A rod-shaped plant virus having an interior surface and an exterior surface, and at least one imaging agent that is linked to the interior and/or exterior surface is described. The rod-shaped viruses can be combined into larger spherical nanoparticles. A rod-shaped plant virus or spherical nanoparticles including an imaging agent can be used in a method of generating an image of a tissue region of a subject such as a tumor or atherosclerotic tissue by administering the virus particle to the subject and generating an image of the tissue region of the subject to which the virus particle has been distributed.