A peripheral blood vessel three-dimensional photoacoustic imaging method and imaging system thereof

Abstract

The application discloses a peripheral blood vessel three-dimensional photoacoustic imaging method and an imaging system thereof. A transparent soft film is arranged at the bottom of a water tank and placed on the surface of an imaging part to be imaged, and is completely attached to the surface. A negative pressure valve is arranged at the top of the water tank, and the air pressure inside the water tank is reduced by a negative pressure control device, so that the deformation of the blood vessels of the imaging part to be imaged of a subject caused by external compression is reduced, and the subject does not need to be immersed in a sound guide liquid. The light outlet end of a light guide irradiation device moves synchronously with an ultrasonic detector, and a dynamic illumination area is formed. In the reconstruction process, only the photoacoustic signal data in the reconstruction illumination angle is used to carry out the back projection of the photoacoustic signal. The application has the advantages that the dynamic illumination enhances the overall uniformity of the light intensity of the scanning area, the dynamic illumination enhances the uniformity and enlarges the imaging area, the problem that the fixed fiber irradiation area is limited in the scanning process of the traditional mode is solved, the device is simple to operate, has strong adaptability, and has low complexity and cost.

Description

TECHNICAL FIELD

[0001] The present application relates to, in particular to a peripheral blood vessel three-dimensional photoacoustic imaging method and its imaging system. BACKGROUND

[0002] In the development of modern imaging technology, photoacoustic imaging technology has attracted much attention due to its combination of high contrast of optical imaging and deep tissue penetration capability of ultrasonic imaging. By receiving the ultrasonic signal generated after the sample absorbs the pulsed laser energy, photoacoustic imaging can provide detailed information about the structure and functional state of the tissue, especially in the aspect of non-invasive blood vessel imaging. With the increasing prevalence of peripheral vascular diseases (PVD), including peripheral arterial disease (PAD) and venous occlusion, the demand for three-dimensional non-invasive imaging of peripheral blood vessels is increasing, which is crucial for disease diagnosis and treatment evaluation. Common PVD lesions occur in the lower limbs, and the possible lesion area covers a range of up to half a meter from the thigh to the calf, and the depth is from 1 centimeter to 10 centimeters, which puts high requirements on photoacoustic blood vessel three-dimensional imaging.

[0003] However, existing photoacoustic blood vessel imaging systems face some limitations. The photoacoustic microscopic imaging method based on point scanning is slow and requires the imaging site to remain stationary for a long time. The most commonly used handheld array and arc array based on self-focusing or lens focusing (whose elements usually adopt a cylindrical focusing method) need to scan the target area and stack the results of multiple two-dimensional tomographic sections, but the focusing characteristics of the array elements in these systems result in a resolution along the scanning axis that is much lower than the in-plane resolution. On the other hand, to obtain large-scale and deep three-dimensional imaging capability, it is most ideal to use a large-scale two-dimensional sensor array, which results in a complex and expensive system. Existing two-dimensional array-based photoacoustic imaging systems include hemispherical two-dimensional arrays and planar two-dimensional arrays. Although the hemispherical array system can provide high-quality three-dimensional imaging within its field of view, the resolution decreases rapidly outside the focal point, limiting the imaging depth. The existing planar two-dimensional array has only a relatively small surface working area, making it difficult to achieve large-field-of-view three-dimensional imaging results in a single scan, and usually requires multi-dimensional scanning and stitching technology to achieve three-dimensional imaging with a larger field of view. To solve this limitation, a large synthetic matrix array scanning technology based on one-dimensional non-focusing linear arrays is proposed (CN2017101885839) and used for breast imaging (CN2019102939869). However, this method uses a fixed illumination method and can only image a range of about 20 centimeters, and uses a light excitation method from the bottom and side of the imaging object, which requires that there be no ultrasonic obstruction in the imaging range, which greatly limits the imaging object, and is more suitable for breast photoacoustic imaging, making it difficult to effectively carry out large-scale imaging of lower limbs and other tissues with larger scales and internal bones.

