INTERMODALITY, RETROSPECTIVE IMAGE REGISTRATION IN THE THORAX

The purpose of this study was to develop an accurate, retrospectively applicable procedure for registering thoracic studies from different m odalities in a short amount of time and with minimal operator interven tion. Methods: CT and PET studies were acquired from six patients. The pleural surfaces in both image sets were determined by segmenting bas ed on 50% of the maximum soft-tissue value in the study. These surface s were converted into three-dimensional volumes and used to register t he CT and PET studies in three dimensions using a sum of a least squar es fitting approach. The registered PET study was then displayed in a hot metal scale overlayed on top of the gray scale CT study. The accur acy of the fit was evaluated through a phantom study and preliminary c linical evaluation. Results: A phantom study was performed to determin e the limits of this technique. The accuracy was determined to be less than 2.3 mm in the x and y direction and 3 mm in the z direction. Pre liminary clinical evaluation was also performed with encouraging resul ts. Conclusion: This technique accurately registers PET and CT images of the thorax, retrospectively, without the need for external fiducial markers or other a priori action.