form an electric heating arm, the lens is made of reflective material, and the connection between the lens and the electrothermal brake is filled with heat insulating material.

Preferably, the signal processing part includes a system state detection part and a photoinduced ultrasonic signal processing part, and the system state detection part includes a photoelectric sensor, a first data collector, a first filter, and a first signal amplifier; The ultrasonic signal processing part includes an ultrasonic transducer, a second data collector, a second filter, and a second signal amplifier. A beam splitter, a MEMS scanning galvanometer, and a light-transmitting acoustic mirror. The laser beam is incident on the MEMS scanning galvanometer at a 45° deviating angle from the horizontal plane.

Preferably, the electrothermal arm of the electrothermal brake is composed of five layers of materials, which are: the first layer of silicon dioxide, the second layer of titanium, the third layer of silicon dioxide, the fourth layer of aluminum and the fifth layer of silicon dioxide, The first layer of silicon dioxide and the fourth layer of aluminum constitute an electrothermal bimorph, while the fourth layer of aluminum and the fifth layer of silicon dioxide constitute a bimorph, and the second layer of titanium is a thermal resistor for generating Joule heat, so The third layer of silicon dioxide is used as an insulating layer between the second layer of titanium and the fourth layer of aluminum.

Preferably, the lens is silver, and the filler between the lens and the electrothermal brake is silicon dioxide.

A portable photoacoustic microscopy imaging system based on a scanning galvanometer, comprising the following control steps:

S1 utilizes the electrothermal brake and simultaneously applies a direct current with a constant amplitude to realize the axial displacement of the MEMS scanning vibrating mirror;

S2 using a certain brake in the electrothermal brake to apply a direct current with a constant amplitude to realize the deflection of the MEMS scanning galvanometer;

S3 utilizes a brake in the electrothermal brake to apply an AC signal to realize the continuous deflection of the MEMS scanning mirror;

S4 applies prestress to the brake during manufacture, increases the displacement range of the MEMS scanning galvanometer, and protects the electrothermal brake from being broken.

Preferably, the four electrothermal brakes are evenly distributed around the lens, and at the same time, a 10V voltage is applied to the second layer of titanium of the four electrothermal brakes to achieve a displacement of 797.42 μm.

Preferably, four electrothermal brakes are evenly distributed around the lens, and a 10V DC voltage is applied to one of the electrothermal brakes, and the MEMS scanning vibrating mirror can achieve a deflection angle of 30.43°.

Preferably, four electrothermal brakes are evenly distributed around the lens, wherein the opposite two electrothermal brakes are a pair of brakes, each pair of electrothermal brakes can drive the MEMS scanning vibrating mirror to rotate around the corresponding rotation axis, and both pairs of electrothermal brakes apply a peak value of 10V A sinusoidal AC signal with frequencies of 40 Hz and 0.2 Hz, respectively, makes the MEMS scanning galvanometer deflect around two axes at 80 Hz and 0.18 Hz, respectively.

Preferably, a tensile stress of 2.3e8Pa is applied to the first layer of silicon dioxide and the third layer of silicon dioxide, and a compressive stress of 2.3e8Pa is applied to the fourth layer of aluminum, so that the MEMS scanning galvanometer has an initial thickness of 331.89 μm. Axial displacement.

A portable photoacoustic microscopy imaging method based on a scanning galvanometer, comprising the steps of:

S1 The first lens, the second lens and the focusing lens perform optical path collimation and beam focusing on the laser light emitted by the laser;

S2 uses the beam splitter to divide the laser into two beams, one of which is used to scan the surface of the biological tissue, and the other is received by the photoelectric sensor to determine the laser power and the direction of the laser light path;

S3 uses the computer for human-computer interaction, selects the scanning mode, and the computer sends a driving command to the function generator, and the function generator applies a driving signal and four electrothermal brakes to drive the MEMS scanning galvanometer to deflect or move axially Realize point-by-point scanning of laser on biological tissue.

