This document discusses radionuclide imaging of the thyroid and parathyroid glands. It describes the use of various radiotracers like I-123, I-131, Tc-99m pertechnetate, and Tc-99m MIBI in thyroid scans, thyroid uptake measurements, and parathyroid scans to evaluate conditions like hyperthyroidism, thyroid nodules, thyroid cancer, and hyperparathyroidism. Imaging findings are presented for different pathological cases. Preparation, technique, interpretation and clinical indications for these nuclear medicine procedures are provided.

1. RADIONUCLIDE IMAGING OF
THYROID AND PARATHYROID

2. THYROID SCAN
A radionuclide thyroid scan is routinely used for
the diagnosis of and guiding the management of
many thyroid conditions.

3. RADIONUCLIDES
I-123 is the most favorable because of its excellent
image quality and relatively low radiation exposure.
 I-131 is usually used for therapeutic purposes because
of its beta emission and higher radiation dose.

4. Technetium-99m pertechnetate is used as a substitute
for iodine because it is:
Trapped by the thyroid
Low radiation dose
Readily available and less time consuming
Inexpensive

5. INDICATIONS
Thyrotoxicosis
Thyroid goiter /nodules
Ectopic thyroid
Diagnosis and follow up of Thyroiditis.

6.  Detection and follow up of thyroid cancer recurrences or
metastases.
 Suspected Occult thyroid malignancy.
 Evaluation of congenital thyroid abnormalities.

7. PREPERATION
 Thyroid supplements and exogenous iodine
source should be stopped.
 Use of radiographic contrast media may
depress the uptake of iodine by the thyroid for
up to a month, so imaging studies should be
scheduled accordingly.

8. Antithyroid drugs need not be stopped, as they do not interfere
with the uptake of iodide, only with its organification.

9. TECHNIQUE
I-123 labeled sodium iodide
or
Tc-99m sodium pertechnetate
is given intravenously.
With I-123 images are obtained 2-3hrs later, while with Tc-99m
images are obtained 20-30 minutes post injection, using a high
resolution or a pinhole collimator.

11.  Markers indicating the position of thyroid cartilage and sternal
notch are helpful.
 Additional markers may be used to indicate the site of palpable
nodules.

12.  Usually anterior and oblique views are taken.
 Lateral view of the neck should be added if ectopic thyroid is
suspected.

13. THYROID UPTAKE MEASUREMENT
Thyroid uptake indicates the level of functional activity of the
gland by measuring the trapped proportion of ingested
radioiodine at a certain time (2, 4 and/or 24 hrs) using a special
probe.

15. Normal thyroid uptake is 10–35% in most laboratories at 4
and 24 h

17. Normal thyroid uptake of the gland

18. 24-year-old woman with raised T4, T3 and low TSH values. The
24-hour RAIU was 84%.

19. Anterior Anterior with marker
RAO LAO
Grave’s disease

20. Thyroid images should be interpreted in association with clinical
and lab data (TFTs) as well as the result of thyroid uptake
especially in case of hyperthyroidism due to Grave’s disease since
near normal images can be present in this condition.

21. Autonomous nodules

22. Tc99m Pertechnetate
Anterior RAO LAO
Multinodular gland

23. 59-year-old woman with a very firm thyroid on examination. Lab
data shows low T3 and T4 .The 24-hour RAIU was 7%.

26. ABSENT / REDUCED THYROID UPTAKE
GENERALIZED
o Sub acute thyroiditis
o Ectopic thyroid
o Ectopic hormone production
o Thyroid supplements or exogenous iiooddiinnee ssoouurrccee

27. LOCALIZED
o Colloid cyst
o Non-functioning adenoma
o Multinodular goiter
o Carcinoma
o Local thyroiditis

28. (A) (B) (C)

29.  “Hot” nodules (autonomously functioning thyroid nodules) are
usually not malignant.
 “Cold” nodules ( either hypo functioning or nonfunctioning) can
be malignant in approximately 5-8% of cases.

31. ECTOPIC THYROID
 Most commonly presents in childhood as a nodule or mass at the
base of the tongue.
 Retrosternal thyroids are usually extensions of a multinodular
goiter in the neck.

32.  For imaging I-123 is preferable to Tc-99m because it shows
greater uptake in the thyroid tissue compared with salivary glands
and mediastinum.

34. A 20-year-old female presented with a submandibular neck swelling. Her
biochemical profile was suggestive of hypothyroidism.

35. PERCHLORATE DISCHARGE TEST
 Disorders characterised by a failure to organify the trapped
iodide(of which the most common is Pendred's syndrome).
 Serial images of thyroid are taken giving first I-123 and 2hrs later
sodium or potassium perchlorate which rapidly discharges the
unbound iodide.

36. The normal gland will retain that proportion of the iodide
which has been bound, whereas with an organification
defect most of the thyroid activity will be eliminated.

37. THYROID CANCER
Well differentiated papillary and follicular tumors retain
the ability to accumulate iodine although to a much
lesser extent than normal thyroid tissue.
 This property is used in the detection of local tumor
recurrence as well as distant metastatic spread of thyroid
cancer after surgery by the whole body iodine scan.

38. Post operative I-131
scan
Anterior

39. Post-op I-123
scan
Anterior
Residual neck thyroid tissue

40. Anterior Posterior
I-123
whole body scan

41. I-123
(a) Initial post op scan. (b) Follow-up 1 year after I-131 ablation.

42. Other imaging studies are used particularly when
I-123 or 131 study is negative such as thallium 201
and particularly in high-risk patients FDG-PET/CT
study.

44. PARTATHYROID SCAN
 Scintigraphy using Tc-99m MIBI(methoxy isobutyl-isonitrile) is
currently the preferred nuclear medicine method for
preoperative localization of hyperfunctioning parathyroid tissue.
 it reduces operative time, cost, and operative failure rates.

45.  Normally Tc-99m MIBI is taken by thyroid gland and it clears
over time.
 In the presence of abnormal parathyroid glands the radiotracer is
retained in these glands and are seen as foci of tracer
accumulation.

46. Tc99m MIBI
Early Delayed
Negative parathyroid study

47. Tc99m MIBI Tc99m Pertechnetate

48. Early
Early Delayed
Tc-MIBI

49. THANK YOU