Thyroid and Parathyroid Imaging
At various times almost every medical imaging modality has been applied to the thyroid and parathyroid glands. The thyroid gland is among the most vascular of tissues and is fed by the superior and inferior thyroid arteries. Nuclear medicine techniques depend on the administration of a suitable radiopharmaceutical which traces an appropriate physiological or metabolic pathway. Quantitative measurements of tracer uptake by the thyroid are among the first clinical nuclear medicine studies and one which is in routine clinical use. The perchlorate ion, like the pertechnetate ion, is trapped in thyroid tissue but not organified. If administered in pharmacological quantities perchlorate will compete with iodine for thyroidal trapping. The thyroid and associated parathyroid glands are highly vascular organs fed by multiple arteries. The parathyroid venous drainage is highly variable, particularly in the case of ectopic glands. Prior surgery can completely alter normal routes and directions of venous flow, rendering interpretation of venous sampling potentially misleading.