Thyroid gland. Coloured gamma scan (scintigram) of a healthy human thyroid gland, in front view. The thyroid is an endocrine gland at the base of the neck, and is divided into two lobes (as seen here). A radioactive tracer, in this case Iodine-131, highlights active areas in the gland. Green indicates low activity, varying to yellow & red: high activity. The thyroid produces and stores hormones that control the body's metabolic rate, influence growth and maturation, and regulate blood calcium levels. A gamma scan is made by a gamma camera, which detects radioactivity from a tracer injected into the body.