Construction And Application Of Photoacoustic Tomography System

Photoacoustic imaging as an emerging biomedicine diagnostic technique that has been developed quickly in the past decade,it bridges traditional optical method and acoustic method.It utilizes the optical absorption coefficient as the major imaging parameter,as a result,it inherits the high sensitivity of optical imaging in evaluating tissue chemical and physiological information;at the same time,the information of tissue is carried by ultrasonic wave,therefore,it also inherits the high spatial resolution of ultrasonography in imaging deep tissue.For these virtues,photoacoustic imaging received widely and increasing attentions in various fields,such as optics,acoustic,and biomedical engineering.One of the major challenge of this technology is that the application of photoacoustic imaging is usually limited to the medium with relatively homogeneous acoustical properties,but the real tissue is inhomogeneous.The propagation of acoustic wave in inhomogeneous medium is an important issue to acoustic researchers;it is of great importance in acoustic imaging and detecting.Besides,photoacoustic imaging mainly used in soft tissue,i.e.vascular and breast,but rarely involved in hard tissues.It is necessary to study the imaging effect of photoacoustic tomography in hard tissue.Finally,the traditional ultrasonic transducer used in photoacoustic tomography imaging system cannot take into account both the lateral resolution and imaging perspective effectively.In order to solve the above problems,this paper focuses on the propagation characteristics of photoacoustic signal and acoustic basic mechanism;we use numerical simulation,experimental samples and other research methods to study how to improve photoacoustic imaging effect in inhomogeneous medium and hard tissue.In the end,according to the theoretical results,we design asymmetrical rectangle transducer to improve the lateral resolution and imaging perspective in photocaoustic tomographic imaging system.This thesis consists of seven chapters:In chapter one,we give an introduction for the various biomedicine imaging techniques,and the comparison with photoacoustic imaging.After that,we introduce the regulation and focusing of both optical and acoustic wave in random scattering medium.At last,a brief outline of this thesis is also given.In chapter two,according to the basic principle of photoacoustic effect and combined with the actual situation,a photoacoustic tomography system platform is built based on single ultrasonic transducer.The imaging performance and performance index of the platform are verified by the simulation experiments.In chapter three,for the tradition ultrasonic,the enlargement of the field of view of photoacoustic tomography system and the improvement of its lateral resolution are often two conflicting goals.In order to solve this problem,we proposed a rectangular focused transducer to solve this problem.Both simulation and experiments confirm that the rectangular focused transducer can improve the FOV and lateral resolution of PAT systems simultaneously.In chapter four,we first analyze the theoretical basis of photoacoustic imaging,including photoacoustic signal excitation mechanism and introduce several kinds of photoacoustic reconstruction algorithm and discussed the respective technical characteristics of the reconstruction algorithm.In chapter five,because the most reconstruction algorithm is based on that the speed distribution in tissue is a constant,we put forward a new method by combining ultrasonic tomography imaging and photoacoustic tomography imaging to improve the imaging quality in the tissue with uneven distribution of speed distribution.In chapter six,we present a new imaging method called dual-contrast photoacoustic tomography to detect the early dental lesions.One contrast,named B-mode,is related to the optical absorption.It is good at providing the sharp image about the morphological and macrostructural features of the teeth.Another contrast,named S-mode,is associated with the microstructural and mechanical properties of the hard tissue.It is sensitive to the change of tissue properties induced by the early dental lesions.In chapter seven,a summary of this thesis and some outlook for future investigation are presented.In summary,based on the photoacoustic tomography system and its research object,we carry out research by numerical simulation,experimental samples and other means.We effectively improve the imaging effect of photoacoustic tomography in speed inhomogeneous medium and successfully to detect early tooth disease.In addition,the design of the square transducer also improves the axial resolution and imaging field of the photoacoustic tomography system.The research content of this paper has certain significance both in theory and practice.