The focus of this project will be to further enhance the image quality of emission tomography. To achieve this we will use (and evantually modify) prototype or recent clinical systems to maximize the sensitivity. On the processing side we will try to minimize the image quality loss in the reconstruction process by accurate modeling of the imaging process. In most ET imaging situations there is a high fraction of contamination in the measured data (scatter, randoms, collimator penetration, contamination from high energy peaks). We have been actively involved in the development of an accurate Monte Carlo simulator (Gate) which has become the gold standard for ET simulation. Monte Carlo techniques make it possible to study interaction of photons with the object and imaging system in detail and allow to minimize contamination by a proper selection of energy and/or time windows. Besides an improvement of technical image quality by more accurate reconstruction techniques for PET and SPECT we will also investigate the benefit of new systems (TOF-PET) on clinical data. Multimodality systems are now entering the market and have a lot of potential. Advanced techniques will therefore be developed to extract useful information from multimodality imaging and use it to further enhance image quality of PET and SPECT reconstructions.