Image artifacts resulting from gamma-ray tracking algorithms used with Compton imagers

For Compton imaging it is necessary to determine the sequence of gamma-ray interactions in a single detector or array of detectors. This can be done by time-of-flight measurements if the interactions are sufficiently far apart. However, in small detectors the time between interactions can be too small to measure, and other means of gamma-ray sequencing must be used. In this work, several popular sequencing algorithms are reviewed for sequences with two observed events and three or more observed events in the detector. These algorithms can result in poor imaging resolution and introduce artifacts in the back projection images. The effects of gamma-ray tracking algorithms on Compton imaging are explored in the context of the 4pi Compton imager built by the University of Michigan.