Experimental results of identification and vector quantization algorithms for DOI measurement in digital PET scanners with phoswich detectors

DOI measurement in phoswich PET scanners still relies mostly on traditional Pulse Shape Discrimination (PSD), transposed from analog electronics. PSD performance is limited in two conditions: measurement noise increases the error rate, as with low-energy Compton photons; and phoswich stacking of the newer, fast crystal materials like LSO, LYSO and LuAP show intrinsic low discrimination success. These impairments somewhat limit the widespread use of such stacking, as well as recuperation and treatment of Compton photons. We propose two new algorithms adapted from other fields of electrical engineering, but unused in radiation detection so far, that mostly circumvent these problems: identification, from command-and-control applications, followed by vector quantization, from speech recognition. These algorithms exhibit operational properties that mitigate the above problems. In our previous work, we explained the steps required to adapt the algorithms to DOI application. This paper presents discrimination results for all photons of energy greater than 100 keV detected in any stacking of BGO, LSO, LYSO, LuAP and/or GSO materials. Errors are un-correlated with crystal statistical noise and/or energy resolution, with electronics white noise and with timestamp uncertainty. For all measurements made (N=40,000), the error rate is null, except for Compton discrimination with the faster crystals, where it does not exceed 0.5%. This far surpasses conventional PSD results.