[0004] Furthermore, achieving the laser light source required for large-scale three-dimensional photoacoustic imaging presents a challenge. When imaging a large area (e.g., a leg or arm), conventional methods require large-area laser irradiation to stimulate the ultrasound signal. To ensure an effective signal-to-noise ratio, the required total laser energy increases linearly with the irradiated area. This not only significantly increases the cost of the excitation light source, but the use of high-energy lasers also brings practical inconveniences, including safety hazards and the risk of damage to supporting optical components. Summary of the Invention

[0005] In order to solve the problems existing in the existing photoacoustic imaging technology and improve the quality of large-scale three-dimensional imaging, especially to meet the needs of imaging multiple peripheral blood vessels in the body, and to reduce costs and technical barriers, the present invention proposes a three-dimensional photoacoustic imaging method for peripheral blood vessels and an imaging system thereof, which are particularly suitable for high-quality three-dimensional imaging of human peripheral blood vessels; the present invention creatively proposes a strategy of laser irradiation following synchronous scanning of ultrasonic transducers, namely dynamic illumination, combined with the corresponding imaging reconstruction algorithm, so that the present invention can perform continuous large-area three-dimensional imaging; the excitation light following scanning strategy proposed in the present invention also makes it easier to expand photoacoustic imaging from the arm to other parts of the body; the integrated negative pressure scanning method proposed in the present invention also effectively reduces the pressure of the scanning device on the body during large-scale scanning, which can affect local blood circulation.

[0006] One object of the present invention is to provide a peripheral blood vessel three-dimensional photoacoustic imaging system.

[0007] The peripheral blood vessel three-dimensional photoacoustic imaging system of the present application comprises: a pulsed laser light source, a coupling device, a light guide irradiation device, a water tank, a sound guide liquid, an experimental bed, a negative pressure control device, an ultrasonic detector, a mechanical scanning device, a data acquisition system and a computer; wherein the inside of the water tank has a sealed space, the side wall of the water tank is of a hard material and has supporting property, the bottom of the water tank is a transparent soft film which is sealingly connected with the bottom edge of the side wall, can transmit light and has the ability of deformation and ultrasonic transmission, the top of the water tank is provided with a negative pressure valve, the negative pressure valve is connected to the negative pressure control device outside the water tank, the side wall of the water tank is provided with an optical window, and the water tank contains the sound guide liquid; the light guide irradiation device, the ultrasonic detector and the mechanical scanning device are all arranged in the water tank, the detection end of the ultrasonic detector is below the liquid level of the sound guide liquid; the light outlet end of the light guide irradiation device is mechanically connected with the ultrasonic detector through an adapter fixing piece to form an integral whole; the top end of the mechanical scanning device is fixed with the light outlet end of a one-to-multiple multi-mode optical fiber and the ultrasonic detector, the fixed end of the mechanical scanning device is fixedly installed on the inside side wall of the water tank, and the mechanical scanning device is connected to the computer outside the water tank through a data line sealingly penetrating through the side wall of the water tank; the ultrasonic detector is connected to the data acquisition system outside the water tank through a data line sealingly penetrating through the side wall of the water tank, and the data acquisition system is connected to the computer; the signal leading-out end of the pulsed laser light source is connected to the signal passive triggering end of the data acquisition system;

[0008] The subject is located on the experimental bed; the part of the subject to be imaged is coated with water or medical ultrasonic coupling agent; the bottom of the water tank is placed on the surface of the part of the subject to be imaged, and the transparent soft film at the bottom of the water tank is completely attached to the surface of the subject; the air pressure inside the water tank is reduced to be less than the standard atmospheric pressure outside by the negative pressure control device, forming a negative pressure, offsetting or partially offsetting the pressure on the surface of the part of the subject to be imaged generated by the gravity suffered by the acoustic-conducting liquid in the water tank, reducing the deformation of the blood vessels of the part of the subject to be imaged caused by external compression, and without the need to immerse the part of the subject to be imaged in the acoustic-conducting liquid, maintaining the comfort and hygiene of the subject during the imaging process; the pulsed laser source generates pulsed laser, which is coupled into the light-in end of the light guide irradiation device through the coupling device, and the light guide irradiation device uniformly irradiates the laser to the surface of the part of the subject to be imaged through the optical window of the side wall of the water tank, excites to generate ultrasonic signals, and the ultrasonic signals are received by the ultrasonic probe through the transparent soft film and the acoustic-conducting liquid, and are converted into electrical signals and transmitted to the data acquisition system; the pulsed laser source emits a trigger signal to the data acquisition system simultaneously every time a laser pulse is emitted, triggering the data acquisition system to synchronously collect photoacoustic signal data; the data acquisition system converts the electrical signals into digital signals and transmits them to the computer for storage, realizing photoacoustic signal acquisition; the computer controls the light-out end of the light guide irradiation device to move synchronously with the ultrasonic probe through the mechanical scanning device, forming an illumination area following the movement of the ultrasonic probe, i.e. a dynamic illumination area; the dynamic illumination area covers the surface of the region to be imaged with an included angle with the normal line of the current ultrasonic probe not less than the reconstruction illumination angle θ; after completing photoacoustic signal acquisition for a region of the part to be imaged, the light-out end of the light guide irradiation device and the ultrasonic probe are moved as a whole to the next region by the mechanical scanning device, until photoacoustic signal acquisition for all parts to be imaged is completed; the computer integrates the photoacoustic signal data stored during the entire scanning process and then reconstructs, and only the photoacoustic signal data within the reconstruction illumination angle θ is used for back projection of the photoacoustic signal during the reconstruction process, i.e. the photoacoustic point sources within the acceptance angle range with the best detection sensitivity of the current ultrasonic probe are reconstructed, realizing high-quality photoacoustic three-dimensional peripheral blood vessel imaging, and the scanning distance and scanning speed are controlled by the mechanical scanning device, meeting different imaging requirements.

