Regensburg 2013 – wissenschaftliches Programm

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ST: Fachverband Strahlen- und Medizinphysik

ST 2: Advances in X-Ray Imaging I

ST 2.2: Vortrag

Mittwoch, 13. März 2013, 15:20–15:40, H41

Characterization of filters applied in Filtered Back-Projection Reconstruction for absorption and differential phase-contrast imaging — •Karin Burger, Michael Chabior, and Franz Pfeiffer — TUM, München, Deutschland

In computed X-ray tomography, window functions like "Ram-Lak" and "Hamming" (absorption) or the "Hilbert filter" (phase-contrast) are commonly used for correct tomographic reconstruction and improvement of image quality in the back-projection process. Choosing the appropriate filter, i.e. the adequate weight of the spatial frequencies, is not obvious. For instance, the noise spectrum of phase-contrast tomography differs considerably from absorption tomography. Existing literature does not provide a clear comparison and characterization, neither of absorption nor of differential phase-contrast (DPC) filters corresponding to the target application. In this study, we examine the modulation transfer function (MTF) of a simulated phantom in contrast to its tomographic reconstructions, obtained by forward- and filtered back-projection with different filters. We thereby optimize the reconstruction with respect to sharpness of edges as well as to remaining noise. Those parameters are especially studied using the "Hilbert filter" in order to improve frequency weighting, considering amongst others the half-pixel shift method introduced in earlier studies. As a result, we provide a set of rules to facilitate the choice of the appropriate filter for both, absorption and DPC tomography. In biomedical imaging, this filter selection allows for individual contrast enhancement depending on the structure of interest (e.g. bones, soft tissue).