Strategies for Film Replacement in Radiography - Films and Digital Detectors in Comparison -

The NDT community has discussed about effective film replacement by Computed Radiography (CR) and the new Digital Detector Arrays (DDA), also known as flat panel detectors, since more than 10 years. Several standards were published by CEN, ASTM and ASME to support the application of phosphor imaging plates in lieu of X-ray film in the year 2005. One of the key concepts is the usage of signal/noise (SNR) measurements as equivalent to the optical density of film and film system class. The radiographic practice with DDAs is not yet described by any standard, but proposals are under discussion. The first qualification standard for DDAs, ASTM E 2597-07, has been published recently. The bad pixel problem has been addressed. Measurement methods were elaborated and tested at BAM for determination of parameters as basic spatial resolution, efficiency, specific material thickness range, contrast sensitivity and image lag. These procedures were used for this study. The achieved image quality is discussed for film replacement by CR and DDAs in weld inspection. New strategies for correct DDA calibration yield an extra ordinary increase of image quality. The contrast sensitivity was enhanced up to 10 times in relation to film radiography. This could not yet be achieved by any other technology. Even restrictions in the spatial resolution, provoked by the individual picture element (pixel) size of the detector, are compensated by the increased contrast sensitivity.