TbF₃ nanoparticles as dual-mode contrast agents for ultrahigh field magnetic resonance imaging and X-ray computed tomography

Considering the development of magnetic resonance imaging (MRI) under ultrahigh magnetic field (> 3 T), the exploration of novel contrast agents (CAs) for ultrahigh field MRI is urgently needed. Herein, we report polyethyleneimine (PEI)-coated TbF₃ nanoparticles (NPs), which were synthesized by a facile solvothermal method, as potential dual-mode CAs for ultrahigh field MRI and X-ray computed tomography (CT). Owing to their strong paramagnetism, the TbF₃ NPs showed excellent transverse relaxivity (395.77 mM^–1·s^–1) and negligible longitudinal relaxivity under an ultrahigh magnetic field (7 T) with a great potential as a T₂-weighted MRI contrast agent. Furthermore, by comparison with the clinically used CT CAs (iohexol), the TbF₃ NPs showed superior X-ray attenuation ability. The practical application for T₂-weighted MRI and CT imaging was demonstrated with an animal model. Moreover, cell cytotoxicity and in vivo toxicity assessments implied the low toxicity of TbF₃ NPs. In summary, the above results indicate that TbF₃ NPs are promising candidates for ultrahigh field MRI and CT dual-mode imaging.