The thyroid is a small, butterfly-shaped gland located in the neck. The thyroid gland produces three hormones, thyroxine (T4), triiodothyronine (T3) and calcitonin. The main two, T4 and T3, control metabolism, the process of transforming food into energy. When the thyroid produces too much or too little of these hormones, serious symptoms or problems may occur. A thyroid imaging scan is a common procedure indicated for people experiencing certain symptoms and/or clinical indicators.