Nanoparticles are becoming multifunctional tools in biomedical applications, especially in the field of biomedical imaging. Nanoparticles can be used to diagnose, monitor physical and pathological processes, treat and control biological systems. Nanoparticles are usually less than 100nm in size, and they can be made of materials with different chemical properties, the most common being metals, metal oxides, silicates, polymers, carbon, lipids, and biomolecules. Nanomaterials have diverse chemical surface properties, unique magnetic properties, and adjustable absorption and emission properties. They can be designed in different sizes, shapes, chemical surface properties and hollow, porous or solid structures.