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16 April 1997 Effect of film size on human observer detection of nodules on chest CT images
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The effect of displayed CT image size and observer viewing protocol on human observer ability to detect nodules was measured. Synthetic nodules (3.0 to 5.0 mm) were added to random locations within the lungs of 80 CT images from spiral CT scans of 13 patients. Each test set consisted of 160 images. Each CT image was presented twice in a trial, once with nodule present and once without nodule present. The images were rendered as film transparencies using 6 pixel sizes (0.074 to 0.259 mm). Four observers read the films using two viewing protocols. In one protocol, the observers could vary their viewing distance and were provided with a magnification lens. In the second protocol, the observers viewing distance was fixed at 55 cm. Observers rated the likelihood that a nodule was present in the image and indicated the lung most likely to contain a nodule. The ratings were used to estimate an ROC curve for each trial. Detectability was better using the variable distance viewing protocol compared to the fixed viewing distance protocol. The area under the ROC curve was constant as a function of pixel size for the variable viewing distance protocol (0.881 plus or minus 0.007) and decreased (0.894 plus or minus 0.013 to 0.668 plus or minus 0.053) as a function of pixel size for the fixed viewing distance protocol. Radiologists should be encouraged to vary their viewing distance when reading CT images rendered as films. In order to reduce costs, some radiology departments may be tempted to reduce the CT image size on the film and there by increase the number of CT images on each film. Our study suggests that this manipulation could impair the radiologist's ability to detect lung nodules on CT images of the chest.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Philip F. Judy, Steven E. Seltzer, Uri Feldman, and Francine L. Jacobson "Effect of film size on human observer detection of nodules on chest CT images", Proc. SPIE 3036, Medical Imaging 1997: Image Perception, (16 April 1997);

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