New metal-based nanoparticles for intravenous use: requirements for clinical success with focus on medical imaging.

Animal studies have during the last years revealed a large potential for in vivo imaging with new metal-based nanoparticles and will certainly during the next years also continue to improve our understanding of basic biological processes. In the present article we discuss what is needed to bring such non-iron oxide particles into clinical imaging. For imaging agents it is essential to have a rapid clearance from blood so as to obtain low background signals and good images. The surface charge and hydrodynamic diameter of the nanoparticles in the presence of plasma proteins are important for their biodistribution, excretion. and a rapid clearance from blood. As discussed, some major challenges remain to be met regarding safety and metabolism issues. Measurements and optimization of the critical parameters will shorten the time needed for such particles to be accepted for widespread medical use.