  This report summarizes work done during PhD rotation that proposes an
algorithm that uses anode- cathode trigger time difference and cathode to anode
pulse height ratio to resolve photon event positioning degeneracy in a novel
Cadmium Zinc Telluride (CZT) photon detector for positron emission tomography
(PET). The detectors used comprise 40 mm x 40 mm x 5 mm monolithic CZT crystals
that employ a cross-strip electrode pattern with interspersed steering
electrodes to obtain high spatial and energy resolution. The specific
positioning degeneracy studied results when a photon event interacts in two
detector pixels, triggering two anode and two cathode strips, hence presenting
four pixels as potential interaction locations. An experiment was performed
where a 1 mm diameter collimated pencil beam of annihilation photons was used
to target a detector pixel of known location. The data acquired provided an
empirical basis to train and test the algorithm. The study shows that,
depending on the restrictions applied on the data set, the proposed algorithm
accurately identifies the true photon interaction locations 59.7% to 66.7% of
the time, which is 19.4% to 33.4% better than an unbiased Bernoulli trial.
Further improvements of the algorithm will enhance the effective system photon
sensitivity by extracting useful information from events which would otherwise
be discarded.
