Positron emission tomography-magnetic resonance imaging (PET-MR) is a novel and promising imaging modality that combines the strengths of both positron emission tomography (PET) and magnetic resonance (MR). It paves the way for a wealth of new clinical imaging applications [1]. PET-MR has comparable performance to PET-computed tomography (PET-CT) in the detection, diagnosis, and monitoring of suspected tumors [2]. In addition, it has the potential to become an important tool for the development of antitumor drugs, such as inhibitors of angiogenesis or modulators of the immune system. For brain imaging, it is obvious that simultaneous acquisition of various metabolic and functional parameters is a natural application of PET-MR that may yield new insights into the organization of the brain and its associated changes in disease [3]. PET imaging of the thorax and abdomen is limited by poor spatial resolution as well as by cardiac and respiratory motion. Simultaneous PET-MR provides a promising approach to continuously compensate for motion during PET acquisition, particularly in cardiology but also in the accurate detection of lesions in the abdomen or thorax [4].