A photoacoustic microscopic imaging device and method based on random access scanning

Abstract

The application discloses a kind of photoacoustic microscopic imaging device and method based on random access scanning.The device includes pulsed laser module, light beam transmission module, light beam scanning module, reflective imaging module, signal detection module, motor drive module, synchronous control module, laser random access scanning and ultrasonic synchronous detection module, and acquisition control and data processing module.The method uses the generated external modulation signal to synchronously control the laser random interval emission pulsed laser, galvanometer random deflection for light beam scanning and rotating motor variable speed motion photoacoustic signal detection, combined with rotary scanning method to realize ultrafast, low excitation energy and high contrast random acquisition photoacoustic imaging.The device design and imaging method of the application can make the light beam random access scanning and ultrasonic detector variable speed rotation to detect photoacoustic signal by external modulation signal, achieving the technical effect of no oversampling, high speed and high contrast random acquisition of the vascular network of the region of interest.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical medical imaging, and particularly relates to a photoacoustic microscopic imaging device and method based on random access scanning. BACKGROUND

[0002] Photoacoustic imaging is a new type of medical imaging technology with high sensitivity and non-invasiveness, which can break through the diffusion limit of photons in biological tissues, reconcile the contradiction between spatial resolution and penetration depth of pure optical imaging, and realize multi-scale imaging of contrast sources. In photoacoustic imaging, light excitation and acoustic detection are two key steps. Through the organic combination of light beam scanning devices and ultrasonic detectors, multi-contrast source photoacoustic imaging of endogenous substances such as hemoglobin, melanin, protein, lipid and DNA / RNA in biological tissues, and exogenous contrast agents such as inorganic materials, organic materials and gene-encoded chromophores can be realized, and it is widely used in biomedical imaging research and clinical imaging diagnosis. Among them, photoacoustic microscopic imaging uses optical focusing and high-frequency ultrasonic detection to obtain optical diffraction-limited high resolution, and is widely used in the imaging research of biological tissue vascular network structure and function.

[0003] Photoacoustic microscopic imaging is an imaging mode of point-by-point scanning of the imaging target. At present, the scanning modes of photoacoustic microscopic imaging mainly include two types: grating scanning imaging mode and rotating scanning imaging mode. The grating scanning imaging mode uses single mechanical point-by-point scanning for light excitation and acoustic detection, which is limited by the speed, size and cost of high-precision stepping motors, and has slow imaging speed and poor portability for the target. The rotating scanning imaging mode adopts the optical-electro-mechanical collaborative idea of combining optical scanning and mechanical scanning, realizes high-speed, large-field and portable imaging of the target by using a galvanometer for optical scanning and a rotating motor for acoustic scanning. However, when imaging the vascular network using the two types of point-by-point scanning modes, the region where the target blood vessels are located and the background region outside the blood vessels are both scanned by the light focus, so that when using a high-repetition-frequency laser for ultrafast imaging, the risk of tissue thermal damage caused by excessively high laser energy density will be faced. In addition, although the rotating scanning mechanism has significant imaging advantages for photoacoustic microscopic imaging, this scanning mechanism will introduce the problem of oversampling caused by the dense distribution of light foci in the central imaging region, which will aggravate the risk of thermal damage to the imaged tissue, and will cause uneven distribution of image contrast and resolution. SUMMARY

[0004] (I) Technical problems to be solved

[0005] The application provides a random access scanning photoacoustic microscopic imaging device and method for synchronously regulating and controlling a pulsed laser emission mode, a galvanometer-driven light beam scanning mode and a rotary motor-driven ultrasonic detector rotation mode by generating an external modulation signal in a region of interest, solves the problem that photoacoustic microscopic imaging cannot avoid scanning a background region and the problem that rotary photoacoustic microscopic imaging exists over-sampling, reduces the laser energy density of an imaged tissue, avoids the risk of thermal damage to the tissue, improves the safety of photoacoustic microscopic imaging, effectively suppresses the background signal of the imaged tissue and improves the contrast of a photoacoustic image.

[0006] On the other hand, the random access scanning based photoacoustic microscopic imaging device and method greatly reduces the number of light foci required by conventional photoacoustic microscopic imaging, thereby significantly improving the speed of conventional photoacoustic microscopic imaging.

[0007] (II) Technical solutions

[0008] To solve the technical problems, the application provides a random access scanning based photoacoustic microscopic imaging device and method, and the specific technical solutions are as follows.

[0009] A random access scanning based photoacoustic microscopic imaging device, characterized in that the device comprises a pulsed laser module, a light beam transmission module, a light beam scanning module, a reflection type imaging module, a signal detection module, a motor transmission module, a synchronous control module, a laser random access scanning and ultrasonic synchronous detection module and an acquisition control and data module.

[0010] The pulsed laser source module comprises a laser, which is used for emitting pulsed laser to the light beam transmission module.

[0011] The light beam transmission module comprises a mirror, a spatial light filter, an optical fiber and a collimating lens, which are used for shaping, collimating and transmitting the pulsed laser emitted by the pulsed laser source module to the light beam scanning module.

[0012] The light beam scanning module comprises a galvanometer and a scanning lens, which are used for scanning and focusing a pulsed laser beam.

