\label{fig:actualsetup} The timing coincidence apparatus set up for DOI measurements. The reference detector, shown on the left of the image, is a $2\times2\times5$ mm$^3$ Agile Ca-co-doped LSO:Ce wrapped in PTFE tape coupled to a Hamamatsu MPPC S10931-050P SiPM using Rhodorsil 47V optical grease. On the right, the source is shown close to the 3D-printed clamp holding the same photodetector coupled to the scintillator crystal under investigation.