The Visualization Toolkit (VTK) is the 3D engine behind many scientific visualization applications, such as MayaVi, the popular scientific data visualizer for Python. It is also the cornerstone of several advanced 3D-enabled biomedical applications, such as ParaView and 3D Slicer.
Perhaps lesser known, VTK provides a built-in high performance DICOM parser, because of its deep roots within the biomedical community. For my own clinical project, I have recently started learning and using VTK.