1-3-2 METHODS
1-3-2-1 Measurement of thyroid uptake

Although once essential, it is now only required:
a) in specific cases of hormone synthesis disorder
b) for the purpose of iodine-131 treatment of hyperthyroidism.

Thyroid uptake determination by external probe

a) Perchlorate Test

• Iodide transformation into organic iodine can be tested by perchlorate ion administration (KClO₄^- : 400 mg) .
• These ions competitively force labelled non-oxidized iodides out of the thyroid.
• The test is positive if thyroid uptake decreases by more than 15% within 15 mn post-administration of perchlorate.

Example of a highly positive perchlorate test.

b)Thyroid uptake for therapeutic use

• Objective : Using a test dose of radioactive iodine, to determine the intrathyroidal residence time of iodine. The thyroid radiation burden induced by a potential therapeutic dose of radioactive iodine is then calculated.
• Technique : Test dose of iodine-131. Multiple counts from 3-8 days.
  Determinations of peak initial uptake and the effective period.

Post-maximal thyroid activity represented by exponential decay curve for the period Te. Depends on : - the biological half-life of the tracer Tb, - the physical half-life of the tracer Tp.

• Indications : Hyperthyroidism.
  Particularly: Graves'disease with small goiter, toxic nodular goiter.

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