For cancer imaging, a class of nanocrystals termed quantum dots have been widely used. Quantum dots are composed of inorganic molecules (such as a cadmium selenide core and a zinc sulphide shell) of particles less than 10nm and emit powerful narrow-band fluorescence of wavelength between 450 - 850nm. Like other nanoparticles, quantum dots can be conjugated to antibodies, ligands or other targeting moieties to mediate specific interactions with cancer cells. They emit intense fluorescence and are exploited in applications for optical imaging of tumours.

A variety of imaging techniques are also used in cancer imaging such as ultrasound, magnetic resonance imaging (MRI), X-ray computed tomography (CT), positron emission tomography (PET), single photon emission computed tomography (SPECT) and various other optical imaging techniques.