The technological advances required for cellular and molecular imaging illustrate that these advances in science are largely dependent on the emergence of new technologies. As with microscope-based histology, the visualization of specific targets by molecular or cellular imaging requires selective dyes and markers, including antibodies, to selectively highlight different types of cells or molecules of interest. Contrast agents are therefore currently the single-most rate-limiting step for molecular and cellular imaging. As MR contrast agents do not have a short half-life like PET agents, it is also conceivable that companies could provide specific kits for molecular MR imaging using this approach. A conditional gene expression of ferritin might therefore be more desirable, as it would only increase the cellular iron load for brief periods of time, during which in vivo imaging could occur. Substantial progress in molecular and cellular MR imaging has been achieved in the past few years.