[0013] The reflection type imaging module comprises a light-transmitting and sound-reflecting device, the light-transmitting and sound-reflecting device is internally inclinedly inserted into a glass sheet and filled with pure water as a coupling medium, and is arranged above the light beam scanning module, and is used for transmitting the focused pulsed laser beam of the light beam scanning module to a target object and reflecting the photoacoustic signal emitted by the target object to the signal detection module.

[0014] The signal detection module comprises an ultrasonic detector, an amplifier, a filter and a data acquisition card connected in sequence, and is used for receiving, amplifying, filtering and collecting the photoacoustic signals detected by the ultrasonic detector; wherein the ultrasonic detector is connected with the sound-transmitting and light-reflecting device, and is used for receiving the photoacoustic signals reflected by the glass sheet;

[0015] The motor transmission module comprises a rotating motor, a lifting motor, a galvanometer fixing device, a motor limiting device and a transmission gear device; wherein the rotating motor is connected with the ultrasonic detector through the transmission gear device, the lifting motor is connected with the motor limiting device, and is connected with the galvanometer of the light beam scanning module through the galvanometer fixing device, and is used for rotating the ultrasonic detector to detect the photoacoustic signals, adjusting the light beam focusing position and preventing the lifting motor from being stuck;

[0016] The synchronous control module comprises a function generator, which is connected with the laser of the pulsed laser source module, the data acquisition card of the signal detection module and the synchronous control card of the laser random access scanning and ultrasonic synchronous detection module, and is used for generating and outputting the synchronization signals among the laser, the galvanometer and the data acquisition card;

[0017] The laser random access scanning and ultrasonic synchronous detection module comprises a synchronous control card, a motor control card and an external modulation signal; wherein the synchronous control card is connected with the laser of the pulsed laser source module, the galvanometer and the motor control card, and the motor control card is connected with the rotating motor and the lifting motor of the motor transmission module; the user generates the external modulation signal in the computer of the acquisition control and data processing module according to the imaging area of interest, and inputs the external modulation signal through the acquisition control software in the computer during the photoacoustic imaging point scanning process, and adjusts the laser to be in the random interval pulse laser mode, adjusts the galvanometer to be in the random jump scanning mode and adjusts the rotating motor to be in the variable speed motion through the synchronous control card and the motor control card respectively, so as to realize the synchronous control of the galvanometer deflection light beam random access scanning and the rotating motor driving the ultrasonic detector variable speed rotation photoacoustic signal detection;

[0018] The acquisition control and data processing module comprises a computer, which is connected with the light beam scanning module, the signal detection module, the motor transmission module and the laser random access scanning and ultrasonic synchronous detection module, and is used for controlling the output of the synchronization signal and the external modulation signal, starting the data acquisition card to collect and store data, reconstructing the photoacoustic signal and processing and displaying the image.

[0019] Preferably, the working mode of the photoacoustic microscopic imaging device is that, for photoacoustic microscopic imaging in a rotating scanning mode, in the case that the number of light foci is known, the number of oversampling light foci of the circular imaging plane is calculated in advance by the data processing software of the computer to generate an external modulation signal not containing the oversampling light foci; in the scanning imaging process, the laser, the galvanometer and the rotating motor are synchronously controlled by the synchronous control card and the motor control card, for each coinciding light focus, the external modulation signal not containing the oversampling light foci is input to the synchronous control card by the acquisition control software of the computer to quickly regulate the laser to close the pulsed laser output and control the galvanometer to skip the coinciding light focus position, so as to avoid the oversampling problem of the light focus scanning, at the same time, the scanning of each path is taken as the feedback control signal of the motor control card to control the rotating motor to drive the ultrasonic probe to rotate once, until the galvanometer and the ultrasonic probe synchronously complete the scanning of the light focus on the last path and the detection of the photoacoustic signal excited by the light focus scanning on the path, so that the photoacoustic image containing the blood vessel network information of the imaging target object can be obtained; then, according to the known blood vessel network information of the target object, the number of effective imaging light foci required to cover the blood vessel network on the imaging plane is calculated by the data processing software of the computer, the number of oversampling light foci is removed on the basis of the number of effective imaging light foci, and the external modulation signal without oversampling and containing only the blood vessel network information of the target object is obtained; finally, the external modulation signal without oversampling and containing only the blood vessel network information of the target object is input to the synchronous control card by the acquisition control software of the computer, and the scanning imaging process of the photoacoustic microscope is repeated, the laser and the galvanometer are regulated by the synchronous control card and the motor control card to perform random access scanning of the light focus, and the ultrasonic probe performs variable speed rotation to detect the photoacoustic signal, so as to realize random access scanning imaging of the target object blood vessel network.

[0020] Preferably, the pulsed laser module emits pulsed laser with adjustable repetition frequency to the target object; when random access scanning imaging is not performed, the laser emits pulsed laser in an equal interval continuous mode; when random access scanning imaging is performed, the laser is changed to a random interval pulsed laser mode by applying an external modulation signal.

