Performance evaluation of aluminium test piece against Catphan700 for computed tomography using modulation transfer function

Abstract

The image quality in diagnostic radiology determines the optimum information about the medical condition of a patient, and the quality is quantified by Modulation Transfer Function (MTF). Catphan700 phantom is a common-ly used phantom to perform MTF measurement on Cone Beam Computed Tomography or conventional computer tomography (CT) system. Image processing with Catphan 700 uses the automated Quality Assurance software restricted to only Digital Imaging and Communications in Medicine images. For this reason, an aluminium (Al) test piece device was fabricated for image processing in different image format for spatial resolution measurement. The performance of the Al test piece was evaluated against Catphan700 phantom using MTF data. The edge spre-ad function (ESF) from the scanned image was evaluated, then differentiated to obtain a Line Spread Function (LSF), from which the MTF was determined by Fourier transform. The 10 % MTF value of the Catphan phantom was found to be ≥ 3.0 (higher in the range 4.0 - 4.6) when compared with the 10 % MTF value of the Al test piece. Sample t-test ANOVA analysis of the data confirmed a high significant (p < 0.005) difference between Catphan phantom and Aluminium test piece, which could be accounted for by the 1.6 g/cm^-3 density difference between the materials. The 10 % MTF values of the Al test piece calculated under the same conditions (at density 2.7 g/cm^-3) with Catphan had only a deviation of ± 0.5 %. The Al test piece could therefore be used for measuring spatial resolution of CT systems, and the study can be useful for directing future research using different materials for the phantom test pieces.

Keywords: Catphan phantom, Modulation transfer function, Diagnostic radiology, Edge spread function, Line spread function