光声断层成像是21世纪初兴起的一种基于光声效应的新型复合成像技术。它兼具超声成像深层分辨率高的优点，又具有光学成像在分子成像、功能成像方面的优势，成为近年来各国竞相优先发展的生物医学成像技术。目前，光声断层成像主要适用于声学特性相对均匀的生物组织，实际生物组织中普遍存在的不均匀声学特性严重制约了其成像效果和应用范围。此外，光声激发过程中的非线性效应及更多的非线性成像参量也有待深入挖掘。为此，本项目将深入研究生物组织中光声激发过程中的非线性效应，挖掘光声信号中的非线性参量，丰富成像信息；同时，深入研究光声信号在非均匀组织中的传播特性及非均匀组织中的光声重构算法，提升非均匀组织的光声成像质量，并拓展光声成像的应用领域。通过本项目研究，可以进一步发展光声断层成像的非线性理论及光声信号在非均匀组织中的传播理论，拓展光声成像的信息内涵、成像质量及应用范围，以更好地满足生物医学对新型成像技术的需求。

Photoacoustic tomography is a new type of composite imaging technology, which combines the advantage in deep high resolution for ultrasonic imaging and the advantage in molecular imaging and functional imaging for optical imaging. In recent years, it becomes a developed priority biomedical imaging technology. Normally, the photoacoustic tomography imaging is mainly suitable for biological tissue with acoustic homogeneous characteristics generally existed in real biological tissue, which seriously restricts the imaging effect and application scope. In addition, the nonlinear effects in the process of photoacoustic excitation and nonlinear imaging parameters should be further explored in photoacoustic imaging. Thus, this project will study the nonlinear effects of the photoacoustic excitation process in biological tissues, explore the nonlinear parameters in photoacoustic signals, and enrich the imaging information. At the same time, we further study the transmission characteristics of photoacoustic signals in biological tissue with acoustic nonhomogeneous characteristics and hence the photoacoustic reconstruction algorithm, which will improve the quality of photoacoustic imaging in biological tissue with acoustic nonhomogeneous characteristics and expand the application field of photoacoustic imaging. Through the objective of the study, we will further develop the nonlinear theory in photoacoustic tomography imaging and the theory for photoacoustic signal propagation in acoustic nonhomogeneous tissue, and increase image quality and application scope, which are essential for the new biomedical imaging technology.