Technetium (99mTc) sestamibi

Technetium (99mTc) setamibi is a radioactive pharmaceutical compound used in medical imaging studies. It is composed of single atoms of technetium, a man-made element, tied to six identical chemical chains. This chemical binds preferentially to the myocardium, the parathyroid gland, and malignancies of the breast, allowing them to be imaged in preference to the rest of the body's tissues. As technetium is a source of gamma rays, the chemical can be detected with a gamma ray camera.
Technetium (99mTc) setamibi at Wikipedia