In the present invention, the portable photoacoustic microscopy imaging system and imaging method based on the scanning galvanometer adopts the electrothermal MEMS scanning galvanometer, which can realize large displacement and large deflection under low power consumption, and can realize low delay at the same time , High-precision motion control to realize fast and precise control of the reflected beam path;

The photoacoustic microscopy imaging equipment and imaging method of the present invention is a laser scanning scheme based on scanning galvanometers, which replaces the traditional scheme of motor-driven laser heads, and utilizes the deflection around the axis of the scanning galvanometers to make the focused beam on the biological tissue scanning. The scanning galvanometer is small in size, high in precision, and fast in response, making the imaging system have the characteristics of high resolution, fast imaging, and portability. In terms of volume, it is several orders of magnitude smaller than the traditional imaging system using motors, which greatly broadens the application scenarios of photoacoustic microscopy imaging equipment;

The laser scans in a "line scan" mode. Under the condition of a certain performance of the ultrasonic transducer, the denser the scan line, the higher the imaging resolution. Each pair of brakes can drive the scanning micromirror to rotate around one axis, respectively use 40Hz and 0.2Hz AC to drive the two brake pairs of the scanning galvanometer, so that the frequencies of the scanning micromirror to rotate around the two axes are 80Hz and 0.18Hz respectively, within 2min Images with a resolution better than 7 μm can be obtained, thereby realizing fast and high-quality imaging of biological samples;

The invention applies MEMS scanning galvanometer technology to the laser point-by-point scanning process in photoacoustic microscopic imaging with optical resolution, so as to reduce the volume of photoacoustic microscopic imaging equipment, improve imaging speed and scanning accuracy, and thus realize application in multiple scenes Fast and high-resolution photoacoustic microscopy imaging.

Description of drawings

Fig. 1 is the device structural representation of electrothermal MEMS scanning vibrating mirror in an embodiment;

Fig. 2 is the structural representation of electrothermal bimorph in an embodiment;

Fig. 3 is a schematic flow chart of the control method of the electrothermal MEMS scanning vibrating mirror in one embodiment;

Fig. 4 is a system structure frame diagram of a portable photoacoustic microscopy imaging system based on a scanning galvanometer in an embodiment;

FIG. 5 is a flowchart of an imaging method of a portable photoacoustic microscopy imaging system based on a scanning galvanometer in an embodiment;

Fig. 6 is a schematic diagram of imaging resolution changing with time in an embodiment;

Fig. 7 is a maximum projection image of ear blood vessels in living mice in one embodiment.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention.

Embodiment one

Referring to Figures 1-7, a portable photoacoustic microscopy imaging system based on a scanning galvanometer includes a laser part, a micromirror part and a signal processing part, the laser part is used to generate laser light, collimate the optical path, and focus the beam; the The micromirror part uses the axial movement or deflection of the MEMS scanning galvanometer to reflect the incident laser light to different positions on the surface of the biological tissue; the signal processing part is used to judge the working state of the system and perform three-dimensional reconstruction of the biological tissue. Part includes lasers, lenses, fiber couplers, optical fibers, beam splitters, and light-transmitting acoustic mirrors. The micromirror part includes MEMS scanning galvanometers and function generators. MEMS scanning galvanometers include four electrothermal brakes and a mirror. The function generator receives instructions from the computer and generates a drive signal to act on the MEMS scanning vibrating mirror. The signal processing part includes a photoelectric sensor, an ultrasonic transducer, a data collector, a filter, and an amplifier. The photoelectric sensor Receive the laser light reflected by the beam splitter, the ultrasonic transducer is used to receive the photoinduced ultrasonic signal reflected by the light-transmitting acoustic mirror, the ultrasonic transducer is a piezoelectric ultrasonic transducer, four The electrothermal brakes are evenly distributed around the lens. The electrothermal brakes adopt a double-chip design. The thermal resistance and two materials with large differences in thermal expansion coefficients are used to realize the conversion of electrical energy to thermal energy and then to mechanical energy. Between two large materials, three kinds of materials are laminated to form an electric heating arm, the lens is made of reflective material, and the connection between the lens and the electric brake is filled with heat insulating material.

