Investigation of optimum anti-scatter grid selection for digital radiography: physical imaging properties and detectability of low-contrast signals.

Our aim in this study was to evaluate the effect of the grid variations on the imaging performance for a computed radiographic system under identical exposure condition. Digital radiographies using a 20-cm Lucite phantom were performed without grid and with grid ratios of 5:1, 8:1, 10:1, 12:1, and 14:1. The scatter fraction, the incident dose to the image receptor, the Wiener spectrum (WS), and the noise-equivalent quanta (NEQ) were measured. Visibility of low-contrast signals was evaluated using a contrast-detail phantom. The scatter fractions decreased considerably with an increase in the grid ratio. On the other hand, the WSs were increased (the noise property deteriorated) as the grid ratio increased due to a decreased incident dose to the image receptor under the identical exposure condition. The NEQs were improved as the grid ratio increased. The high grid ratios provided higher low-contrast detectability compared to the low grid ratios. Our results indicated that the removal of scattered radiation was very effective in improvement of the NEQ in the digital system under the identical exposure condition.