Archive | 2019
Three-dimensional Image Reconstruction in Transcranial Photoacoustic Computed Tomography
Abstract
OF THE DISSERTATION Three-dimensional Image Reconstruction in Transcranial Photoacoustic Computed Tomography by Joemini Poudel Doctor of Philosophy in Biomedical Engineering Washington University in St. Louis, 2019 Professor Hong Chen, Chair Professor Mark A. Anastasio, Co-Chair 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 pressure 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 dissertation, 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 proposed matched forward-adjoint operator pair is then utilized to develop an optimization-based image reconstruction method for 3D transcranial