Evaluation of the Performance of Computed Radiography Systems with Different Sources and Different Configurations

Computed radiography (CR) is a digital radiographic technique, which uses very similar equipment to conventional radiography except that in place of a film to create the latent image, an imaging plate (IP) made of a photostimulable phosphor is used [1]. CR systems are commonly used in medical applications since they have proven reliability over more than two decades. Conversely, the NDT community has discussed the efficacy of film replacement by CR for more than 15 years. Though some standards were introduced in 2005 [ASTM E 2033, CEN EN 14784-2] and in 2013 [ISO 17636-2], CR is currently not included within the French RCCM although the technique is commonly used in US for nuclear applications according to ASME (Section V, article 2). Since 2006, AREVA has had a research and development project on this issue. This project aims to evaluate the performance differences between these two techniques within the framework of the NF standard EN 14784 for the CR and the RCCM for the film. The objective was to build a technical justification report to eventually support introduction of CR into the RCCM. In 2009 the subject gave rise to collaboration between AREVA NP – NETEC and EDFCEIDRE, for a joint project to establish performance limits of CR towards EN 14784 specifications and RCCM image quality indicator (IQI) requirements [2]. In this paper, we present performance comparison results of four different CR systems. The measurements were conducted in 2012 and they demonstrate the current states of achievable image quality in CR. Benchmark comparisons included two gamma sources (Selenium 75 and Iridium 192), and three different material thicknesses. Image quality was assessed in terms of EN 462 and ASTM (E 747, E 1742) IQI. The results have been scored considering ISO 17636-2, RCCM 2007, and ASME V-2010. This also permitted comparison among the different standards. Additionally, detectability measurements have been performed with the Selenium 75 gamma source and one system. Trials considered a real mock-up and different geometry configurations.