Effect of window width and viewing distance in CT display

From this preliminary analysis, it may be seen that the noise-limited detectability of a 20 mm diameter object reaches a maximum at a viewing distance of about 4 m at low window widths, when a quarter of the scan field is displayed in a 74 mm diameter image. For the more usual situation in which the whole scan field is imaged, the optimum distance would be in the region of 2 m, considerably larger than the distance at which a radiologist normally views a patient scan. The alternative to increasing the viewing distance is to reduce the size of the image, and the author's hospital has now increased the number of images per film to nine. This should result in an increase in the detectability of low-contrast lesions as well as effecting a considerable reduction in film costs. (author)