Visibility of Image Quality Indicators (IQI) by Human Observers in Digital Radiography in Dependence on Measured MTFs and Noise Power Spectra

Ewert, U.; Federal Institute for Materials Research and Testing (BAM); Germany

Ewert, U.; Federal Institute for Materials Research and Testing (BAM); Germany
Zscherpel, U.; Federal Institute for Materials Research and Testing (BAM); Germany
Vogel, J.; Federal Institute for Materials Research and Testing (BAM); Germany
Zhang, F.; Dresden International University; Germany
Long, N.X.; VINATOM; Vietnam
Nguyen, T.P.; VINATOM; Vietnam

ID: ECNDT-0550-2018
Download: PDF
Session: X-ray radiography 1
Room: G3
Date: 2018-06-11
Time: 14:30 - 14:50

The visibility of flaws and image quality indicators (IQI) by human operators has been discussed for film radiography (RT-F) over decades. Wire type image quality indicators (IQIs) have been used in Germany for evaluation of the radiographic image quality since 1935 (DIN 1915:1935) and later in most European countries. In the USA and France traditionally hole type IQIs (ASTM E 1025 since 1984 or E 1742 since 1992 or its predecessor MIL STD-543 since 1962) are used. With introduction of digital radiography and the globalization of the NDT market the formulas for prediction of the visibility of wire and hole type IQIs for human observers were discussed and investigated again. Current standard requirements are given in ISO 19232-3, ISO 17636-1 and -2, French RCCM code, ASTM E 747 and ASME BPVC Section V Article 2, Table T-276. The fixed pattern noise of some digital detectors result in different noise spectra, which influences the visibility of different IQIs, depending on the hole diameter. Studies, based on measurement of basic spatial resolution, and contrast to noise ratio, were performed together with presampled modulation transfer function measurements and normalized noise power spectra in dependence on the spatial frequency. Plate hole IQIs, step hole IQIs, and EPS IQIs based on ASTM E 746 were measured to verify the influence of the different parameters. Modelling of digital images was used to verify the used numeric tools. A study has been performed for imaging plates and digital detector arrays to analyse differences. Formulas for the calculation of visibility functions for hole type IQIs are derived. In consequence the standards for characterization and classification of computed radiography (ASTM E 2446, ISO 16371) and radiography with DDAs (ASTM E 2597) need to be revised.