Respiratory displacement modelling in cone beam computed tomography

Any organ motion during the projection acquisition causes blurring artefacts in the computed tomography (CT) reconstructions. It is a drawback in applications of cone beam CT (CBCT) for which, the complete scanning cannot be performed during a single breath hold. Our study proposes a new approach for estimation of the organ's respiratory displacement, from the same projection data, required for the CBCT with sampling over a circular trajectory. The processing includes semiautomatic outlining of the organ's boundaries on the X-ray projections, creating approximate shadow images, and constructing, from them, of a convex 3D organ-like structure, with the property to perform the same respiratory displacement as the one of the organ of interest. The motion is derived as a function of the respiration and can be used for respiratory motion correction in the following CBCT algorithm. Simulation results reveal significant improvements of the image quality in a cardiac tomogram reconstruction.