Gamex CR 2.0 - exposure calculator for Computed Radiography
Posted: 2013-2-3
By:
Slawomir Mackiewicz, PhD
Source:
Z.U.T. NDT SOFT
The basic requirement for getting a good quality radiograph is the proper exposure of radiographic film. This old truth seems to be underestimated by many users of modern CR systems which are misled by the extensive possibilities of digital image processing in CR viewing software. The underexposure of Imaging Plate seems to be easily corrected by adjustment of contrast and latitude of radiographic image displayed on the computer screen. Even if this approach may be practical in some simple applications (e.g. corrosion monitoring) it is fundamentally wrong and unacceptable in more demanding examinations (e.g. welding inspection).
Inevitable condition for high quality radiograph is sufficiently large number of X-ray photons incident and absorbed by the radiation detector (IP, film, crystal). If the number of absorbed photons per image pixel is too low the radiographic image shows poor Signal-To-Noise (SNR) ratio what is equivalent to poor detectability of fine details in radiographed object. This condition cannot be rectified by digital image processing in CR viewer.
The above consideration is reflected in international standards on Computed Radiography by introduction of requirements for minimal normalized SNR of digital radiographs. Unfortunately the concept of normalized SNR is not as straightforward as film density in conventional radiography, even if both parameters play the same role. Also, the methodology of checking SNR on digital radiographs is much more complex and prone to errors than measurements of density on radiographic films.
All this means that exposure control in Computed Radiography is equally important but much more difficult to achieve than in conventional film radiography. So we are pleased to present the new version of our Gamex CR exposure time calculator for Computed Radiography with gamma-ray sources. This program can greatly help the CR systems users to meet the quality requirements for digital radiographs.
Gamex CR 2.0 is the second, considerably modified version of the program. The most important novelty is a fundamental change in exposure time calculation methodology. It is no longer based on the ISO/CEN speed of IP plates as this approach created some problems for program users. The ISO/CEN speeds specified by the CR systems manufacturers were not always adequate for the exposures executed with gamma-ray sources and independent determination of ISO/CEN speeds was rather difficult task for an industrial NDT laboratory.
The new Gamex CR 2.0 is based on the first principles approach what means that the whole CR process is mathematically modeled starting from the gamma-ray emissions at the radioactive source and finishing at the gray level image retrieved from the exposed IP in the CR reader. The basic parameter controlling the exposure time (in a similar way as the film density) is the normalized Signal to Noise Ratio (nSNR) of the digital radiograph.
To calculate the exposure time for the planned CR examination the user needs to enter to the program only the standard exposure parameters (source activity, material thickness, source to IP distance, imaging plate type etc.) and nSNR required for the radiographic image. Speed (sensitivity) of the used IP is no longer required as it is effectively calculated by the program based on the specification of IP type.
The second most important novelty is the possibility to prepare and printout complete CR techniques with all parameters necessary for their implementation by qualified RT personnel. It is a very convenient tool for RT supervisors who can provide operators with detailed exposure parameters effectively reducing the number of reshoots.
The program functionality is optimized for CR examinations performed in line with major international standards (EN 14784, ASTM E 2446, prEN ISO 17636-2). To this end the selectable SNR values and metal screens combinations are predefined according to the specified standard. The unique feature is the possibility to compensate calculated exposure times for the fading effect of IP plates after exposure.
To learn more about Gamex CR 2.0 program see our web site http://www.ndtsoft.eu.
Inevitable condition for high quality radiograph is sufficiently large number of X-ray photons incident and absorbed by the radiation detector (IP, film, crystal). If the number of absorbed photons per image pixel is too low the radiographic image shows poor Signal-To-Noise (SNR) ratio what is equivalent to poor detectability of fine details in radiographed object. This condition cannot be rectified by digital image processing in CR viewer.
The above consideration is reflected in international standards on Computed Radiography by introduction of requirements for minimal normalized SNR of digital radiographs. Unfortunately the concept of normalized SNR is not as straightforward as film density in conventional radiography, even if both parameters play the same role. Also, the methodology of checking SNR on digital radiographs is much more complex and prone to errors than measurements of density on radiographic films.
All this means that exposure control in Computed Radiography is equally important but much more difficult to achieve than in conventional film radiography. So we are pleased to present the new version of our Gamex CR exposure time calculator for Computed Radiography with gamma-ray sources. This program can greatly help the CR systems users to meet the quality requirements for digital radiographs.
Gamex CR 2.0 is the second, considerably modified version of the program. The most important novelty is a fundamental change in exposure time calculation methodology. It is no longer based on the ISO/CEN speed of IP plates as this approach created some problems for program users. The ISO/CEN speeds specified by the CR systems manufacturers were not always adequate for the exposures executed with gamma-ray sources and independent determination of ISO/CEN speeds was rather difficult task for an industrial NDT laboratory.
The new Gamex CR 2.0 is based on the first principles approach what means that the whole CR process is mathematically modeled starting from the gamma-ray emissions at the radioactive source and finishing at the gray level image retrieved from the exposed IP in the CR reader. The basic parameter controlling the exposure time (in a similar way as the film density) is the normalized Signal to Noise Ratio (nSNR) of the digital radiograph.
To calculate the exposure time for the planned CR examination the user needs to enter to the program only the standard exposure parameters (source activity, material thickness, source to IP distance, imaging plate type etc.) and nSNR required for the radiographic image. Speed (sensitivity) of the used IP is no longer required as it is effectively calculated by the program based on the specification of IP type.
The second most important novelty is the possibility to prepare and printout complete CR techniques with all parameters necessary for their implementation by qualified RT personnel. It is a very convenient tool for RT supervisors who can provide operators with detailed exposure parameters effectively reducing the number of reshoots.
The program functionality is optimized for CR examinations performed in line with major international standards (EN 14784, ASTM E 2446, prEN ISO 17636-2). To this end the selectable SNR values and metal screens combinations are predefined according to the specified standard. The unique feature is the possibility to compensate calculated exposure times for the fading effect of IP plates after exposure.
To learn more about Gamex CR 2.0 program see our web site http://www.ndtsoft.eu.