[0021] Preferably, the working mode of the light beam transmission module and the light beam scanning module is that, after the light beam emitted by the laser is shaped and collimated by the reflector, the spatial light filter, the optical fiber and the collimating lens, the light beam is converged into a light focus with a diameter of microns through the galvanometer, the scanning lens and the light-transmitting anti-acoustic device in turn, and irradiates on the target object; when random access scanning imaging is performed, the galvanometer is driven by the applied external modulation signal to control the light focus to jump and scan along the initial path of the imaging area at a high speed until the last path is completed to cover the blood vessel network of the target object in the entire imaging plane, and the scanning of the light focus is completed.

[0022] Preferably, the motor drive module works in a way that the focusing position of the light focus in the target object is moved by the lifting motor, the distance of the lifting motor moving up and down is controlled by the motor limiting device to avoid the problem of being stuck due to exceeding the moving range, the ultrasonic detector is driven to rotate to detect the photoacoustic signal by the cooperation of the rotating motor and the transmission gear device; when random access scanning imaging is performed, the input external modulation signal determines the number of light foci on each scanning path and the time required for the light foci to traverse each scanning path, and the ultrasonic detector is driven to rotate at variable speed by the rotating motor to realize that the photoacoustic signal receiving surface always coincides with the light focus scanning surface.

[0023] Preferably, the light focus scanning and photoacoustic signal detection are time-synchronously controlled by the laser random access scanning and ultrasonic synchronous detection module; in the photoacoustic point scanning process, the synchronous control card outputs the external modulation signal to the laser to modulate the laser to perform the random interval pulsed laser mode, and simultaneously drives the galvanometer to perform the light focus random access scanning; the motor control card synchronously controls the speed of the ultrasonic detector rotating driven by the rotating motor according to the feedback of the time required for the light focus to randomly access scan on each scanning path, so that the synchronous detection of the photoacoustic signal is realized in the random scanning process.

[0024] Preferably, the refractive indexes of the pure water and the glass sheet in the light-transmitting and sound-reflecting device are close, so that the pulsed laser beam vertically incident to the light-transmitting and sound-reflecting device is radiated to the target imaging object through the device; the acoustic impedance of the pure water and the glass sheet is significantly different, so that the ultrasonic wave generated by the target imaging object absorbing the pulsed laser is reflected to the ultrasonic detector; the ultrasonic detector receives the photoacoustic signal and converts it into an electric signal, which is stored in the computer after being amplified, filtered and collected; the photoacoustic signal is reconstructed by the computer, and the image is processed and displayed.

[0025] The application further discloses a random access scanning based photoacoustic microscopic imaging method, which adopts the random access scanning based photoacoustic microscopic imaging device to obtain photoacoustic imaging, and the specific steps are as follows:

[0026] Step S1, for the case that the number of rotating photoacoustic imaging light foci is known, the number of oversampling light foci of the imaging plane is calculated, and an external modulation signal not containing the oversampling light foci is generated;

[0027] Step S2, preparing the imaging tissue, smearing ultrasonic coupling agent on the surface of the tissue, and closely attaching to the surface of the transparent preservative film of the light-transmitting and sound-reflecting device, adjusting the imaging tissue to be located in the imaging field of view, and fixing the imaging tissue on the photoacoustic microscopic imaging device;

[0028] Step S3, the pulsed laser emitted by the laser through the external modulation signal in step S1 is modulated to emit a pulsed laser mode, and the emitted pulsed laser sequentially passes through a mirror, a spatial light filter, an optical fiber, a collimating lens, a galvanometer, a scanning lens, a light-transmitting anti-sound device and a transparent preservative film, is focused into an imaging tissue, and after hemoglobin in a blood vessel network in the tissue absorbs light energy, ultrasonic waves, i.e. photoacoustic signals, are excited and are reflected by a tilted fixed glass sheet in the light-transmitting anti-sound device to an ultrasonic detector and are received; wherein each light focus generates a photoacoustic signal with depth information that can be distinguished in the tissue and is referred to as an "A-line"; under the action of the external modulation signal, the galvanometer controls the light focus to jump and scan along an initial scanning path of the imaging area to generate two-dimensional photoacoustic data containing multiple "A-line" information and is referred to as a "B-scan";

[0029] Step S4, after the initial angle "B-scan" data is acquired in step S3, the galvanometer controls the light focus trajectory to rotate by a small angle in a counterclockwise or clockwise direction, the rotating motor drives the ultrasonic detector to synchronously rotate by a small angle in the same direction, and "B-scan" data on a next scanning path is acquired;

[0030] Step S5, steps S3 and S4 are repeated until the rotation angle reaches 180°, a rotation scanning imaging of the imaging tissue is completed, and a photoacoustic image without oversampling is obtained;

[0031] Step S6, a binaryzation processing is performed on the photoacoustic image of the imaging tissue without the problem of oversampling, an external modulation signal containing only the information of the blood vessel network in the tissue is acquired, and the external modulation signal in step S1 is point multiplied with the external modulation signal in the current step to obtain an external modulation signal for realizing random access scanning;

[0032] Step S7, the external modulation signal for realizing random access scanning in step S6 is input to the laser, the galvanometer and the rotating motor through a synchronous control card and a motor control card, the laser is controlled to emit a pulsed laser mode at an arbitrary interval, the galvanometer and the rotating motor are simultaneously controlled to perform random access scanning of the light focus and variable-speed rotation of the ultrasonic detector for photoacoustic signal detection, respectively, steps S3-S5 are repeated, a random access scanning imaging of the tissue is completed, and a photoacoustic image without oversampling and containing only the information of the blood vessels in the tissue is obtained.

