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
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.
10.
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.
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.
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%.
24.
25.
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
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.
30.
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.
33.
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.
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.
43.
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.
Thyroid scintigraphy. Normal thyroid uptake of the gland.
99 `TcO4
Graves disease in a 24-year-old woman. Laboratory values were as follows: T4 = 16.7 μg/dL, T3 = 311 ng/dL, and TSH < 0.01 μIU/mL. The 24-hour RAIU was 84%. Anterior distant image obtained with Tc-99m pertechnetate shows an enlarged thyroid. The target-to-background activity is increased to such an extent that the submandibular salivary glands (arrowhead) are barely visualized. Note the appearance of the pyramidal lobe (large arrow). The round photopenic area (small arrow) in this and subsequent figures represents the 2-cm lead marker placed at the suprasternal notch.
Typical pattern of Grave’s disease with uniform gland uptake and decreased background
activity in the surrounding soft tissue
Autonomous nodules. patients with solitary 'hot‘ nodules of overactive thyroid tissue and relative suppression of the remainders
Multinodular gland
Late-stage Hashimoto thyroiditis
Scintigraphic pattern of thyroiditis where poor uptake and lack of delineation of thyroid
gland borders are the typical features
Solitary 'cold' nodules in three patients subjected to FNA.
(A) Benign non-functioning adenoma (arrow); (B) carcinoma (arrows);
(C) chronic thyroiditis affecting only the right lobe.
Thyroid scan and CT image (sagittal section) showing dual ectopia - sublingual and suprahyoid - with absence of normal thyroid
The patient with hemiagenesis presented with a neck swelling and a normal thyroid profile. The thyroid scan revealed normal tracer uptake in the right lobe of the thyroid and absent tracer uptake in the region of the left lobe of the thyroid. CT images confirmed the finding
The case of triple ectopia was a 20-year-old female who presented with a submandibular neck swelling. Her biochemical profile was suggestive of subclinical hypothyroidism. The thyroid scan revealed three areas of abnormal tracer uptake in the region of the base of the tongue and the suprahyoid and the subhyoid locations. CT images showed hyperdense soft tissue in the region of base of tongue and hyperdense tissue with cystic degeneration in suprahyoid and subhyoid locations
Imaging does not discriminate between iodide that is trapped in the thyroid and that which has been both trapped and organified.
Postoperative I-131 whole-body study with no functioning thyroid tissue in the neck or the rest of the body. Note the physiologic uptake in the salivary glands, stomach, and urinary bladder
I-123 24-h whole-body scan following surgical removal of thyroid gland for differentiated carcinoma. Residual neck thyroid tissue with or without residual tumor is evident (arrow)
Anterior and posterior views of an I-123 whole body scan of a patient with thyroid cancer after surgical resection who is now presenting for I-131 therapy. The scan shows multiple foci of intense activity in the neck, mediastinum, thorax, abdomen, and right humerus. These findings suggest widespread disease with bone involvement
Initial (a) and follow-up (b) I-123 24-h whole-body scans showing resolution of the neck
activity (arrow) 1 year after I-131 postoperative ablation
image of an F-18 FDG PET/CT study of a patient with differentiated thyroid cancer showing residual tissue in the nick (arrow head)
Negative parathyroid study
Parathyroid adenoma. 99 "'Tc-MIBI images at 10 min (A) and 3 h (B) showing a persistent focus of activity inferior to the right lobe of the thyroid; image (C) shows normal thyroid uptake
Ectopic adenomas are usually sited in the superior mediastinum, often adjacent to the aortic arch