[0009] The pulse laser light source adopts a pulse laser. The side wall of the water tank is made of transparent hard material, i.e. acrylic, which can be used to observe the internal condition through the side wall of the water tank; the optical window of the water tank is made of optical glass sheet. The sound-conducting liquid is heavy water or deionized water. The transparent soft film is made of polyvinyl chloride plastic material. The coupling device adopts a concave lens to adjust the size of the laser to be consistent with the light-in end of the light guide irradiation device. The light guide irradiation device adopts a multi-branch multi-mode optical fiber bundle or a light guide arm; when the light guide irradiation device is the light guide arm, the light guide arm is located in the water tank, the light-in end of the light guide arm is tightly attached to the inner wall of the optical window of the water tank, and the light-out end of the light guide arm is connected with the ultrasonic probe as a whole; when the light guide irradiation device is the multi-branch multi-mode optical fiber bundle, the multi-branch multi-mode optical fiber bundle has one light-in end and multiple light-out ends, the multiple light-out ends are connected with the ultrasonic probe as a whole, and the light-in end of the multi-branch multi-mode optical fiber bundle is tightly attached to the inner wall of the optical window of the water tank or is sealedly extended to the outside of the water tank through the light guide hole arranged in the side wall of the water tank. The mechanical scanning device adopts a mechanical arm or a one-dimensional, two-dimensional or three-dimensional translation stage. The ultrasonic probe adopts a one-dimensional linear unfocused ultrasonic transducer array or a small-sized focused probe.

[0010] The reconstruction illumination angle θ is 30°-70°. The negative pressure formed in the water tank is 300-1000 Pa less than the standard atmospheric pressure.

[0011] Another object of the present application is to provide a peripheral blood vessel three-dimensional photoacoustic imaging method.

[0012] The peripheral blood vessel three-dimensional photoacoustic imaging method of the present application comprises the following steps:

[0013] 1) The subject is located on the experimental bed; the part to be imaged of the subject is coated with water or medical ultrasonic coupling agent;

[0014] 2) The bottom of the water tank is placed on the surface of the part to be imaged of the subject, the transparent soft film of the bottom of the water tank is completely attached to the surface of the subject; the air pressure in the water tank is reduced by the negative pressure control device, which is less than the standard atmospheric pressure outside, to form a negative pressure, which offsets or partially offsets the pressure on the surface of the part to be imaged of the subject caused by the gravity of the sound-conducting liquid in the water tank, reduces the deformation of the blood vessels of the part to be imaged of the subject caused by external compression, and does not need to immerse the part to be imaged of the subject in the sound-conducting liquid, thereby maintaining the comfort and hygiene of the subject during the imaging process;

[0015] 3) The pulse laser light source generates pulse laser, which is coupled into the light-in end of the light guide irradiation device through the coupling device;

[0016] 4) The light guide irradiation device uniformly irradiates the laser to the surface of the part to be imaged of the subject through the optical window of the side wall of the water tank;

[0017] 5) the excitation light irradiates the part to be imaged, the excitation generates ultrasonic signals, the ultrasonic signals are received by the ultrasonic detector through the transparent soft membrane and the acoustic-conducting liquid, and the ultrasonic signals are converted into electric signals and transmitted to the data acquisition system;

