Automatic image registration of diagnostic and radiotherapy treatment planning CT head images

Purpose: Accurate image registration is an essential step to integrate info rmation from diagnostic and radiotherapy treatment planning (RTP) CT images . In this paper a fully automatic algorithm is presented to quickly registe r such diagnostic and RTP CT head scans, Methods and Materials: The registration algorithm, which regards one image as the moved version of the other, was applied to seven clinically obtained diagnostic and RTP CT data set pairs. During the RTP scan patients were in treatment position and wearing mold masks. Hence, patient position differe d strongly in both image sets. Registrations were inspected visually and co mpared with results obtained minimizing the sum-of-square difference, Results: Registrations were accurate upon visual inspection. Differences be tween the two algorithms were at subvoxel level. All cases were successfull y registered, using several different starting points. Registration calcula tions took 1-2 minutes. Minimization of the sum-of-square difference took 1 -1.5 hours. Conclusions: The results show that a fast and accurate image registration i s achieved without prior segmentation or feature extraction and that the al gorithm is robust, which makes it clinically applicable. (C) 2000 Elsevier Science Inc.