[0033] (Three) beneficial effects

[0034] Compared with the prior art, the present application has significant positive technical effects, and the beneficial effects are at least embodied in the following aspects.

[0035] (1) The present application utilizes the combination of optical scanning and mechanical scanning, and generates an external modulation signal for the synchronous control of the mode of laser pulse emission, the mode of galvanometer scanning of the light beam and the speed of the rotating motor movement, so that the random access scanning photoacoustic microscopic imaging device based on random access scanning can perform random access scanning imaging on any region of interest. Compared with the traditional photoacoustic microscopic imaging, the random access scanning photoacoustic microscopic imaging of the present application realizes the arbitrary modulation of the pulse laser emission mode, optical scanning and acoustic scanning, while maintaining a large imaging range and high imaging resolution.

[0036] (2) When the existing photoacoustic microscopic imaging technology performs superfast continuous imaging through point-by-point scanning, there is a risk of tissue thermal damage caused by excessively high laser energy density. When the random access scanning photoacoustic microscopic imaging device of the present application is used for in-vivo biological tissue photoacoustic imaging, the laser can be modulated to be turned off in the non-interest region (background region in the imaging plane), the galvanometer can be modulated to perform random acquisition scanning of the light beam, the laser energy deposition caused by the irradiation of the focal point to the background tissue region is reduced, the number of focal points in the imaging plane of the biological tissue is significantly reduced, the laser energy density in the biological tissue is reduced, and the signal of the background region is effectively suppressed, thereby improving the image contrast of the photoacoustic imaging.

[0037] (3) The random access scanning mechanism of the present application can solve the problem of oversampling caused by the dense distribution of focal points in the central imaging region in the traditional rotating photoacoustic microscopic imaging, thereby reducing the number of focal points in the central imaging region and the risk of tissue damage, and enabling the rotating photoacoustic microscopic imaging to obtain uniform image contrast and resolution.

[0038] (4) The random access scanning mechanism of the present application can be applied to photoacoustic microscopic imaging to significantly reduce the number of focal points required in the imaging plane, which means that under the condition that the pulse repetition frequency of the laser is known, the photoacoustic microscopic imaging based on random access scanning can significantly improve the imaging speed. Taking the traditional rotating photoacoustic microscopic imaging as an example, the imaging speed depends on the imaging range, the focal point scanning step, the rotating scanning step and the pulse repetition frequency of the laser. Under the conditions of an imaging range of 10 mm in diameter, a scanning step of 10 μm, a rotating scanning step of 0.18° and a laser repetition frequency of 200 kHz, the traditional rotating photoacoustic microscopic imaging takes 5 s to obtain a three-dimensional mouse brain cortex vascular network image, while the photoacoustic microscopic imaging based on random access scanning only takes a few hundred milliseconds to obtain a three-dimensional mouse brain cortex vascular network image. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1System structure schematic diagram of the photoacoustic microscopic imaging device based on random access scanning of the present application.

[0040] Figure 2 Optical scanning and acoustic scanning mechanism schematic diagram of the present application.

[0041] Figure 3 (a) is a non-over-sampling rotary scanning schematic diagram of the present application, Figure 3 (b) is a random access scanning mechanism schematic diagram of the present application.

[0042] Figure 4 Mouse brain blood vessel network imaging result diagram (a) obtained by the photoacoustic microscopic imaging device based on random access scanning of the present application when random access scanning imaging is performed and mouse brain blood vessel network imaging result diagram (b) obtained when random access scanning is not performed.

[0043] In the figure, corresponding technical component names and their reference numerals are as follows: laser 1, laser coupler 2-1, collimating lens 2-2, galvanometer 3-1, scanning lens 3-2, focused light beam 3-3, light-transmitting and sound-reflecting device 4, ultrasonic detector 5-1, amplifier 5-2, filter 5-3, data acquisition card 5-4, lifting motor 6-1, rotating motor 6-2, transmission gear device 6-3, function generator 7, synchronous control card 8-1, motor control card 8-2, computer 9, imaging plane 10-1, light focus 10-2, light focus scanning path 10-3, sound focus area 10-4, rotating path 10-5, laser opening pulse laser output 11-1, laser closing pulse laser output 11-2, blood vessel network in biological tissue 12-1, laser opening pulse laser output in blood vessel area 12-2, laser closing pulse laser output in background tissue area except blood vessels 12-3. DETAILED DESCRIPTION

[0044] The present application provides a photoacoustic microscopic imaging device and method based on random access scanning in order to solve its technical problems. The technical solutions of the present application are further illustrated by specific embodiments in combination with the accompanying drawings.

