Optimum Voxel Size for the Reconstruction of In-Beam PET Data

Introduction At the experimental heavy ion therapy facility at the GSI Darmstadt the in-beam PET scanner BASTEI is operated for quality assurance monitoring simultaneously to the therapeutic irradiation [1-3]. Due to the relatively short irradiation time, low number of positron emitters production rate and limited-angle geometry in-beam PET data are characterized by very low counting statistics. The important requirement for in-beam PET is fast availability of reconstructed images for analysis in order to make conclusions about performed irradiation and propose corrections for further treatment as soon as possible. Therefore, the parameters of reconstruction algorithms must be optimized in order to achieve maximum speed keeping the image quality on the acceptable level. In this work we propose an optimum size for the imaging element (voxel). The small voxel size increases the resolution but may produce high fluctuations of the signal (noise) in low statistics case. In contrast, large voxel produces homogeneous images, however, with low resolution. Increasing the voxel size also allows to speedup the reconstruction keeping the image quality on the acceptable level which is very important for fast availability of in-beam PET images.