Endocrine System :Endocrine System Presented by Mathew Variamattom


Objectives :Objectives Discuss the Organs of the Endocrine system Describe the Role of Nuclear medicine Explain the Anatomy of Thyroid gland Discuss the Thyroid imaging Explain the Thyroid hormone secretion Describe the Thyroid radiopharmaceutical Discuss the Clinical indications Explain the Thyroid carcinoma Describe the Clinical procedure Discuss the Thyroid uptake Explain the Radioiodide whole body imaging Describe the Parathyroid imaging Discuss the Adrenal gland imaging


Organs of the Endocrine system :Organs of the Endocrine system Endocrine means internal secretions. Endocrine system applies to the small group of organs that have the principal function of secretion of hormones. Hormones are biologically active substances that have regulatory effects on diverse metabolic and biochemical processes throughout the body.


Role of Nuclear medicine :Role of Nuclear medicine The primary endocrine glands are the pituitary gland (anterior and posterior), the thyroid gland, the parathyroid glands, the islet cells of the pancreas, the adrenal glands (cortex and medulla) and the gonads (ovaries and testes). In vivo nuclear medicine, both imaging and non-imaging applications, has played a significant role in the current understanding of the function and disorders of the endocrine glands.


Role of Nuclear medicine cont’d :Role of Nuclear medicine cont’d The thyroid, parathyroid, and adrenal glands are the distributed neuroendocrine cells. The nuclear medicine diagnostic techniques are useful to monitor treatment of the disorders that affect these organs and cells, as well as tumors arising from them.


Anatomy of Thyroid gland :Anatomy of Thyroid gland The thyroid gland is located in the anterior neck between the suprasternal notch and the thyroid cartilage. The gland consists of two lobes, each 3-4 centimeters long from pole to pole. The isthmus, thyroid tissue connecting the right and left lobes of the gland overlies the trachea.


Thyroid imaging :Thyroid imaging Thyroid imaging is based on the physiologic process of thyroid hormone production. The thyroid hormones T3 and T4 are manufactured from iodine absorbed into the blood from the digestive tract. The absorbed blood transports the iodine, in the form of iodide, to the thyroid gland, where it is trapped by the thyroid follicular cells. The process of concentrating iodide in the follicles is referred to as the iodide pump.


Thyroid imaging cont’d :Thyroid imaging cont’d T3 and T4 hormones are stored in the thyroid gland until they are required by the body for a wide variety of metabolic processes, including: growth and development body temperature regulation and the metabolism of proteins, lipids, carbohydrates, vitamins and minerals.


Thyroid hormone secretion :Thyroid hormone secretion Thyroid hormone production and secretion are controlled by a negative feedback mechanism. Thyroid stimulating hormone (TSH), secreted by the anterior pituitary gland, regulates thyroid iodide uptake and release of the hormones into the circulation. The levels of T3 and T4 circulating hormones may also affect the hypothalamus, which secretes thyrotropin-releasing factor (TRF), a hormone that stimulates the anterior pituitary gland to produce TSH.


Thyroid Radiopharmaceuticals :Thyroid Radiopharmaceuticals 99mTc-pertechnetate 123I-sodium iodide 131I-sodium iodide Because of significantly higher radiation dose, iodine-131 sodium iodide is not recommended for routine imaging.


Clinical indications :Clinical indications Diseases of the thyroid gland can be classified into two types: functional disorders and structural disorders. Thyroid imaging is performed to relate gland structure to function and to evaluate gland size and palpable nodules or masses in the neck. It is also used to identify ectopic thyroid tissue that may be located at the base of the tongue or below the sternum.


Clinical indications cont’d :Clinical indications cont’d The disorders of thyroid gland function are hyperthyroidism and hypothyroidism. These clinical disorders have an impact on diverse body functions and may be associated with a variety of thyroid anatomic findings and laboratory results. Hyperthyroidism is a clinical disorder characterized by an increase in metabolism and the effects of this increased metabolic rate on the entire body.


