The Medical Imaging Interaction Toolkit (MITK) is a C++ class library for the development of medical imaging software with a high degree of interaction. The example application features DICOM viewing, measurement, image segmentation and registration.
Registration of 2D and 3D images
Reviewing vessels (based on MITK -- not part of MITK)
Measurement and image statistics
GPU accelerated volume visualization
interactive segmentation of volumetric images (MR, CT, US)
Fast marching segmentation (based on but not part of MITK)