Semi-automated quantitation of Tc-99m pertechnetate trapping as an index of thyroid function

1950 Objectives The purpose of this study was to develop a reproducible unbiased method to quantify thyroid function on a pertechnetate (Tc) thyroid scan. Methods 49 patients (9 males, 40 females; ages 19-83) who underwent Tc thyroid scans followed by 24 hour I-131 thyroid uptake measurements within 1 week analyzed. Each Tc scan was reviewed by a nuclear medicine physician who visually estimated thyroid function on the 4-6 minute images, expressed in terms of 24 hour I-131 uptake. This was performed using comparison with index Tc images that visually compared the uptake of Tc-99m in the thyroid gland vs. the salivary glands, in which the 24 hour I-131 uptake was known. Regions of interest were then drawn over thyroid gland, the salivary glands, and to the right of the sternum for background correction. The thyroid function was calculated by (thyroid counts-background counts)/(thyroid counts+ salivary gland counts). 24 hour I-131 uptake was used as the gold standard. The data was analyzed by Pearson’s correlation, Bland-Altman plots, and cumulative distribution analysis. Results The calculated Tc uptake had a stronger correlation with I-131 uptake with r= 0.96 (95% CI 0.93-0.98) compared with r= 0.79 (0.65-0.88) for the visual estimate (p Conclusions The semi-automated calculated Tc thyroid uptake provides a more accurate, reproducible, and un-biased quantitative estimation of thyroid function than by visual comparison with index images. This method can predict 24 hour I-131 uptake to within 10% accuracy.