Thyroid cancer. Coloured SPECT (single photon emission computed tomography) scan showing thyroid cancer in a patient after thyroid surgery. The cancerous cells are seen as white and yellow areas in the neck of the patient. Thyroid cancer may grow rapidly, pressing on the voice box and spreading to lymph nodes. It is one of the cancers associated with exposure to radioactive fallout. SPECT scans of the thyroid gland are made by injecting the patient with a radioactive tracer, in this case Iodine-131, which concentrates in the thyroid and can be detected by gamma camera.