In the present invention, the signal processing part includes a system state detection part and a photo-ultrasonic signal processing part, and the system state detection part includes a photoelectric sensor, a first data collector, a first filter, and a first signal amplifier; the optical The ultrasonic signal processing part includes an ultrasonic transducer, a second data collector, a second filter, and a second signal amplifier. The laser part of the laser passes through the first lens, the second lens, the focusing lens, the fiber coupler, and the , a beam splitter, a MEMS scanning vibrating mirror, and a light-transmitting acoustic mirror, and the laser beam is incident on the MEMS scanning vibrating mirror at an angle of 45° to the horizontal plane.

In the present invention, the electrothermal arm of the electrothermal brake is composed of five layers of materials, which are: the first layer of silicon dioxide, the second layer of titanium, the third layer of silicon dioxide, the fourth layer of aluminum and the fifth layer of silicon dioxide , the first layer of silicon dioxide and the fourth layer of aluminum constitute an electrothermal bimorph, while the fourth layer of aluminum and the fifth layer of silicon dioxide constitute a bimorph, and the second layer of titanium is a thermal resistor for generating Joule heat, The third layer of silicon dioxide serves as an insulating layer between the second layer of titanium and the fourth layer of aluminum.

In the present invention, the lens is silver, and the filler between the lens and the electrothermal brake is silicon dioxide.

A portable photoacoustic microscopy imaging system based on a scanning galvanometer, comprising the following control steps:

S1 utilizes the electrothermal brake and simultaneously applies a direct current with a constant amplitude to realize the axial displacement of the MEMS scanning vibrating mirror;

S2 using a certain brake in the electrothermal brake to apply a direct current with a constant amplitude to realize the deflection of the MEMS scanning galvanometer;

S3 utilizes a brake in the electrothermal brake to apply an AC signal to realize the continuous deflection of the MEMS scanning mirror;

S4 applies prestress to the brake during manufacture, increases the displacement range of the MEMS scanning galvanometer, and protects the electrothermal brake from being broken.

In the present invention, four electrothermal brakes are evenly distributed around the lens, and a 10V voltage is applied to the second layer of titanium of the four electrothermal brakes at the same time to achieve a displacement of 797.42 μm.

In the present invention, four electrothermal brakes are evenly distributed around the lens, and a 10V DC voltage is applied to one of the electrothermal brakes, and the MEMS scanning vibrating mirror can achieve a deflection angle of 30.43°.

In the present invention, four electrothermal brakes are evenly distributed around the lens, and the two opposite electrothermal brakes are a pair of brakes. Each pair of electrothermal brakes can drive the MEMS scanning vibrating mirror to rotate around the corresponding rotating shaft, and both pairs of electrothermal brakes apply a peak value. A 10V sinusoidal AC signal with frequencies of 40Hz and 0.2Hz makes the MEMS scanning galvanometer deflect around two axes at 80Hz and 0.18Hz respectively.

In the present invention, the tensile stress of 2.3e8Pa is applied to the first layer of silicon dioxide and the third layer of silicon dioxide, and the compressive stress of 2.3e8Pa is applied to the fourth layer of aluminum, so that the MEMS scanning vibrating mirror has a diameter of 331.89 μm. initial axial displacement.

A portable photoacoustic microscopy imaging method based on a scanning galvanometer, comprising the steps of:

S1 The first lens, the second lens and the focusing lens perform optical path collimation and beam focusing on the laser light emitted by the laser;

S2 uses the beam splitter to divide the laser into two beams, one of which is used to scan the surface of the biological tissue, and the other is received by the photoelectric sensor to determine the laser power and the direction of the laser light path;

S3 uses the computer for human-computer interaction, selects the scanning mode, and the computer sends a driving command to the function generator, and the function generator applies a driving signal and four electrothermal brakes to drive the MEMS scanning galvanometer to deflect or move axially Realize point-by-point scanning of laser on biological tissue.

