Discussion on effect of observation circumstances for image in digital radiography

The discriminability of the IQI in the film radiography is affected by the observation circumstance and the luminance of film viewer. ISO17636-2 states that the images of digital radiograph shall be examined in a dimmed room. However, it does not describe requirements for the observation environment in digital radiography, despite the fact that the environment is similar to that of a normal professional PC and the display of the images can be easily adjusted. In this report, the influence of the observation environment in digital radiography was compared as the parameters the wire diameter and the WL value of a display adjustment value when the minimum wire diameter of the image quality indicator (IQI) was percepted, using images of welded steel at t25mm and t50mm. For welded steel of t25mm, differences due to SNRN values and differences due to the observation environment of light and dark room were compared. For t50mm, differences due to the presence or absence of the observation mask for the single wire of wire IQI which is places in front of the display, differences due to the resolution and brightness of the PC monitor, and differences when the WL was adjusted arbitrarily or fixed were compared. For the Digital Radiographic testing (RT-D), the basic spatial resolutions (SRb) were obtained by measuring the profile and applying of visual observation with the duplex wire type IQI. On the other hand, when observing the image of wire type IQI, the observation ways that one was obtain the perceptible image for all wires and another was to get the perceptible single wire image by using the observation mask for watching each wire were applied. Moreover, the influence of window width (WW) and window level (WL) adjustment on the discrimination of wire-type IQI was examined by quantifying it as WW/WL. As a result, it was confirmed that the discriminality in the dimmed room and the adjustment of WW and WL were effective. In addition, using the observation a mask showed that the perception of the adjacent wire image affected observer cognition in IQI discrimination during image observation. When using viewer software profiling, SRb measurements were not affected by the observation environment, but the visual observation was affected by the environment, and when observing images in the dimmed room with RT-D, it was found that adjusting WW and WL had a greater effect on discrimination for images with low SNRN and low contrast.