Thyroid & Adrenal
The usual dose of Il31 for thyroid scanning is:
a. Whereas ultrasound allows anatomic evaluation, radionuclide scans allow assessment of thyroid function.
b. Technetium pertechnetate (99mTc) is taken up rapidly by the normal activity of follicular cells. It is trapped by follicular cells, but not organified. 99mTc has a short half-life and low radiation dose. Its rapid absorption allows quick evaluation of increased uptake (so-called hot) or hypofunctioning (so-called cold) areas of the thyroid.
c. 123I and 131I iodine scintigraphy is also used to evaluate the functional status of the gland . Both are trapped by active follicular cells and organified. 123I has a shorter half-life (12-13 hours) and allows a quicker image.
d. Advantages of scanning with 123I include a low dose of radiation (30 mrad) and short half-life. 123I is a good choice for evaluating suspected lingual thyroids or substernal goiters.
e. 131I has a longer half-life (8 days) and emits higher levels of β-radiation. 131I is optimal for imaging thyroid carcinoma. It is the screening modality of choice for the evaluation of distant metastasis.
f. Radionuclide scanning demonstrates the function of thyroid nodules as hot (excess uptake) or cold (no uptake) in comparison to surrounding tissue.
g. Malignancy has been shown to occur in 15% to 20% of cold nodules and, additionally, in 5% to 9% of nodules with uptake that is warm or hot, thus mandating a continued aggressive approach to clinically suspicious nodules, even if they are not cold.
h. Positron emission tomography (PET) with 18F-fluorodeoxyglucose can be used to provide three-dimensional reconstruction images.