Khan, Muzibur; National Research Council, Canada; Canada
Khan, M.; National Research Council Canada; Canada
Brothers, M.; National Research Council Canada; Canada
Session: X-ray radiography 1
Time: 14:10 - 14:30
To obtain radiographic images which are adequate for nondestructive inspection requirements, methods are required to evaluate the performance of the imaging technique. Although visual observation of radiographs can meet part of the quality assessment, this is neither a sufficient nor a reliable way for true assessment of image quality. Image quality indicators (IQI) are used in film-based industrial radiography as means to determine if the quality of the radiographic technique is satisfactory. These IQI gauges are available as thin plaques, step wedges, or wires. Visualization of a specific IQI in a production radiograph measures the sensitivity or effectiveness of a radiographic technique in detecting small density changes in the evaluated object. Sensitivity is usually represented by a percentage of test piece thickness, where the smaller the percentage means a better radiographic sensitivity.
For digital computed radiography (CR), the primary metrics for establishing the performance of a radiographic technique are signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and basic spatial resolution (SRb). However, it has been established that SNR, CNR or SRB do not provide enough information for a quick quantitative performance evaluation of the technique. Moreover, the use of IQI in CR demonstrated that often the required IQI hole can be seen in the radiograph even when the computed radiography system’s performance, in terms of SNR or CNR, is inadequate for the application. To address these limitations, the concept of equivalent penetrameter sensitivity (EPS) is being used in CR. The EPS is a measure of the intrinsic (inherent) contrast sensitivity of an imaging system and gives an indication of how well small density changes in objects can be detected at a given exposure level. Instead of seeing a single IQI hole, an EPS test requires a plate with series of holes and evaluates the number of visible holes. Although the EPS test is a subjective test, it is considered to be a reliable means to establish and monitor a critical performance metric of CR systems.
This paper will discuss the EPS concept for CR systems, reasons for EPS test measurement and its relationship with performance of CR system. A case study that performed during the qualification of our CR system, is also included.