Nanoparticles made of a polysiloxane matrix and surrounded by 1,4,7,10‐tetraazacyclododecane‐1‐glutaric anhydride‐4,7,10‐triacetic acid (DOTAGA)[Gd3+] and 2,2'‐(7‐(1‐carboxy‐4‐((2,5‐dioxopyrrolidin‐1‐yl)oxy)‐4‐oxobutyl)‐1,4,7‐triazonane‐1,4‐diyl)diacetic acid) NODAGA[68Ga3+] have been synthesized for positron emission tomography/magnetic resonance (PET/MRI) dual imaging. Characterizations were carried out in order to determine the nature of the ligands available for radiolabelling and to quantify them. High radiolabelling purity (>95%) after 68Ga labelling was obtained. The MR and PET images demonstrate the possibility of using the nanoparticles for a combined PET/MR imaging scanner. The images show fast renal elimination of the nanoparticles after intravenous injection.Copyright © 2014 John Wiley & Sons, Ltd.