[0045] Figure 1 The present application provides a photoacoustic microscopic imaging device based on random access scanning, which comprises a pulse laser source module 1, a light beam transmission module 2, a light beam scanning module 3, a reflection imaging module 4, a signal detection module 5, a motor transmission module 6, a synchronous control module 7, a laser random access scanning and ultrasonic synchronous detection module 8, and an acquisition control and data processing module 9.

[0046] As Figure 1As shown, the pulse laser source module includes a laser 1; the beam transmission module includes a laser coupler 2-1, a collimating lens 2-2; the beam scanning module includes a galvanometer 3-1, a scanning lens 3-2, a focused beam 3-3; the reflective imaging module includes a light-transmitting and sound-reflecting device 4; the signal detection module includes an ultrasonic detector 5-1, an amplifier 5-2, a filter 5-3, a data acquisition card 5-4; the motor drive module includes a lifting motor 6-1, a rotating motor 6-2, a transmission gear device 6-3; the synchronous control module includes a function generator 7; the laser random access scanning and ultrasonic synchronous detection module includes a synchronous control card 8-1, a motor control card 8-2; the data processing and image output module includes a computer 9. In addition, the computer 9 is provided with acquisition control software and data processing software; the acquisition control software controls the beam scanning module 3 to perform beam scanning on the imaging target object and the signal detection module 5 to receive and collect the generated photoacoustic signals through the laser random access scanning and ultrasonic synchronous detection module 8; the data processing software is used to process the collected photoacoustic signals and reconstruct the photoacoustic image of the imaging target object or generate the external modulation signal required for random access scanning imaging according to the region of interest.

[0047] Specifically, under the action of the synchronization signal output by the function generator 7, the pulsed laser emitted by the laser 1 passes through the laser coupler 2-1 composed of a mirror, a spatial light filter and an optical fiber and the collimating lens 2-2, enters the galvanometer 3-1 and the scanning lens 3-2, and finally converges into the focused beam 3-3. The focused beam 3-3 irradiates onto the imaging target object through the light-transmitting and sound-reflecting device 4, and the ultrasonic signal (i.e. photoacoustic signal) generated by the thermal elastic expansion of the target object after absorbing light energy enters the light-transmitting and sound-reflecting device 4 through the transparent preservative film, is transmitted in pure water to the glass sheet inserted obliquely, is reflected to the ultrasonic detector 5-1, is then amplified and filtered by the amplifier 5-2 and the filter 5-3, is collected by the data acquisition card 5-4, and is stored in the computer 9 for processing and reconstruction.

[0048] As Figure 2(a) As shown, after the collection of the photoacoustic signal (i.e. "A-line") with depth information distinguishable generated by one focal point 10-2 in the imaging plane 10-1 is completed, the light beam scanning module 3 controls the focal point to scan along the focal point scanning path 10-3 (i.e. the diameter of the imaging plane) in the imaging plane, and a two-dimensional photoacoustic "B-scan" data containing multiple "A-line" information is generated. After the "B-scan" data collection on the acoustic focal zone 10-4 of the ultrasonic probe at the current angle is completed, the light beam scanning module 3 and the motor drive module 6 respectively drive the focal point scanning path 10-3 and the acoustic focal zone 10-4 to rotate by a small angle a, and the "B-scan" data on the next scanning path is obtained. Until the rotation angle along the rotation path 10-5 reaches 180°, the entire imaging plane is covered and the rotation scanning imaging of the imaging target is completed, and a photoacoustic image is obtained. As shown in Figure 2 (b) As shown, after the collection of the photoacoustic image data is completed, the focal points in the central region of the imaging plane show an overlapping distribution, which indicates that the traditional rotating photoacoustic microscopic imaging has the problem of oversampling in the central region of the imaging.

[0049] In order to solve the oversampling problem of the traditional rotating photoacoustic microscopic imaging in the prior art, Figure 2 In order to solve the oversampling problem of the traditional rotating photoacoustic microscopic imaging in the prior art, according to the imaging range, the focal point scanning step and the rotation scanning step, the number N×M of focal points required for completing one rotating photoacoustic microscopic imaging can be calculated, wherein N represents the number of focal point scanning paths on each imaging plane, and M represents the number of focal points on each focal point scanning path; under the condition that the number of focal points is known, the oversampling focal point number on the imaging plane can be calculated by the data processing software in the computer 9, the repetition rate μ of the focal points is obtained, and then the external modulation signal 1 not containing the oversampling focal points is generated. Then, the external modulation signal 1 controls the mode of the pulsed laser emitted by the laser 1, the mode of the light beam scanning by the galvanometer 3-1 and the speed of the rotating ultrasonic probe 5-1 by the rotating motor 6-2 through the laser random access scanning and ultrasonic synchronous detection module 8 and the acquisition control software in the computer system 9. Specifically, the external modulation signal 1 is input to the laser 1 and the galvanometer 3-1 through the synchronous control card 8-1, and after the "B-scan" data collection of the initial focal point scanning path is completed under the control of the acquisition control software, the next focal point scanning path is rotated by a small angle a. When the overlapping focal point with the previous focal point scanning path is encountered, the laser closes the pulsed laser output, the galvanometer controls the light beam to skip the overlapping position for focal point scanning, and at the same time, the scanning of the focal points on each path is transmitted to the motor control card 8-2 as a feedback control signal, and then the rotating motor drives the ultrasonic probe to rotate at variable speed for synchronous photoacoustic signal detection. Until the rotation angle reaches 180°, the focal points cover the entire imaging plane without overlapping distribution, and a non-oversampling photoacoustic image is obtained. The schematic diagram of the non-oversampling rotating photoacoustic imaging is as follows:Figure 3 As shown in (a), the light focal points are distributed without overlap on the imaging plane. Solid dots on the imaging plane represent the laser output pulse 11-1 when the laser is turned on, and hollow dots represent the laser output pulse 11-2 when the laser is turned off. The number of laser focal points required on each imaging plane is N×M×(1-μ).