[0018] 6) the pulsed laser light source emits a trigger signal to the data acquisition system each time a laser pulse is emitted, the data acquisition system is triggered to synchronously collect photoacoustic signal data; the data acquisition system converts the electric signals into digital signals and transmits the digital signals to the computer, and the computer stores the digital signals to realize photoacoustic signal acquisition;

[0019] 7) the computer controls the light-emitting end of the light guide irradiation device to move synchronously with the ultrasonic detector through the mechanical scanning device, so as to form an illumination area that moves with the ultrasonic detector, i.e., a dynamic illumination area; the dynamic illumination area covers the surface of the part to be imaged within an angle of no less than the reconstruction illumination angle θ with respect to the normal line of the current ultrasonic detector;

[0020] 8) after the photoacoustic signal acquisition of a region of the part to be imaged is completed, the light-emitting end of the light guide irradiation device and the ultrasonic detector are moved as a whole to the next region by the mechanical scanning device, until the photoacoustic signal acquisition of all the parts to be imaged is completed;

[0021] 9) the computer reconstructs the photoacoustic signal data stored in the whole scanning process after integration, and only the photoacoustic signal data within the reconstruction illumination angle θ is used for the back projection of the photoacoustic signal in the reconstruction process, i.e., the photoacoustic point sources within the acceptance angle range with the best detection sensitivity of the current ultrasonic detector are reconstructed, so as to realize high-quality photoacoustic three-dimensional peripheral blood vessel imaging, and the scanning distance and the scanning speed are controlled by the mechanical scanning device to meet different imaging requirements.

[0022] In step 2), the negative pressure range formed in the water tank is 300-1000 Pa less than the standard atmospheric pressure.

[0023] The reconstruction illumination angle θ is 30°-70°.

[0024] In step 9), for a large-area imaging region, the scanning distance is correspondingly lengthened, for a small-area imaging region, the scanning distance is shortened; when the imaging quality is pursued, slow scanning is adopted; when the imaging speed is pursued, fast scanning is adopted.

[0025] Advantages of the present application:

[0026] The present application is particularly applicable to the imaging of peripheral blood vessels of human body, and uses a dynamic light excitation mode for ultrasound probe-based photoacoustic scanning imaging, and uses pulsed laser and corresponding data acquisition and processing to realize high-quality three-dimensional imaging of peripheral blood vessels of human body; the present application solves the problem of limitation of imaging of large-scale peripheral blood vessels of various parts of human body in traditional photoacoustic imaging technology; meanwhile, the imaging method of the present application has the advantages of simple operation, high imaging quality and strong adaptability; the present application is particularly applicable to three-dimensional imaging of peripheral blood vessels of human body; the present application can be widely applied to medical diagnosis, monitoring and treatment effect evaluation of peripheral vascular diseases, and is particularly suitable for early detection and continuous monitoring of diseases such as vascular lesions and inflammation, for example, evaluation of peripheral vascular conditions of arms or legs in diseases such as atherosclerosis or venous obstruction; the present application has the advantage of dynamic illumination enhancing the overall uniformity of light intensity in the scanning area; dynamic illumination enhances the uniformity and expands the imaging area, solving the problem of limitation of fixed fiber irradiation area in the scanning process of traditional methods; the device is simple to operate, has strong adaptability, low complexity and low cost. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Fig. 1 is a schematic diagram of an embodiment of the peripheral vascular three-dimensional photoacoustic imaging system of the present application; Figure 2 Fig. 2 is a schematic diagram of a one-dimensional non-focused transducer array of an embodiment of the peripheral vascular three-dimensional photoacoustic imaging system of the present application;

[0028] Figure 3 Fig. 4 is a schematic diagram of scanning of a one-dimensional non-focused transducer array to form a synthetic two-dimensional surface array of an embodiment of the peripheral vascular three-dimensional photoacoustic imaging system of the present application;

[0029] Figure 4 Fig. 5 is a schematic diagram of a three-dimensional reconstruction principle of photoacoustic based on delay-and-sum algorithm (DAS) of an embodiment of the peripheral vascular three-dimensional photoacoustic imaging method of the present application. DETAILED DESCRIPTION

[0030] The present application will be further described below by specific embodiments with reference to the accompanying drawings.

