Abstract
OBJECTIVES: To develop a simple way to compute the approximated modulation transfer function (MTF) manually using conventional spreadsheet software. METHODS: Basing on an edge-image a method was developed, facilitating computation of the edge spread and line spread function in open-source spreadsheet software (Gnumeric; http://projects.gnome.org/gnumeric/downloads.shtml ). By means of the integrated fast Fourier transformation Fourier coefficients are obtained from the line spread function which can then be plotted vs spatial frequency to obtain MTF-plots. For the experimental evaluation an edge test object was exposed in five commercial CBCT devices for maxillofacial applications. RESULTS: The MTF as obtained from the above-described manual method at 10% modulation ranged between 1.6 and 2.3 cycles/mm. Reproducibility as expressed as relative differences between single assessments ranging between 3% and 11%. The computed MTF-values compare well with results from the literature. CONCLUSIONS: The method introduced can be used to manually and reliably estimate a CBCTs' MTF as one central parameter for the imaging systems' performance.