Experimental comparison of mechanical and electronic collimation

Electronically-collimated gamma cameras based on Compton scattering are gaining increased attention as the associated hardware and physical principles on which they rely become more developed. Though there has been some modeling of the performance of electronically-collimated cameras, and several prototypes have been built, there has not been a direct, simultaneous experimental comparison with mechanical collimation. We have built a mechanically-collimated (pinhole) camera and compare its performance to the Ring Compton Camera (RCC) operating at the University of Michigan. A single radioactive source is imaged simultaneously by both cameras for identical periods of real time. Data are presented for several radioactive sources of various energies and shapes, including multi-energy sources. Both iterative and analytic image reconstruction techniques are examined, and various processing techniques are used to develop the final images. Bias-variance curves are presented demonstrating the relative performance of the two cameras. Additionally, the data from the two cameras are combined, creating a 'dual-collimated camera' and its bias-variance performance is also presented.