A cone-beam CT geometry correction method based on intentional misalignments to render the projection images correctable

CT systems, in particular industrial CTs used for dimensional measur ements, require an excellent geometrical accuracy. The geometry of a cone-beam CT system is characterised by 9 parameters that m ust meet specific values. Therefore, CT systems consist of several stages, which allow adjusting some of these parameters , while other parameters are expected to remain fixed. However, stages suffer from geometrical imperfections, such as positioning a d uideway errors, which cause distorted CT projections. If misalignment errors are known, e.g. by calibration, s me of them can be corrected in the projections by image processing. Nevertheless, geometry errors that alter the ray directions th r ugh the investigated object cannot be corrected in the projection images, even if the corresponding geometrical parameters are kno wn. We propose a method to convert CT geometry errors into image correctable o nes, by repositioning some of the available stages. Repositioning is required in all cases where the x-rays would no t cross the object in nominal directions. The resulting geometry is still misaligned but the projections can now be fully cor re ted using image processing. The such obtained corrected projection image set can then be reconstructed using efficient stan dard lgorithms. The method was evaluated by simulations and enables recovering dimensional measurements with sub-v oxel accuracy.