Euromedim 2006 :1st European Conference on Molecular Imaging Technology

Investigations of the tomographic reconstruction issue in particular acquisition geometry in the framework of a bimodal microPET/CT

9 May 2006, 14:00

1h

Palais du Pharo, Marseille

poster • Image reconstruction and processing Poster Session :Simulation, Modeling, Reconstruction

Speaker

Mrs Solene Valton (CREATIS)

Description

Biological research on small animals is constantly demanding for imaging devices with higher performances. Innovative micro-scanners are being developed in particular to enable combined acquisition of anatomical and molecular data. In this framework, we consider the idea of using the hybrid pixel detectors with the ClearPET (see poster " PIXSCAN: Pixel Detector CT-Scanner for Small Animal Imaging " at this conference) to built a prototype of microPET-CT which will permit simultaneous acquisition of the two modalities. The hybrid pixel detector XPAD used in the PIXSCAN microCT will be placed in front of the gamma detectors since it is expected not to interfere with the gamma rays of the PET. However the X-ray source will optimally be fastened to an independent gantry outside the PET ring which will involve a non-conventional off-centered circular geometry for the CT data acquisition. The purpose of this work was to investigate CT reconstruction with this geometry. Projection data collection along a circular source path is known to lead to approximate reconstruction due to missing projection data, except in the plane containing the source. No exact reconstruction can therefore be expected in off-centered geometry where the region of interest is shifted outside this mid plane. We first adapted the popular FDK algorithm to the reconstruction in off-centered geometry. Although our formulation slightly improves the results compared to that obtained with original FDK, strong artifacts remain when the off-center angle involved is important. These artifacts are well-known in reconstruction from data acquired along a circular source trajectory and are referred to as cone beam (CB) artifacts. We then evaluated several CB artifacts compensation methods as well as an algebraic reconstruction formula (SART) on off-centered data. If some attenuation of the reconstructed function can be corrected, strong geometrical deformations remain, in particular when the phantom used for simulation has strong gradients along the rotation axis.