Evaluation of image quality according to the distance to the anterior surfaces on CT with barium composite shielding in a phantom study

Abstract

This study aimed to determine the optimal distance between the evaluated shielding agent and a patient's superficial organs by evaluating the quantitative noise in the image on performing CT scans using an anthropomorphic phantom. The shielding agent was composed of barium sulfate and was employed to protect superficial organs with high radiation sensitivity during the CT scan. More specifically, a barium sulfate (BaSO4)-based shielding agent was employed. The distance between the anthropomorphic phantom and the shielding agent was delineated using a sponge at intervals of 10, 20, 30, and 40 mm, as well as in a no-gap condition. The size of the shielding agent used for the breast was 430 × 205 mm, and the lead equivalent was 0.06 mmPb. To evaluate Hounsfield unit (HU) values and noise on CT imaging when using a barium shielding agent, the region of interest in the phantom was set to 100 mm2. Quantitative noise on CT imaging was observed only in the no-gap condition. Moreover, HU values and quantitative image noise were significantly increased in images scanned with no gap between the shielding agent and the phantom (p < .05), HU values and noise decreased as the distance from the shield to the surface increased. In images in which the shield and phantom surface were in direct contact, streak artifacts were observed only in the no-gap image. Therefore, in CT scans performed using a shielding agent, we conclude that the distance between the shielding agent and surface should be 10 mm or more in order to obtain an image with reduced noise.