Impact of TOF information in OpenPET imaging

We are developing an open-type PET geometry that we named OpenPET. One possible geometry is the dual-ring OpenPET, which consists of two detector rings separated by a gap for entrance of the radiation beam. The gap can also be used for different modalities such as X-ray CT to realize a simultaneous multi-modality system. In addition, the dual-ring OpenPET has an effect to enlarge the axial field-of-view. In our previous simulations and experiments the OpenPET imaging geometry was shown to be feasible by applying iterative reconstruction methods. However, the gap violates Orlov´s completeness condition for accurate tomographic reconstruction. Therefore, the gap could lead to artifacts caused by lost low-frequency components in the projection data depending on the shapes of imaging subjects. In this study, we investigate the effect of time-of-flight (TOF) information, which is expected to compensate for the lost low-frequency components in OpenPET imaging. We simulated the dual-ring OpenPET geometry with a numerical phantom and analyzed frequency components of the reconstructed images. The result showed that the low-frequency components were not fully estimated in the gap region of the dual-ring OpenPET while those components were well recovered with the TOF information.