**2.2 Imaging artefacts and image processing**

CXµT imaging is a two phased process. First, a tomographic scanner is utilised to acquire a series of 2D shadowgraphs of a sample from multiple angles. Then, the 3D reconstruction of the sample is computed from the shadowgraphs using special algorithms (Kak & Slaney, 1988). The process involves many sources of artefacts.

Typical CXµT imaging system is comprised of a light source, optical elements and a camera which all pose certain imaging artefacts (Gonzales & Woods, 2002). Basically, the main imaging artefacts are noise and edge blurring caused by optics or the non-optimal light source of laboratory scale devices. In addition, the reconstruction procedure can add more artefacts to the tomographic reconstructions (Stock, 2009). The main reconstruction -based artefacts are rings, streaks and shadows caused by hardening of x-rays (Stock, 2009) or mechanical inaccuracy of the system.

Many image processing tools have been developed in order to overcome the problems related to the imaging artefacts, see e.g. Stock (2009) and references therein. However, most of the artefacts cannot be fully removed algorithmically and they thus require either removal by hardware optimisation or robust analysis software.
