An imaging test used to find overactive parathyroid glands (four pea-sized glands found on the thyroid) and breast cancer cells, and to diagnose heart disease. The patient receives an injection of a small amount of a radioactive substance called technetium which is bound to another substance called sestamibi. This substance collects in overactive glands, cancer cells, heart muscle, or other tissues and a picture is taken by a gamma camera (a special camera that detects radioactivity).