“…Over the last two decades, many imaging tools have been applied in biological and biomedical research, such as magnetic resonance imaging (MRI) [1-3], computed tomography (CT) [4, 5], positron emission tomography (PET) [6-10], single-photon emission computed tomography (SPECT) [11], fluorescence/bioluminescence [12-15], ultrasound (US) [16], as well as multimodality approaches that can combine the benefit of various imaging techniques [17-20]. With the size comparable to biological molecules, but orders of magnitude smaller than human cells, nanoparticles (NPs) can offer unprecedented interactions with biomolecules both on the surface of and inside the cells which may revolutionize disease diagnosis and treatment.…”