Comparison of analytical and algebraic 2D tomographic reconstruction approaches for irregularly sampled microCT data.

APD-based detectors with individual channel readout were developed for multi-crystal applications and have been implemented for the detection of annihilation radiation in the LabPET micro-scanner. The use of these APD-based detectors in X-ray imaging is currently being assessed with a microCT demonstrator in order to later combine PET and CT in one apparatus. This paper is focused on the tomographic reconstruction of the X-ray transmission data acquired with this demonstrator. Two aspects of the acquisition geometry need to be carefully considered: the radius of the detector arc and the irregular sampling of the detector bins. A specific shift-variant filtered backprojection formula derived to account for the detector curvature is applied to equiangularly resampled projection data while the simultaneous algebraic reconstruction technique is applied to both resampled and original projections. Images of physical phantoms reconstructed from measured projections using the different methods are presented and compared.