iaea human health series publications - SEDIM

8.10. IMAGE DISPLAY QUALITYThe accuracy of the diagnosis and the efficiency of the radiologist are influenced by the conditions underwhich the mammograms are viewed. Viewing conditions may affect the diagnostic potential of even the best qualitymammograms. These conditions are determined by: the luminance and calibration of the monitors used for softcopy interpretation; the luminance of the viewboxes used for hard copy interpretation; the ambient roomillumination or the amount of light falling on the monitor and/or viewbox surface; and effective masking of films onthe viewbox.Contrast is extremely important in the mammography image and is degraded by extraneous light.Consequently, monitors and viewboxes should be positioned so as to avoid light from windows, other monitors orviewboxes, and other sources of bright light, either direct or reflected. General lighting in the room should bediffuse and at a low level.Ambient room lighting is as important as monitor and viewbox luminance for the radiographic readingenvironment. Ambient illumination should be low to improve low contrast object detectability. Glare falling uponthe monitor face and being reflected into the eyes of the radiologist should be as low as possible. In the past, it wasrecommended that the ambient room illumination be no greater than 10 lx and ideally less than 5 lx. Currently,levels between 20 and 40 lx are considered to be more reasonable [69]. Furthermore, it recently has been suggestedthat there is a benefit in terms of reduced eyestrain if room lighting levels are somewhat higher and room finishesare chosen such that light the brightness of the reflected from the walls of the room in the radiologist’s line of sightis similar to the average brightness emanating from the monitors when a grey image (~30% of full imagebrightness) is displayed. However, again it must be ensured that as little of this light as possible falls upon, and isreflected from, the monitor face. Under such conditions, ambient room lighting up to 75–100 lx may be acceptable.It should be confirmed that the luminance of light reflected off the monitor screen toward the eyes of the radiologistdue to ambient light (e.g. tested with the monitor turned off) is considerably less than 1/250 of the maximumluminance provided by full image brightness. This ensures that the reflection of ambient light does not have anappreciable effect on the contrast ratio of the display.Radiologists should experiment with the lighting conditions while viewing the TG18-QC test patterns andalso while viewing clinical mammograms. Once the illumination conditions for reading have been established, theyshould be kept constant, and monitors should be set up for those conditions [70].Illuminance is measured by placing the detector–filter–diffuser combination at the viewbox or monitorsurface, pointed away from and parallel to the surface. These measurements can be influenced by the individualtaking the measurement, especially if he or she stands between a source of light and the detector–filter–diffusercombination, or wears reflective clothing.Some vendors provide software packages and procedures for evaluation of monitor performance. Suchpackages may be convenient for carrying out the assessment and tracking of display performance. If such packagesare used, however, it should be ensured that all the functionality discussed below is assessed.119