Hybrid collimation for industrial gamma-ray imaging: combining spatially coded and compton aperture data

The combination of a mechanically collimated gamma-ray camera with an electronically collimated gamma camera offers both the high-efficiency and good angular resolution typical in a mechanically collimated camera for lower photon energies and the uncoupling of spatial resolution and efficiency provided by an electronically collimated camera at higher energies. The Hybrid Portable Gamma Camera (HPGC) combines a MURA coded aperture camera with a Compton scatter camera to provide a broad range of energy response suitable for industrial imaging situations (50 keV-2 MeV). This paper compares the relative information content per photon for the three imaging modalities possible with the HPGC: mechanical collimation, electronic collimation and hybrid collimation, which combines information from the spatially coded aperture with Compton aperture information. The analysis is done for point sources at two incident energies (412 and 662 keV) in the medium-energy range of operation for the HPGC (400- 800 keV) where neither mechanical collimation nor electronic collimation performs particularly well acting independently. A resolution-variance analysis is used to compare the three modalities. Results show that hybrid collimation is superior to mechanical and electronic collimation at both 412 and 662 keV over the resolution range likely to be used for such a camera.