[0031] As Figure 1As shown, the peripheral blood vessel three-dimensional photoacoustic imaging system of the embodiment comprises a pulsed laser light source 1, a coupling device 2, a one-to-many multi-mode optical fiber 3, a water tank 4, a sound-conducting liquid 5, an experimental bed 6, a negative pressure control device, a one-dimensional linear unfocused ultrasonic transducer array 7, a mechanical arm 8, a data acquisition system 9 and a computer 10; wherein the inside of the water tank 4 has a sealed space, the side wall of the water tank 4 is made of a hard material and has supportability, the bottom of the water tank 4 is a transparent soft film which is sealingly connected to the bottom edge of the side wall, can transmit light and has deformation, the top of the water tank 4 is provided with a negative pressure valve, the negative pressure valve 11 is connected to the negative pressure control device which is located outside the water tank 4, the side wall of the water tank 4 is provided with an optical window, and the water tank 4 contains the sound-conducting liquid 5; the one-to-many multi-mode optical fiber 3, the one-dimensional linear unfocused ultrasonic transducer array 7 and the mechanical arm 8 are arranged in the water tank 4; the light-incident end of the one-to-many multi-mode optical fiber 3 is located inside the optical window, the light-incident end of the one-to-many multi-mode optical fiber 3 and the one-dimensional linear unfocused ultrasonic transducer array 7 are mechanically connected into an integral whole through an adapter fixing piece; the top end of the mechanical arm 8 is fixed with the light-incident end of the one-to-many multi-mode optical fiber 3 and the one-dimensional linear unfocused ultrasonic transducer array 7 which are connected into an integral whole, the fixed end of the mechanical arm 8 is fixedly installed on the inside side wall of the water tank 4, and the mechanical arm 8 is connected to the computer 10 which is located outside the water tank 4 through a data line sealingly penetrating through the side wall of the water tank 4; the one-dimensional linear unfocused ultrasonic transducer array 7 is connected to the data acquisition system 9 which is located outside the water tank 4 through a data line sealingly penetrating through the side wall of the water tank 4, and the data acquisition system 9 is connected to the computer 10; the signal leading-out end of the pulsed laser light source 1 is connected to the signal passive triggering end of the data acquisition system 9.

[0032] In the embodiment, the pulse width of the pulsed laser light source 1 is about 16 ns, and the repetition frequency of the pulse is 10 Hz. When working at a wavelength of 1064 nm, the single-pulse energy of the laser can reach 650 mJ, and the spot diameter is 5 mm; the light guide irradiation device adopts the one-to-many multi-mode optical fiber 3, the light-incident end of the one-to-many multi-mode optical fiber 3 is circular with a diameter of 9 mm, and the light-incident end is rectangular with a size of 1 mm x 40 mm; the data acquisition system 9 has a total of 256 receiving channels, the sampling rate is 40 MHz, and passive triggering is adopted for acquisition; the hard material adopted for the side wall of the water tank 4 is acrylic, the sound-conducting liquid 5 adopts water, the transparent soft film adopts polyvinyl chloride plastic material with a thickness of 0.2 mm, the optical window of the water tank 4 adopts K9 optical glass sheet, the coupling device 2 adopts a concave lens, and the reconstruction illumination angle θ is 60°. The ultrasonic detector adopts the one-dimensional linear unfocused ultrasonic transducer array 7; the mechanical scanning device adopts the mechanical arm 8.

[0033] As shown in Figure 2 the elements of the one-dimensional linear unfocused ultrasonic transducer array 7 are arranged in a line, there are a total of 256 elements, the center frequency is 3.5 MHz, and the bandwidth is 2-5 MHz. The size of each element is 0.5 mm x 0.4 mm, and the spacing of the elements is 0.1 mm.

