In computed radiography, the optical density of images does not depend on the exposure conditions. Therefore, the same density image is obtained even if the anti-scatter grid ratio is changed. In this case, the more scattered X-rays are removed, the incident dose to the detector decreases. Conversely, the more scattered X-rays increase, then the incident dose increases. We investigated the visual detection of simulated low-contrast object changing incident dose related to quantum noise, scatter fraction related to radiographic contrast and contrast enhancement. This means that visual detectability is more seriously affected by such factors as incident dose, scatter fraction or contrast enhancement. The results indicate that when the incident dose to the detector is almost equivalent to the medium-speed screen-film system, the lower scattered X-rays are more visually detectable. However, when the incident dose is less than that of the high-speed screen-film system, the removal of too much scattered X-rays results in less visual detection. This shows that if the incident dose is too low, it is better not to remove almost all of the scattered X-rays. Contrast enhanced effect is greater in a larger incident dose than in a smaller one.
