Nuclear Medicine Studies involve
making the patient temporarily radioactive, with a very small amount of
an isotope. The images are obtained by looking for the small amount of
radioactivity given off by the patient. By choosing the right isotopes
and attaching them to physiologic molecules, the radioactivity (and the
image) can be isolated to reveal certain organs and tissues (like imaging
the thyroid with a radioactive Iodine scan).
this for more information about Nuclear Medicine.