THYROID GLAND
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anatomy and physiology of the Thyroid gland
Clinical indication for thyroid
scintigraphy
1. To
relate the general structure of the thyroid gland to its function.
2. To
correlate thyroid palpitation with scintigraphic findings to determine the
degree of
function in a clinically defined area or nodule.
3. To
locate ectopic thyroid tissue or determine whether a suspected “thyroglossal
cyst” is the only functioning thyroid tissue present.
4. To
assist in evaluation of congenital hyperthyroidism.
5. To
evaluate a neck or substernal mass.
6. To
differentiate thyroiditis and factitious hyperthyroidism from Grave’s disease
and other forms of hyperthyroidism.
Patient preparation:
1. Patient
should always be questioned of prior neck surgery
2. Medications
such as thyroid hormones and anti–thyroid agents which affect the
pituitary–thyroid axis should always be asked.
3. Iodine–containing
food and contrast media like:
Substance Duration of effect
Iodine
containing products
Lugol’s iodine 2 – 4 weeks
Tropical iodine products 2 weeks or longer
Kelp 2
– 4 weeks
Vitamins and Mineral 2 – 4 weeks
Radiographic
Contrast Media
Water soluble intavascular
contrast 2 – 4 weeks
Other oral and fat soluble
contrast 4 weeks or
longer
Thyroid
medications
Thyroxine 4 – 6 weeks
Triiodothyronine 4 weeks or longer
Anti- thyroid
medication
Propylthiouracil 2 – 8 days
Methimazole 2 – 8 days
Other drugs
Salicylates unknown
ACTH, adrenal steroids 8 days
Competing ions
Perchlorate 1 week
Pertechnetate 1 week
Radiopharmaceuticals used
1.
Tc99m
pertechnetate
a. T½ : 6 hours
b. keV : 140
c. Dose : 5 – 10 mCi
d. Absorbed
dose : 0.20
mrad/µCi
e. Advantages
: Less
expensive
More readily
available
More rapid
examination
f.
Disadvantages : Trapped
but not organified
Activity in
esophagus or vascular structures
can be misleading
Poor image
quality when uptake is low
2.
Iodine – 123
a. T½ : 13 hours
b. keV : 159
c. dose : 10 – 20 µCi (uptake only)
: 100 – 400 µCi (imaging)
d. Absorbed
dose : 11
mrad/Ci
e. Advantages : Better
for visualization of retrosternal
thyroid
tissue
Yields
better images when uptake is low
f.
Disadvantages : Higher
cost
Activity
in esophagus or vascular structures
can
be misleading
3.
Iodine–131
a. T½ : 8 days
b. keV : 364
c. Dose : 6 µCi (uptake only)
d. Absorbed
dose : 1100
mrad/ µCi
Acquisition of images
1. When
Tc99m pertechnetate is used, imaging should begin 15–30 minutes after injection
at 100,000 to 200,000 or for 5 minutes whichever comes first.
2. When
I–123 is used, images can be obtained 3–4 hours after and after 16–24 hours at
50,000–100,000 counts or 10 minutes.
Image findings:
1.
Normal
findings
a. Normal
thyroid appears “butterfly–shaped” structure with uniform symmetrical
distribution of activity. The right lobe is often slightly larger than the left
and the isthmus is usually not visualized.
 |
| Normal Thyroid Scan |
 |
| Thyroid Scan with no gland uptake. Either the patient didn't stop the above mentioned medication or has prior radiological examination with contrast media injected. If patient stopped medication and has no prior radiological examination, then the zero uptake is attributed to Thyroiditis |
2.
Abnormal
findings
a. Gland
enlargement and visualization of functioning or non–functioning thyroid
nodules. The role of scintigraphy is to determine whether a nodule concentrates
tracer.
 |
| Notice the high concentration of Technetium at the thyroid gland and diminished background uptake, all indicative of hyperthyroidism |
b. Non–functioning
nodules are known as cold nodules and can be benign adenoma, cyst, hematoma,
inflammation or carcinoma.
 |
| Cold Nodule at lateral side of left lobe |
 |
| Cold Nodule at lateral side of Right lobe |
Fine needle
aspiration biopsy (FNAB) is usually done to further evaluate the cold nodule
and if surgery is warranted thus there is a probability that patient will come
back to the department and do I–131 Whole Body Scan or Ablation therapy.
c. Hot
nodules are generally benign
 |
| Hot nodule at the inferior pole of Left lobe |
 |
| Hot nodule at inferior pole of Right Lobe |
d. Depending
on the machine used, normal uptake is between 0.5 to 5%, above this value may
indicate Grave’s thyrotoxicosis.