[0034] The peripheral blood vessel three-dimensional photoacoustic imaging method of the embodiment comprises the following steps:

[0035] 1) The subject is located on the experimental bed 6; the bottom of the water tank 4 is placed on the surface of the part to be imaged of the subject, and the transparent soft film at the bottom of the water tank 4 is completely attached to the surface of the subject, and the part to be imaged in the embodiment is the abdomen;

[0036] 2) The air pressure inside the water tank 4 is reduced to be less than the standard atmospheric pressure outside by the negative pressure control device, forming a negative pressure, which offsets or partially offsets the pressure on the surface of the part to be imaged of the subject caused by the gravity suffered by the acoustic-conducting liquid 5, reduces the deformation of the blood vessels of the part to be imaged of the subject caused by external compression, and does not need to immerse the subject in the acoustic-conducting liquid 5, thereby maintaining the comfort and hygiene of the subject during the imaging process;

[0037] 3) The pulsed laser light source 1 adopts a pulsed laser to generate pulsed laser light, which is expanded by the coupling device 2 to the same size as the diameter of the entrance end of the one-to-many multi-mode optical fiber 3, and is coupled into the one-to-many multi-mode optical fiber 3 through the optical window of the side wall of the water tank 4;

[0038] 4) The one-to-many multi-mode optical fiber 3 evenly divides the pulsed laser light into multiple beams of light with uniform energy, which is emitted from multiple light exit ends as excitation light and uniformly irradiates the surface of the part to be imaged of the subject;

[0039] 5) The excitation light irradiates the part to be imaged to generate ultrasonic signals, which are received by the one-dimensional linear non-focused ultrasonic transducer array 7 through the transparent soft film and the acoustic-conducting liquid 5, and are converted into electrical signals and transmitted to the data acquisition system 9;

[0040] 6) The pulsed laser light source 1 emits a trigger signal to the data acquisition system 9 simultaneously every time a laser pulse is emitted, triggering the data acquisition system 9 to synchronously collect photoacoustic signal data; the data acquisition system 9 converts the electrical signals into digital signals, which are amplified by two-stage preamplifier circuits, and finally amplified by 1500 times to be transmitted to the computer 10 for storage, thereby realizing photoacoustic signal acquisition;

[0041] 7) The computer 10 controls the light exit end of the one-to-many multi-mode optical fiber 3 to move synchronously with the one-dimensional linear non-focused ultrasonic transducer array 7 through the mechanical arm 8, forming a dynamic illumination area that moves with the one-dimensional linear non-focused ultrasonic transducer array 7; the dynamic illumination area covers the surface of the imaged area with an angle of not more than 60° with respect to the normal line of the current one-dimensional linear non-focused ultrasonic transducer array 7;

[0042] 8) After the photoacoustic signal acquisition of one region of the part to be imaged is completed, the mechanical arm 8 drives the light emitting end of the multimode optical fiber 3 and the one-dimensional linear unfocused ultrasonic transducer array 7 to move as a whole to the next region until the photoacoustic signal acquisition of all the parts to be imaged is completed, so as to realize the scanning synthesis of the two-dimensional surface array by the one-dimensional linear unfocused ultrasonic transducer array 7, as shown in FIG. 8; Figure 3

[0043] 9) The computer 10 integrates the stored photoacoustic signal data and then performs reconstruction, and in the reconstruction process, only the photoacoustic signal data within the reconstruction illumination angle is used to perform the back projection of the photoacoustic signal, that is, the photoacoustic point source within the acceptance angle range of the current one-dimensional linear unfocused ultrasonic transducer array 7 is reconstructed, as shown in FIG. 9, so as to realize the high-quality photoacoustic three-dimensional peripheral blood vessel imaging, and at the same time, the scanning distance is controlled by the mechanical arm 8 to meet different imaging requirements. Figure 4

[0044] Finally, it should be noted that the purpose of the disclosed embodiments is to help further understand the present application, but those skilled in the art can understand that various replacements and modifications are possible without departing from the spirit and scope of the present application and the appended claims. Therefore, the present application should not be limited to the disclosed content of the embodiments, and the scope of protection claimed by the present application is subject to the scope defined by the claims.​​