Clinical indications cont’d :Clinical indications cont’d Another basis for clinical hyperthyroidism may be subacute thyroiditis. Hypothyroidism is a syndrome caused by thyroid hormone deficiency. Usually it is due to the failure of the thyroid gland to synthesize and release thyroid hormone. Thyroid carcinoma is the most common endocrine neoplasm and mortality from thyroid carcinoma exceeds mortality from all other malignant endocrine tumors.


Thyroid carcinoma :Thyroid carcinoma Thyroid carcinoma presents in a variety of ways: A suspicious nodule without evidence of local or distal spread A large nodule without additional evidence of disease With cervical lymph node involvement Vascular invasion Invasion of soft tissues adjacent to the thyroid


Clinical procedure :Clinical procedure Before dose administration, the patient should always be questioned about previous thyroid problems or symptoms, neck surgery, medications and recent radiographic procedures. A low iodine diet for 3-10 days before radioiodine administration may be recommended. Laboratory values for thyroid hormone levels in the blood aid in the interpretation of both the thyroid image and the thyroid uptake.


Clinical procedure cont’d :Clinical procedure cont’d The radiopharmaceutical is administered orally if radioiodine is being used and intravenously if Tc99m pertechnetate is the tracer of choice. Imaging is performed 15-30 minutes after 99mTc pertechnetate administration, 3-4 or 16-24 hours after 123I-sodium iodide, and 6-24 hours after 131I-sodium iodide. The patient is placed in supine position with the neck hyperextended.


Thyroid imaging :Thyroid imaging Using a scintillation camera with a pinhole collimator, the thyroid is centered in the field of view at a distance from the face of the collimator that will produce an image corresponding to the actual size of the thyroid gland. Images are acquired in the anterior and oblique projections. Images with markers placed in the suprasternal notch or over palpable modules also may be useful.


Thyroid imaging cont’d :Thyroid imaging cont’d To enhance structural detail, magnified views may be obtained by moving the collimator close to the surface of the neck. An anterior view of the mediastinum is indicated if ectopic thyroid tissue is suspected. When radioiodine is used as the tracer, a thyroid uptake is usually performed immediately before or after imaging.


Thyroid uptake :Thyroid uptake Thyroid uptake measures the amount of radioactive iodide taken up and retained within the thyroid gland. Different aspects of thyroid metabolism are reflected in the uptake value, depending on how long after tracer administration the uptake is measured. Under normal circumstances, thyroid uptake at 2-6 hours after administration reflects iodide trapping and organification within the gland.


Thyroid uptake cont’d :Thyroid uptake cont’d Uptake values at 24-48 hours are reflected by the rate at which iodine is lose from the gland. Radioiodine uptakes are useful in patients with hyperthyroidism in whom 131I therapy is indicated and in patients with organification defects, which are seen in cases of congenital organification defect and certain types of thyroiditis.


Radiopharmaceuticals :Radiopharmaceuticals Radioiodine 123I or 131I is preferred, although it is possible to determine thyroid uptake with 99mTc pertechnetate. Radioiodine capsules are easier to handle than radioiodine liquid and minimize the potential for accidental spills and contamination.


Clinical Procedure :Clinical Procedure Patient preparation is similar to that for radioiodine thyroid imaging. The patient should be instructed not to eat after midnight on the night before the test and to remain fasting for 2 hours after capsule administration to facilitate the intestinal absorption of iodide. Data are collected with a thyroid uptake probe with a 2-inch-thick sodium iodide crystal and a flat field collimator connected to a pulse height analyzer and scaler.


Radioiodide whole body imaging :Radioiodide whole body imaging After total thyroidectomy for differentiated thyroid carcinoma, whole body imaging with radioiodine may be performed. The purpose of this type of imaging is to identify residual functioning thyroid tissue and or areas of metastases. 131I-sodium iodide is the tracer most commonly used to perform this type of imaging.


Parathyroid Scan :Parathyroid Scan Indications Detection and localization of primary and secondary parathyroid cancer. Identification of single adenomas, multiple adenomas, or glandular hyperplasia in patients with newly diagnosed hypercalcemia and elevated parathyroid hormone (PTH) levels. Localization of cancer for surgery candidates,. Localization of parathyroid tissue after surgery for persistent or recurrent hyperparathyroidism.


