Combined Reconstruction Approach for Holotomography: Joint Phase Retrieval and Tomography

DASHH Doctoral Researcher: Daniel Hernández Durán

Supervisors: Prof. Christian Schroer (DESY, UHH), Dr. Johannes Dora (DESY), Prof. Tobias Knopp (TUHH)

Full-field X-ray microscopy with phase contrast at large-scale facilities is a powerful tool for investigating a wide range of small samples. The acquired holograms that combine phase and absorption contrast provide access to information otherwise hidden in classical computed tomography. Nanotomography at synchrotron radiation sources can produce three-dimensional complex-valued images of samples with nanometer resolution.
However, such tomograms are not directly accessible during the measurement process but must be calculated from many individual two-dimensional images. This calculation is usually done in two steps, each being an ill-posed inverse problem. In the first step, complex-valued projections of the object are reconstructed from intensity-only measurements. In the second step, the projections are processed into three-dimensional (3D) tomograms using commonly applied algorithms from computed tomography.
The project aims to generalize the two-step reconstruction procedure to a joint reconstruction. The goal is to consider all intensity measurements simultaneously and to use the 3D consistency as an additional constraint to perform the phase retrieval directly on the tomogram. It is necessary to investigate several subproblems to solve this task. A new inverse problem has to be formulated, a suitable solver has to be found, and a rigid motion model of the object's movement during the data acquisition needs to be used.