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Textbook reading. Thyroid imaging function studies Radioiodine therapy 蔡碧瑜 李永隆 陳修弘. Thyroid imaging and function studies. Evaluation for clinical palpable nodules Thyroid scintigraphy and radiotracer uptake studies U.S. and F.N.A Laboratory data. Thyroid scintigraphy.

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Textbook reading

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  1. Textbook reading Thyroid imaging function studies Radioiodine therapy 蔡碧瑜 李永隆 陳修弘

  2. Thyroid imaging and function studies Evaluation for clinical palpable nodules • Thyroid scintigraphy and radiotracer uptake studies • U.S. and F.N.A • Laboratory data

  3. Thyroid scintigraphy • Determining the functional status of the thyroid nodules. • Detection of the extra-thyroid metastasis form thyroid carcinoma. • The thyroid tissue origins from mediastinal masses. • Correcting the physical finding with abnormalities in the image.

  4. Radiopharmaceuticals • Iodine-131 • Iodine-123 • Technetium-99m

  5. Pertechnetate ion (TcO4-) concentration Radiopharmaceuticals • Iodine • a precursor of thyroid hormone . • concentration (100:1 than plasma) • Organification. • Bound to thyroglobulin.

  6. Physics and dosimetryiodine-131

  7. Iodine-131 • not good choice for routine thyroid scintigraphy • The presence of beta particle emissions • The relative high energy of the principal gamma ray emissions for gamma camera. • The long half-life

  8. Physics and dosimetryiodine-123

  9. Iodine-123 Better for thyroid image • Electron capture • Gamma energy is ideally suited for gamma camera(159 keV) • Half-life is suitable (13.2hr)

  10. Iodine-123 Disadvantage • Prepared from I-124 and I-125 • Higher radiation precursors • Short half-life • Commercial limited • Higher cost

  11. Physics and dosimetryTechnetium-99m

  12. Technetium-99m • Better for thyroid scintigraphy • Reliably available from molybdenum-99 /Tc99m generator system • Ideal half-life (6hr) • Suitable energy (only gamma ray 140KeV)

  13. Pharmacokineticsradioiodine • GI absorbs ion by Oral administration • Into circulation • Rapid uptake and Organification of iodine • Detectable within minutes. • Reached the follicular lumen within 20-30 minutes • Normal range for uptake is 10%-30% of the administered dose at 24 hr

  14. I-123 Detection after several hours delay I-131 Detection after 1 day delay Pharmacokineticsradioiodine

  15. PharmacokineticsTechnetium-99m • Iv administration • Rapid uptake by thyroid but not organification • Optimal uptake for imaging is 20-30 min with the 0.5-3.75% of the reagent

  16. Technetium-99m & radioiodine • Concordant localization and identical scintigraphy • Dis-concordant in a small percentage of thyroid nodules for the loss of the organification

  17. Precautions • Breast feeding • Pregnancy • Interference of stable iodine contained in foods and medications

  18. Breast feeding I-123 • Resumed after several days if the amount used if no more than 30 uCi used • Usual imaging dosage is 100-400 uCi I-131 • Should be terminated for several weeks Tc99m pertechnetate • Resumed in 24 hr

  19. radioiodine precaution for pregnancy • Radioiodine can cross placenta • Fetal thyroid can concentrate iodine after 10th -12th gestation weeks. • Resulting in hypothyroidism and cretinism.

  20. Interference for radioiodine uptake • Several non-iodine drug can affect that. • 1 mg of stable iodine can cause significant reduction of the 24 hr radioiodine uptake • 10 mg can effectively block the gland, with 98% reduction uptake.

  21. Normal thyroid scintigraphy • In the euthyroid adult the thyroid gland weights 15-20 g. • Butterfly shape with lateral lobe extending along each side of the thyroid cartilage of the larynx • The lateral lobes are connected by an isthmus that crosses the trachea anteriorly below the level of the cricoid cartilage.

  22. The right lobe is often larger than the left. The lateral lobes typically measure 4-5 cm from superior to inferior poles and 1.5-2 cm wide. The pyramidal lobe is a paramedian structure that arises from the isthmus, either to the right or left lobe of the middle, and represents functioning thyroid tissue in the thyroglossal duct tract.

  23. Normal thyroid scintigraphy • Homogeneous • Uniform distribution • Variation • Middle or medial of the lateral lobes owing to the thickness • Activity of the Isthmus varies greatly among patients, with little or no activity and prominent activity

  24. TC-99m pertechnetate • Thyroid tissue • Salivary gland • Esophagus activity seen to the left of middle and can confirm by having patient swallow, hollowed by a repeat image.

  25. Clinical applications indication for thyroid scintigraphy • Further evaluation of findings on physical examination • Detection of metastases with thyroid carcinoma • Follow-up of radioiodine therapy for differentiated thyroid cancer • Determination of functional status of thyroid nodules • Differential diagnosis of mediastinal masses • Detection of extra thyroidal tissue (lingual thyroid) • Screening after dead and neck irradiation.

  26. Clinical applicationsGoiter • Refers to an enlargement of the thyroid gland • Endemic goiters • Iodine deficiency-induced hyperplasia • Colloid nodular goiters • Nontoxic goiters • Graves’ disease • Toxic goiter • Thyroid carcinoma • Other neoplasm-lymphoma • Active phase of thyroiditis

  27. Scintigraphy of Goitermultinodular colloid goiters • Inhomogeneous uptake of tracer • Cold areas of various sites • Carcinoma changes rate is low (1-5%) • Highly suspicion: out of proportion in size to other cold areas or enlarging suddenly.

  28. Scintigraphy of GoiterGraves’ disease • Uniform with intensely increased uptake • The pyramidal lobe is frequently seen • Not generally considered an indication for obtaining a thyroid scinitigram (?)

  29. Clinical applicationsthyroid nodules • Extremely common • The incidence increases with age • More common in women • Likehood of malignancy: • Multiple nodule (multiple nodular goiters, less than 5%) • Solitary cold nodule (5-40%)

  30. Scintigraphy for thyroid nodules • Cold nodules-nonfunctioning • The majority of the thyroid nodules • As small as 3 cm can be detected by pinhole collimator • Hot nodules-functioning • Function equal to the surrounding normal thyroid • Indeterminate • Need to close to correct between physical examination and scintigraphy findings. • Oblique view with a pinhole collimator • The management is the same as the cold nodules.

  31. Cold nodules Risk factors of malignancy • prior history of radiation to the head and neck or mediastinum • >1000-1500 rads • Solitary cold nodules in young female • Multiple nodular goiters in elderly

  32. Hot nodules • Hyper functioning • Autonomous • Out of negative feedback control

  33. Hot nodules • Autonomous nodules • Thyroid gland produces much hormone • Greater than 3-4 cm • suppress pituitary TSH • Extra-nodular thyroid tissue is not visualable • Small nodules • Extra-nodular thyroid tissue is visualable • Spontaneous involution • Cystic degeneration

  34. Hot nodules • Hot nodules with hyperthyroidism • Large(3-4 cm), multiple nodules • Autonomous hot nodule with Thyrotoxicosis • Plummer’s disease

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