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- 2012 (4) (entfernen)
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- Englisch (4)
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- Computed tomography (4) (entfernen)
A novel approach to strongly suppress artifacts in radiography and computed tomography caused by the effect of diffuse background signals ('backlighting') of 2D X-ray detectors is suggested. Depending on the detector geometry the mechanism may be different, either based on the optical scattering by the fluorescent screen materials into optical detection devices or Compton or X-ray fluorescence scattering by the detector components. Consequently, these erroneous intensity portions result in locally different violations of Lambert–Beer's law in single projections (radiographs). When used as input data for computed tomography these violations are directly observed via modulation of the projected mass as a function of the rotation phase and the samples aspect ratio (dynamics). The magnitude of the diffuse background signal depends on the detector area covered by the projected sample. They are more pronounced the smaller the shadowed area and the stronger the total attenuation. This implies that the reconstruction suffers from additional anisotropic artifacts caused by elongated sample structures. This issue is studied simply by absorption of flat plates in a conventional laboratory radiography set-up and at a synchrotron radiation facility. In the latter case beam hardening artifacts can be excluded due to the monochromatic radiation. The proposed correction procedure requires simple integral intensity offsets as a constant (non-local) light scattering mechanism is assumed.
Incomplete tomographic data sets such as limited view (missing wedge) data represent a well-known challenge
for reconstruction algorithms, since they unavoidably lead to substantial image artefacts. Such data sets may
occur in industrial computed tomography of limited access (e.g. extended components, fixed objects), directional
opacity, limited sample life time or laminographic set-up. We present strategies to effectively suppress the
typical elongation artefacts (e.g. lemon-like deformed pores) by our iterative algorithm DIRECTT which offers
the opportunity to vary the versatile reconstruction parameters within each cycle. Those strategies are applied to
experimental data obtained from metallic foams as well as model simulations. Comparison is drawn to state-ofthe-
art techniques (filtered backprojection and algebraic techniques). Further reference is made to reconstructions
of complete data sets serving as gold standards. For quantitative assessment of the reconstruction
quality adapted techniques based on spatial statistics are introduced.
A novel approach to strongly suppress artifacts in radiography and computed tomography caused by the effect of
diffuse background signals ('backlighting') of 2D X-ray detectors is suggested. Depending on the detector
geometry the mechanism may be different, either based on the optical scattering of the fluorescent screen
materials into optical detection devices or Compton or X-ray fluorescence scattering by the detector components.
Consequently, these erroneous intensity portions result in locally different violations of Lambert Beers law in
single projections (radiographs) as function of the detector area coverage and the magnitude of the attenuation.
The absorption of multiple metal sheets is investigated by monochromatic synchrotron radiation, thus excluding
beam hardening. The proposed correction procedure simply requires the individual subtraction of one and the
same fraction of the primary and transmitted mean intensity, as a constant (non-local) scattering mechanism is
assumed.