Chulalongkorn Medical Journal


Background : Measurement of the thyroid uptake is usually performed with 131Ito determine therapeutic dose in patients treated hyperthyroidismwith 131I. 99mTc-pertechnetate is also trapped by the thyroid glandin a manner and to a degree very similar to iodine. This studymay help identify patients who have discordance in diagnosticand radioactive iodine uptake (RAIU), for better managementand treatment results. The thyroidal uptake performed by99mTc-pertechnetate takes 30 minutes shorter than that performedby 131I for 2 days.Objective : To study the thyroidal uptake by 99mTc-pertechnetate in relationto RAIU in the same patients and to estimate RAIU at 24hr from99mTc-pertechnetate uptake.Design : Prospective and descriptive study.Setting : King Chulalongkorn Memorial Hospital.Materials and Methods : Two hundred and six patients who perform RAIU were enrolledinto the study. Images were acquired with LEHR collimator ofgamma camera system. Images of the syringe were obtainedboth before and after radiopharmaceutical injection; the imageon the injection site was obtained to check for subcutaneousinfiltration. The images for anterior thyroid at 5 minutes and20 minutes after injection were performed. 99mTc- pertechnetateuptake was calculated from thyroid scan image.Results : The study showed that RAIU at 24hr were correlation with 99mTcpertechnetatethyroid uptakes at 5 and 20 minutes asthe following equations: Estimated 24hr RAIU = 14.863 *ln(Pertechnetate Uptake at 5min) + 36.741; R2 = 0.744 Estimated24hr RAIU = 14.441 *ln (Pertechnetate Uptake at 20min) + 34.314;R2 = 0.708 99mTc uptakes at 20min were mostly greater thanuptakes at 5min but 99mTc uptake at 5min showed bettercorrelation than the uptake at 20min. RAIU at 3hr is used todetect early uptake especially in case of rapid turnover and canpredict estimated 24-hour Iodine uptake as equation: Estimatediodine uptake at 24hr = 27.43 *ln (iodine uptake at 3hr) – 34.233;R²= 0.85Conclusion : 99Tc-pertechnetate uptake can be used to estimate 24hr iodineuptake but it depends on the acquisition and calculationtechniques. This is an alternative method to determine RAIdose.


Faculty of Medicine, Chulalongkorn University

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