The Choi laboratory at the Gordon Center for Medical Imaging of MGH focuses on the development of novel tissue- and organ-specific contrast agents for diagnosis, staging, and treatment of human diseases. Of particular interest is tumor-targeted fluorophores, which can be used for image-guided surgery by specifically visualizing target tissue with high optical properties and by avoiding nonspecific uptake in normal background tissues. Since 2008, we have been systematically probing the relationship among the hydrodynamic diameter, shape, charge, and hydrophobicity of nanoparticles and small molecule contrast agents on in vivo biodistribution and clearance (Nature Biotech. 2007, Quant Imaging Med Surg. 2012).