iaea human health series publications - SEDIM

8.10.3. Viewbox luminance and viewing conditionsSome facilities using digital mammography print and interpret mammograms from hard copy films. Manyfacilities have the need to view analogue (film) mammograms for comparison with the current (digital) study. It isimportant that these images be viewed under appropriate conditions. Because many of the tests described here areanalogous to those performed on the soft copy displays and use the same equipment, it is convenient to perform thetwo sets of tests together.8.10.3.1. ScopeViewboxes should be positioned so as to avoid light from windows, monitors, other viewboxes and othersources of bright light, either direct or reflected. Viewboxes should have functioning masks in the area around themammograms to exclude extraneous light, which reduces image contrast and low contrast perceptibility, and alsolimits the maximum densities that can be seen without ‘bright lighting’ each image.This procedure should be performed on all viewboxes used for interpretation of screen film mammograms orhard copy digital mammograms.— Objective: To ensure that the luminance of the viewboxes for interpretation or QC of mammography imagesmeets or exceeds minimum levels, that the room illuminance levels are below prescribed levels and thatviewing conditions have been optimized.— Minimum frequency: Annually.8.10.3.2. Instrumentation(1) Illuminance meter (as specified in Table 24 in Appendix II).(2) Luminance meter (photometer) (as specified in Table 24 in Appendix II).8.10.3.3. Methodology(a)Viewing conditions(1) Reproduce the typical ambient lighting conditions for the reading room, including the overhead and tasklighting that is typically used when mammograms are interpreted. Doors and window coverings should be intheir normal (open or closed) positions. If light from other viewboxes can fall on the surface of the viewboxbeing evaluated, those viewboxes should be on, but their viewing surfaces should be covered withradiographs.(2) With the light level set for film reading and the viewbox turned off, measure the ambient luminance of theviewbox with film on it by pointing the photometer at the viewbox. If the photometer used is a near rangecontact type (not telescopic), the distance that the meter is held away from the viewbox surface should bechosen based on the meter’s acceptance angle. A large amount of the viewbox should be included in themeasurement without any surrounding objects.(3) Place the illuminance meter so that its detector is parallel to and facing away from the viewbox surface, withthe rear side of the detector in contact with the viewbox surface. The meter should be held so that the medicalphysicist’s body is not within the angle of acceptance.(4) Take the measurement and record the result of the illuminance falling on the viewbox surface on the viewboxluminance and room illuminance chart (Chart 16 in Annex II).(5) Place the illuminance meter 50 cm from the viewbox with its detector parallel to and facing towards theviewbox surface, centred on the viewbox (Fig. 38).(6) Take the measurement and record the result of the illuminance seen by the observer on Chart 16 in Annex II.(7) Confirm that the viewbox has available appropriate, functioning masks to exclude extraneous light from thelight box.128