Wikipedia
Fusionviewer
FusionViewer is an open source medical image display package developed by Insightful Corporation and the Imaging Research Laboratory at University of Washington. It is designed to improve the physician's ability to interpret the results of combined positron emission tomography (PET) and computed tomography (CT) studies. This software is a display application for facilitating and improving visualization. The effective display of the fused data permits easy viewing of the anatomical information provided by the CT images while simultaneously displaying the functional data provided by PET.
FusionViewer is released under the GNU GPL v2.