[0050] Furthermore, in order to achieve random access scanning photoacoustic imaging of any region of interest of the imaging target, the present invention firstly... Figure 3 (a) The oversampling-free rotating photoacoustic imaging method acquires a photoacoustic image of a biological tissue. Then, the acquired photoacoustic image is binarized using data processing software in a computer to generate an external modulation signal 2 containing only the feature information of the biological tissue of interest (e.g., vascular network), and the density η of the biological tissue's vascular network is obtained. Finally, the external modulation signal 1 and external modulation signal 2 are multiplied by the data processing software to obtain an external modulation signal capable of random access scanning. When performing random access photoacoustic imaging with the input external modulation signal, the same optical focus scanning and photoacoustic signal detection steps as in the oversampling-free rotating photoacoustic imaging are performed to acquire a photoacoustic image based on random access scanning. This image has no oversampling problem and contains only the vascular network information of the biological tissue of interest. A schematic diagram of photoacoustic imaging based on random access scanning is shown below. Figure 3 As shown in (b), the light focal points are randomly distributed without overlap on the imaging plane. The curved shapes on the imaging plane represent the vascular network in biological tissue 12-1, solid dots represent the laser pulse output being turned on in the vascular region 12-2, and hollow dots represent the laser pulse output being turned off in the background tissue region other than the blood vessels 12-3. The number of laser focal points required on each imaging plane is reduced to N×M×(1-μ)×η. Therefore, the random access scanning mechanism can improve the speed of traditional rotating photoacoustic imaging. In practical applications, random access photoacoustic imaging is typically used for long-term continuous imaging monitoring of vascular networks in biological tissues, acquiring changes in hemoglobin content during real-time imaging to analyze changes in hemodynamic parameters under different physiological states or external stimuli. Furthermore, due to the significant reduction in the number of optical focal points, random access photoacoustic imaging can acquire dynamic changes in hemodynamic parameters at a much faster pace.

[0051] The photoacoustic microscopy imaging device and method based on random access scanning proposed in this invention were used to continuously image mouse brain tissue, obtaining a photoacoustic image of the cerebral cortex vascular network at 500 s (4(a)). A conventional rotating photoacoustic microscopy imaging method was also used to continuously image mouse brain tissue, obtaining a photoacoustic image of the cerebral cortex vascular network at 500 s (4(b)). The area indicated by the white arrow in the image is a hemorrhage point, which is caused by vascular damage due to laser energy deposition caused by oversampling. The method employed... Figure 3 (b) The random access scanning mechanism shown in photoacoustic microscopy can obtain the vascular network of mouse brain tissue in 4(a). Because random access photoacoustic imaging eliminates the oversampling focal points in traditional rotating photoacoustic microscopy and skips background tissue areas outside the vascular network of mouse brain tissue, it significantly reduces the number of focal points on the imaging plane of mouse brain tissue, thereby reducing the laser energy density on the imaging plane and avoiding the risk of tissue thermal damage. The technical advantages are specifically reflected in the following aspects: Figure 4 In (a), after 500 seconds of continuous imaging, no hemorrhage points were found in the vascular network of the mouse brain tissue, whereas this was not observed using conventional rotating photoacoustic microscopy. Figure 4 (b) Due to the failure to avoid scanning the background tissue area and the existence of oversampling issues, the mouse brain tissue showed obvious bleeding after 500 seconds of continuous imaging.

