Salivary and thyroid glands. False-colour computer enhanced gamma scan (scintigram) of healthy salivary glands and thyroid gland. The outline of the head is blue. At ear-level, the parotid sali- vary glands are seen (yellow) as the largest pair of glands which secrete saliva. Beneath them at jaw-level, a pair of submandibular salivary glands (yellow with red centre) are seen. In the neck at bottom frame are the thyroid glands (red, partly obscured) coloured brightly with the radioactive tracer Iodine 131. Gamma scanning involves intro- ducing a radioactive tracer into the body, which is taken up by certain organs and detected by a gamma camera. Slices" of tissue can be examined."