NUCLEAR MEDICINE IN DIAGNOSIS AND TREATMENT OF Thyroid DISEASES

2. NUCLEAR MEDICINEINDIAGNOSIS AND TREATMENT OF Thyroid DISEASES M.Moslehi Nuclear physician

3. Diagnostic Aim

4. Imaging Methods

5. Advantages of Thyroid Scintigram over other Imaging Techniques • Allowing correlation of physical exam and anatomical imaging findings with physiology.

6. PATIENT PREPARATION Need to cease anti thyroid drugs or thyroxine replacement prior to scanning - ( in consultation with the referring doctor).

7. Scanning Techniques & Devices

8. Scanning Techniques & Devices

9. Scanning Techniques & Devices

11. The thyroid

13. RADIONUCLIDE GENERATORSallow to separate chemically short-lived radioactive daughter nuclei with good characteristics for medical imaging from long-lived radioactive parent nuclei. Milking cow analogy

14. Comparison of lifespan death risk from nuclear medicine procedures with the lifespan death risk of smoking, driving in a highway and natural irradiation

15. Nuclear medicine and pregnant patients… • Most diagnostic procedures are done with short-lived radionuclides (such as technetium-99m) that do not cause large fetal doses • Often, fetal dose can be reduced through maternal hydration and encouraging voiding of urine • Some radionuclides do cross the placenta and can pose fetal risks (such as iodine-131) INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION ——————————————————————————————————————

16. Nuclear medicine and pregnant patient (cont’d) • The fetal thyroid accumulates iodine after about 10 weeks gestational age • High fetal thyroid doses from radioiodine can result in permanent hypothyroidism • If pregnancy is discovered within 12 h of radio-iodine administration, prompt oral administration of stable potassium iodine (60-130 mg) to the mother can reduce fetal thyroid dose. This may need to be repeated several times INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION ——————————————————————————————————————

17. Recommendations for cessation of breast feeding

18. Which one? • I-131: is not the agent of choice for routine diagnostic scintigraphies (because of high energy emissions and the long half life). • Technetium-99m: A frequently used alternative.

19. Physical Characteristics of Tc-99m • Half life: 6 hr • Generator produced • Usual dose: 3-10 millicurie

20. Tc-99m Thyroid Scintigraphy: Applications • Further evaluation of findings on physical examination. • To determine the functional status of thyroid nodules. • Detection of extrathyroidal tissue (such as lingual thyroid). • Differential diagnosis of hyperthyroidism.

22. Normal Thyroid Scintigram

23. Normal Thyroid Scintigram

24. Thyroid Nodule • The major challenge is to determine whether a thyroid nodule is benign or malignant

25. Most important tools in the assessment of thyroid nodules • History and clinical exam • Thyroid Function Tests • Fine Needle Aspiration (FNA) • Thyroid Scan

26. Scintigraphy in Evaluation of Thyroid Nodules • Can not be used to exclude or confirm the malignancy. • FNA with Scintigraphy is a more direct means

27. Scintigraphic classification of thyroid nodules • Cold (Hypofunctioning) • Hot (Functioning) • Indeterminate: Function equals to that of surrounding normal thyroid

28. A Functional Thyroid Nodule

29. A Functional Thyroid Nodule

30. Thyroid Nodules (continue) • Nonfunctioning nodules appear cold and require further evaluation by FNA. • Autonomously functioning nodules may appear hot . Only a few patients with autonomous nodules have been found to have thyroid cancer , and only a few of these cancers were aggressive . Furthermore, in some of these patients, the cancer was adjacent to the autonomous nodule rather than within it.

31. Multinodular Goiter

32. Multinodular Goiter

33. Cold Nodule

34. Cold Nodule

36. Differential Diagnosis of thyrotoxicosis • Grave’s Disease • Toxic Multinodular goiter • Toxic Adenoma • Thyroiditis • Thyrotoxicosis Factitia

37. Grave’s Disease

38. Grave’s Disease

39. Thyroiditis Clinical Picture (can be confusing) Plasma Levels of Thyroid Hormones (may be misdiagnosed as Grave’s Dis.) Scan Pattern RAIU

41. Ectopic Thyroid Tissue • lingual, substernal, pelvic/ovarian teratoma (struma ovarii) • Pertechnetate is not useful for imaging the substernal area due to attenuation or superimposed blood pool activity

44. Thyroglossal duct cyst • Midline along the migratory path of the embryologic gland, anywhere from the foramen cecum at the base of the tongue to the lower neck • The vast majority of patients have normal thyroid scans. • Complications: Infection, and rarely papillary thyroid carcinoma

47. Physical Characteristics of I-131 • Half-life of 8.05 days • Emits a high energy gamma (364 keV) and particulate emissions • Reactor produced

48. Dose of I-131 • Diagnostic • Retrostenal Goiter: 50-200 Microcurie • whole body scans for following of thyroid carcinoma: 2-5 mCi • Therapeutic • Non-neoplastic applications: 5-29 mCi • Differentiated thyroid CA: 100-200 mCi

49. I-131 Thyroid Scintigraphy: Applications • Evaluation of a substernal mass • Detection of persistent residual tissue after thyroid surgery for DTC • Detection of regional cervical lymph node involvement or distant metastatic involvement

50. Substernal Thyroid Masses • I-131 is the preferred imaging agent due to mediastinal blood pool activity with Tc-99m and significant attenuation of low energy gamma photons by sternum • Most intra-thoracic goiters demonstrate anatomic continuity, but not necessarily functional continuity with cervical thyroid tissue.