I-123 vs. Tc- pertechnetate
- I-123 shows both trapping and organification while Tc-pertechnetate shows only trapping
- I-123 more expensive but provides concurrent radioiodine uptake and images with a relatively low radiation dose
- Tc-pertechnetate requires no prior preparation of the patient
- Tc has lower radiation thus higher dose can be used leading to faster scan time
- Tc shows uptake in the salivary glands (unless there’s increased thyroid uptake such as in Graves disease)
Indications for uptake vs scan
- Scan requires higher dose compared to uptake alone
Medications that may decrease iodine uptake
No contrast for 1-2 months prior
Measurements
- Each lobe should measure about 2 x 5 cm
- Slight asymmetry common, right usually bigger than left
- Isthmus can show relatively decreased activity
Cold nodules
Discordant nodules
- Rare case where hot on pertechnetate and cold on I-123
- Avid trapping but not organification within the nodule
- Pertechnetate scans done at 20 minutes so really see the effect of trapping
- Radioiodine performed at 24 hours so see less trapping effect and moreso activity reflecting organification which is why you can get these discordant nodules
- 20% of these are carcinoma
Multinodular goiter
