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.

中文翻译：

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基于弹性波方程的前向伴随算子对，用于经颅光声计算机断层扫描。

光声计算机断层扫描 (PACT) 是一种新兴的成像方式，它利用光学对比度和超声检测原理来形成组织内光声感应初始压力分布的图像。PACT 重建问题对应于源逆问题，其中初始压力分布是从辐射波场的测量中恢复的。经颅 PACT 脑成像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的畸变。超声波在穿过颅骨传播时会经历吸收、散射以及纵波到横波模式的转换。为了正确解释这些影响，应采用基于波动方程的反演方法来模拟头骨的异质弹性特性。本文建立了基于三维弹性波方程时域有限差分离散化的正演模型，并给出了计算正演算子相应伴随的过程。还开发了使用多个图形处理单元 (GPU) 的这些运算符的大规模并行实现。所开发的数值框架在计算机模拟和实验模型研究中得到验证和研究，其设计受到经颅 PACT 应用的启发。