COMPARISON OF FIXED AND ADJUSTABLE WINDOW WIDTH AND LEVEL SETTINGS INTHE CT EVALUATION OF DIFFUSE LUNG-DISEASE

Objective: The purpose of this investigation was to assess the utility of allowing free adjustment of window width and level in comparison w ith the use of a fixed lung window in the CT evaluation of diffuse lun g disease. Materials and Methods: Six radiologists each judged 36 case s (28 diffuse lung disease and 8 normal) using a standardized form. In half of the sessions, images were viewed in a fixed lung window (leve l = - 500 HU; width = 2,000 HU). In the other sessions, the observer w as able to adjust the window and level freely while viewing the images . Each case was seen twice in separate sessions: once in a fixed lung window and once with window width and level adjusted by the reader. A variety of diagnostic features were evaluated using a 5 point scale. T hese included visibility of fine lung structures, abnormalities of the lung parenchyma, and overall evaluation of the lung. Results: The vis ibility of lung structures was not improved with adjustable window set tings. Receiver operating characteristic (ROC) analysis showed fixed w indows to be superior to adjustable windows for overall evaluation of the cases [fixed A(z) = 0.90, adjustable A(z) = 0.84, p < 0.05, jackkn ife method]. Time to rate each case was increased by 15% with window w idth and level adjustment. Conclusion: Free adjustment of window width and level produced no improvement in reader performance over that ach ieved with fixed window width and level.