IMPROVEMENT OF SIGNAL-TO-NOISE AND CONTRAST-TO-NOISE RATIOS IN DUAL-SCREEN COMPUTED RADIOGRAPHY

A dual-screen computed radiography (CR) technique has been developed t o improve and optimize the overall image signal-to-noise ratio (SNR) a nd contrast-to-noise ratio (CNR). With this technique, two CR screens are exposed together and separately scanned to form a front and a back image. These two images are then superimposed to form an image of imp roved SNR and CNR. A mathematical model has been derived to describe t he improvement and optimization of the SNR and CNR. Based on this mode l, the front and back images should be weighted in proportion to their SNR squared to optimize the SNR of the composite image. Imaging exper iments have been conducted to verify the theoretical model under mammo graphic and chest imaging conditions. The results largely agree with t he theoretical predictions. It has also been found that optimization o f the SNR results in nearly optimal CNR and vice versa. For mammograph ic imaging, a 14%-22% improvement in the SNR and a 13%-19% improvement in the CNR have been demonstrated. For chest imaging, a 31%-36% impro vement in the SNR and a 28%-30% improvement in the CNR has been demons trated. (C) 1997 American Association of Physicists in Medicine.