new types of nanoparticle - based dual - modality positron emission tomography / magnetic resonance imaging and positron emission tomography / computed tomography tumorspecific contrast agents have been developed . the base of the new type contrast agents is biopolymer - based nanoparticle with pet , mri and ct active ligands . the nanoparticle contains at least one polyanion and polycation , which form nanoparticles via ion - ion interaction . the self - assembled polyelectrolytes can transport gold nanoparticles as ct contrast agents , or spion or gd ions as mri active ligands , and are labeled using a complexing agent with gallium as pet radiopharmacon . furthermore , these dual modality pet / mri and pet / ct contrast agents are labeled with targeting moieties to realize the tumorspecificity .