Pappaconstantinou Mary, Heston Thomas F., Tran Huyen D.
Philadelphia College of Osteopathic Medicine – Georgia Campus, Suwanee, GA
Private Practice
The radioactive iodine uptake (RAIU) test measures the overall metabolism and kinetics of iodine in the thyroid gland by quantifying how much orally ingested iodide is concentrated in the thyroid gland. Iodine-123 (I-123) is the most commonly used radioisotope for RAIU testing. Iodine is essential for metabolism, as it is required for the intrathyroidal synthesis of triiodothyronine (T3) and thyroxine (T4). Dietary iodide (I), the ionized form of iodine, is rapidly absorbed into the plasma through the gastrointestinal tract. Dietary iodide then enters the follicular cells of the thyroid gland via the sodium-iodide symporter (NIS). NIS utilizes a gradient generated by sodium-potassium ATPase for cotransport. NIS is predominantly located in the basolateral membrane of the thyroid follicular cells, where it can increase the concentration of the iodide in the thyroid gland up to 40 times the plasma level. NIS is one factor that affects the concentration of iodine within the thyroid gland, and its expression is regulated by thyroid-stimulating hormone (TSH). Once in the thyroid gland, iodide undergoes organification into thyroglobulin, where it is used to produce T3 and T4. I-123, a radioisotope of iodine, is often used for RAIU and nuclear medicine thyroid imaging, also known as a thyroid scan. I-123 is an ideal radiopharmaceutical due to its low radiation burden and optimal imaging quality compared to I-131 sodium iodide (NaI). I-123 is produced in a cyclotron by bombarding xenon-124 (Xe-124) or tellurium-123 (Te-123) with protons. I-123 emits gamma radiation at 159 keV and has a half-life of 13 hours, decaying by electron capture to form Te-123. I-123 sodium iodide is administered orally as a pill or liquid. The iodide is rapidly absorbed in the upper gastrointestinal tract. The radioisotope begins concentrating in the thyroid gland within 20 to 30 minutes. RAIU with I-123 is typically measured 24 hours after administration to minimize background activity, with an additional uptake measurement sometimes taken at 4 to 6 hours.
放射性碘摄取（RAIU）试验通过量化口服摄入的碘化物在甲状腺中浓缩的量，来测量甲状腺中碘的整体代谢和动力学。碘-123（I-123）是RAIU试验最常用的放射性同位素。碘对新陈代谢至关重要，因为甲状腺内合成三碘甲状腺原氨酸（T3）和甲状腺素（T4）都需要碘。膳食碘化物（I），即碘的离子形式，通过胃肠道迅速吸收进入血浆。膳食碘化物然后通过钠-碘同向转运体（NIS）进入甲状腺滤泡细胞。NIS利用钠钾ATP酶产生的梯度进行协同转运。NIS主要位于甲状腺滤泡细胞的基底外侧膜，在那里它可以将甲状腺中的碘化物浓度提高到血浆水平的40倍。NIS是影响甲状腺内碘浓度的一个因素，其表达受促甲状腺激素（TSH）调节。一旦进入甲状腺，碘化物会有机化进入甲状腺球蛋白，在那里用于产生T3和T4。I-123，一种碘的放射性同位素，常用于RAIU和核医学甲状腺成像，也称为甲状腺扫描。与碘-131碘化钠（NaI）相比，I-123由于其低辐射负担和最佳成像质量，是一种理想的放射性药物。I-123是在回旋加速器中通过用质子轰击氙-124（Xe-124）或碲-123（Te-·123）产生的。I-123以159 keV发射伽马射线，半衰期为13小时，通过电子俘获衰变形成Te-123。碘-123碘化钠作为药丸或液体口服给药。碘化物在上消化道迅速吸收。放射性同位素在20至30分钟内开始在甲状腺中聚集。使用I-123进行的RAIU通常在给药后24小时测量，以尽量减少背景活性，有时在4至6小时进行额外的摄取测量。
