Figure 6.

Lines-of-response joining a crystal pair at opposite ends of a ring diameter (A), a crystal pair off the scanner axis (B), and a crystal pair off the scanner axis but with depth-of-interaction readout of scintillation light collected for each event by individual solid state photosensors at each end (C, see text). APD: avalanche photodiode; SiPM: silicon photomultiplier; (C): dotted parallel lines: maximum constraints on LOR choices measured by U_i; L_i: length of LOR between interaction sites; x_i: distance between annihilation site and LOR midpoint; t_i: time of arrival of photon; E_i: energy deposited by photon; M_i: ID number of crystal in detector array.