Embodiment two

As shown in FIG. 1 , the electrothermal MEMS scanning mirror 2 includes a lens 2-1, a covering mirror layer 2-2, a brake 2-3, a brake 2-4, a brake 2-5 and a brake 2-6.

In this embodiment, the lens 2-1 is circular, so that the mirror layer 2-2 is made of silicon dioxide, which is used for heat insulation and reduces the influence of temperature on the lens 2-1.

In this embodiment, the brake 2-3 and the brake 2-5 are the brake pair 1; the brake 2-4 and the brake 2-6 are the brake pair 2, and the DC voltage excitation of the same amplitude is applied to the four brakes at the same time. Drive the mirror surface 2-1 to move axially, the brake pair 1 drives the mirror surface 2-1 to rotate around the rotation axis 1; the brake pair 2 drives the mirror surface to rotate around the rotation axis 2, and apply AC excitation to the brake pair 1 and brake pair 2 to drive the mirror 2-1 Perform two-dimensional deflection.

Specifically, as shown in Figure 2, the bimorph structure of the brake is mainly composed of three layers, which are the first layer of silicon dioxide 2-11, the fourth layer of aluminum 2-12, and the fifth layer of silicon dioxide 2-12. 13.

In this embodiment, the first layer of silicon dioxide 2-11 and the fourth layer of aluminum 2-12 sandwich the second layer of titanium as a conductive layer and the third layer of silicon dioxide as an insulating layer.

In this embodiment, in the second aspect, a control method for an electrothermal MEMS scanning vibrating mirror is proposed, as shown in FIG. 3 , including the following steps:

Step S1-1: the computer selects a control mode, the control mode includes the deflection and axial movement of the scanning galvanometer;

Step S1-2: the function generator sends out a driving signal based on the mode selection of the computer, and the driving signal is divided into AC and DC signals, respectively controlling the deflection and axial movement of the scanning galvanometer;

Step S1-3: deflection or axial movement of the scanning galvanometer;

In this embodiment, the third aspect provides a portable photoacoustic microscopy imaging system based on a scanning galvanometer.

Specifically, as shown in Figure 4, the main part of the photoacoustic microscopic imaging system includes a beam splitter 1-7, an electrothermal MEMS scanning vibrating mirror 2, a light-transmitting anti-acoustic glass slide 1-9, a photoelectric sensor 3-1 and an ultrasonic transducer 3-2.

In this embodiment, the laser is emitted by a laser 1-1, and the optical path is collimated through the first lens 1-2 and the second lens 1-3. The collimated laser light is focused by the focusing lens 1-4 and then incident on the fiber coupler 1-5, and then transmitted to the main part of the photoacoustic microscopy imaging through the optical fiber 1-6.

In this embodiment, the focused laser is input through an optical fiber and incident on the beam splitter 1-7 and is divided into beam 1 and beam 2. The beam 1 is incident on the photoelectric sensor 3-1 for detecting the working state of the system, and the beam 2 is divided into beam 1 and beam 2. The electrothermal MEMS scanning galvanometer 2 passes through the light-transmitting anti-acoustic glass slide 1-9 and acts on the biological tissue 4 after being reflected by the electrothermal MEMS scanning mirror 2; 9 is received by the ultrasonic transducer 3-2 after reflection.

In this embodiment, the function generator 2-7 generates a driving signal based on an instruction issued by the computer 5 to control the movement of the electrothermal MEMS scanning galvanometer.

In this embodiment, after the photoelectric sensor 3-1 receives the light beam 1, the first data collector 3-3 collects signal data, and performs data preprocessing through the first filter 3-5 and the first amplifier 3-7, Finally, the transmission computer 5 realizes the data analysis.

