Schemes for the optimization of chest radiography using a computer model of the patient and x-ray imaging system

A computer program has been developed to model chest radiography. It incorp orates a voxel phantom of an adult and includes antiscatter grid, radiograp hic screen, and film. Image quality is quantified by calculating the contra st (Delta OD) and the ideal observer signal-to-noise ratio (SNRI) for a num ber of relevant anatomical details at various positions in the anatomy. Det ector noise and system unsharpness are modeled and their influence on image quality is considered. A measure of useful dynamic range is computed and d efined as the fraction of the image that is reproduced at an optical densit y such that the film gradient exceeds a preset value. The effective dose is used as a measure of the radiation risk for the patient. A novel approach to patient dose and image quality optimization has been developed and imple mented. It is based on a reference system acknowledged to yield acceptable image quality in a clinical trial. Two optimizations schemes have been stud ied, the first including, the contrast of vessels as measure of image quali ty and the second scheme using also the signal-to-noise ratio of calcificat ions. Both schemes make use of our measure of useful dynamic range as a key quantity. A large variety of imaging conditions was simulated by varying t he tube voltage, antiscatter device, screen-film system, and maximum optica l density in the computed image. It was found that the optical density is c rucial in screen-film chest radiography. Significant dose savings (30%-50%) can be accomplished without sacrificing image quality by using low-atomic- number grids with a low grid ratio or an air gap and more sensitive screen- film system. Dose-efficient configurations proposed by the model agree well with the example of good radiographic technique suggested by the European Commission. (C) 2001 American Association of Physicists in Medicine.