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1. ENDOCRINE-THYROID AND
PARATHYROID GLAND
OGBE ALEX
RADIOLOGY DEPARTMENT
KAMPALA INTERNATIONAL UNIVERSITY-WC
05/10/24

2. Thyroid Anatomy and Physiology
The Thyroid gland is located anterior to the tracheal and below the
thyroid cartilage. Laterally, it extends from C5-T1. it weighs
approximately 15-20g.
Anatomically, the gland comprises many follicles of varying size, The
epithelia follicular cells ae the periphery of the follicle synthesize and
secrete thyroid hormone into the follicular lumen, which contains
colloid, where it is stored.
Physiologically, the ingested iodine is reduced to iodide in the proximal
small intestine, which greater percentage is absorbed systemically.

3. Iodine Trapping and organification
The thyroid follicular cells trap(absorb) or uptake iodide by a high-
energy sodium iodide symporter (Thyroid pump). Through the action of
the thyroid pump, the intracellular iodine amount can be raised up to
500 times the amount in circulation in the plasma.
However, in a normal thyroid gland, organification (The incorporation of
iodine into thyroglobulin, for the production of thyroid hormone.)
follows immediately the process of trapping.
The process of iodide uptake, organification and release of thyroid
hormone is being controlled by the Thyroid-stimulating hormone.

5. Radiopharmaceuticals
Radioiodine Iodine-123 and Iodine-131
Because radioiodine is selectively trapped and organified by the
thyroid and incorporated into thyroid hormone, it is an ideal
physiological radiotracer, providing clinically pertinent information
about thyroid function. Iodine-123 (I-123) and iodine-131 sodium
iodide (I-131) are the two radiopharmaceuticals used. Because of
iodine’s rapid gastrointestinal absorption, uptake, and organification,
radioiodine is detectable in the thyroid gland within minutes of oral
ingestion and normally reaches the thyroid follicular lumen by 20 to 30
minutes.

6. Physis of Iodine I-131
Normally, I-131 undergoes beta-minus decay and eventually emits a
principle primary gamma photons of 364 kiloelectron volts, 81%
abundance, with an 8-day physical half-life.
The 364-keV photons are not optimal for gamma cameras. Count
detection sensitivity for I-131 is poor; approximately half of the photons
penetrate a ⅜-inch crystal without being detected. Other higher energy I-
131 emissions penetrate the collimator septa and result in image
degradation. High-energy beta particles of 0.606 megaelectron volt (MeV)
(89% abundance) are also emitted from I-131 decay. They cannot be
imaged but are valuable for therapy

7. Physics of Iodine-123
I-123 decays by electron capture with a half-life
of 13.2 hours. The principal gamma emission is
a 159-keV photon (83.4% abundance), which is
well suited for gamma camera imaging. I-123
emits a small percentage of higher energy
emissions—440 to 625 keV (2.4%) and 625 to
784 keV (0.15%). No beta particle emissions
occur.

8. Characteristics Tc-99m I-123 I-131
Mode of decay Isometric transition Electron capture Beta minus
Physical half-life (T½ 6 hr 13.2 hr 8.1 days
Photon energy 140 keV 159 keV 364 keV
Abundance* (%) 89% 83% 81%
Beta emissions 606 keV
Abundance is the percent likelihood that a certain photon emission will occur with each radioactive decay

9. Radioiodine uptake after oral administration.
In normal subjects the percent radioactive
iodine thyroid uptake (%RAIU) increases
progressively over 24 hours to values of 10%
to 30% (gray area). With Graves disease, the
%RAIU rises at a more rapid rate to higher
levels, often 50% to 80% and greater (lower
broken line). However, some patients with
Graves disease have rapid iodine turnover
within the thyroid with early, rapid, high
uptake at 4 to 12 hours, but returning to a
mildly elevated or even normal uptake by 24
hours (top broken lin

10. Technetium-99m Pertechnetate
Technetium-99m pertechnetate has been used as an alternative to I-
123 for thyroid scintigraphy because of its ready availability from
molybdenum99/Tc-99m generators and its low patient radiation dose.
Physics
The 140-keV photopeak of Tc-99m (89% abundance) is ideally suited for
use with a gamma camera. It has a short 6-hour half-life and no
particulate emissions

11. Pharmacokinetics of Technetium-99m Pertechnetate
Tc-99m pertechnetate is administered intravenously. It is trapped by
the thyroid by the same mechanism as iodine but is not organified nor
incorporated into thyroid hormone. Thus it is not retained in the
thyroid and imaging must be performed early, usually at peak uptake,
20 to 30 minutes after injection.

12. Choice of Radiopharmaceutical
For an adult thyroid imaging, the choice of pharmaceutical is I-
123.
For children imaging, Tc-99m pertechnetate is more the choice of
radiopharmaceutical used. This is because of its low radiation
dosimetry and high count rate. The main drawback is that it is not
organified, not suitable for nodule evaluation or uptake
calculation.
For thyroid cancer imaging, the long half-life of I-131 is an advantage,
allowing time for whole-body washout and improved target-to-
background ratio, increasing detectability of thyroid cancer metastases.

14. Special considerations and precautions
Studies have shown that food stable in iodine and medications
often interferes with thyroid studies. Hence, with this suppression
of uptake by the exogeneous iodine, the success of the imaging
process or uptake measurement is compromised.
Pregnancy: Fetal hypothyroidism, when mother is treated with I-
131 between 10 and 12 weeks.
Nursing mothers: Resumes breast feeding 48hrs after treatment
with I-123 and 24hrs after treatment with Tc-99m pertechnetate.

