Assessment of the quantitation in 3D PET: Influence of out of the field of view radioactive sources

Using the Utah scatter phantom with different density media and activity proportions, we tested the accuracy of quantification in the 2D and 3D modes of acquisition of the new ECAT Exact HR+ tomograph. The influence of radioactive sources outside the Field Of View (FOV) was also investigated, using different bed positions. We measured the activities in regions of interest drawn in the reconstructed images and compared the mean through several planes to the activities expected from well counter measurements. The 3D scatter correction algorithm successfully restored the activity concentration in the various chambers of the phantom, with relative errors between 3.5 and 12.0%, slightly larger than those observed in 2D (1.3 to 8.6%), but similar when no activity was out of the FOV(≤6.2%). The activity out of the FOV increased the relative errors and introduced non-uniformities along the axial direction. The attenuation coefficient of the substances tested also influenced the results: negative activity values were observed in substances with high attenuation coefficient in the 3D scatter corrected data