Bildqualitätsparameter in der digitalen Radiographie: Zur Messung von Modulationsübertragungsfunktion und Wiener-Spektrum

Abstract

The image quality of a radiographic system is characterised by parameters like spatial resolution, noise and contrast resolution. For an objective comparison of different systems these characterisation parameters must be determined with sufficient accuracy under fixed adjustment and evaluation conditions, for a defined plane of observation. Digital systems specifically offer the possibility to calculate transfer functions. The Modulation Transfer Function (MTF) and the Wiener Spectrum (WS) can be calculated directly, using the image data (i.e. edge, slit and homogeneous exposures). Influences of the sampling, which effect especially the MTF calculation due to the aliasing effect, can be sufficiently compensated by the choice of special exposure and evaluation techniques. A quantitative description of physical image quality results from combination of Modulation Transfer Function and Wiener Spectrum in form of the signal/noise ratio or the NEQ (Noise Equivalent Quanta).