RT Journal Article SR Electronic T1 Effects of Thyroid Uptake Probe Placement on 123I Capsule Counts JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 158 OP 158 VO 62 IS supplement 1 A1 Rebecca Sondrol A1 Amy Bell A1 Carlyn Johnson YR 2021 UL http://jnm.snmjournals.org/content/62/supplement_1/158.abstract AB 158Purpose: Precise thyroid uptake measurements are essential in obtaining accurate results that may influence a patient’s care or treatment pathway. Counting of both the 123I capsule and patient thyroid can be greatly affected by the placement of the probe. This study was conducted to emphasize the importance of probe placement when measuring an 123I capsule. Methods: A 62 µCi 123I capsule was placed in an Abbot-Orins No. 6782 thyroid uptake phantom. A total of 17 two minute capsule counts were obtained in 0.5 cm increments from 0 cm to 2 cm in both the horizontal and vertical directions using a Captus 3000 Thyroid Uptake and Well System. All measurements were collected at a distance of 25 cm from the probe with the measuring rod removed from the probe’s field of view (FOV) prior to counting. The capsule counts were averaged and background corrected. The probe height remained the same for all measurements and a level was used to ensure no probe tilt for the horizontal counts. Vertical measurements were obtained by tilting the probe up or down while maintaining the standard probe height. The difference in uptake percentages in each direction was calculated and averaged for every 0.5 cm radius. Results: The average percent uptake error from the center for a 0.5 cm, 1 cm, 1.5 cm, and 2 cm radius was 2.36%, 2.24%, 2.37%, 2.42%, respectively. Using a one-tail paired T-test (alpha value &lt 0.05) of the average percent uptake error compared to 0% at center, a t-value of 63.42 and a p-value of 4.32x10-6 was obtained. Conclusion: Since the p-value being considerably lower than the alpha-value, the results demonstrate that minor measurement errors can produce uptake errors that are statistically significant. These counting errors have the potential to affect a patient’s care, especially if therapy or treatment may be required.