Collimators for High Spatial Resolution Imaging of High-Energy Photons

Ziel/Aim Imaging of high-energy radiation sources with a spatial resolution in mm-range is difficult to realize with technologies currently available. Therefore, the aim of this study was to adapt previously introduced principles of a rotating collimator for imaging of radiation sources with photon energies of >1 MeV. This technology could potentially be useful for many clinical applications, such as imaging of prompt and delayed gammas in external beam radiation therapy or imaging of high-energy gamma-emitting isotopes such as e.g. Fe-59 (1.1, 1.3 MeV) for studying iron metabolism. Furthermore, it could be used for monitoring of nuclear power plants and/or radioactive waste disposal by facilitating imaging of several relevant isotopes, e.g. Cs-137 (0.66 MeV) and Co-60 (1.2, 1.3 MeV).

Methodik/Methods Feasibility and performance characteristics were derived from Monte-Carlo simulations (GATE) of a carefully designed rotating cylinder. Point sources at several photon energies (0.36, 1.0, 1.3 MeV) were implemented. The simulated scintillator was based on NaI (density 3.7 g/cc, energy resolution 7 % FWHM @662 keV). Intrinsic resolution of the scintillator was not taken into account.

Ergebnisse/Results Collimation of photons at all energy levels could be successfully demonstrated. It was possible to achieve a geometric spatial resolution in the range of ~2 mm FWHM. Photon detection efficiency was ~1E-4 %.

Schlussfolgerungen/Conclusions This study shows that it is feasible to construct a collimator capable of imaging radiation sources of energies above 1 MeV with high spatial accuracy. Further simulations will be carried out in order to define parameters of a future experimental validation of the technology. Furthermore, detector materials featuring higher densities, e.g. CeBr3 (5.2 g/cc, 4 % FWHM @662 keV) or LYSO (7.1 g/cc, 8.2 % FWHM @662 keV) will be considered for improving detection efficiency.