Automatic measurement of CT number in the ACR CT phantom and its implementation to investigate the impact of tube voltage on the measured CT number

Abstract

This study aims to develop a software for measuring the computed tomography (CT) number of multiple materials automatically and investigate the impact of tube voltage on the measured CT numbers. The software was specifically design to automatically measure CT number of multiple materials on images of an ACR 464 CT phantom (Gammex, Inc.). Automatic measurements were performed using the matching technique based on the centroids of the phantom and bone objects. The software was tested first on images of the phantom scanned using a GE Revolution EVO 128-slice with rotation variations from 1° to 10° to evaluate its accuracy against rotation. The software was then implemented on images of the phantom scanned with tube voltage variations of 80, 100, 120, and 140 kV. Results of automatic measurements were compared with manual measurements. Manual measurements were performed using a MicroDicom Viewer (MicroDicom Ltd, Sofia, Bulgaria). The results of the two methods were analysed using a paired t-test. The developed software is able to accurately measure the CT number of multiple materials from images reconstructed with variations of rotation and tube voltage. The results of automatic method are not significantly different from the results of manual measurements with a p-value of >0.05. This study indicated that there is a dependency between the CT number values and the tube voltage. Thus, it is recommended in the quality control (QC) program to measure the CT number of multiple materials using all tube voltages available on the CT machine.