Claims

1. A peripheral blood vessel three-dimensional photoacoustic imaging system, characterized in that, The peripheral blood vessel three-dimensional photoacoustic imaging system comprises a pulsed laser light source, a coupling device, a light guide irradiation device, a water tank, a sound guide liquid, an experimental bed, a negative pressure control device, an ultrasonic detector, a mechanical scanning device, a data acquisition system and a computer; wherein the inside of the water tank has a closed space, the side wall of the water tank is made of hard material and has supporting property, the bottom of the water tank is a transparent soft film which is sealingly connected with the bottom edge of the side wall, can transmit light and has deformation ability and ultrasonic transmission ability, the top of the water tank is provided with a negative pressure valve, the negative pressure valve is connected to the negative pressure control device outside the water tank, the side wall of the water tank is provided with an optical window, and the water tank contains the sound guide liquid; the light guide irradiation device, the ultrasonic detector and the mechanical scanning device are all arranged in the water tank, the detection end of the ultrasonic detector is below the liquid level of the sound guide liquid; the light outlet end of the light guide irradiation device is mechanically connected with the ultrasonic detector through an adapter fixing piece to form an integral whole; the top end of the mechanical scanning device is fixed with the light outlet end of a one-to-multiple multi-mode optical fiber and the ultrasonic detector, the fixed end of the mechanical scanning device is fixedly installed on the inside side wall of the water tank, the mechanical scanning device is connected to the computer outside the water tank through a data line sealingly penetrating through the side wall of the water tank; the ultrasonic detector is connected to the data acquisition system outside the water tank through a data line sealingly penetrating through the side wall of the water tank, and the data acquisition system is connected to the computer; the signal leading-out end of the pulsed laser light source is connected to the signal passive triggering end of the data acquisition system. The subject is located on an examination bed; the part of the subject to be imaged is coated with water or medical ultrasonic coupling agent; the bottom of the water tank is placed on the surface of the part of the subject to be imaged, and the transparent soft film at the bottom of the water tank is completely attached to the surface of the subject; the air pressure inside the water tank is reduced to be less than the standard atmospheric pressure outside by a negative pressure control device, forming a negative pressure, which offsets or partially offsets the pressure on the surface of the part of the subject to be imaged generated by the gravity of the acoustic-conducting liquid in the water tank, reduces the deformation of the blood vessels of the part of the subject to be imaged caused by external compression, and does not need to immerse the part of the subject to be imaged in the acoustic-conducting liquid, thereby maintaining the comfort and hygiene of the subject during the imaging process; a pulsed laser source generates pulsed laser light, which is coupled into the light-in end of the light guide and irradiation device through a coupling device, and the light guide and irradiation device uniformly irradiate the laser light to the surface of the part of the subject to be imaged through the optical window in the side wall of the water tank, excite to generate ultrasonic signals, and the ultrasonic signals are received by the ultrasonic probe through the transparent soft film and the acoustic-conducting liquid, converted into electrical signals, and transmitted to the data acquisition system; the pulsed laser source emits a trigger signal to the data acquisition system simultaneously each time a laser pulse is emitted, triggering the data acquisition system to synchronously collect photoacoustic signal data; the data acquisition system converts the electrical signals into digital signals and transmits them to the computer for storage, thereby realizing photoacoustic signal acquisition; the computer controls the light-out end of the light guide and irradiation device to move synchronously with the ultrasonic probe through a mechanical scanning device, forming a dynamic illumination area that moves with the ultrasonic probe; the dynamic illumination area covers the surface of the region to be imaged at an angle of not less than the reconstruction illumination angle θ with respect to the normal line of the current ultrasonic probe; after the photoacoustic signal acquisition of a region of the part to be imaged is completed, the light-out end of the light guide and irradiation device and the ultrasonic probe are moved as a whole to the next region by the mechanical scanning device, until the photoacoustic signal acquisition of all the parts to be imaged is completed; the computer integrates the photoacoustic signal data stored during the entire scanning process and performs reconstruction, and only the photoacoustic signal data within the reconstruction illumination angle θ is used for the back projection of the photoacoustic signal during the reconstruction, i.e., the photoacoustic point sources within the acceptance angle range with the best detection sensitivity of the current ultrasonic probe are reconstructed, thereby realizing high-quality photoacoustic three-dimensional peripheral blood vessel imaging; and the scanning distance and scanning speed are controlled by the mechanical scanning device, thereby meeting different imaging requirements.

2. The peripheral vascular three-dimensional photoacoustic imaging system of claim 1, wherein, The side wall of the water tank is made of transparent hard material; and the optical window of the water tank is made of optical glass sheet.

3. The peripheral vascular three-dimensional photoacoustic imaging system of claim 1, wherein, The acoustic-conducting liquid is heavy water or deionized water.

