4π Compton imaging using a 3-D position-sensitive CdZnTe detector via weighted list-mode maximum likelihood

In this work we describe a 4π Compton imager composed of a single 15 mm × 15 mm × 10 mm CdZnTe detector. The anode is pixellated into an 11 × 11 array to provide position sensitivity in two dimensions. The third coordinate is determined from the observed timing of signals in the detector. The position resolution is approximately 1.2 mm in each dimension. The energy resolution is about 2% for two-pixel events at 662 keV. Images are reconstructed via list-mode maximum likelihood (ML). A new weighting method for ML reconstruction is proposed in which the contributions of small-uncertainty sequences are enhanced relative to sequences with large uncertainties. The new reconstruction method is compared with traditional ML techniques for measured imaging data.