Contraindications :Contraindications Patient on calcium medications. Patient on thyroid medications and/or received recent iodine contrast studies. Patient should be off thyroid medications for 5 days, contrast studies at 7-10 days. Patient too agitated or prone to movement or claustrophobia.


Parathyroid imaging :Parathyroid imaging The four parathyroid glands are located on the posterior aspects of the poles of the thyroid gland. The parathyroid glands produce and secrete parathyroid hormone (PTH), the hormone responsible for regulating the level and distribution of calcium and phosphorus. Radionuclide imaging of the parathyroid is useful when primary hyperparathyroidism is suspected.


Parathyroid imaging cont’d :Parathyroid imaging cont’d This condition results from a tumor in one of the parathyroid glands or from hyperplasia of all four glands, both of which lead to excess secretion of PTH. Excess PTH stimulates removal of large amounts of calcium from the bones, causing weakening and increased fracture risk. The excess calcium level in the blood affects the nervous system function and muscle contraction.


Adrenal gland imaging :Adrenal gland imaging The adrenal glands are located at the superior poles of the kidneys. They are small glands, weighing only 6-7 grams, and consist of an outer cortex and inner medulla. The cortex produces steroid hormones (aldosterone, cortisol etc). Cholesterol is a precursor or building block of these hormones.


Adrenal gland imaging cont’d :Adrenal gland imaging cont’d It has been radiolabeled with 131I and has been used to image adrenal adenomas and certain other adrenal pathology. Iodocholesterol is an investigational drug and not available commercially. The adrenal medulla manufactures catecholamine's (epinephrine and norephinephrine), hormones that control the body’s response to stress. Tumors of the adrenal medulla are called pheochromocytomas. These tumors secrete excessive amounts of catecholamine's and may be benign or malignant.


Adrenocortical Scan :Adrenocortical Scan Indications Detection and localization of adrenal glands Evaluation of documented primary hyperaldosteronism Detection and localization of adrenal incidentalomas Evaluation for biopsy or surgical intervention. Evaluation of adrenal lesions visualized on other imaging techniques.


Localization :Localization Compartmental, blood flow, into the adrenal cortex, bound to and transported by plasma low-density lipoproteins. Taken up by low-density lipoprotein receptors on adrenocortical cells. Cholesterol is the main precursor in the production of adrenocortical steroid; NP-59 is a cholesterol analog.


Question 1 :Question 1 Endocrine means what?


Answers :Answers Ans. Endocrine means internal secretions


Question 2 :Question 2 Hormones are biologically active substances that have regulatory effects on diverse metabolic and biochemical processes throughout the body. True or False.


Answer :Answer True.


Question 3 :Question 3 Which glands are the distributed neuroendocrine cells.


Answer :Answer The thyroid, parathyroid, and adrenal glands are the distributed neuroendocrine cells.


Question 4 :Question 4 The Thyroid gland consists of how many lobes?


Answer :Answer The thyroid gland consists of two lobes.


Question 5 :Question 5 Which tissue connecting the right and left lobes of the thyroid gland?


Answer :Answer The isthmus, thyroid tissue connecting the right and left lobes of the gland.


Question 6 :Question 6 The process of concentrating iodide in the follicles is referred to as the what pump?


Answer :Answer The process of concentrating iodide in the follicles is referred to as the iodide pump.


Question 7 :Question 7 Thyroid hormone production and secretion are controlled by a negative feedback mechanism. True or False.


Answer :Answer True.


Question 8 :Question 8 What are the disorders of thyroid gland function?


Answer :Answer The disorders of thyroid gland function are hyperthyroidism and hypothyroidism.


Question 9 :Question 9 Hypothyroidism is a syndrome caused by what deficiency?


Answer :Answer Hypothyroidism is a syndrome caused by thyroid hormone deficiency.


Question 10 :Question 10 The four parathyroid glands are located on the posterior aspects of the poles of the thyroid gland. True or False.


Answer :Answer True.


References :References Book “Nuclear medicine and PET/CT Technology and Techniques”, by Paul E. Christian, sixth edition. Book “Review of Nuclear Medicine Technology preparation for certification examinations, by Patricia C. Wells, MAE, CNMT, third edition.