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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 l.jpg

Textbook reading

Thyroid imaging

function studies

Radioiodine therapy

蔡碧瑜 李永隆 陳修弘

Thyroid imaging and function studies l.jpg
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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  • Iodine-131

  • Iodine-123

  • Technetium-99m

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Pertechnetate ion (TcO4-)



  • Iodine

  • a precursor of thyroid hormone .

  • concentration (100:1 than plasma)

  • Organification.

  • Bound to thyroglobulin.

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  • 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

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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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  • Prepared from I-124 and I-125

  • Higher radiation precursors

  • Short half-life

  • Commercial limited

  • Higher cost

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Physics and dosimetryTechnetium-99m

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  • 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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  • 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

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Detection after several hours delay


Detection after 1 day delay


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  • 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

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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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  • Breast feeding

  • Pregnancy

  • Interference of stable iodine contained in foods and medications

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Breast feeding


  • Resumed after several days if the amount used if no more than 30 uCi used

  • Usual imaging dosage is 100-400 uCi


  • 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 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.

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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 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.

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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

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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.

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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 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

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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.

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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 (?)

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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%)

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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.

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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

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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 applicationsother 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 applicationsthyroiditis

  • 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

  • Acute 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 applicationsthyroid 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 48-72 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


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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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inhibit active iodide transport

cause the release of the intrathyroidal iodide not bound to thyroid protein

thiocyanate (SCN-)

perchlorate (ClO4-)

Per chlorate discharge test

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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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Hyperthyroidismindications for iodine-131 therapy

  • Graves’ disease (diffuse toxic goiter)

  • Plummer’s disease (toxic nodular goiter)

  • Functioning thyroid cancer (metastasis)

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HyperthyroidismContraindication 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-80-120 uCi/g

      • Standard dose:5-10mCi

      • Higher for Graves’ opthalmopathy

    • More than 90% patients are cured with a single dose

    • Hypothyroidism-hormone replacement

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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 15-29 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 150-200mCi

  • 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