面向光声显微成像的高灵敏度光纤超声传感器研究

Photoacoustic imaging is an emerging biomedical imaging technology which has received great interests. It detects optically induced ultrasound wave in tissues and reconstructs distribution of vessels via time-to-space transformation. Ultrasonic detection is a critical link in photoacoustic imaging. Current optical and photonic sensors have presented relatively low sensitivity and can not fulfill the requirements of developing fast scanning, wide-vision and endoscopic photoacoustic imaging. This project proposes a new ultrasound sensor based on dual-frequency fiber laser. The laser outputs two orthogonal polarization modes with slight frequency difference, yielding a radio-frequency beat signal. The laser can be exploited as ultrasound sensor by detecting the beat-frequency change. We will investigate the interaction between the spherical ultrasound waves and the optical fibers, the sensitivity mechanism of the laser sensor to ultrasound waves, as well as optimize the ultrasound sensitivity via polymer coating, geometrical control and adjustment of the laser parameters. We attempt to develop highly sensitivity, wide-vision, compact unfocused fiber optic ultrasound sensors, towards the requirement photoacoustic microscopy with better performances and flexibility in system construction. The objective of this project is to promote the development of dynamic functional photoacoustic imaging and their preclinical applications, by improving the performance of the fiber optic ultrasound sensor.

光声成像是近年来引人瞩目的新型医学成像方法，它通过对激光脉冲在活体组织内激发出的超声信号进行探测，还原血管等生理结构的三维空间分布形态。微弱超声信号探测是光声成像过程中的关键技术环节，本项目针对当前超声传感器的不足，提出以正交双频光纤激光器为敏感基元、通过测量拍频频漂实现高灵敏度的超声信号检测。项目拟从球面超声波与光纤之间的相互作用机理入手，研究正交双频光纤激光器的超声响应机理，并采取聚合物涂覆、光纤几何形状控制、激光器参数优化等手段对超声响应进行优化，实现具有高灵敏度、宽敏感区域、体积小巧的光纤超声传感器，以赋予光声显微成像更为灵活的系统构成方式和更佳的成像性能。本项目旨在通过对关键器件进行创新推动成像系统性能的有效提升，使光声显微成像技术朝着动态功能性医用成像迈进坚实的一步。

光声成像技术融合了光学成像与超声成像的各自优势，具有高对比度和深穿透能力。受压电超声换能器探测灵敏度与器件尺寸关系制约，小型化光声成像技术发展受到阻碍。本项目针对这一问题，提出发挥光纤的结构优势，研制出高性能光纤超声传感器，并将其应用于光声成像。主要成果如下：（1）建立了超声场—光纤耦合与响应放大机制，实现了高灵敏度光纤超声传感器，其探测灵敏度比同尺寸压电传感器高出两个量级；（2）以光纤超声传感器为探测元件，实现了光纤光声成像技术，解决了光声成像面临的小型化、柔性化与功能成像难题，实现了光纤光声内窥成像、跨尺度脑成像和血氧功能成像。（3）提出并实现了光纤光声传感新机制，以光纤为超声换能元件实现了高空间分辨率的声阻抗探测。本项目研究成果荣获国际光纤传感会议（OFS）最佳论文奖和杰出创意奖，均为中国大陆学者首次获得（也是目前唯一）；被美国光学学会《Optics&Photonics News》作为“光纤在现代医学中应用”的三项代表性技术之一进行专题报道，并被多家科技媒体报道。