Mitsuhashi Kenji, Poudel Joemini, Matthews Thomas P, Garcia-Uribe Alejandro, Wang Lihong V, Anastasio Mark A
Department of Biomedical Engineering, Washington University in St.Louis, St.Louis, MO USA.
SIAM J Imaging Sci. 2017;10(4):2022-2048. doi: 10.1137/16M1107619. Epub 2017 Nov 16.
Photoacoustic computed tomography (PACT) is an emerging imaging modality that exploits optical contrast and ultrasonic detection principles to form images of the photoacoustically induced initial pressure distribution within tissue. The PACT reconstruction problem corresponds to an inverse source problem in which the initial pressure distribution is recovered from measurements of the radiated wavefield. A major challenge in transcranial PACT brain imaging is compensation for aberrations in the measured data due to the presence of the skull. Ultrasonic waves undergo absorption, scattering and longitudinal-to-shear wave mode conversion as they propagate through the skull. To properly account for these effects, a wave-equation-based inversion method should be employed that can model the heterogeneous elastic properties of the skull. In this work, a forward model based on a finite-difference time-domain discretization of the three-dimensional elastic wave equation is established and a procedure for computing the corresponding adjoint of the forward operator is presented. Massively parallel implementations of these operators employing multiple graphics processing units (GPUs) are also developed. The developed numerical framework is validated and investigated in computer19 simulation and experimental phantom studies whose designs are motivated by transcranial PACT applications.
光声计算机断层扫描（PACT）是一种新兴的成像模态，它利用光学对比度和超声检测原理来形成组织内光声诱导的初始压力分布图像。PACT重建问题对应于一个逆源问题，即从辐射波场的测量中恢复初始压力分布。经颅PACT脑成像中的一个主要挑战是补偿由于颅骨的存在而导致的测量数据中的像差。超声波在穿过颅骨传播时会经历吸收、散射和纵波到剪切波模式转换。为了适当地考虑这些影响，应采用一种基于波动方程的反演方法，该方法可以对颅骨的非均匀弹性特性进行建模。在这项工作中，建立了基于三维弹性波动方程的有限差分时域离散化的正向模型，并提出了计算正向算子相应伴随算子的过程。还开发了使用多个图形处理单元（GPU）对这些算子进行大规模并行实现的方法。所开发的数值框架在计算机模拟和实验体模研究中得到验证和研究，这些研究的设计受经颅PACT应用的推动。
