The emergence of (pre)clinical PET/MRI scanners is accompanied by the development of novel contrast agents. Aluminum hydroxide magnetic nanoparticles (Fe3O4@Al(OH)3 NPs) can overcome limitations of iron oxide NPs after labeling with Na18F, allowing visualization with PET (high sensitivity, low background) and MRI (high resolution, longitudinal NP follow-up). In this study, labeling of novel Fe3O4@Al(OH)3 nanostructures with Na18F was rapid. In vivo, radiolabeled NPs accumulated in liver of healthy mice, while cells labeled with radiolabeled NPs were also seen in lungs. Our results indicate the potential of these novel nanostructures for cell tracking with high sensitivity, specificity and resolution using PET/MRI.