Seminars Archive

Possible ways of improving image quality for X-ray Computed Tomography

Abstract
There are several approaches for improving quality of data acquired at synchrotrons. Some of them are related to changing of an experimental setup, the others require modification of data processing or reconstruction algorithms. Ring artefacts in x-ray tomography often do not allow having a proper segmentation of a reconstructed volume. Standard “hardware” approach consists of acquisition of flat/dark field images. However, for many beamlines intensity profile is often continuously translated in presumably vertical direction during one experiment. Variation in angular position of a monochromator may also shrink the profile. As the result background images consist of two (sometime three) parts: constant one depending on a scintillator, optics and moving one related to a monochromator (or Be window). Additional experiments may allow us to find all three components of a background image. Ring artefacts may also be divided into several groups. Regular ring artefacts (their strength does not depend on angle of rotation) can usually be successfully processed by filtering of original sonogram. An analytical formula for processing of one slice and algorithm for processing several slices are explained. Defects on a scintillator may lead to “bright” ring artefacts, their strength depends on illumination of the scintillator and they are very pronounced for elongated samples. Other ways of improvement of image quality are related to noise processing, image deblurring, taking into account prior information about a sample.