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There are currently many kinds of imaging plates available on the market, originating from different manufacturers. Each kind of imaging plate distinguishes itself from the others by its particular physical structure and composition, which have a direct influence on the quality of the digital radiographic images obtained. Several kinds of imaging plates were tested to determine how such physical characteristics were correlated to their response in the final image. This characterization process was conducted by determining the thickness of the sensitive layer and by evaluating its grain size and elemental composition. In order to assess the quality of the digital radiographic images, the readout intensity (gray value), basic spatial resolution (BSR) and normalized signal-to-noise ratio (SNRN) were analyzed. As for the final result, it was observed that, in most cases, the smaller the grain and thickness of the sensitive layer, the lower the imaging plate readout intensity and the better BSR and SNRN. Moreover, imaging plates containing a higher iodine concentration were found to be lower resolution. [ABSTRACT FROM AUTHOR]

The image quality of radiographs is determined by reading image quality indicators (IQIs), exposed together with the test object. This has been performed for decades for quality assurance in technical radiography, achieving the present high quality of industrial radiographs. During the last two decades, X-ray film as a detector medium has been increasingly replaced by digital X-ray detectors. Two major technologies are accepted for film replacement: computed radiography and digital radiography with digital detector arrays (DDAs). In 2005, the first set of European Committee for Standardization (CEN) and ASTM International standards was published for computed radiography, and in 2010 the ASTM standards for DDAs were finalized and published. Presently active computed radiography standards and some DDA standards already need a major revision. It was observed by many users that the ¡mage quality for class B of CEN EN 14784-2:2005 is not achievable with most computed radiography systems under the same exposure conditions as used for film exposure following the practice of CEN EN 444:1994 or ISO 5579:1998. A mathematical model was developed and tested, which allows the calculation of the image quality, proven by IQIs, depending on the fixed pattern noise and the efficiency of the imaging plate scanner system for computed radiography. All tested systems provide a fixed correlation between the measured signalto- noise ratio (SNR) and the gray values in the digital images. The maximum achievable SNRmax depends on the fixed pattern noise of the imaging plates (high dose limit). For DDAs, the achievable SNR depends additionally on the calibration procedure and frame integration used for the image acquisition. Depending on the exposure dose, the visibility of IQIs can be predicted using the SNR, the effective attenuation coefficient, ueff, for calculation of the contrast-to-noise ratio (CNR) and the basic spatial resolution of the image for calculation of the normalized CNRN. The diameter of the just visible wire or IQI hole is inversely proportional to the square root of CNRN. This relation is used to evaluate IQI visibility and is presented in this paper. A conversion formula was also derived for calculation of the equivalent penetrameter sensitivity from CNRN. [ABSTRACT FROM AUTHOR]