Thyroid gland. Coloured computer-enhanced gamma scan (scintigram) of a healthy human thyroid gland. The thyroid gland is a main endocrine gland situated at the base of the neck, and is divided into two lobes (as seen). The radioactive tracer Technetium-99m used in this gamma scan shows areas of activity (yellow) within the gland. The thyroid produces and stores hormones which control the basal metabolic rate of the body, influence growth and maturation, and regulate blood calcium levels. Gamma scanning involves introducing a radioactive tracer into the body, which is taken up by certain organs and detected as gamma rays by a gamma camera.