Nanotechnology is an interdisciplinary field as a combination of engineering, biology and medicine. It manipulates atoms and molecules to create devices at atomic, molecular and supramolecular levels for potential clinical use. Cancer nanotechnology as the latest trend in cancer diagnosis and treatment has provided nanoscale tools like biosensors, dendrimers, quantum dots and magnetic NANOPARTICLES such as iron oxide with unique optical, magnetic and electronic properties. They are 100 to 1,000-fold smaller than cancer cells and may be conjugated with several functional molecules like imaging probes, specific ligands and antibodies. The capability of transferring through leaky blood vessels, passive and active targeting, intracellular delivery and subcellular localization has made them dual-purpose and multifunctional probes in cancer. Conventional imaging techniques such as CT and MRI using nontargeted contrast agents have limitations in early and accurate diagnosis and monitoring of treatment that may be eventually removed through the use of nanostructures' properties.Cancer diagnosis in an early stage, which influences the patient's survival, is possible earlier than ever imaginable. For example in contrast to mammography, which can detect breast cancer when it has at least 1000,000 cells, these new tools can accurately detect the tumor when it has less than 100 cells. This article is a review on applications of nanotechnology, as a rapidly growing field for cancer imaging in medicine contributing to the early detection of cancer cells through available imaging techniques.