Signal-to-noise and spatial resolution in in-line imaging. 2. Phase-contrast tomography.

In the first part of this paper, quantitative aspects of propagation-based phase-contrast imaging (PBI) were investigated using theoretical and numerical approaches, as well as experimental two-dimensional PBI images collected with plane monochromatic X-rays at a synchrotron beamline. In this second part, signal-to-noise ratio, spatial resolution and contrast are studied in connection with the radiation dose in three-dimensional PBI images of breast tissue samples obtained using propagation-based phase-contrast computed tomography (PB-CT) with energy-integrating and photon-counting detectors. The analysis is based on the theory of PBI and PB-CT using the homogeneous Transport of Intensity equation (Paganin's method). A biomedical X-ray imaging quality characteristic, suitable for quantitative assessment of X-ray images of biological samples, is introduced and applied. The key factors leading to high values of the biomedical X-ray imaging quality in PBI and to relatively low values of the same quality metric in CT imaging are identified and discussed in detail. This study is aimed primarily at developing tools for quantitative assessment and optimization of medical PB-CT imaging, initially at synchrotron facilities, with the prospect of subsequent transfer of the technology to medical clinics.