Scatter and attenuation corrections for a PEM detector using List-Mode OSEM

Emission Tomography imaging techniques are known for its quantitative potential. As in whole-body Positron Emission Tomography (PET), also in breast dedicated Positron Emission Mammography (PEM) systems, this goal can only be achieved if a set of corrections for known physics processes is implemented thoroughly. Corrections for Compton scattered events, photon attenuation and random events are examples of such important data corrections. In this work, we report the performance of scatter and attenuation corrections, specifically implemented for PEM. These correction methods were tested on data from the ClearPEM scanner, a dual-head planar system. The ClearPEM scanner does not incorporate transmission images for attenuation correction. With no anatomical information available, the PEM emission image was used to obtain the acquisition´s characteristics needed as input for both the Monte Carlo (MC) based scatter correction method and the attenuation correction algorithm. A MC scatter correction can accurately model the scatter distribution of a PEM acquisition, but removing this estimate from the acquired data can result in a severe bias and increased noise in low counts PEM studies. To avoid such drawbacks, an approach based on a smoothed imaged of the scatter distribution was used. Due to the typically low counts nature of PEM acquisitions, correction procedures were combined with a 3D-OSEM-LM reconstruction, so reconstructed images could be obtained in a short period of time. Results demonstrated that both corrections perform as expected. The presence of scattered events was strongly reduced. Counts loss due to photon attenuation was clearly compensated, along with the recovery of the correct activity distribution.