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Thyroid imaging function studies Radioiodine therapy 蔡碧瑜 李永隆 陳修弘
Textbook reading Thyroid imaging function studies Radioiodine therapy 蔡碧瑜 李永隆 陳修弘
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Thyroid imaging and function studies
Evaluation for clinical palpable nodules Thyroid scintigraphy and radiotracer uptake studies U.S. and F.N.A Laboratory data
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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.
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Radiopharmaceuticals
Iodine-131 Iodine-123 Technetium-99m
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Radiopharmaceuticals
Iodine a precursor of thyroid hormone . concentration (100:1 than plasma) Organification. Bound to thyroglobulin. Pertechnetate ion (TcO4-) concentration
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Physics and dosimetry iodine-131
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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 Setal penetration of the collomator and poor detection sensitivity in the relative thin sodium iodine crystal of the gamma camera. But suits for delay studies at 24,48,72hr For thyroid cancer metastasis and mediastinal masses
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Physics and dosimetry iodine-123
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Iodine-123 Better for thyroid image Electron capture
Gamma energy is ideally suited for gamma camera(159 keV) Half-life is suitable (13.2hr)
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Iodine-123 Disadvantage Prepared from I-124 and I-125
Higher radiation precursors Short half-life Commercial limited Higher cost
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Physics and dosimetry Technetium-99m
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Technetium-99m Better for thyroid scintigraphy
Reliably available from molybdenum-99 /Tc99m generator system Ideal half-life (6hr) Suitable energy (only gamma ray 140KeV)
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Pharmacokinetics radioiodine
GI absorbs ion by Oral administration Into circulation Rapid uptake and Organification of iodine Detectable within minutes. Reached the follicular lumen within minutes Normal range for uptake is 10%-30% of the administered dose at 24 hr
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Pharmacokinetics radioiodine
Detection after several hours delay I-131 Detection after 1 day delay For background clearance but nor for the slow uptake
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Pharmacokinetics Technetium-99m
Iv administration Rapid uptake by thyroid but not organification Optimal uptake for imaging is min with the % of the reagent
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Technetium-99m & radioiodine
Concordant localization and identical scintigraphy Dis-concordant in a small percentage of thyroid nodules for the loss of the organification
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Precautions Breast feeding Pregnancy
Interference of stable iodine contained in foods and medications
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Breast feeding I-123 Resumed after several days if the amount used if no more than 30 uCi used Usual imaging dosage is uCi I-131 Should be terminated for several weeks Tc99m pertechnetate Resumed in 24 hr
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radioiodine precaution for pregnancy
Radioiodine can cross placenta Fetal thyroid can concentrate iodine after 10th -12th gestation weeks. Resulting in hypothyroidism and cretinism.
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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.
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Normal thyroid scintigraphy
In the euthyroid adult the thyroid gland weights 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.
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The right lobe is often larger than the left.
The lateral lobes typically measure 4-5 cm from superior to inferior poles and 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.
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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 Activity at Graves’ disease for the hyperplasia of the tissue in the duct
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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. I-123 the salivary gland are not usually seen
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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.
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Clinical applications Goiter
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
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Scintigraphy of Goiter multinodular 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.
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Scintigraphy of Goiter Graves’ disease
Uniform with intensely increased uptake The pyramidal lobe is frequently seen Not generally considered an indication for obtaining a thyroid scinitigram (?)
