Real-time fusion imaging technologies are increasingly being used among interventional radiologists, mostly Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) dataset, fused with Ultrasound (US) imaging. In addition, fusion of Positron Emission Tomography (PET) and CT is increasingly diffused in clinical practice, due to the wide availability of PET scanners and the capability to make either a direct (acquisitions performed within the same system) or an indirect (procedure performed on an external workstation, merging the two different sets of acquired data) fusion with CT data. The present work describes the feasibility of real-time fusion imaging directly between PET data and US imaging, with CT scans being used only for PET-US fusion registration. Data on multimodality registration precision and clinical applications are presented as well.