I–131 Whole Body Scan
1. This
is indicated to determine the presence and location of residual functioning
thyroid tissue and/or functioning thyroid cancer.
2. For
detection of functioning metastases, absence of residual normal thyroid is
required since it requires a TSH level of 30 – 50 microU/ml or more and can be
achieved by waiting 4–6 weeks.
PARATHYROID
GLAND
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anatomy and physiology of the parathyroid gland
Clinical indication of
parathyroid scintigraphy
1. To
localize hyperfunctioning parathyroid tissue which results from a tumor in one
of the parathyroid glands or from hyperplasia of all four glands. This is
useful to help the surgeon find the lesion thus shortening the time of the
procedure.
Procedure of the test
1.
Using Tc99m
pertechnetate–Thallium 201 subtraction:
a. After
2.5–3 mCi Thallous chloride are administered intravenously and allowed to clear
from the major vessels, an anterior image of the mediastinum is acquired
b. 5–10
mCi Tc99m pertechnetate are administered through the intravenous line
c. After
5–10 minutes, an anterior image of the neck is acquired for the same number of
counts as Thallium image.
2.
Tc99m setaMIBI
/ Tetrofosmin
a. A
20 mCi Tc99m sestaMIBI or Tetrofosmin is injected.
b. An
early image, 10–15 minutes after tracer administration is obtained which
demonstrates tracer uptake in the thyroid gland.
c. A
second image obtained 2–3 hours later will show decreased tracer uptake in the
thyroid gland but persistent tracer activity in parathyroid adenoma.
 |
| Parathyroid Adenoma at left lobe |
 |
| Parathyroid adenoma at right lobe |
THE ADRENAL
GLAND
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anatomy and physiology of the Adrenal gland
Clinical Indication of adrenal
gland scintigraphy
1. To
aide in the diagnosis of pheochromocytoma or neuroblastoma
I–131 Methyliodobenzylguanidine
(MIBG) Scan:
0.5 mCi I–131 MIBG or 10 mCi MIBG
administered intravenously is used to identify sites of excessive catecholamine
secretion within the adrenal bed or in metastatic sites outside of these areas
which maybe visualized in the liver, bone, lymph nodes, heart or lungs.
Patients should receive several drops
of Lugol’s iodine at least 1 day before tracer administration and for 6–7 days
thereafter. Lugol’s solution is a concentrated solution of potassium iodide.
The solution saturates the thyroid gland with cold iodine, preventing the
uptake of any “free” radioiodine (radioiodine not attached to MIBG) that may be
present in the tracer.
Whole body images should be acquired
at 5 cm/minutes and static images of neck, chest, abdomen and pelvis at 24 and
48 hours.
Normally, MIBG uptake is visualized in
the liver, spleen and heart. The salivary gland and bladder may also be
visualized due to uptake of free iodine in the tracer.
 |
| Normal MIBG Scan |
 |
| Positive MIBG Scan of Left Adrenal Gland |
 |
| Positive MIBG Scan of Left Adrenal Gland, however, there is increased concentration of the tracer at the thyroid gland. Patient was not given Lugol's iodine prior to MIBG injection. |
Drugs to avoid prior to study
1. Tricyclic
antidepressants and related drugs – should be avoided for 6 weeks prior to
study.
a. Amitrypline
and derivatives (Elavil, Endep, Etrafon, Triavil, Amitril, Emitrip, Enovil)
b. Amoxapin
(Asendin)
c. Loxapin
d. Doxepin
(Adapin, Sinequan)
e. Imipramine
and derivatives (Tofranil, Imavate, Janimine, Presamine, SK – Pramine,
Tipramine)
2. Anti–hypertensives
a. Labetalol
(Normodyme, Trandate)
b. Calcium
channel blockers
c. Reserpine
(Serpasil, Sandril)
3. Sympathetic–amines
– should be avoided for 2 weeks prior to
study
a. Pseudophedrine
(Halofed, Sudafed, Sudrin, others)
b. Phenylpropanolamine
HCl (Propagest, Sucrets Cold Decongestants, Entex, others)
c. Phenylephrine
HCl (Neo–synephrine, Alconefrin, Rhinail, others)
d. Ephedrein
4. Cocaine
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