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Clinical applications thyroid 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%)
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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. Oblique view with a pinhole collimator can be helpful in separation the nodule from adjacent thyroid tissue
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Cold nodules Risk factors of malignancy
prior history of radiation to the head and neck or mediastinum > rads Solitary cold nodules in young female Multiple nodular goiters in elderly
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Hot nodules Hyper functioning Autonomous
Out of negative feedback control
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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
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Hot nodules Hot nodules with hyperthyroidism
Large(3-4 cm), multiple nodules Autonomous hot nodule with Thyrotoxicosis Plummer’s disease
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Discordant nodules Possibility of discordant between radioiodine and Tc-99m pertechnetate Radioiodine-cold Tc-99m pertechnetate-hot 2-3 % in Tc-99m pertechnetate hot nodules
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Substernal thyroid D.D mediastinal masses
Goitrous enlargement with downward extension Abnormal migration during develop
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Substernal thyroid I-131 is better than Tc99m
Delayed performed (48-72 hr) Function and tracer uptake in sternal thyroid is poor Blood clearance of the background activity Cervical thyroid should also be noted
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Clinical applications other ectopic thyroid tissue
The thyroglossal duct runs from the foramen cecum at the base of the tongue to the thyroid Lingual thyroid –complete failure to migrate Absence of tracer uptake in the expected cervical area Thyroid tissue may be found along the tract of the thyroglossal duct.
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Clinical applications thyroiditis
Acute thyroiditis Suppurative bacterial infection Focal abscess subacute thyroiditis Granulomatous thyroiditis De Quervain’s disease Non-suppurative Etiology unproved-virus infection (URI, neck tenderness) Initial phase would be a Thyrotoxicosis Chronic thyroiditis Hashimoto’s thyroiditis Lymphocytic infiltration More common in women with goiter or hypothyroidism Rarely with hyperthyroidism-hashitoxicosis
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Scintigraphy for acute & subacute thyroiditis
Cold nodule for the focal abscess Subacute thyroiditis Decrease or absent uptake of radioiodine in the affected part of the gland Gallium-67 imaging :inflammatory process
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Scintigraphy for chronic thyroiditis
Highly variable and depend on the stage in the natural history Normal in the early stage Later, diffuse enlargement Eventually, hypothyroidism, inhomogeneous with hot and cold areas
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Clinical applications thyroid cancer metastasis
Follicular carcinoma Mixed papillary-follicular carcinoma Papillary carcinoma Medullary carcinoma Ana plastic carcinoma
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Thyroid cancer metastasis
The most common sites of metastasis are locally in the lymph nodes of the neck, lung ,and bone. nodal activity is focal ,intense, starburst pattern on parallel-hole collimators
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Thyroid cancer metastasis
Imaging is performed hr after radioiodine administration. More lesion are demonstrated in this time than at 24 hr.
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I-131 follow-up imaging The preparations and dosage are controversial.
Thyroid hormone replacement is withdraw for 4-6 weeks to stimulate TSH secretion. Use bovine TSH before imaging. Not satisfactory for increasing I-131 uptake allergy
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Scanning dosages for follow-up imaging
Controversial More metastasis deposits are seen with higher doses 5-10 mCi of I-131 for detecting metastasis As little as 5 mCi with less satisfactory uptake of sequent therapeutic dose Diagnostic dose should be limited 1-2 mCi
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Tumor imaging Thalium-201 chloride Tc-99m sestamibi
For location metastasis in patients with increased thyroglobulin and negative radioiodine whole body scintigraphy
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Iodine -131 MIBG for Medullary carcinoma
meta-iodo-benzyl-guanidine Neurosecretory storage vesicles of chromaffin cells Sensitivity is low (30%) Soft tissue metastasis is more visualized than bone metastasis.
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Medullary carcinoma of thyroid
Indium -111 somatostatin receptor scintigraphy for Medullary carcinoma Iodine -131 MIBG FDG-PET
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Thyroid function studies
Thyroid percent uptake Suppression test Stimulation test Per chlorate discharge test
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Thyroid percent uptake
The earliest applications radiotracer in medicine. The degree of radioiodine uptake parallels the functional activities of the thyroid hormone produced Normal uptake range 10-30% Sensitivity and specific test of serum T3 T4
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Thyroid percent uptake
DD hyperthyroidism Increase uptake Graves’ disease Plummer’s disease Decrease uptake Subacute thyroiditis Thyrotoxicosis factitia
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Suppression test Not used in current routine practice.
