Description: STIR is an Open Source software for use in tomographic imaging. Its aim is to provide a Multi-Platform Object-Oriented framework for all data manipulations and corrections in tomographic imaging. Currently, the emphasis is on (iterative) image reconstruction in PET and SPECT, but other application areas and imaging modalities can and might be added.

Source Code: Link 1 (official releases) & Link 2 (GitHub)
Tutorials: Link 1 (User’s Manual), Link 2 (Wiki), Link 3 (Exercises/Examples) & Link 4 (Doxygen)