The United States experience in patient dose and image quality

In the United States the Nationwide Evaluation of X-ray Trends (NEXT), a cooperative federal-state survey programme, measures the average radiation air kerma associated with several specific diagnostic X-ray examinations. Chest radiography was surveyed in 1984 and 1986, the abdomen-L/S spine in 1987 and 1989, computed tomography in 1990, and dental radiography in 1993. Since 1984, patient exposure equivalent phantoms have been used for each annual survey. Three examinations, mammography (1985, 1988, 1992); fluoroscopy (1991), and dental radiography (1993) have incorporated image quality test objects. The surveys are comprehensive, collecting data such as screen and film type, whether a grid is used, selected X-ray tube potential, measured beam quality, the measurement of processing speed, and entrance air kerma. The trend in mammography, which has been observed for three separate surveys, shows an overall decrease in the average examination dose during this period of time, while image quality has improved. The main reason for the reduction in dose is the elimination of xerography relative to screen-film mammography. Within screen-film mammography an improvement has been observed in film processing, an improvement in beam quality, and an increase in mean glandular dose for screen-film systems. The fluoroscopy survey showed an average air kerma of 43 Gy.min-1. The image quality evaluation showed 87% of surveyed facilities able to resolve at least the 20 wire mesh (equivalent to 0.8 1p.mm-1); while 51% of facilities had a per cent contrast sensitivity greater than 4%. (Author)