A Fully 3D Maximum Likelihood Estimator Algorithm with Attenuation and Scatter Cor- rection Adapted to a Limited Angle Positron Camera

The in beam dual head positron camera BASTEI (Beta Activity meaSurements at the Therapy with Energetic Ions) is used to monitor and control the applied dose distributions simultaneously to tumour irradiations with carbon ion beams at the experimental heavy ion therapy facility at GSI Darmstadt. Therefore, the PET system has been mounted directly at the treatment site. A fully 3D reconstruction algorithm based on the Maximum Likelihood Estimator algorithm has been developed and adapted to a strongly spatial varying imaging situation. The scatter and attenuation correction is applied to the measured list mode data before each iterative step. This requires an attenuation map containing the information on the tissue composition and densities. This information is derived from the X-ray computed tomograms (CT) of the patient and the patient fixation system including the head rest. The scatter correction method uses the subtraction of calculated scattered from measured data. The normalization of scattered events relative to the unscattered events is done by a global scatter fraction factor. The results are presented.