15. Methodology for Thyroid uptake studies
and Thyroid scan.
Although both studies are performed together, the mode of acquisition
is different. Whereas scans are acquired with a gamma camera, %RAIU study
is usually acquired with a nonimaging gamma scintillation probe detector.
Before the procedure, all the medications that can interfere with the % RAIU
should be discontinued for a time based on their half lives.
4 hours before the appointed time, the patient should not eat anything. This
is to ensure good absorption.
Since, the I-123 and I-131 are usually administered in capsule form, though I-
131 can sometimes be given in liquid form.

16. The unit-dose capsule formulation is convenient to handling and
decreases potential airborne exposure of radioiodine to the
technologist and physicians.
The %RAIU is usually performed at 24hrs after the ingestion,
although some acquired the %RAIU at 4hours and others at both 4
and 24hours.
To calculate the %RAIU, counts are obtained for the patient’s neck
and the thigh (for background). The patient radioiodine uptake is
calculated according to the formula:

17. Normal values
The normal range for the %RAIU is approximately 4%
to 15% at 4 to 6 hours and 10% to 30% at 24hours. The
early %RAIU uptake confirms that %RAIU is indeed
elevated without the need for the patience to return the
next day.
However, the %RAIU measures how much radioactive
iodine is taken up by the Thyroid gland in certain time
period. Thus, it indicate high uptake mean the gland is
hyperactive, when it is low, the gland is hypoactive.

18. Gamma scintillation Probe detector
A nonimaging gamma scintillation probe detector used for thyroid
uptake studies has a 2cm thick x 2-cm diameter sodium iodine
crystal with an open, cone-shaped, single-hole lead collimator
coupled to a photomultiplier tube and electronics.
The probe is place over the thyroid gland to measure the amount
of radioactivity in your gland.

20. Clinical Utility of the Percent Radioactive Iodine Thyroid
Uptake and Thyroid Scan
Graves disease.
The patient is thyrotoxic. The anterior view shows
both thyroid lobes to be plump with convex borders
and evidence of a pyramidal lobe arising from the
isthmus. The thyroid to background ratio is high.
The percent radioactive iodine thyroid uptake was
63%

21. Multinodular Toxic Goiter (Plummer Disease)
Thyroid scan shows multiple areas of
increased uptake consistent with hot nodule
in both lobes. However, there is suppression
of the remaining normal functioning thyroid
gland.

22. THYROID SCINTIGRAPHY
The thyroid scan provides functional, not anatomical information.
Thus, a nodule may be confirmed by manual palpation of ultrasound
scan.
The Thyroid scintigraphy can determine the functional status of a
nodule and thus guide further diagnosis procedure.
On scintigrams, nodules are classified as:
Cold: Hypofunctioning compared to adjacent normal tissues).
Hot: Hyperfunctioning with suppression of the extra nodular gland.
Warm: Increased uptake compared to adjacent tissue but without
suppression of the extranodular tissue).
Indeterminate: Palpable or seen on anatomical imaging but not
visualized on scintigraphy.

23. Cold nodule. Focal decrease in
iodine-123 uptake in the left lobe of
the thyroid that corresponded to a
palpable nodule

24. Warm nodule in euthyroid patient.
Patient presented with a palpable 1.5-cm
nodule. Increased uptake is seen in the
inferior aspect of the right lobe of the
thyroid. The extranodular gland does not
appear to be suppressed. The patient
had normal thyroid function tests

25. Warm nodule. Focal decrease in
iodine-123 uptake in the right
lower lobe of the thyroid.

26. Indeterminate Nodule.

27. PARATHYROID UPTAKE STUDIES
The goal of parathyroid imaging is to identity all sources
of excess parathyroid hormone secretion pre-operatively.
Hence the nuclear medicine parathyroid imaging is
important in the identification of hyper-functioning
parathyroid glands in primary hyperparathyroidism.
Currently, the most widespread preoperative imaging
procedure is the combination of (99mTc)Tc-MIBI
scintigraphy and cervical ultrasound. However Tc-99m
Sestamibi is normally gets highly taken up by the
parathyroid.

28. PARATHYROID SCINTIGRAPHY
After intravenous injection, peak accumulation of Tc-
99m sestamibi occurs in a hyperfunctioning
parathyroid gland at 3 to 5 minutes. It has a variable
clearance half-time of approximately 60 minutes.
Similar rapid uptake occurs in the thyroid; however,
it usually washes out more rapidly than it does in the
parathyroid. This is the rationale for two-phase
parathyroid scintigraphy.

29. Methodologies
Tc-99m sestamibi, 20 to 25 mCi, is injected
intravenously. Imaging begins 10 to 15
minutes later. Generally, two different
acquisition methodologies have been used.

30. Single-Photon Emission Computed
Tomography with Computed Tomography.
Hybrid SPECT/CT systems are increasingly used
because they combine the functional information from
SPECT Tc-99m sestamibi and the anatomical
information from CT

31. Image Interpretation
Initial images at 10 to 15 minutes after injection
typically show prominent thyroid uptake. On
delayed 2-hour imaging, much of the thyroid
uptake has washed out and the hyperfunctioning
parathyroid gland is a focus of residual activity.

32. Parathyroid subtraction scintigraphy. Tc-99 sestamibi and I-123.
A, Tc-99m sestamibi scan. B, I-123 scan. C, Computer subtraction of the I-123 scan from the Tc-
99m sestamibi scan reveals uptake only in the parathyroid, consistent with an adenoma.

33. . Tc-99m sestamibi parathyroid scan, delayed planar imaging method. Patient has hypercalcemia and
increased parathormone. A, Early planar imaging at 15 minutes with Tc-99m sestamibi reveals somewhat
asymmetrical activity with slightly more uptake on the right in the region of the thyroid gland. B, Delayed
imaging at 2 hours demonstrates washout of thyroid activity, and focal uptake on the right is retained,
consistent with a parathyroid adenoma

34. THANKS
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