Rationale and Objectives
Radiologic image details are best discriminated at luminance levels to which the eye is adapted. Recommendations that ambient light conditions are matched to overall monitor luminance to encourage appropriate adaptation are based on an assumption that clinically significant regions within the image match average monitor luminance. The current work examines this assumption.
Materials and Methods
Three image types were considered: posteroanterior (PA) chest; PA wrist; and computed tomography (CT) head. Luminance at clinically significant regions was measured at hilar region and peripheral lung (chest), distal radius (wrist), and supraventricular white matter (head). Average monitor luminances were calculated from measurements at 16 regions of the display face plate. Three ambient light levels—30, 100 and 400 lux—were employed. Thirty samples of each image type were used.
Results
Statistically significant differences were noted between average monitor luminances and clinically important regions of interest of up to a factor of 3.8, 2, and 6.3 for chest, wrist, and CT head images respectively ( P < .0001). Values for the hilum of the chest and distal radius were higher than average monitor levels, whereas the reverse was observed for the peripheral lung and CT brain. Increasing ambient light had no impact on results.
Conclusions
Clinically important radiologic information for common radiologic examinations is not being presented to observers in a way that facilitates optimized adaptation. This may have a significant impact on the ability of the observer to identify details with low contrast discriminability. The importance of image-processing algorithms focussing on clinically significant abnormalities rather than anatomic regions is highlighted.
Ambient lighting in a medical imaging reading room has a significant impact on image interpretation and hence on diagnostic efficacy ( ). Excessive ambient lighting impacts the visualization of normal and abnormal features in two ways. First, the reflected ambient lighting increases the luminance in the darker areas of the displayed image and reduces the contrast ratio ( ). Second, the lighting interferes with the eye’s adaptation to the luminance emitted from the screen resulting in a diminished ability to detect subtle contrasts within the gray levels of the image ( ).
Light adaptation, which largely results from changes in the concentrations of photochemicals in the retina, enables our eyes to function effectively over an enormous range of lighting, which includes more than 10 log 10 values ( ). However, it has long been established that optimum response to changes in luminance occurs within a narrow range of values around the average luminance level to which the eye is adapted ( ). This has significant consequences for the interpretation of diagnostic images.
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Figure 1
Luminance discrimination at a particular adaptive state (100 cd/m 2 ). Adapted from Badano A, Flynn MJ, Kanicki J. High fidelity medical imaging displays. Bellingham, WA: SPIE Press, 2004.
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Materials and methods
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Results
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Table 1
Mean Luminance (cd/m 2 ) at Each of the 16 Sites Measured for the Chest Image Along With the Luminances at the Hilum and Left and Right Lungs
Site 30 lux 100 lux 400 lux 1 5539.1 66.744.8 66.342.9 2 31.725.5 29.519 31.323.9 3 23.618.4 24.421.5 20.817.5 4 62.645 73.542.8 65.835.7 5 8254.5 81.653.5 76.746.8 6 44.650.6 41.742.1 39.538.9 7 13.912.2 31.128.3 33.237.2 8 120.952.1 10746.1 10545.5 9 108.2 76.6 108.479.5 96.677.7 10 23374.2 236.472.4 23578 11 203.475.1 203.774.1 228.658.2 12 82.979.9 78.982.4 74.880.6 13 61.916.4 57.65.2 6114.9 14 72.140.8 69.637.7 70.337.8 15 70.935.3 69.334.5 70.636 16 64.17.3 62.25.4 63.53.5 Overall mean 77.3 (16.9) 83.8 (17.4) 83.7 (17.2) Hilum 124.628.4 131.930.1 131.132.4 Right lung 21.719 21.918.8 23.321.9 Left lung 25.719.8 28.822.6 33.529
Standard deviations are shown in italics; standard error of the mean in parentheses.
Table 2
Mean Luminance (cd/m 2 ) at Each of the 16 Sites Measured for the Wrist Image Along With the Luminances at the Region of Interest (Distal Radius)
Site 30 lux 100 lux 400 lux 1 625.4 611.0 58.810 2 70.733.9 75.953.4 70.649.1 3 6328.8 66.977 6639.3 4 65.31.6 62.91 62.41 5 60.810.6 58.910.4 58.410.2 6 89.664.1 92.394.3 80.163 7 37.926.4 30.921.6 39.537 8 65.61.7 63.91 63.31 9 621.3 60.11.4 602.2 10 136.1147 142.1146.5 124.2132.7 11 65.164.8 69.484.8 39.528.8 12 651.3 63.11 63.31 13 57.32.6 56.11.21 56.41.9 14 63.34.1 61.61.42 64.213.5 15 63.42.9 61.85.4 60.89.9 16 63.22.3 68.11 62.31.2 Overall mean 68.2 (12.5) 68.1 (15.8) 64.4 (11.4) Distal radius 127.864.8 130.360.3 13062.8
Standard deviations are shown in italics; standard error of the mean in parentheses.
Table 3
Mean Luminance (cd/m 2 ) at Each of the 16 Sites Measured for the CT Brain Image Along With the Luminances at the Region of Interest (White Matter)
Site 30 lux 100 lux 400 lux 1 19.37.7 177.5 16.88.4 2 266.4237.1 298.6227.4 247.7237.1 3 202.3246.9 228.5238.6 265.6231.1 4 35.556.5 27.19.2 27.111.4 5 67.1128.6 105.3153 64.1107 6 156.7228.4 31.5117.8 149.9229.3 7 112.5208.7 75.4186.4 63.3178.1 8 21.713.7 120.9176.7 123206 9 143.9203.7 155.8200.9 244.7240.1 10 20.795.2 71.2166.4 107.6208.2 11 10 18.861.8 34.6118.5 12 216.9250.1 295.2254.7 232.4246.5 13 21.15.9 21.16.9 31.731.7 14 315.8230.7 280.3238.9 206212.6 15 334.3241.6 147201.2 196.8210.4 16 22.7 10.4 20.9 10.3 19.417.4 Overall mean 122.4 (30.8) 119.7 (38.6) 126.9 (31) White matter 23.45.3 24.76.0 20.36.6
Standard deviations are shown in italics; standard error of the mean in parentheses.
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Discussion
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