Digital chest radiography with a solid-state flat-panel x-ray detector: contrast-detail evaluation with processed images printed on film hard copy

Abstract

Purpose: To evaluate and compare human observer performance in a contrast-detail test by using postprocessed hard-copy images from a digital chest radiography system and conventional screen-film radiographs.

Materials and methods: The digital radiography system is based on a large-area flat-panel x-ray detector with a structured cesium iodide scintillator layer and an amorphous silicon thin-film transistor array for image readout. Images of a contrast-detail phantom were acquired at two exposure levels by using two standard thoracic screen-film systems and the digital system at matched dose. By using images of the phantom processed with standard chest image postprocessing techniques, a four-alternative forced-choice observer perception study was performed, and the number of detectable test signals (disk-shaped objects 0.3-4.0 mm in diameter) was determined for each image type.

Results: On average, observers detected more test signals on digital images than on screen-film radiographs at all diameters up to 2.0 mm and an equivalent number at larger diameters. Test signals with lower inherent subject contrast were detected more readily on digital images than on screen-film images, even when x-ray exposure levels for the digital system were reduced by 20%.

Conclusion: Observer performance in a contrast-detail detection task can be improved by using images acquired with the flat-panel digital chest radiography system as compared with those acquired with state-of-the-art screen-film combinations.