Registration of planar film radiographs with computed tomography

The authors describe a method to register computed tomography (CT) data with planar film radiographs. Previous methods applied to the problem of CT-radiograph registration rely on determining the correspondence between occluding contours of the 3D surface in the CT data with 2D contours in the projection image. These methods implicitly assume that the correspondence is accurate, ignoring fundamental nonlinear differences in the underlying measurements. In contrast, the authors' emphasis has been to directly exploit the relationship between imaging devices. This is performed by registering radiograph data with intensity-corrected simulated radiograph data derived from CT measurements. The authors show that by exploiting the physical relationship between CT and radiograph measurements one can significantly improve registration accuracy. Concomitantly, the authors detail the relationship between CT and radiograph measurements and the primary factors influencing discrepancies between simulated and real radiograph data.