Date of Award
Doctor of Philosophy (PhD)
Photoacoustic computed tomography (PACT) is an emerging imaging modality that exploitsoptical contrast and ultrasonic detection principles to form images of the photoacousticallyinduced initial pressure distribution within tissue. The PACT reconstruction problemcorresponds to an inverse source problem in which the initial pressure distribution is recoveredfrom measurements of the radiated pressure wavefield. A major challenge in transcranialPACT brain imaging is compensation for aberrations in the measured data due to the presenceof the skull. Ultrasonic waves undergo absorption, scattering and longitudinal-to-shear wavemode conversion as they propagate through the skull. To properly account for these effects, awave-equation-based inversion method should be employed that can model the heterogeneouselastic properties of the skull. In this dissertation, a forward model based on a finite-differencetime-domain discretization of the three-dimensional elastic wave equation is established anda procedure for computing the corresponding adjoint of the forward operator is presented.Massively parallel implementations of these operators employing multiple graphics processingunits (GPUs) are also developed. The proposed matched forward-adjoint operator pair is thenutilized to develop an optimization-based image reconstruction method for 3D transcranialPACT. The optimization-based image reconstruction method employs the developed numericalframework to compute penalized least squares estimates of the initial pressure distribution.Computer-simulation and experimental studies are conducted to investigate the robustnessof the optimization-based reconstruction method to noise, model mismatch and its abilityto effectively resolve cortical and superficial brain structures. To properly compensate forthe distortions in measured pressure data caused by the presence of the skull, the developedoptimization-based image reconstruction methods require knowledge of the spatial distributionof the acoustic parameters of the skull. However, estimating the spatial distribution of theacoustic properties of the skull prior to the PACT experiment remains challenging. Inspiredby the observation that information about the distribution of skull acoustic parameters isencoded in PACT measurements, in this dissertation a method to jointly reconstruct theinitial pressure distribution and the low-dimensional representation of the spatial distributionof the acoustic properties of the skull from PACT data alone is proposed. The proposed jointreconstruction (JR) algorithm is evaluated through three-dimensional computer-simulationstudies that closely mimic transcranial PACT experiments.
Hong Chen Mark Anastasio
Joseph Culver, Joseph A. O'Sullivan, Quing Zhu,