In this embodiment, after the ultrasonic transducer 3-2 receives the photoinduced ultrasonic signal generated by the biological tissue 4, the second data collector 3-4 collects the signal data, and passes through the second filter 3-6 and the second Amplifiers 3-8 realize data preprocessing, and finally transmit to computer 5 to realize data analysis.

In this embodiment, in the fourth aspect, a photoacoustic microscopy imaging method is also proposed, as shown in FIG. 5, including the following steps:

Step S2-1: generating a short pulse laser, which is used for real-time monitoring of the working state of the system and acting on the measured biological tissue;

Step S2-2: Generate monitoring light, the beam splitter divides the short pulse laser into beam 1 and beam 2, and the beam 1 is used to judge the working state of the system;

Step S2-3: deflecting the scanning galvanometer to realize the scanning of the focus of the short pulse laser on the surface of the biological tissue to be measured;

Step S2-4: The ultrasonic transducer collects the photoacoustic signal generated by the measured biological tissue, and after preprocessing, transmits it to the computer to generate a microscopic image corresponding to the measured object based on the amplitude of the photoacoustic signal.

In this embodiment, the method and device of the present invention are used to image blood vessels in the ear of living mice, as shown in FIG. 7 .

Specifically, use the device of Embodiment 2 to image the ear blood vessels of living mice, wherein the output wavelength of the pulsed laser 201 is 1064 nm, the pulse width is 15 ns, and the scanning galvanometer 300 scans along the diameter of the imaging area, and the scanning range is 15 mm × 30 mm , the scanning step length is 5 μm, a total of 1000 sets of signals are collected, and the image shown in the above figure is obtained. It can be seen from the image that the capillaries in the ear of the living mouse are clearly presented, indicating that the method and device of the present invention can be used to Imaging of target objects with very high resolution.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (8)

