Biomedicum Imaging Unit In Vivo Imaging (BIU-IVI) is an open-access core service research infrastructure at the Faculty of Medicine, University of Helsinki, part of the Helsinki In Vivo Animal Imaging Platform (HAIP) of Helsinki Institute of Life Science (HiLife). BIU-IVI provides unique multimodal live animal imaging equipment and services for pre-clinical biomedical research. BIU-IVI acquired a modular imaging system for rodent positron emission tomography (PET) and X-ray computed tomography (CT) of rodents in 2022 from Molecubes, currently part of Bruker. With this system, the PET signal from radiolabeled tracers can be automatically co-registered with a CT image as an anatomical reference, with easy transfer of experimental animals between the two imaging modules. The current location of the PET/CT system is in Biomedicum Helsinki Laboratory Animal Centre, within a room retrofitted for this purpose, which enables combining nuclear imaging with e.g. the optical imaging modalities we offer in Biomedicum; however, the PET & CT modules can also be transported to other suitable locations e.g. in Kumpula or Viikki campuses when required. One of the most important criteria for the selection of the Molecubes imaging system at the time of procurement was the possibility of adding a third imaging module for single photon emission computed tomography (SPECT). The requirements for a SPECT system can only be met by upgrading the existing Molecubes PET/CT system.