The phantom for quality evaluations of the nonlinear noise reduction filter in multidetector row computed tomography

In this paper we propose the phantom for quality evaluations of the nonlinear noise reduction filter in multidetector row computed tomography (MDCT). A nonlinear filter is a filter whose output is not proportional to its input (CT number or contrast value). Generally, a standard phantom for CT cannot be used for the quality evaluation of such a filter. The maximum feature of our phantom is being able to obtain edge spread functions of a maximum of six edge intensities under the influence of a certain maximum contrast by choosing a slice position...The edge-preserving adaptive filter for selectively eliminating noise in low-dose scanning known as the Quantum Denoising System (QDS) developed by Toshiba Medical Systems was chosen as a nonlinear noise reduction filter for this study. For evaluation of the filter characteristics, three types of evaluation, the noise statistical values (mean and standard deviation of CT numbers), noise characteristics (noise Wiener spectrum, WS) and resolution characteristics (modulation transfer function, MTF) were measured using the phantom. As a result, the statistics value of obtained noise, and WS and MTF were able to demonstrate the performance of the filter clearly. Further, our phantom was able to investigate the capability of edge-preserving adaptive filters such as QDS using MTFs with different edge intensities. As compared with a digital phantom, our actual phantom is considered to be a useful tool in order to know the overall processing results containing the feature of each CT scanner and reconstruction filter of manufacturing companies and the performance of a nonlinear noise reduction filter.