1. A portable photoacoustic microscope imaging system based on scanning galvanometer, it is characterized in that, comprises laser part, micromirror part and signal processing part, and described micromirror part comprises MEMS scanning galvanometer, function generator, described The laser part is used to generate laser light, collimate the optical path, and focus the beam; the micromirror part uses the axial movement or deflection of the MEMS scanning galvanometer to reflect the incident laser light to different positions on the surface of the biological tissue; the signal processing part is used to Judging the working status of the system and performing three-dimensional reconstruction of biological tissues, the laser part includes lasers, lenses, fiber couplers, optical fibers, beam splitters, light-transmitting anti-acoustic mirrors, and the MEMS scanning vibrating mirror includes four electrothermal brakes and a mirror. The function generator receives instructions from the computer and generates a drive signal to act on the MEMS scanning vibrating mirror. The signal processing part includes a photoelectric sensor, an ultrasonic transducer, a data collector, a filter, and an amplifier. The photoelectric sensor Receive the laser light reflected by the beam splitter, the ultrasonic transducer is used to receive the photoinduced ultrasonic signal reflected by the light-transmitting acoustic mirror, the ultrasonic transducer is a piezoelectric ultrasonic transducer, four The electrothermal brakes are evenly distributed around the lens. The electrothermal brakes adopt a double-chip design. The thermal resistance and two materials with large differences in thermal expansion coefficients are used to realize the conversion of electrical energy to thermal energy and then to mechanical energy. Between two large materials, three kinds of materials are laminated to form an electric heating arm, the lens is made of reflective material, and the connection between the lens and the electric brake is filled with heat insulating material, and the signal processing part includes a system state detection part and a photo-induced ultrasonic signal processing part, the system state detection part includes a photoelectric sensor, a first data collector, a first filter, a first signal amplifier; the photo-induced ultrasonic signal processing part includes an ultrasonic transducer, a second data The collector, the second filter and the second signal amplifier, the laser part of the laser passes through the first lens, the second lens, the focusing lens, the fiber coupler, the optical fiber, the beam splitter, the MEMS scanning galvanometer, and the light-transmitting acoustic mirror in sequence , the laser is incident on the MEMS scanning galvanometer at an angle of 45° from the horizontal plane, and the electrothermal arm of the electrothermal brake is composed of five layers of materials, which are: the first layer of silicon dioxide, the second layer of titanium, the third layer of two Silicon oxide, the fourth layer of aluminum and the fifth layer of silicon dioxide, the first layer of silicon dioxide and the fourth layer of aluminum form an electrothermal bimorph, while the fourth layer of aluminum and the fifth layer of silicon dioxide form a double wafer, so The second layer of titanium is a thermal resistor for generating Joule heat, and the third layer of silicon dioxide is used as an insulating layer between the second layer of titanium and the fourth layer of aluminum. 2. A portable photoacoustic microscopy imaging system based on a scanning galvanometer according to claim 1, wherein the lens is silver, and the filling between the lens and the electrothermal brake is silicon dioxide. 3. A kind of portable photoacoustic microscopy imaging system based on scanning galvanometer according to claim 1, is characterized in that, comprises following control step: S1 utilizes the electrothermal brake and simultaneously applies a direct current with a constant amplitude to realize the axial displacement of the MEMS scanning vibrating mirror; S2 using a certain brake in the electrothermal brake to apply a direct current with a constant amplitude to realize the deflection of the MEMS scanning galvanometer; S3 utilizes a brake in the electrothermal brake to apply an AC signal to realize the continuous deflection of the MEMS scanning mirror; S4 applies prestress to the brake during manufacture, increases the displacement range of the MEMS scanning galvanometer, and protects the electrothermal brake from being broken. 4. A kind of portable photoacoustic microscopy imaging system based on scanning galvanometer according to claim 1, is characterized in that, four electrothermal brakes are evenly distributed around the lens, and simultaneously on the second layer of titanium of the four electrothermal brakes A displacement of 797.42μm can be achieved by applying a voltage of 10V. 5. A portable photoacoustic microscopy imaging system based on a scanning galvanometer according to claim 1, wherein four electrothermal brakes are evenly distributed around the lens, and a 10V DC voltage is applied to one of the electrothermal brakes, and MEMS scans The deflection angle of the galvanometer can reach 30.43°. 6. A portable photoacoustic microscopy imaging system based on a scanning galvanometer according to claim 1, characterized in that four electrothermal brakes are evenly distributed around the lens, wherein the opposite two electrothermal brakes are a pair of brakes, Each pair of electrothermal brakes can drive the MEMS scanning galvanometer to rotate around the corresponding shaft. Both pairs of electrothermal brakes apply a sinusoidal AC signal with a peak value of 10V, and the frequencies are 40Hz and 0.2Hz respectively, so that the MEMS scanning galvanometer can rotate at 80Hz and 0.18Hz respectively. Deflection around two axes. 7. A kind of portable photoacoustic microscopy imaging system based on scanning galvanometer according to claim 1, is characterized in that, the tensile stress of 2.3e8Pa is applied on the first layer of silicon dioxide and the third layer of silicon dioxide , applying a shrinkage stress of 2.3e8Pa on the fourth layer of aluminum can make the MEMS scanning galvanometer have an initial axial displacement of 331.89 μm. 8. A portable photoacoustic microscopy imaging method based on the scanning galvanometer according to any one of claims 1-7, characterized in that, comprising the steps of: S1 The first lens, the second lens and the focusing lens perform optical path collimation and beam focusing on the laser light emitted by the laser; S2 uses the beam splitter to divide the laser into two beams, one of which is used to scan the surface of the biological tissue, and the other is received by the photoelectric sensor to determine the laser power and the direction of the laser light path; S3 uses the computer for human-computer interaction, selects the scanning mode, and the computer sends a driving command to the function generator, and the function generator applies a driving signal and four electrothermal brakes to drive the MEMS scanning galvanometer to deflect or move axially to achieve Point-by-point scanning of laser light on biological tissue.