4. The peripheral vascular three-dimensional photoacoustic imaging system of claim 1, wherein, The light guide irradiation device adopts a multi-branch multimode optical fiber bundle or a light guide arm; the light guide irradiation device is the light guide arm, the light guide arm is located in the water tank, the light inlet end of the light guide arm is tightly attached to the inner wall of the optical window of the water tank, and the light outlet end of the light guide arm is connected with the ultrasonic detector in an integrated manner; or the light guide irradiation device is a multi-branch multimode optical fiber bundle, the multi-branch multimode optical fiber bundle has one light inlet end and multiple light outlet ends, the multiple light outlet ends are connected with the ultrasonic detector in an integrated manner, and the light inlet end of the multi-branch multimode optical fiber bundle is tightly attached to the inner wall of the optical window of the water tank or is sealed and extended to the outside of the water tank through the light guide hole arranged on the side wall of the water tank.

5. The peripheral vascular three-dimensional photoacoustic imaging system of claim 1, wherein, The mechanical scanning device adopts a mechanical arm or a one-dimensional, two-dimensional or three-dimensional translation stage.

6. The peripheral vascular three-dimensional photoacoustic imaging system of claim 1, wherein, The ultrasonic detector adopts a one-dimensional linear unfocused ultrasonic transducer array or a small-sized focused probe.

7. The peripheral vascular three-dimensional photoacoustic imaging system of claim 1, wherein, The reconstruction illumination angle θ is 30°-70°.

8. The imaging method of the peripheral blood vessel three-dimensional photoacoustic imaging system according to claim 1, characterized in that, The imaging method comprises the following steps: 1) The subject is located on an experimental bed; the part of the subject to be imaged is coated with water or medical ultrasonic coupling agent; 2) The bottom of the water tank is placed on the surface of the part of the subject to be imaged, the transparent soft film at the bottom of the water tank is completely attached to the surface of the subject, the air pressure inside the water tank is reduced to be less than the standard atmospheric pressure outside by the negative pressure control device, a negative pressure is formed, the pressure on the surface of the part of the subject to be imaged generated by the gravity of the sound guide liquid in the water tank is offset or partially offset, the deformation of the blood vessels of the part of the subject to be imaged caused by external compression is reduced, and the part of the subject to be imaged does not need to be soaked in the sound guide liquid, the comfort and hygiene of the subject during the imaging process are maintained; 3) The pulsed laser source generates pulsed laser, and the laser is coupled into the light inlet end of the light guide irradiation device through the coupling device; 4) The light guide irradiation device uniformly irradiates the laser to the surface of the part of the subject to be imaged through the optical window on the side wall of the water tank; 5) The excitation light irradiates the part to be imaged, excitation generates ultrasonic signals, the ultrasonic signals are received by the ultrasonic detector through the transparent soft film and the sound guide liquid, the ultrasonic signals are converted into electric signals and transmitted to the data acquisition system; 6) The pulsed laser source emits a trigger signal to the data acquisition system simultaneously every time a laser pulse is emitted, the data acquisition system synchronously acquires photoacoustic signal data; the data acquisition system converts the electric signals into digital signals and transmits the digital signals to the computer, the computer stores the digital signals, and photoacoustic signal acquisition is realized; 7) The computer controls the light outlet end of the light guide irradiation device to move synchronously with the ultrasonic detector through the mechanical scanning device, forming an illumination area following the movement of the ultrasonic detector, i.e. a dynamic illumination area; the dynamic illumination area covers the surface of the part to be imaged at an angle not less than the reconstruction illumination angle θ with the normal line of the current ultrasonic detector; 8) After the photoacoustic signal acquisition of one area of the part to be imaged is completed, the light outlet end of the light guide irradiation device and the ultrasonic detector are moved as a whole to the next area by the mechanical scanning device, until the photoacoustic signal acquisition of all the parts to be imaged is completed. 9) The computer reconstructs the photoacoustic signal data stored in the whole scanning process after integration, and only uses the photoacoustic signal data within the reconstruction illumination angle θ to perform back projection of the photoacoustic signal in the reconstruction process, that is, the photoacoustic point source within the acceptance angle range with the best detection sensitivity of the current ultrasonic detector is reconstructed to realize high-quality photoacoustic three-dimensional peripheral blood vessel imaging, and the scanning distance and scanning speed are controlled through the mechanical scanning device to meet different imaging requirements.

9. The imaging method of claim 8, wherein, The reconstruction illumination angle θ is 30°-70°.

10. The imaging method of claim 8, wherein, In step 2), the negative pressure range formed in the water tank is 300-1000 Pa less than the standard atmospheric pressure.

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