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How is iodine-131 used to study and treat thyroid conditions?

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What are isotopes and how do they work? — isotope An overview of isotopes.

Iodine-131 is a radioactive isotope widely used in nuclear medicine because it is chemically identical to stable iodine and naturally accumulates in the thyroid gland.12

Diagnostic Use

Physicians use iodine-131 as a tracer to measure thyroid function. Because the isotope emits radiation, its concentration in the gland can be detected using devices like gamma-ray spectrometers, providing a quantitative assessment of the organ's metabolic activity.12

Therapeutic Use

Iodine-131 is also used to treat conditions such as hyperthyroidism, goitre, and thyroid cancer. When ingested, the isotope is taken up by thyroid cells; the resulting radiation destroys a portion of the glandular tissue. This process reduces the size of the gland and lowers the production of thyroid hormones, effectively treating overactive thyroid conditions. While highly effective, this therapy can lead to hypothyroidism and requires careful dosage calculation.435