• Indications: to determine function of thyroid gland or nodule, identify ectopic thyroid tissue (including retrosternal goiter, lingual thyroid, and metastasis), determine size, shape, and symmetry of gland
• 131I: high radiation burden, results available in 48—72 hours, tracer of choice to evaluate metastasis, also used to induce local tissue damage for hyperthyroidism
• 123I: expensive, must be delivered daily, testing requires 2 visits at 4 and 24 hours (shorter half-life)
• 99mTc pertechnetate: trapped by follicular cells, does not measure uptake, low dose radiation, less expensive, image obtained in single visit within 30 minutes
• hypofunctioning ("cold") nodules have a 5—20% malignancy rate, consider lobectomy and isthmusectomy, decision of completion of thyroidectomy based on accuracy of pathology (may consider a frozen section)
• hyperfunctioning ("hot") nodules may be observed, 4% malignancy rate
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