Visual detection and physical characteristics of roentgenographic systems. Investigations on chest imaging chains

The relationship between physical characteristics (physical resolution, large object contrast and radiographic mottle) and visual detection parameters was evaluated in a water phantom. To measure visual observer performance a minified Snellen E-plate made of gold (three contrast zones) and a high contrast lead bar test pattern were investigated. A trial to test four types of equipment chains for chest radiography was further done with the E-plate technique by simulating a clinical radiography with an Alderson thorax phantom. The observer performance of the high contrast lead bar test pattern showed a good linear correlation to the physical parameters. However, none of the physical system-related parameters fully predicted the visual detectability when the equipment chains were investigated with the E-plate technique. In Alderson phantom studies the rare-earth screens and the air gap technique considerably reduced the radiation dose compared with that of the ordinary grid technique chest radiography, without impairing visual detectability significantly. The RP- and spotfilm techniques showed relatively poor properties of visual detectability.