An automation of radial modulation transfer function (MTF) measurement on a head polymethyl methacrylate (PMMA) phantom

Abstract

The measurement of modulation transfer function (MTF) using a head polymethyl methacrylate (PMMA) phantom has been introduced previously. However, measurement is performed using a rectangular region of interest (ROI) at the upper edge of phantom. The purpose of this study is to automatically measure radial MTF using a head PMMA phantom.The head PMMA phantom was scanned using CT scanner in axial mode. Software for an automated radial MTF measurement was developed with MATLAB. The steps of automated measurement were started with segmentation and determination of the center of the image. From the center of the phantom then lines were drawn radially so that it passed over the edge of the phantom. These lines indicated the ROIs for MTF measurement. The profiles of the ROIs were taken. The profiles were then averaged to obtain a single profile called edge spread functions (ESF). The ESF was differentiated to get line spread function (LSF). The Fourier transformation was applied to the LSF to get the MTF. The MTFs resulted from the proposed method were compared to those obtained using a rectangular ROI, different CT scanners, and filters.The software for an automated radial MTF using a head PMMA has been proposed and successfully developed using MATLAB. The MTF 50% values for the rectangular and radial ROIs are 0.30 ± 0.00 cycles / mm and 0.32 ± 0.00 cycles / mm, respectively. The MTF10% values for the rectangular and radial ROIs are 0.58 ± 0.00 cycles / mm and 0.59 ± 0.00 cycles / mm, respectively. This software for automated radial MTF can be used for different CT scanners and different filters. So, it indicates that the radial MTF on the head PMMA phantom is more accurate than rectangular MTF.