Estimating the Modulation Transfer Function at Natural Structures in Clinical CBCT Images Using the Edge Technique.

In dental radiography, where fine details need to be recognizable, image quality and spacial resolution play an important role. This is particularly the case in 3d imaging (CBCT), because the radiation exposure is significantly higher compared to any 2d imaging method. The gold standard for measuring spatial resolution and especially for relating it with contrast is the measurement of the modulation transfer function (MTF). The usual procedure to obtain the MTF is to take a CBCT scan of a test phantom, which consists of different materials. The MTF is then measured at the interface of two materials. In this work, we propose an approach in which we determine the MTF in clinical CBCT-scans at the boundary of physiological, implanted, or restored tooth as well as surrounding tissue structures of different density. It is assumed that all CBCTs inhibit some kind of interface between a radio-dense and radio-translucent area. Following the methodology used by the German standard DIN 6868-161 we developed our own numerical software for the computation of the MTF. The method enables a stable estimation of spatial resolution (MTF) in clinical CBCT-images.