1. 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

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

6. Physics and dosimetry iodine-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
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

8. Physics and dosimetry iodine-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 dosimetry Technetium-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. 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

14. Pharmacokinetics radioiodine
Detection after several hours delay
I-131
Detection after 1 day delay
For background clearance but nor for the slow uptake

15. Pharmacokinetics Technetium-99m
Iv administration
Rapid uptake by thyroid but not organification
Optimal uptake for imaging is min with the % 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 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.

27. 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.

28. 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.

29. 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

31. 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

32. 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.

34. 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

36. 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.

37. 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 (?)

42. 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%)

43. 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

45. 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

47. Hot nodules Hyper functioning Autonomous
Out of negative feedback control

48. 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

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

54. 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

55. Substernal thyroid D.D mediastinal masses
Goitrous enlargement with downward extension
Abnormal migration during develop

56. 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

59. 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.

60. 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

61. 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

62. 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

63. Clinical applications thyroid cancer metastasis
Follicular carcinoma
Mixed papillary-follicular carcinoma
Papillary carcinoma
Medullary carcinoma
Ana plastic carcinoma

64. 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

65. Thyroid cancer metastasis
Imaging is performed hr after radioiodine administration.
More lesion are demonstrated in this time than at 24 hr.

66. 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

67. 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

70. Tumor imaging Thalium-201 chloride Tc-99m sestamibi
For location metastasis in patients with increased thyroglobulin and negative radioiodine whole body scintigraphy

71. 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.

72. Medullary carcinoma of thyroid
Indium -111 somatostatin receptor scintigraphy for Medullary carcinoma
Iodine -131 MIBG
FDG-PET

73. Thyroid function studies
Thyroid percent uptake
Suppression test
Stimulation test
Per chlorate discharge test

75. 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

76. Thyroid percent uptake
DD hyperthyroidism
Increase uptake
Graves’ disease
Plummer’s disease
Decrease uptake
Subacute thyroiditis
Thyrotoxicosis factitia

77. Suppression test Not used in current routine practice.
Autonomous functioning glands
TSH level is a sensitivity test now

78. 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.

79. 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

80. Stimulation test Receiving 10 units of TSH iv
The radiotracer repeats beginning the next day.
Primary-no response
Secondary-radiotracer doubling

81. Per chlorate discharge test
to detect defects in
Intra-thyroidal iodide organification

82. 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

83. 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

84. Per chlorate discharge test
inhibit active iodide transport
cause the release of the intrathyroidal iodide not bound to thyroid protein
thiocyanate (SCN-)
perchlorate (ClO4-)

85. 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

86. 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

87. Per chlorate discharge test
Less than 10% discharge of radioiodine:
Normal
Hyperthyroidism on inadequate antithyroid drug therapy
Greater than 10% washout:
Organification defect

88. Radioiodine treatment
Hyperthyroidism
Thyroid cancer

89. Hyperthyroidism indications for iodine-131 therapy
Graves’ disease (diffuse toxic goiter)
Plummer’s disease (toxic nodular goiter)
Functioning thyroid cancer (metastasis)

90. 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)

91. 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

92. Radioiodine treatment
Plummer’s disease
Hyperthyroidism caused by toxic nodules
More radio-resistant
Inhomogenity, rapidly radioiodine turnover ,low retain dose
Increase dose to mCi

93. Radioiodine treatment
Metastases from differentiated thyroid cancer
Controversial with small , early stage lesions
Residual, recurrence differentiated thyroid cancer - improved survival rate with I-131

94. 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

95. 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

97. 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

98. Thanks for your attention