Simple computation of the approximated Modulation-Transfer-Function (MTF) using spreadsheet-software: method and evaluation in five maxillofacial CBCT-devices.

OBJECTIVES:: To develop a simple way to compute the approximated modulation transfer function (MTF) manually using conventional spreadsheet software.

METHODS AND MATERIALS:: Basing on an edge-image a method was developed, facilitating computation of the edge spread (ESF) and line spread function (LSF) in open-source spread-sheet software (Gnumeric; https://projects.gnome.org/gnumeric/downloads.shtml ). By means of the integrated Fast Fourier Transformation (FFT) Fourier coefficients are obtained from the LSF which can then be plotted versus spatial frequency to obtain MTF-plots. For the experimental evaluation an edge test object was exposed in five commercial Cone Beam Computed Tomography (CBCT) devices for maxillofacial applications.

RESULTS:: The MTF as obtained from the above described manual method at 10% modulation ranged between 1.6 cycles/mm 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.