Autonomous functioning glands TSH level is a sensitivity test now
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Suppression test Receiving 25 mg T3 qid for 8 day
24hr uptake is repeated beginning at 7th day. It is fall in the percentage of uptake to less 50% of the baseline and less the 10% overall.
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Stimulation test Infrequent use now.
D.D primary and secondary (pituitary) hypothyroidism Primary-failure to response to exogenous TSH Secondary-increasing radioactivity after TSH administration
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Stimulation test Receiving 10 units of TSH iv
The radiotracer repeats beginning the next day. Primary-no response Secondary-radiotracer doubling
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Per chlorate discharge test
to detect defects in Intra-thyroidal iodide organification
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Per chlorate discharge test
Dissociation of the trapping and organification function Congenital enzyme deficiency associated with deafness (Pendred's syndrome), Some chronic thyroiditis During the treatment of PTU
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Per chlorate discharge test
I is "trapped" by the thyroid gland through an energy-requiring active transport mechanism Once in the gland, it is rapidly bound to thyroglobulin
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Per chlorate discharge test
inhibit active iodide transport cause the release of the intrathyroidal iodide not bound to thyroid protein thiocyanate (SCN-) perchlorate (ClO4-)
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Per chlorate discharge test
administration of radioiodine orally counts are obtained at frequent intervals (every 10 or 15 minutes). Two hours later, 1g of KClO4 orally repeated epithyroid counts continue to be obtained for an additional 2 hours
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In normal individuals little loss of the thyroidal radioactivity accumulated prior to induction of the "trapping" block radioiodine accumulation in the thyroid gland ceases after the administration of the iodide transport inhibitor
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Per chlorate discharge test
Less than 10% discharge of radioiodine: Normal Hyperthyroidism on inadequate antithyroid drug therapy Greater than 10% washout: Organification defect
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Radioiodine treatment
Hyperthyroidism Thyroid cancer
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Hyperthyroidism indications for iodine-131 therapy
Graves’ disease (diffuse toxic goiter) Plummer’s disease (toxic nodular goiter) Functioning thyroid cancer (metastasis)
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Hyperthyroidism Contraindication for iodine-131 therapy
Thyrotoxicosis factitia Subacute thyroiditis Silent thyroiditis (atypical ,subacute, lymphocytic, transient, postpartum) Struma ovarii Thyroid hormone resistance Secondary hyperthyroidism Thyrotoxicosis associated with Hashimoto’s disease (hashitoxicosis) Jod-Basedow phenomenon (iodine-induced hyperthyroidism)
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Radioiodine treatment
Goal Euthyroid in a reasonable length of time with a single radioiodine dose Graves’diseas uCi/g Standard dose:5-10mCi Higher for Graves’ opthalmopathy More than 90% patients are cured with a single dose Hypothyroidism-hormone replacement I-131 can be used in any age
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Radioiodine treatment
Plummer’s disease Hyperthyroidism caused by toxic nodules More radio-resistant Inhomogenity, rapidly radioiodine turnover ,low retain dose Increase dose to mCi
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Radioiodine treatment
Metastases from differentiated thyroid cancer Controversial with small , early stage lesions Residual, recurrence differentiated thyroid cancer - improved survival rate with I-131
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Radioiodine treatment
Metastasis more common at neck, lung and bone Bone metastasis is more difficult eradicated than lung metastasis Initial dose mCi Repeated doses up to 1Ci
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Radioiodine treatment
Follow-up imaging is performed yearly until the metastatic lesions are elimination Serum thyroglobulin –tumor marker If the level is increase in a post-op patient. it may be a recurrence Then performed imaging to localize the lesion
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Radioiodine treatment
Not statistically significances of leading the secondary cancer by radioiodine Tx Not reduce fertility Congenital defects are not increased in the child of treated patients
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Thanks for your attention
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