题目：Redefining the Spatiotemporal Limits of Optical Imaging:Photoacoustic Tomography, Wavefront Engineering, and Compressed Ultrafast Photography

报告人：Dr. Lihong V. Wang

时间：2016年11月01日 星期二 13:00-15:00

地点： 北京大学王克桢楼1113会议室

Photoacoustic tomography (PAT) has been developed for in vivo functional, metabolic, molecular, and histologic imaging by physically combining optical and ultrasonic waves. Broad applications include early-cancer detection and brain imaging. Conventional high-resolution optical imaging of scattering tissue is limited to depths within the optical diffusion limit (~1 mm in the skin). Taking advantage of the fact that ultrasonic scattering is orders of magnitude weaker than optical scattering per unit path length, photoacoustic tomography beats this limit and provides deep penetration at high ultrasonic resolution and high optical contrast. PAT holds great promise for whole small-animal brain imaging of functions and neural activities. The annual conference on PAT has become the largest in SPIE’s 20,000-attendee Photonics West since 2010.Wavefront engineering overcomes the optical diffusion limit by actively controlling the wavefront of the incident light to optimize the light intensity at a target position inside tissue. One such technology is called time-reversed ultrasonically encoded (TRUE) optical focusing, which can noninvasively deliver light to a dynamically defined focus deep in a scattering medium. First, diffused coherent light is encoded by a focused ultrasonic wave to provide a virtual internal “guide star”; then, only the encoded light is time-reversed and transmitted back to the ultrasonic focus.Compressed ultrafast photography (CUP) can image in 2D non-repetitive time-evolving events at up to 100 billion frames per second. CUP has a prominent advantage of measuring an x, y, t (x, y, spatial coordinates; t, time) scene with a single camera snapshot, thereby allowing observation of transient events occurring on a time scale down to tens of picoseconds. Further, akin to traditional photography, CUP is receive-only—avoiding specialized active illumination required by other single-shot ultrafast imagers. Given CUP’s capability, we expect it to find widespread applications in both fundamental and applied sciences including biomedical research.

邀请人：Dr. Changhui Li