Scanning slit mammography.

The importance of scatter in mammography and the performance of conventional mammographic grids are reviewed. Without scatter control image contrast is significantly degraded. Conventional mammography grids improve the situation; however, their performance is limited. As a result for 5 to 8 cm thick breasts, a more ideal method of scatter control could result in a 25 to 45% improvement in contrast over that possible with conventional grids. One such approach is scanning slit mammography. The principles of this approach are presented along with the design and geometrical specifications of a prototype multiple scanning slit unit. The unit has a measured primary transmission of 91% and scatter transmission of 3%. Similarly measured performance values for a commonly used grid are 62% and 19%, respectively. Compared are images of a 6 cm breast phantom obtained with the scanning slit unit and a conventional grid. The scanning slit unit achieved noticeably greater image contrast with 30% less radiation. Also discussed are the limitations and engineering challenges of the technology.