Simultaneous emission and fluorescent scanning of the thyroid.

A comparison study of lithium-drifted silicon [Si(Li)] and high purity germanium (HpGe) was performed to explore the feasibility of replacing the current Si(Li) detector with the higher-efficiency HpGe detector. The improved efficiency of HpGe permits the use of collimators with higher resolution, which results in improved image quality over that achieved by the current Si(Li) system in use at Vanderbilt with an overall reduction in sensitivity of 29%. Since a 10 mm thick HpGe detector is about 75% efficient at 140 keV, the added advantage exists of simultaneously (a) imaging the stable-iodine distribution within the thyroid by x-ray fluorescence, and (b) the distribution of administered radiotracers such as [99mTc] pertechnetate. This comparison study shows that HpGe can compete with Si(Li) in overall detector efficiency, with the added benefits of better collimation to improve spatial resolution plus the simultaneous imaging of Tc-99m, all at the same equipment cost.