Deadtime Error with Iodine-123 Thyroid Uptake Measurements

Abstract

Thyroid uptake measurements performed using iodine-123 (¹²³I) are subject to a systemic error due to deadtime loss when the standard is derived based on a decay factor. Higher deadtime loss with ¹²³I is due to using more activity along with its better detection efficiency, higher count rate, and shorter half-life compared to that of ¹³¹I. The degree of error due to deadtime loss may range from insignificant to extreme, depending on a number of factors. Degree of error is related to the activity administered, the window settings, the age and energy resolution of the instrumentation, and the elapsed time between standard and patient counts.