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Image Quality Indicator(s) and Software for Computed Radiography (CR)

Description:

OBJECTIVE: Define a standardized method using resident software tools, and/or adapt existing third-party software, to measure an image quality metric (e.g. signal-to-noise ratio (SNR); contrast-to-noise ratio (CNR), etc.) on any CR system. DESCRIPTION: A penetrameter, or IQI, is used to determine radiography quality and qualify (whether a shot can be read and allowed to be interpreted) each x-ray shot processed with regular film in radiographic testing. Computed radiography systems are now used in lieu of traditional wet films to process images in some radiographic testing inspection requirements in the ALCs and field installations. It is widely expected that due to rapid advances in CR technology and with the worldwide effort to eliminate hazardous waste by-product of radiographic testing (i.e., silver, chemicals, etc.), use of CR will increase AF wide. An Image Quality Indicator (penetrameter) is often required when performing radiographic inspection in the ALCs. IQIs are required to ensure that the quality of the radiograph could be trusted to show flaws or defects of interest could be identified. However, visual evaluation of an IQI is subjective, and one of the potential advantages of digital radiography is the ability to implement advanced software tools which allow discrete measurements. One of the findings in the recently concluded CR projects conducted by the AF showed that penetrameters used in film radiography are not always effective when used with CR image processing and cannot always ensure that flaws or defects of interest on CR images are acceptable. An image quality approach implementing measurement of image metrics needs to be developed to ensure that when performing radiographic inspection, defects and flaws of interest could be seen in the CR images at all times. Using image metrics with CR has been evaluated by several programs. The recently concluded AF CR project demonstrated that using resident software tools to measure SNR or CNR resulted in inconsistent measurements, not only from manufacturer to manufacturer, but even within the same region on an image. Third-party software has been developed and is available that reportedly provides consistent SNR data, but integration into AF systems has not been demonstrated. ASTM is implementing CNR guidance for digital detector arrays, but this approach was found ineffective for CR in a Metals Affordability Initiative study. Likewise, IQI development efforts are underway at some OEMs, but have not been demonstrated on CR systems (only on digital detector arrays). It is important to design, develop and create CR IQIs and accompanying software measurement tools to ensure that radiographic images provide the necessary quality required for critical applications. Once validated, verified, and proper probability of detection is conducted, this image quality approach could be used, not just by the AF and the DoD, but by users of CR throughout the world. Using CR, evaluate typical aluminum airframe cracks in specimens or structures up to 2 inches thick. Crack specimens are available as GFE. Access will be provided to up to three types of USAF CR systems (two CR manufacturers) at one or more USAF facilities to collect data. Two different manufacturer"s CR workstations will be provided as GFE for data analysis. Identify types and sizes of cracks in CR images that couldn"t be identified when traditional wet film penetrameter indicates that the CR images are acceptable (i.e., crack visible only at proper technique, but IQI visible at improper technique as well). PHASE I: Research, design and provide a concept demonstration that can be used to detect defects and flaws that could be missed when using traditional wet film penetrameters. Draft a Phase II plan to develop, validate and implement an image quality solution applicable to computed radiography system.commercially available in the US. PHASE II: Finalize CR IQI design, build, validate and verify IQI performance on all types of CR systems qualified for crack detection in the AF inventory (4 systems) using software and crack specimens. Perform POD by demonstrating the flaw detection rate of the new CR IQI and software compared to traditional wet film penetrameter using various specimens with known cracks, and using sample of AF NDI technicians reading images and identifying crack indications. PHASE III: Concern for lack of CR image quality assessment that could be used for radiographic inspection in the AF is not limited to the USAF or to the DoD. A reliable CR images IQI could be used throughout the nondestructive testing industry worldwide. REFERENCES: 1."USAF Computed Radiography System Performance Qualification Test Procedure for Airframe Crack Detection Applications", 24 Oct 2011, AFRL/RXSA (Appendix A of report No. AFRL/RXS 12-002"Computed Radiography Systems for USAF Airframe Crack Detection Applications and Development of System Performance Requirements and Product Description", 2 Feb 2012). 2."Guidelines for the Use of Digital Detector Arrays and Computed Radiology for Aerospace Casting Inspections", Metals Affordability Initiative (MAI) program, 18 Aug 2011.
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