It took only fifty years to realize that it is possible to view bones through flesh using X-rays, that our body can be imaged as thin slices of tissues and that tumors and lesions hidden anywhere in the body can be located. Soon it will be possible to monitor molecular and physiological changes occurring inside the body. Dark-brown iron oxide nanoparticles, about 100,000 times smaller than the diameter of a single hair, can enhance the capabilities of available medical imaging techniques.