I. Introduction
Currently, there is strong research and clinical interests in developing next-generation silicon photomultiplier (SiPM) based dedicated brain PET systems with ultra-high sensitivity and spatial resolution, with an extended axial field of view. The NeuroEXPLORER (NX) is under development in a collaborative effort among teams from Yale, UC Davis, and United Imaging Healthcare America (UIHA) to meet the requirements of clinical needs for next-generation dedicated brain PET systems [1]. In this work, we investigate timing calibration with DOI for the NX.