Establishment Of The Photoacoustic Tomography System And Study Of The Signal Enhancement Mechanism

Photoacoustic tomography(PAT),a novel,noninvasive,nonionizing and cost-effective imaging modality,which combines the merits of optical and ultrasonic imaging,is recently prosperous for biomedical applications.Compared with these traditional imaging technologies,including PET,CT,MRI and OCT,PAT has better molecular imaging effect.The theoretical basis of PAT is the photoacoustic effect,that is,when the biological tissue irradiated by periodic electromagnetic wave,the endogenous absorber(such as hemoglobin,melanin)inside the tissue absorbs light to produce the thermoelastic effect and generates the ultrasonic wave.And the ultrasonic wave is received by the ultrasonic transducer and converted to electrical signal to reconstruct the image.From the generation mechanism of the photoacoustic signal,it can be seen that the light energy deposition caused by the absorption of light from the biological tissue leads to the generation of the photoacoustic signal.Therefore,the quality of the light source and the absorption of light by the biological tissue directly affect the signal-to-noise ratio of the photoacoustic signal.The nonuniform distribution of laser energy leads to the fact that the generated photoacoustic signal can not be the basis for judging the distribution of light absorption of biological tissue.Therefore,the quality of the light source and the absorption of the biological tissue to the laser directly affect the quality of the photoacoustic signal.In this paper,a photoacoustic tomography(PAT)system was built,and a beam shaping optical path was designed and an iron oxide based photoacoustic contrast agent was prepared.From the excitation light source,transducer matching,tissue absorption and so on to enhance the photoacoustic signal and improve the quality of photoacoustic imaging.The specific research contents are as follows.(1)First of all,the research significance of PAI was summarized in this paper.Domestic and international development status of PAT was introduced specifically,including imaging mode,performance and effect.(2)The theoretical basis of PAI was systematically studied and summarized,including the photo-acoustic effect and the photoacoustic signal generation mechanism.The main factors that influence the quality of the photoacoustic signal were the excitation source,the ultrasonic transducer,the absorption of the light.On this basis,a PAT system was built and introduced from hardware and software the two aspects.(3)The optical path was designed to improve the quality of the excitation light source(uniformity of the spot and the laser energy intensity)and its influence on the quality of the excited photoacoustic signal was studied.The relationship between the characteristic parameters(center frequency,scanning step length and scanning radius)of the ultrasonic transducer and the received photoacoustic signal and the influence on the stability of the signal transmission and conversion were studied.(4)In this paper,the in vitro cytotoxicity,the photoacoustic properties and the in vitro photoacoustic contrast enhancement properties of iron oxide-based nanomaterials were tested.On the basis of this,the intensity of the PA signal was increased by 65% and the signal-to-noise ratio and contrast of the PAT image were improved obviously by the addition of DA@Fe2O3 contrast agent by PAT of mouse cerebral cortical.