An artifact-free thyroid shield in CT examination: a phantom study

This study was to evaluate dose reduction and resulting image quality of a new synthetic thyroid shield based on silicon rubber (SR)-lead (Pb) composites and compare to tungsten paper (WP) and a Radibabarrier thyroid shields in CT examination of the neck. The synthetic SR-Pb thyroid shield had a Pb percentage from 0 to 5 wt% and a thickness of 0.6 cm. Scanning on the neck of an anthropomorphic phantom was performed with and without the SR-Pb, WP, and Radibarrier thyroid shields. The thyroid shields were placed directly on the neck surface. The thyroid dose was measured using radiophoto-luminescence (RPL) detectors. Image quality was characterized by consistency of the Hounsfield unit (HU) on the areas of anterior, posterior and lateral of the neck phantom. Detailed evaluation of the image quality was employed by image subtraction. It was found that the thyroid dose at the surface decreased with an increase of Pb percentage in the SR-Pb shield. The thyroid dose reduction was 34% for a Pb percentage of 5 wt%. The reduction of the dose using WP and Radibarrier were 36% and 67%, respectively. The dose reduction when using the WP and Radibarrier was higher than when using the SR-Pb 5 wt% thyroid shield. However the existence of artifact in the WP and the Radibarrier reduced the image quality, indicated by a significant change of HU, i.e. the increases of HU in the posterior area were 77% for the WP and 553% for the Radibarrier. The SR-Pb shield produced only a very small artifact, resulting in an increase of HU in the posterior area of only 9%. The SR-Pb shield is suitable in the daily clinical setting for thyroid dose reduction in CT examinations while maintaining image quality.