Realization and applications of collimator-less gamma-ray imaging systems

Due to advances in manufacturing large and highly segmented semi-conductor detectors, it is now possible to build efficient and compact gamma-ray imaging systems for gamma-ray energies up to several MeV. These new devices allow one to obtain positions and energies of individual gamma-ray interactions and enable the use of "Compton" tracking algorithms not only to determine the scattering sequence of the interactions, but also to determine the origin of the incident gamma rays. The main gain in this approach for localizing and characterizing gamma-ray sources is the increased sensitivity due to the removal of the collimator, which allows to significantly increase the efficiency while maintaining the spatial resolution even of ultra-high resolution collimators. The basic concept of gamma-ray imaging based on tracking and different possible approaches to optimize the sensitivity for different gamma-ray energies. will be presented. Applications in nuclear medicine to enhance cancer diagnostic but in particular therapeutic capabilities, in nuclear nonproliferation as well as in nuclear physics will be addressed.