Visual Detection and Physical Characteristics of Roentgenographic Systems

Abstract

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.