  The aim of this work is to show the potential capabilities of monolithic
crystals coupled to large SiPM arrays, to be considered as detector blocks for
PET scanners enabling Time Of Flight (TOF) capabilities. Monolithic blocks
allow one to decode the 3D photon impact position. This approach, along with
TOF information, can be of high interest in clinical Positron emission
tomography (PET) applications where a typical ring configuration is used. In
this manuscript, we evaluate an ASIC- based readout for digitizing all signals
coming from analog photosensors. Validation results with one-to-one coupling
resulted in a Coincidence Time Resolution (CTR) of 202 ps FWHM. Providing
timing resolution when using detectors based on monolithic crystals is however
challenging. The wide distribution of scintillation light on the photosensors
causes a poor SNR, which makes the system sensible to false triggering and to
time walk errors. In this direction, we present a calibration method, designed
to correct all recorded timestamps and also to compensate variations in
time-paths among all channels. Thereafter, a CTR improvement nearing 45% is
observed for all measurements. Moreover, we show a novel approach that
describes the use of averaging methods to assign a single timestamp to each
gamma impact. This approach results in a further improvement of the CTR in the
range of 100 ps FWHM, reaching a time resolution of 585 ps FWHM when using a
large 50x50x10 mm3 LYSO scintillator coupled to an 8x8 SiPM (6x6 mm2) array.
These pilot studies show detector capabilities regarding TOF information when
using monolithic scintillators.
