Chemie und Prozesstechnik
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X-Ray Computed Tomography (CT) is applied in industry for flaw detection, flaw evaluation and dimensional measurement. This requires the correct CT system settings for sufficient visibility and detectability of flaws and structure elements. The visibility of indications for human observers on a monitor depends on the square root of the reconstructed flaw area (here pores with diameter < ½ inch) in the cross sectional 2D images, the Contrast to Noise Ratio (CNR) and the Modulation Transfer Function (MTF). This applies also to 2D-projections, meaning also to “normal” digital radiographs. The ASTM guide E 1441 describes three essential functions for prediction of the visibility of small circular indications in slice images of a 3D reconstruction or a 2D reconstruction. This is the Contrast Discrimination Function (CDF), the MTF (see also the revision of ASTM E 1695), and the Contrast Detail Dose (CDD) function. The prediction of the visibility of circular indications in reconstructed slice images can be determined from the Contrast Detail Dose function, which is the combination of CDF and MTF and a physiological factor c. The measurement procedures and formulas for the prediction of the detail visibility by CDD will be corrected, tested and verified by modelling and in a Round Robin Test with modern commercial 3D CT systems of different manufacturers. Conclusions will be reported and recommendations will be given for the correct psychological factor c and the consideration of the influence of artefacts, as e.g. cupping and scatter.