Modulation Particle Size And Lattice Parameter Of Calcium Fluoride Nanoparticles And Its Effect On 19F-MRI Property

Magnetic Resonance Imaging（Magnetic Resonance Imaging,MRI）is a diagnostic method with high resolution,high sensitivity,no tissue damage,and deep penetration,which is widely used in the field of biomedicine and molecular imaging.The current magnetic resonance imaging technology is mainly hydrogen proton magnetic resonance imaging（1H-MRI）.However,when using 1H-MRI for in vivo imaging,due to the large amount of water in the body and the small difference in 1H relaxation time in certain substances in tissues causes large background noise during in vivo 1H-MRI,which promote the development of non-hydrogen magnetic imaging technology.The introduction of non-hydrogen magnetic resonance imaging technology,especially the fluorine magnetic resonance imaging technology（19F-MRI）with no background noise in the body,has further improved the signal-to-noise ratio of magnetic resonance imaging.After years of development,19F-MRI imaging tracers are very diverse,and began to extend from perfluorocarbon-based organic substances to inorganic fluorides,the emergence of inorganic CaF₂ nanoparticles 19F-MRI imaging tracers.The simple crystal structure,high symmetry,and controllable size of inorganic substances are beneficial to 19F-MRI.However,the research on which properties of inorganic fluoride 19F-MRI imaging tracers affect the relaxation of particles or the properties of 19F-MRI imaging is not perfect.Therefore,in this paper,by adjusting the surface ligands content and ratio in the synthesis of CaF₂ nanoparticles,CaF₂ nanoparticles with different particle size and lattice constant were obtained,and the relationship between particle size,lattice constant and relaxation,19F-MRI image properties was explored.The main research conclusions are as follow:（1）In the method of thermal decomposition with calcium trifluoroacetate as the precursor,OA and OM as the ligand,and ODE as the solvent,CaF₂nanoparticles with different the yield,particle size and dispersion,lattice constants are obtained.The necessary conditions for the synthesis of CaF₂ nanoparticles are obtained:the content of OA is greater than 12.5%.The relationship between the ligand ratio,particle size and lattice constant is explored:in the reaction system,when the ODE content is not zero,the particle size and lattice constant of nanoparticles decrease with the increase of the sum of OA and OM;when the ODE content is zero and the content of OA and OM is equal to 50%,CaF₂ nanoparticles with a minimum particle size of 3.9 nm and a lattice constant of 5.30?were obtained in this experiment.（2）By examining the relaxation properties and 19F-MRI of different CaF₂ nanoparticles,the relationship between the particle size,lattice constant and relaxation,19F-MRI properties of CaF₂ nanoparticles was explored:Changing of lattice constants affect the relaxation and imaging properties of nanoparticles.The smaller the lattice constant of CaF₂nanoparticles,the smaller longitudinal relaxation time of the particles,and the higher the average brightness of 19F-MRI images obtained under the same image acquisition conditions.By comparing the relaxation time of CaF₂ nanoparticles with the same particle size and different lattice constants,or with the same lattice constant and different particle size,the relationship between particle size,lattice constant and relaxation,19F-MRI imaging properties was further verified.