Direction dependent projection fields for the fast DRR generation for medical 2D/3D registration

The fast generation of digitally reconstructed radiographs is a prerequisite for intensity-based registration approaches. For our approach, extensive pre-calculations are necessary that are saved in what we call a direction dependent projection field. The projection field approach reduces the complexity of the DRR calculation from O(n(3)) to O(n(2)). This paper develops the theoretical background and gives first examples of the application of projection fields for the 2D/3D registration of X-rays to CT data.