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/sup 3/) to O(n/sup 2/). This work 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.