Thyroid Uptake of Tc-99m and Its Agreement with I-131 for Evaluation of Hyperthyroid Function

Abstract

Thyroid uptake and scintigraphy using Tc-99m pertechnetate has proven to be more advantageous than with I-131 iodide, since the images have better quality, the procedure is faster and the patient is submitted to a lower radiation dose. Tc-99m has been used worldwide to study the thyroid function because of a number of advantages such as short half-life, short biological half-life, short effective half-life, short retention in gland and no Beta (β-) radiation, providing low dose to gland (10,000 times less than that of I-131), low cost and readily availability. Otherwise, I-131 with its high radiation burden (1-3 rad/mCi) has long half-life and causes Beta (β-) particle emission. Its main gamma photon has high energy (364 keV) which also causes poor image quality.

Correlation between <sup>99m</sup>TcO<sub>4</sub><sup style="margin-left:-7px;">-</sup> Thyroid Scintigraphy and Blood Test in Primary Hyperthyroidism

“…TcO − and 123 I or 131 I. A correlation coefficient of 0.88 has previously been reported for test values 20 minutes after 99m 4 TcO − and 24 hours after 131 I administration, indicating a strong positive correlation between the two [8]. Recently, the potential of 99m 4 TcO − in predicting 131 I uptake in 131 I therapy has also been reported [9].…”

Determination of Normal Thyroid Technetium-99m Uptake Value in a Single Centre Pakistani Population

“…The mechanism of 99mTc uptake by the thyroid gland is the same as for radioiodine uptake 18 . When there is Iodine deficiency, increased amount of thyroid stimulating hormones are released by the pituitary gland to maintain the circulating levels of T4 within normal limits which in turn stimulate the increased uptake of radio iodine/99mTc pertechnetate whenever administered 19 .…”

“…Due to obvious advantages, I-131 can be replaced with 99mTc as it uses the same mechanism of thyroid uptake 18 . It is useful in assessing patients known to have hyperthyroidism as well as acquiring uptake studies at the same time it's convenient for the patients and compliance rate is better.…”

Comparison of Otsu and an adapted Chan–Vese method to determine thyroid active volume using Monte Carlo generated SPECT images

“…For the individualised planning of radioactive treatment of thyrotoxicosis by Iodine-131 ( I) (radioiodine therapy), single-photon emission computed tomography (SPECT) can be utilised as the imaging modality to determine the active volume of the thyroid gland. SPECT imaging is preferably performed with Technetium-99 m ( Tc) pertechnetate: the uptake levels of Tc pertechnetate and I are highly correlated, whereas Tc SPECT imaging offers better quality, due to lower gamma photon energies, resulting in a lower patient absorbed radiation dose than from I SPECT imaging [ 10 ]. Despite the critical importance of accurate volume determination for the effective prescription of radioactive iodine, there is a lack of consensus among hospitals in Sweden on the preferred method for calculating thyroid volume and Tc uptake levels from SPECT or PS images [ 11 ].…”