A phantom-based evaluation of an exposure equalization technique in mammography

An anatomical filter based exposure equalization technique in mammography i s evaluated quantitatively using a phantom. The evaluation is carried out b y a comparative observer performance study, comparing the equalization tech nique with a conventional one based on visualization of low contrast, 6 mm circular details and high contrast, 0.5 mm and 0.25 mm small size details. These details are situated at the phantom edge, simulating the breast perip hery. Visualization of these details is studied with respect to the paramet ers of tube voltage, optical density, detail location and phantom thickness . Phantom images are interpreted independently by three observers using a f our-point grading scale. Use of the Wilcoxon signed ranks test for paired d ata shows statistically highly significant improvement (p<0.0001) in the vi sualization of details for the equalization technique for all values of the parameters studied. The improvement is independent of tube voltage but dep endent on optical density, detail location and phantom thickness. Optimal p erformance is obtained for detail location closer to the outer border of th e simulated breast periphery and/or further away from the film, as well as for a greater phantom thickness simulating both thick and dense breast.