[0052] The specific embodiments described in this application are merely illustrative examples of the main ideas of the present invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A photoacoustic microscopy imaging device based on random access scanning, characterized in that: The device includes a pulsed laser source module, a beam transmission module, a beam scanning module, a reflective imaging module, a signal detection module, a motor drive module, a synchronization control module, a laser random access scanning and ultrasonic synchronous detection module, and an acquisition control and data processing module. The pulsed laser source module includes a laser for emitting pulsed laser light to the beam transmission module; The beam transmission module includes a reflector, a spatial light filter, an optical fiber, and a collimating lens, used for shaping, collimating, and transmitting the pulsed laser emitted by the pulsed laser source module to the beam scanning module; The beam scanning module includes a galvanometer and a scanning lens for scanning and focusing a pulsed laser beam; The reflective imaging module includes a light-transmitting and sound-reflecting device. A glass plate is inserted at an angle inside the light-transmitting and sound-reflecting device, which is filled with pure water as a coupling medium and placed above the beam scanning module. It is used to transmit the focused pulsed laser beam of the beam scanning module to the target object and reflect the photoacoustic signal emitted by the target object to the signal detection module. The signal detection module includes an ultrasonic detector, an amplifier, a filter, and a data acquisition card connected in sequence, used to receive, amplify, filter, and acquire photoacoustic signals detected by the ultrasonic detector; wherein, the ultrasonic detector is connected to a sound-transmitting reflective device to receive photoacoustic signals reflected by a glass plate; The motor drive module includes a rotary motor, a lifting motor, a galvanometer holder, a motor limiting device, and a transmission gear device. The rotary motor is connected to the ultrasonic detector through the transmission gear device, and the lifting motor is connected to the motor limiting device and to the galvanometer of the beam scanning module through the galvanometer holder. This is used to rotate the ultrasonic detector to detect photoacoustic signals, adjust the beam focusing position, and prevent the lifting motor from jamming. The synchronization control module includes a function generator, which is connected to the laser of the pulsed laser source mode, the acquisition card of the signal detection module, and the synchronization control card of the laser random access scanning and ultrasonic synchronous detection module, respectively, and is used to generate and output synchronization signals between the laser, the galvanometer, and the data acquisition card. The laser random access scanning and ultrasonic synchronous detection module includes a synchronization control card, a motor control card, and an external modulation signal. The synchronization control card is connected to the laser, galvanometer, and motor control card of the pulsed laser source mode, respectively. The motor control card is connected to the rotary motor and lifting motor of the motor drive module, respectively. The user generates an external modulation signal in the computer of the acquisition control and data processing module based on the imaging area of ​​interest. During the photoacoustic imaging point scanning process, the user inputs the external modulation signal through the acquisition control software in the computer and adjusts the laser to a random interval pulsed laser mode, the galvanometer to a random skip scanning mode, and the rotary motor to variable speed motion via the synchronization control card and motor control card, respectively. This enables synchronous control of the galvanometer deflecting the beam for random access scanning and the rotary motor driving the ultrasonic detector to rotate at variable speed for photoacoustic signal detection. The acquisition control and data processing module includes a computer, which is connected to the beam scanning module, signal detection module, motor drive module, and laser random access scanning and ultrasonic synchronous detection module, respectively. It is used to control the output of synchronization signals and external modulation signals, start the data acquisition card for data acquisition and storage, reconstruct photoacoustic signals, and process and display images.

2. The photoacoustic microscopy imaging device based on random access scanning according to claim 1, characterized in that, The photoacoustic microscopy imaging device operates as follows: For photoacoustic microscopy imaging using a rotational scanning method, given a known number of optical focal points, the number of oversampled optical focal points on the circular imaging plane is calculated in advance using computer data processing software. An external modulation signal, excluding oversampled optical focal points, is then generated. During the scanning imaging process, a synchronous control card and a motor control card synchronously control the laser, galvanometer, and rotary motor. For each overlapping optical focal point, the computer's acquisition control software inputs the external modulation signal, excluding oversampled optical focal points, to the synchronous control card. This rapidly adjusts the laser to shut down its pulsed laser output and controls the galvanometer to skip overlapping optical focal point positions, thus avoiding oversampling issues during optical focal point scanning. Simultaneously, the completion of each path scan serves as a feedback control signal for the motor control card to control the rotary motor to rotate the ultrasonic transducer once, until the galvanometer and ultrasonic transducer synchronously complete the optical focal point scan. The photoacoustic image containing information about the vascular network of the target object can be acquired by scanning the last path and detecting the photoacoustic signal excited at the optical focal point scan on that path. Then, based on the known vascular network information of the target object, the number of effective imaging focal points required to cover the vascular network on the imaging plane is calculated by computer data processing software. The number of oversampled focal points is removed from the effective number of imaging focal points to obtain an external modulation signal that is not oversampled and contains only the vascular network information of the target object. Finally, the external modulation signal that is not oversampled and contains only the vascular network information of the target object is input to the synchronous control card through the computer acquisition control software, and the scanning imaging process of photoacoustic microscopy is repeated. The laser and galvanometer are controlled by the synchronous control card and the motor control card to perform random access scanning of the optical focal points, and the ultrasonic detector is rotated at variable speed to detect the photoacoustic signal, so as to realize random access scanning imaging of the vascular network of the target object.

3. The photoacoustic microscopy imaging device based on random access scanning according to claim 1, characterized in that: The pulsed laser source module emits pulsed lasers with adjustable repetition frequency to the target object; when not performing random access scanning imaging, the laser emits pulsed lasers in a continuously pulsed laser mode with equal intervals; when performing random access scanning imaging, the laser is changed to emit pulsed lasers at random intervals by applying an external modulation signal.

4. The photoacoustic microscopy imaging device based on random access scanning according to claim 1, characterized in that: The beam transmission module and beam scanning module operate as follows: the laser beam emitted by the laser is shaped and collimated by a reflector, a spatial light filter, an optical fiber, and a collimating lens, and then converges into a light focus with a diameter of micrometers after passing through a galvanometer, a scanning lens, and a light-transmitting reflector in sequence, and then illuminates the target object. During random access scanning imaging, an applied external modulation signal drives the galvanometer to control the light focus to perform high-speed skip scanning along the initial path of the imaging area until the last path is completed to cover the vascular network of the target object in the entire imaging plane, at which point the light focus scanning ends.

