Textbook reading

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Textbook reading

• Thyroid imaging
• function studies
• Radioiodine therapy
• ??? ??? ???

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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 (1001 than plasma)
• Organification.
• Bound to thyroglobulin.

• Pertechnetate ion (TcO4-)
• concentration

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Physics and dosimetryiodine-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

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Physics and dosimetryiodine-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 dosimetryTechnetium-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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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

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Pharmacokineticsradioiodine

• I-123
• Detection after several hours delay

• I-131
• Detection after 1 day delay

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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

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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 100-400 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
  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
• gt1000-1500 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
• Plummers 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 Quervains disease
• Non-suppurative
• Etiology unproved-virus infection (URI, neck
  tenderness)
• Initial phase would be a Thyrotoxicosis
• Chronic thyroiditis
• Hashimotos 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
• 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
• Plummers 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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Hyperthyroidismindications for iodine-131 therapy

• Graves disease (diffuse toxic goiter)
• Plummers 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 Hashimotos
  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
• Gravesdiseas-80-120 uCi/g
• Standard dose5-10mCi
• Higher for Graves opthalmopathy
• More than 90 patients are cured with a single
  dose
• Hypothyroidism-hormone replacement

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Radioiodine treatment

• Plummers 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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