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Figure 1. Reprojection distance modified from [11]. Each point Pi(i=1,...,Nreproj) within the volume of interest is projected onto the imaging plane using the gold standard registration matrix G, to create corresponding 2D points ui. These 2D points are then reprojected using a given transformation matrix T to produce lines Li. The reprojection distance, Di, is then equal to the minimum distance from this line to the original point Pi. For a perfect registration the line Li will pass directly back through Pi and the reprojection error distance, Di, will be equal to zero. The root mean square (RMS) target reprojection error, 
