基于聚焦声场模型的光声层析成像时间延迟快速校正反投影方法

Back-projection method with fast time-delay correction for photoacoustic tomography reconstruction based on a focused sound field model

光声层析成像是一种发展迅速的成像技术,其可提供生物组织的结构和功能信息,结合了光学成像高光学对比度与声学成像高穿透深度的优点.然而,由于现有的反投影成像算法通常将围绕目标扫描的超声换能器等效为一个点探测器,导致非中心成像区域图像的切向模糊,严重影响了图像质量.本文提出一种新的光声层析成像算法,其采用聚焦声场等效模型,可以快速有效地克服换能器孔径效应所造成的声场畸变,恢复非中心成像区域的切向分辨率.仿真结果表明,该方法对直径5 mm,距离旋转中心6 mm的目标,切向分辨率提升至少达2倍.实验结果表明,该方法可以有效地恢复边缘图像的切向模糊,使得复杂目标的微小结构能被清晰探测.这种新方法为传统的反投影方法提供了一种有价值的替代选择,对基于圆/球扫描的光声层析成像系统的设计具有重要的指导作用.

Photoacoustic tomography is a rapidly developing imaging technology,which can provide structural and functional information of biological tissues.It can integrate the advantage of high optical contrast from optical imaging with those from high penetration depth from ultrasound imaging.However,the existing back-projection algorithm in photoacoustic tomography equates the ultrasonic transducer scanning around the target to a point detector,which leads to a notable tangential blur in the eccentric imaging regions,and thus seriously degrading the image quality.In this paper,we propose a novel photoacoustic tomography reconstruction algorithm,which employs a focused sound field equivalent model to overcome the sound field distortion caused by the transducer’finite aperture effect and can quickly and effectively restore the elongated tangential resolution in the eccentric imaging regions.Simulation results show that for the target with a diameter of 5 mm and a distance of 6 mm from the rotation center,the tangential resolution is improved by at least twice.Experimental results show that this method can effectively restore the image tangential blur in the off-center regions,where the tiny structures of complex targets can be detected.This new method provides a valuable alternative to the conventional backprojection method and plays an important guiding role in the design of photo acoustic tomography systems based on circle/sphere scanning.