UNFOLDING PATIENT MOTION WITH BIPLANE RADIOGRAPHS

A method of unfolding patient movement between biplane radiographs is presented. This method requires biplane projections of two points with a known separation to determine a translation motion or biplane proje ctions of two or three point pairs to determine a general patient moti on. Such a point pair can be provided by two ends of a line source or two radiopaque marks, with a fixed distance between them. The point pa irs can be taped on skin, implanted in the target volume, or embedded in the bony structures. After obtaining the point locations on each fi lm, the three-dimensional coordinates of points of interest at the ins tant of each view can be reconstructed, with an error of less than 0.5 mm. The motion parameters, characterized by a pseudotranslation vecto r and three axial rotational angles for the region of interest relativ e to the machine coordinate system, are also provided. In comparing wi th some other reconstruction algorithms, the point pair method can sig nificantly improve source localization or point reconstruction in the presence of patient motion. Computer simulations and phantom experimen ts demonstrates the feasibility and accuracy of the method.