Effects of radiation dose and display contrast on low-contrast phantom image visibility

摘要

Abstract: Computed radiography (CR) radiographs were generated of a low contrast phantom with 5 mm diameter disks. The radiation exposure incident on the imaging plate was varied from approximately 0.1 mR to approximately 10 mR, with the phantom images printed to film using a range of display contrast settings. Changing the radiation exposure by two orders of magnitude had only a modest effect on disk detection performance (approximately 20%), and much less than predicted by signal detection theory for the perception of noise limited objects. For images generated at approximately 1 and approximately 10 mR, increasing the display contrast markedly improved the disk detection performance (approximately 50%). There was approximate agreement between the experimental data and the corresponding theoretical predictions for the detection of contrast limited objects. For the contrast detail phantom employed in this study, disk detection was primarily contrast limited, with image noise being relatively unimportant. Lesion detection with an anthropomorphic phantom containing a structured background wold be unlikely to change this conclusion, since noise is expected to be most important for low contrast objects viewed against a uniform background. Contrast enhancement, as opposed to increasing radiation exposure, is therefore the method of choice for improving the detection of 5 mm diameter sized low contrast lesions in CR images. !14