Development of a LSO based quality check procedure for the microPET® animal scanner

In Positron Emission Tomography (PET) hardware problem of the detector system could result in image degradation or image artifacts. Therefore a quality check (QC) procedure is needed to identify defective photomultipliers (PMTs) or electronic components while using the scanner in routine studies. For the microPET® animal scanner no built-in transmission source is available to perform quality scans with reproducible conditions. Therefore the use of the natural radioactive background of the scintillator material LSO was intuitive for the realization of a QC. A QC for the microPET® system was developed. Initial values of relative detector crystal sensitivities are measured in an initial measurement. Sensitivity values in subsequent measurements are compared to the initial values. A logfile is generated, which informs the user about changes in detector sensitivities. The quality check was implemented for a microPET® R4 scanner. Around 1.5 × 10⁶ single counts per detector block can be acquired in a 200-800 keV energy window during a 1800 s scan. Differences in crystal sensitivities yield information about drop outs of PMTs or electronic components. Therefore hardware problems can be easily detected without the use of an additional phantom or line source. In addition, the validity of the detector setup and normalization can be tested. This will avoid image artifacts and resolution degradation.