[Evaluation of scatter rejection system using a metal filter]

Grids are used for the purpose of reducing scattered radiation. In portable radiography, however, accurate positioning of the grid is difficult. Errors in alignment may cut off the primary beam, which can result in misdiagnosis. We devised a metal filter with scatter rejection properties and evaluated its performance. The filter, which has no intrinsic alignment mechanism, is placed in front of the IP. We evaluated aluminum (Al), copper (Cu), and tantalum (Ta) filters by comparing them with low-ratio grids of 3:1 and 5:1. In the total evaluation, Ta (0.03mm) demonstrated high visualization of light and minute vascular shadow and visceral pleura, and the Bucky factor was lower than that of the 3:1 grid, while the clinical target was very clear. Because of its high atomic number, Ta can absorb a low energy component effectively even if it is very thin. Because of the K absorption edge, Ta also decreases the high-energy components that cause photographic contrast to decline. Therefore, Ta proved to be a highly suitable material for this research. An air gap within 4cm was not effective for the purpose of supporting the reduction in scattered radiation of the metal filter. The method of placing a metal filter in contact with the patient is more practical and makes the system very thin. This system is thought to be effective for portable radiography because it is light, easy to use, and flexible in structure and does not cause misalignment.