The development of tracer imaging agents with sufficiently high label activity can lead to problems of poor aqueous solubility of the labeled tracer, causing formulation difficulty, inadvertent accumulation by phagocytic cells, or inadequate signal to noise. Our approach to solving these problems is to administer the tracer in the form of monodispersed nanoparticles which can safely be administered intravenously. Since the phagocytosis of these particles can be controlled or avoided in a predictable manner by altering particle size and surface characteristics, imaging tracers can be designed for a variety of intended applications. This paper summarizes the results and ideas for several applications involving computed tomography, ultrasound, magnetic resonance imaging, and radioisotope imaging modalities.