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Hai đồng vị phổ biến nhất được sử dụng 123I và 99mTc pertechnetate, sau này là đại lý của sự lựa chọn, bởi vì chi phí thấp hơn và tính sẵn sàng cao hơn. Quét cung cấp một biện pháp của các chức năng i-ốt-bẫy trong hạch so với các mô tuyến giáp xung quanh. | 134 Castro and Gharib Radioisotope Scanning Scintigraphy is the standard method for functional imaging of the thyroid. The two isotopes most commonly used are 123I and 99mTc pertechnetate the latter being the agent of choice because of lower cost and greater availability. Scanning provides a measure of the iodine-trapping function in a nodule compared with the surrounding thyroid tissue. Normally there is uniform tracer uptake throughout both lobes and sometimes even in the isthmus Fig. 1A . On the basis of tracer uptake nodules may be classified as hypofunctioning cold indeterminate warm or hyperfunctioning hot . Most are cold decreased uptake 80-85 Fig. 1B or warm uptake similar to surrounding tissue 10 including cancers and benign nodules 18 . Only the finding of a hot nodule increased nodular uptake with suppression of uptake in the surrounding tissue occurring in 5 of cases is helpful in suggesting autonomously hyperfunctioning adenomas. Multinodular glands exhibit a heterogeneous patchy uptake with increased uptake suggestive of toxic Fig. 1C or nontoxic Fig. 1D multinodular gland. The sensitivity of 123I scanning is about 83 1 whereas that of technetium scanning is about 91 18 . The specificity of thyroid scans is low 25 for radioiodine scans and 5-15 for technetium scans and this low specificity is mostly because other thyroid lesions interfere with uptake of the radioisotopes 1 18 . Because as stated previously most solitary thyroid nodules are cold on scanning and only a fraction of these nodules are malignant 5-15 19 20 a large proportion of positive scans are falsely positive. Because of its low diagnostic accuracy the utility of thyroid scintigraphy in the evaluation of thyroid nodules is limited and at present its major role is in confirming the functional status of a suspected autonomously functioning thyroid nodule. Ultrasonography Current ultrasound technology using high-resolution 5-10 MHz transducers is an excellent method for detection of .
