  We are exploring a scintillator-based detector with potential of high
sensitivity, DOI capability and timing resolution in a single-side readout
configuration. Our concept combines: 1) A design with 2+ crystal arrays stacked
with relative offset, with inherent DOI information but good timing performance
has not been shown with conventional light sharing readout. 2) Single crystal
array with one-to-one coupling to the photodetector (PD) array, with good
timing performance, but no DOI. We believe the combination, where the first
layer of a staggered design is coupled one-to-one to a PD array may provide
both DOI and timing. The concept is here evaluated through light transport
simulations. Results show that: 1) In terms of DOI one-to-one readout of the
first layer allows for accurate DOI extraction using a single threshold
relative to the PD sum signal, for up to 4 layers. The number of PD pixels
exceeding the threshold corresponds to the layer of interaction. The
corresponding approach is not possible for the same geometries with a light
sharing readout scheme. 2) When employing a low threshold of 2 optical photons
the layered approach with one-to-one readout of the first layer improves timing
close to the PD compared to single layer, due to reduced crystal thickness.
Single detector timing resolution values of 91, 127, 151 and 164 ps were seen
in the 4-layer design with unpolished pixels, compared to 148 ps for single
array with one-to-one coupling. 3) For the layered design with light sharing
readout, timing improves with increased PD pixel size, with an apparent
tradeoff between spatial resolution and timing not observed for the one-to-one
coupled counterpart. The combination of straightforward and accurate DOI
determination, good timing performance and relatively simple design makes the
proposed detector a promising candidate for brain dedicated DOI TOF-PET.
