RadteraThyroid Uptake and Scan (I-123 / Tc-99m Pertechnetate)
NM+ ContrastHead & Neck
Indications
- Hyperthyroidism evaluation (Graves, toxic nodular goiter, thyroiditis)
- Differentiate causes of thyrotoxicosis
- Functional status of thyroid nodules (hot vs cold)
- Pretreatment quantification for I-131 therapy dosing
Patient prep
- Discontinue interfering medications: antithyroid drugs (methimazole/PTU) 3-5 days, thyroid hormone (levothyroxine ~4-6 weeks, T3 2 weeks)
- Avoid iodinated contrast for 4-6 weeks; avoid amiodarone (months)
- Avoid iodine-rich foods/supplements ~1-2 weeks
- Fast ~2-4 h before oral I-123 capsule (for uptake)
- Verify not pregnant/breastfeeding
Contrast
AgentI-123 sodium iodide (uptake + scan) or Tc-99m pertechnetate (scan only)
RouteI-123 oral capsule; Tc-99m pertechnetate IV
DoseI-123: 100-400 uCi (3.7-14.8 MBq) for uptake/scan; Tc-99m pertechnetate: 1-10 mCi (37-370 MBq)
TimingI-123 uptake at 4-6 h and 24 h; I-123 scan at 4-24 h; Tc-99m scan at 20-30 min
Technique
- Pinhole collimator for thyroid scan; thyroid uptake probe or gamma camera for RAIU quantification
- I-123 photopeak 159 keV; Tc-99m 140 keV
- Anterior and oblique pinhole views with neck extended
- Uptake calculated as % of administered dose at 4-6 h and 24 h (normal 24-h RAIU ~10-30%)
Series / Sequences
| # | Series / Sequence | Plane | Notes |
|---|---|---|---|
| 1 | Radioactive iodine uptake (RAIU) | N/A (probe/quantitative) | 4-6 h and 24 h; compare to standard/neck phantom |
| 2 | Thyroid scan | Anterior + obliques (pinhole) | Marker over sternal notch/palpable nodule |
Key points
- Graves: diffusely elevated uptake; toxic adenoma: focal hot nodule with suppressed remainder; thyroiditis/exogenous: low uptake
- I-123 preferred for uptake/scan (organified, low dose); Tc-99m pertechnetate is trapped only (faster but more background, discordant nodules possible)
- Recent iodinated contrast falsely lowers uptake for weeks
- Confirm pregnancy status before administering radioiodine
References
• SNMMI Procedure Standard for Thyroid Scintigraphy and Uptake 4.0
• ACR-SPR-SNMMI Practice Parameter for Thyroid Scintigraphy and Uptake Measurement
• Radiopaedia: Thyroid scintigraphy link
• ACR-SPR-SNMMI Practice Parameter for Thyroid Scintigraphy and Uptake Measurement
• Radiopaedia: Thyroid scintigraphy link
Source: Researched — verify against your institution
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Reference template — verify and adapt to your scanner, vendor and institution before clinical use. Not a substitute for clinical judgment.