Understanding phase contrast artefacts in micro computed absorption tomography

Abstract

Phase contrast imaging is a technique which captures objects with little or no light absorption. This is possible due to the wave nature of light, i.e., diffraction. In computerised tomography, the aim is most often to reconstruct the light absorption property of objects but many objects can not be imaged without obtaining a mix of both absorption and phase, this is especially true for weakly absorbing objects at high resolution. Hence, phase contrast is usually considered an unwanted artefact which should be removed. Traditionally this is done directly on the projection data prior to the filtered back projection algorithm and the filter settings are derived from the physical setup of the imaging device. In this paper we show how these operations can be carried out on the reconstructed data, without access to the projection images, which yields much flexibility over previous approaches. Especially, filtering can be applied to small regions of interest which simplifies fine tuning of parameters, and some low pass filtering can be avoided which is inherent in previous methods. We will also show the filter parameters can be estimated from step edges in the reconstructed images