Silver and Gadolinium Ions Co-substituted Hydroxyapatite Nanoparticles as Bimodal Contrast Agent for Medical Imaging

Developing multimodal contrast agents is an upcoming area and hydroxyapatite nanoparticles substituted with various elements like gadolinium, eurobium etc., seems to be a promising contrast agent, especially for multimodal imaging of bone-tissue interface. A bimodal contrast agent using silver (Ag+) and gadolinium (Gd3+) ions co-substituted hydroxyapatite nanoparticles has been developed for X-ray and magnetic resonance imaging. Ag+ and Gd3+ ions were co-substituted into hydroxyapatite at various atomic percentages (Ag:Gd=0.25:0.25, 0.25:0.5, 0.25:0.75) using microwave accelerated wet chemical synthesis. Pure as well as Ag+ and Gd3+ ions substituted hydroxyapatite samples were also synthesized for comparison. All samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy etc., and found to be monophasic, nanocrystalline with the substituted ions. These co-substituted hydroxyapatite samples were then tested in different diagnostic modalities such as X-ray, computed tomography imaging and magnetic resonance imaging. Appreciable variation in contrast was observed with different amount of substitutions. All the Ag+ and Gd3+ ions co-substituted hydroxyapatite nanoparticles showed higher contrast in all imaging modalities compared to those substituted with either Ag+ or Gd3+ ions only. Hydroxyapatite sample co-substituted with 0.25Ag and 0.75Gd at. % substitution showed the best bimodal CT-MRI contrast.