  X-Ray Phase-Contrast Imaging (PCI) yields absorption, differential phase, and
dark-field images. Computed Tomography (CT) of grating-based PCI can in
principle provide high-resolution soft-tissue contrast. Recently, grating-based
PCI took several hurdles towards clinical implementation by addressing, for
example, acquisition speed, high X-ray energies, and system vibrations.
However, a critical impediment in all grating-based systems lies in limits that
constrain the grating diameter to few centimeters. In this work, we propose a
system and a reconstruction algorithm to circumvent this constraint in a
clinically compatible way. We propose to perform a phase-sensitive
Region-of-Interest (ROI) CT within a full-field absorption CT. The biggest
advantage of this approach is that it allows to correct for phase truncation
artifacts, and to obtain quantitative phase values. Our method is robust, and
shows high-quality results on simulated data and on a biological mouse sample.
This work is a proof of concept showing the potential to use PCI in CT on large
specimen, such as humans, in clinical applications.
