An Approach for Automation of CT Number Linearity Measurement on the TOS Phantom Image

Abstract

Assessment of the computed tomography (CT) number linearity is an important part in the Quality Control (QC) procedures of CT images. An automated method is needed for simplify the measurement process of this parameter. This study aims to develop an automated method for measuring CT number linearity on the TOS phantom images scanned with Toshiba Aquilion Lightning CT scanner with variations of tube current, tube voltage, and slice thickness. The automation began with segmenting the phantom object with a threshold of - 200 Hounsfield units (HU). Then, the centroid was determined for the phantom mask. The air object inside the phantom and its centroid were segmented utilizing a threshold of - 900 HU. By performing a simple rotation operation between the two obtained centroids (i.e., phantom and air centroids), the central coordinates of Delrin, acrylic, nylon, and polypropylene materials were determined. CT number linearity and its coefficient of determination (R2) were calculated. The proposed method was evaluated with datasets scanned from variations of tube current, tube voltage, and slice thickness. The automated CT number linearity measurements were successfully developed. The CT number linearity showed acceptable results for all variations (R2>0.99). Moreover, no significant changes in CT numbers of all materials compared to the standard values were noticed.