5. The photoacoustic microscopy imaging device based on random access scanning according to claim 1, characterized in that: The motor drive module operates by adjusting the focusing position of the optical focus on the target object through the movement of the lifting motor. The motor limit device controls the upward and downward movement distance of the lifting motor to avoid jamming caused by exceeding the movement range. The rotating motor and transmission gear device work together to drive the ultrasonic detector to rotate and detect the photoacoustic signal. During random access scanning imaging, the input external modulation signal determines the number of optical focuses on each scanning path and the time required for the optical focus to traverse each scanning path. The rotating motor drives the ultrasonic detector to rotate at variable speed to ensure that the photoacoustic signal receiving surface always coincides with the optical focus scanning surface.

6. The photoacoustic microscopy imaging device based on random access scanning according to claim 1, characterized in that: The optical focus scanning and photoacoustic signal detection are time-synchronized through the laser random access scanning and ultrasonic synchronous detection module. During the photoacoustic point scanning process, the synchronization control card outputs an external modulation signal to the laser to modulate the laser to execute a random interval pulse laser emission mode, while driving the galvanometer to perform random access scanning of the optical focus. The motor control card synchronously controls the rotation speed of the rotary motor to drive the ultrasonic detector to rotate based on the feedback of the time required for random access scanning of the optical focus on each scanning path, so as to realize the synchronous detection of photoacoustic signals during random scanning.

7. The photoacoustic microscopy imaging device based on random access scanning according to claim 1, characterized in that: The refractive indices of the pure water and the glass plate in the light-transmitting and acoustically reflecting device are close, allowing the pulsed laser beam incident perpendicularly to the device to radiate onto the target image. The significant difference in acoustic impedance between the pure water and the glass plate causes the image to absorb the ultrasonic waves generated by the pulsed laser and reflect them onto the ultrasonic detector. The ultrasonic detector receives the photoacoustic signal and converts it into an electrical signal. After amplification, filtering, and acquisition, the signal is stored in a computer. The data processing software in the computer is used for photoacoustic signal reconstruction, image processing, and display.

8. A photoacoustic microscopy imaging method based on random access scanning, characterized in that, The photoacoustic imaging is obtained using the photoacoustic microscopy device based on random access scanning as described in any one of claims 1-7, and the specific steps are as follows: Step S1: Given the known number of optical focal points in the rotating photoacoustic imaging, calculate the number of oversampled optical focal points on the imaging plane and generate an external modulation signal that does not contain oversampled optical focal points. Step S2: Prepare the imaging tissue, apply ultrasonic coupling agent to the tissue surface, attach it tightly to the transparent plastic wrap surface of the light-transmitting and sound-reflecting device, adjust the imaging tissue to be located in the imaging field of view, and fix the imaging tissue on the photoacoustic microscopy imaging device. Step S3: The laser emits a pulsed laser mode by modulating the external modulation signal from step S1. The emitted pulsed laser passes sequentially through a reflector, a spatial light filter, an optical fiber, a collimating lens, a galvanometer, a scanning lens, a light-transmitting reflector, and a transparent plastic wrap, and is focused onto the imaging tissue. Hemoglobin in the tissue's vascular network absorbs the light energy and excites ultrasound, i.e., a photoacoustic signal, which is reflected by a tilted and fixed glass plate in the light-transmitting reflector onto the ultrasound detector and received. Each optical focus generates a photoacoustic signal with depth information in the tissue, referred to as "A-line". Under the action of the external modulation signal, the galvanometer controls the optical focus to perform a skip scan along the initial scanning path of the imaging area, generating two-dimensional photoacoustic data containing multiple "A-line" information, referred to as "B-scan". After obtaining the initial angle "B-scan" data in step S3, the galvanometer controls the optical focus trajectory to rotate a small angle in the counterclockwise or clockwise direction, and the rotary motor drives the ultrasonic detector to rotate a small angle synchronously in the same direction to obtain the "B-scan" data on the next scanning path. Step S5: Repeat steps S3 and S4 until the rotation angle reaches 180°, completing one rotational scan imaging of the imaging tissue and obtaining a photoacoustic image without oversampling; Step S6: The photoacoustic image of the imaging tissue without oversampling problem is binarized to obtain an external modulation signal that contains only the vascular network information in the tissue. The external modulation signal in step S1 is multiplied by the external modulation signal in the current step to obtain the external modulation signal for random access scanning. Step S7: The external modulation signal for random access scanning in step S6 is input to the laser, galvanometer, and rotary motor through the synchronous control card and motor control card. The laser is controlled to execute the arbitrary interval pulse laser emission mode. At the same time, the galvanometer and rotary motor are synchronously controlled to perform random access scanning of the optical focus and photoacoustic signal detection by the variable speed rotating ultrasonic detector, respectively. Steps S3-S5 are repeated to complete one random access scan imaging of the tissue and obtain a photoacoustic image without oversampling and containing only tissue vascular information.

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