Resolution recovery for Compton camera using origin ensemble algorithm

Spatial resolution that can be achieved by a Compton camera (CC) is limited by finite energy and spatial resolutions of camera´s detectors and by Doppler broadening. In principle, modeling of these effects in image reconstruction would allow for at least partial recovery of the lost resolution. Unfortunately, a substantial increase in computing time precludes practical implementations of such modeling when using standard iterative reconstruction algorithms, such as Maximum Likelihood Expectation Maximization (MLEM). In this work we propose a new method to model resolution degrading effects using origin ensemble (OE) image reconstruction algorithm. The basic principle of the resolution recovery with OE is the stochastic modeling of distributions of deposited energies and locations of photon interactions within the detectors. To test the developed algorithm we designed a high sensitivity CC aimed at small animal/mammography imaging, with scatter and absorption detectors replaced by a single thick, multi-layer CZT detector. The simulated radioactive source consisted of four 3 mm in diameter hot spheres placed in a warm background. Single detection of 511 keV photons was modeled. Results show that proposed method substantially improved not only image resolution but also quantitative accuracy of the reconstructed activity distributions.