Research On Transmission Coaxial Photoacoustic Endoscopic Imaging Method

Photoacoustic imaging is a new medical imaging method based on photoacoustic effect,which has the advantages of both optical and ultrasonic imaging.The technology can acquire the information of tissue light absorption with high sensitivity,so it has high contrast characteristics comparable to traditional optical imaging.At the same time,it has the same imaging depth and depth resolution as ultrasound imaging because it is based on ultrasonic detection.Furthermore,combined with different excitation wavelengths,the photoacoustic spectral information of the imaging object can be obtained,so as to realize the functions of material composition discrimination,concentration quantitative analysis and so on.Therefore,based on the principle of photoacoustic imaging,three-dimensional imaging technology with high contrast and large imaging depth can be developed,and it can also provide structural and functional information,which is expected to provide help for early detection and accurate diagnosis of cardiovascular diseases,digestive tract tumors and other diseases.According to the position relationship between imaging system and imaging object,photoacoustic imaging can be divided into in vitro imaging(including photoacoustic microscopy and photoacoustic computed tomography)and endoscopic imaging.In order to facilitate in vivo imaging of animals and human bodies,most of the current photoacoustic imaging systems are reflective imaging methods,i.e.light excitation and sound detection on the same side of the imaging object.This is especially true in photoacoustic endoscopy systems.However,due to the volume limitation of endoscopic imaging probe,such systems inevitably have the disadvantages of low optical transmission efficiency,low ultrasound receiving efficiency and shallow imaging depth.In view of the shortcomings of the existing technology,a transmission photoacoustic endoscopy imaging method is proposed.The main research work is as follows:Firstly,Concerning the idea of coaxial optical-acoustic coupling of light irradiation inside tissue and cavity and external acoustic detection,and combining with the principle of photoacoustic imaging and photoacoustic spectral correlation algorithm,theoretical research is carried out to guide the system design and construction,and it is flexibly applied to the field of photoacoustic endoscopy of digestive tract and quantitative analysis of lipid composition of vulnerable plaques in blood vessels.Secondly,in order to realize the transmission coaxial optical-acoustic coupling mode of the system,the structure design and construction of the system are carried out from the four parts of optics,acoustics,mechanical design and system control.Among them,the design and assembly of photoacoustic endoscope probe and the design of transmission coaxial imaging structure are the key core of the system.Thirdly,Based on the software(LabVIEW),the program of data acquisition and display is designed,and the precise scanning,data acquisition and image reconstruction of the system are realized.The main program adopts the program structure design of "state machine";the "producer/consumer" structure program design is proposed for data acquisition;and the function module of real-time image display is developed for experimental requirements.Fourth,in the experiment of photoacoustic endoscopy of digestive tract,the transmission coaxial imaging system was compared with the reflection non-coaxial imaging system.Photoacoustic imaging of porcine intestine in vitro and the phantom was performed.The imaging ability of the two systems was compared under the condition of laser scattering and in biological tissues.The results showed that the signal-to-noise ratio of the transmission coaxial photoacoustic endoscopy imaging system was increased by at least 7.0 dB compared with the reflection non-coaxial photoacoustic endoscopy imaging system and the imaging depth was increased by 14.5%.In the quantitative analysis,the accurate photoacoustic spectroscopy experiment of vascular plaque phantom was realized by using the transmission coaxial photoacoustic endoscopy imaging system,and the concentration of multi-groups of mixed dyes was quantitatively distinguished by combining the photoacoustic spectral decomposition algorithm.The above results show that the transmission coaxial photoacoustic endoscopy imaging system designed in this paper has excellent signal-to-noise ratio,which makes it possible to obtain large-depth endoscopy imaging in vivo.It lays a foundation for obtaining high-quality photoacoustic spectroscopy,accurate tissue composition discrimination and analysis in vivo,and verifies the photoacoustic technology in endoscopy imaging of digestive tract,endovascular interventional imaging and so on.The tremendous development potential of this field provides a certain impetus for the clinical conversion of photoacoustic.