LSO Background Radiation Time Properties Investigation: Toward Data Driven LSO Time Alignment

Data-driven Time Alignment (TA) is currently part of scanner Quality Control (QC) procedure, where dedicated cylindrical phantom is used. An object is reconstructed based on non-TOF data (or imperfect TOF data). Based on the object knowledge, TOF modeled data can be subsequently generated and compared against measured data to estimate detectors time offsets (TO). The distinguished feature of data-driven TA is that no assumption about scanned object is needed.LSO background radiation was suggested for monitoring scanner properties. Currently long acquisition overnight disrupts the clinical service; detector energy properties, such as 511 keV energy spectrum potential drift, are indirectly monitored. The disadvantage is that LSO emits lower than 511 keV energies photons, requiring a different scanner setup and resulting in potentially different detector responses. The advantage is that no specially designed sources are used, and LSO total activity is large enough in long axial filed-of-view (LAFOV) scanners. In addition, detector time properties can be checked during patient scans.The goal of this work is to investigate the LSO background radiation detection timing properties in connection to 511 keV photons detection. The data-driven TA is applied on LSO background distribution and results are compared against dedicated source TA. The reconstruction of LAFOV Biograph Vision Quadra scanner LSO activity revealed non-uniform block pattern, different from one observed with 511 keV coincidences. The LSO TA time offsets were relatively close to TOs, derived from standard QC.