In Vivo Thyroid 131I Monitoring System using an Imaging Plate

The counting efficiency and detection limit of an in vivo thyroid 131I monitoring system using an imaging plate (IP) was estimated using an anthropomorphic thyroid neck phantom. The counting efficiency of the IP system was approximately constant for thyroid volumes between 11.7 and 20 ml and neck diameters between 10 and 14 cm. The detection limits were distributed from 288 to 451 Bq depending on the combination of neck diameter, thyroid volume and tissue thickness. The IP monitoring system gives a reliable counting efficiency notwithstanding the variation of thyroid volume and neck diameter. The IP system is a new option for thyroid 131I monitoring.