I-123 thyroid imaging

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Patient preparation

Radiopharmaceutical

I-123

Photon energy	159 keV
Adult dose	Routine uptake and scan (100-400 microCi po); thyroid cancer scan (1.5 mCi po)
Peds dose
Physical half life	13.2 hours
Biological half life
Normal distribution	Thyroid, nasopharynx, salivary glands, stomach, colon, bladder, lactating breasts
Pharmacokinetics	Rapidly absorbed from GI tract; detectable activity within gland in minutes; reaches thyroid follicular lumen in 20-30 min; trapping and organification rapid; delayed imaging for background clearance; image at 6 and 24 hours; 10-30% uptake at 24 hours.
Excretion	Renal
Target organ	Thyroid, bladder, stomach, SI
Other	Secreted in breast milk; crosses placenta; may cause cretinism; discontinue interfering medications

Dose and route of administration

100-400 microCi orally in capsule form

Time of imaging

At 4-6 or 24 hours

Equipment

Procedure

Position the patient supine with the chin up and the neck extended.
Position the collimator so that the thyroid fills about two-thirds of the diameter of the field of view.
Obtain anterior, 45-degree LAO and RAO views (move the collimator, if possible, rather than the patient).
Obtain 100k-250k counts per view.
Mark the chin and suprasternal notch.
Note the position and mark palpable nodules and surgical scars.
Place marker sources lateral to the thyroid to calibrate size.

References

Ziessman, Harvey A, O’Malley, Janis P, and Thrall, James M. Nuclear Medicine: The Requisites. 3rd ed. Philadelphia, Pennsylvania: Mosby, 2006. ISBN 0323029469

Patient preparation