In vivo small animal imaging with multiple modalities has become an important tool in modern biomedical research. Indeed, combining exploratory techniques allows simultaneous recording of complementary data, which is required to elucidate complex physiopathological mechanisms. In this field, because of strict technical constraints in vivo, an exciting challenge remains in the combination of Nuclear Magnetic Resonance (NMR) and Positron Emission Tomography (PET). Coupling NMR with a radiosensitive Beta MicroProbe offers therefore a very interesting technical alternative. Here, we assessed the feasibility of this new combination by theoretically evaluating the ability of the Beta MicroProbe to monitor radioactivity in a magnet. To that aim, we modelled with Geant4 the effect of an intense magnetic field on the probe field of view and showed that the field should not have an impact on the global efficiency of the probe.