Thyroid Scan Nuclear Medicine

1. RADIONUCLIDE THYROID
IMAGING

2. INDICATIONS

3. • 1. Assessment of the gland anatomy e.g size and
shape.
• 2. Assessment of the gland function (hyper- or
hypo- thyroidism).
• 3. Detection of thyroid nodules and differentiate
between cold and hot ones.

4. • 4. Post-operative (e.g. post-thyroidectomy)
assessment
• 5. detection of functioning metastatic tissues
in known cases of thyroid malignancy
 6. Detection of Retrosternal Goiter

5. CONTRAINDICATIONS

6. • 1 .pregnancy
• 2 .Patients with Hypersensitivity reaction to iodine
• 3 .Pertechnetate is excreted in breast milk, so
breastfeeding women are advised to express and
discard breast milk for 26 hours after injection.

7. RADIOPHARMACEUTICALS

8. 99MTC PERTECHNETATE :
• Used mainly in anatomical assessment
• It carries the properties of 99m Tc
• Gamma-emitter = 140 Kev
• Physical half life = 6 hrs.
• Dose: 3-5 mCi.
• Route: IV.
• Advantages: cheap and available

9. 131 I -SODIUM IODIDE:
• Used in full Assessment (Function & Anatomy)
• Gamma-emitter = 364 Kev
• Half life: 8 days.
• Dose: 3 - 5 mCi
• Route: Orally.
• Disadvantage: Relatively expensive , Difficult preparation & B
particle emitter

10. 123 I-SODIUM IODIDE
• Used in full Assessment (Function & Anatomy)
• Gamma-emitter = 159 Kev
• Half life: 13 hours.
• Dose: 100 mCi
• Route: orally.
• Advantage: Pure Gamma emitter (Does not emit B particles)
• Disadvantage: Very expensive with limited availability

11. EQUIPMENT:
• Gamma camera with pinhole collimator

14. PATIENT PREPARATION

15. • 1. Stoppage of anti-thyroid drugs e.g. Carbimazole
for 2 days before scanning.
• 2. Stoppage of thyroid hormones e.g. thyroxin 4
weeks prior to examination.
• 3. The patient should avoid iodinated IV contrast
media e.g. for IVP for 4 weeks before examination.

16. • 4.Stoppage of iodine rich food for one week (fish,
cauliflower milk )
• 5.patients should be fasted 4 hours prior to
examination

17. PATIENT POSITION:
• The patient lies supine, with hyper - extended neck and
the camera anterior to the neck.
• Fixed Distance Between Camera and neck (20 cm )
• Radio-opaque land mark e.g piece of lead or radioactive
tracer is put at chin and suprasternal notch to help detect
actual site of the gland and retrosternalgoiter if present

20. • In patients who are unable to lie supine, a sitting position
may be employed.

22. VIEWS :
• Anterior
• Right & Left oblique
• Whole body scan only in detection of functioning
metastatic tissues in known cases of thyroid malignancy
( Anterior- Posterior –oblique)

23. SCANNING TIME :
• 1. When Tc-99m is used, imaging should begin 15–
30 min after injection.
• 2. When I-131 is used, the images should be
obtained at 2h, 24 hr & 3- 4 days after ingesting
the radioiodine.
• 3.When I-123 is used, images can be obtained as
early as after 4-6 H, then at 16 – 24 H

24. INTERPRETATION

25. NORMAL
• 99 Tc normal uptake : 1-3 % of total dose
• Radioactive iodine 131 I normal uptake :
• Early uptake after 2 h : 10-20 % of total dose
• Late uptake after 24 hours : 20 – 60% of total dose
• In case of evaluating functioning cancer thyroid metastasis
in whole body scan uptake after 3-4 days will appear as
Hot spot any where in the body

26. • Gland Should be situated mid-way between symphysis
menti & suprasternal notch
• butterfly shaped
• Right lobe is somewhat larger than the left
• In 10% of the patients pyramidal lobe may be present.
• Homogenous uniform symmetrical uptake all over the
gland

28. ANTERIOR R ANT. OBLİQUE L ANT. OBLİQUE

29. ABNORMAL STUDY :
• 1. site : ectopic thyroid tissue , retrosternal Goiter
• 2. size : Enlarged ( Goiter )
• 3. Function increased (hyperthroidism ) , decreased
(Hypothyroidism)
• 4 . Distribution  Diffuse ( Graves Disesae )
 Local ( Hot ,cold nodule)

30. • Cold Nodule : 80 % (cyst , abcess ,hematoma ) 20%
Tumor benign ( Adenoma ) ,Malignant (Non functioning
carcinoma)
• Hot nodule :  Solitary (Autonomous nodule, functioning
adenoma or adenocarcinoma )
 Multiple ( multiple nodular goiter )

31. SCINTIGRAPHY WITH TC-99M PERTECHNETATE REVEALED A
DIFFUSELY ENLARGED THYROID GLAND WITH HOMOGENOUS
UPTAKE, SUGGESTING DIFFUSE TOXIC GOITER.

32. RETROSTERNAL GOITER

34. THE ACTIVITY UPTAKE DECREASES WITH VARIABLE SIZES IN
HYPOTHYROIDISM

35. HOT NODULE COLD NODULE

36. • Radioactive iodine Uptake may increase in following :
• Hyperthyroidism ,Iodine deficiency ,Pregnancy ,Recovery phase of subacute,
silent or postpartum thyroiditis ,Rebound after withdrawal of antithyroid
medication ,Lithium carbonate therapy ,Hashimoto thyroidites
• May decrease in the following :
Hypothrodism , Destructive thyroiditis (subacute thyroiditis, silent thyroiditis,
postpartum thyroiditis)

37. Because of the large radiation dose to the thyroid
(approximately one to three rads per mCi
administered), the use of I-131 for thyroid
scintigraphy should be discouraged (except
when a subsequent treatment with I-131 is
planned). (Society of nuclear medicine procedure
guide lines for thyroid scintigraphy)
I-131 is usually spared for metastatic disease
screening for its high radiation dose and
inferior image quality.
Due to its mode of beta decay, iodine-131 is notable for
causing mutation and death in cells that it penetrates,
and other cells up to several millimeters away. For this
reason, high doses of the isotope are sometimes less
dangerous than low doses, since they tend to kill thyroid
tissues that would otherwise become cancerous as a
result of the radiation. For example, children treated
with moderate dose of I-131 for thyroid adenomas had
a detectable increase in thyroid cancer, but children
treated with a much higher dose did not. Likewise, most
studies of very-high-dose I-131 for treatment of Graves
disease have failed to find any increase in thyroid
cancer, even though there is linear increase in thyroid
cancer risk with I-131 absorption at moderate
doses.[2] Thus, iodine-131 is increasingly less
employed in small doses in medical use (especially
in children), but increasingly is used only in large
and maximal treatment doses, as a way of killing
targeted tissues. This is known as "therapeutic
use."

38. • Dr.Mohamed Nader Fouad
• Dr.Asmaa Youssry Alkasaby