Adjustable anti-scatter grid system for mammography tomosynthesis final report

Abstract

Thirteen Engineering Co. (TEC) was tasked with developing a concept for an anti-scatter grid system that is compatible with mammography tomosynthesis machines, for CancerCare Manitoba (CCM). In the initial phases of the project, 16 concepts were generated. This was then narrowed down to the four most promising designs, from which two concepts were chosen to be developed further. The two designs chosen are the adjustable septa, and the multiple grid changer designs. In the adjustable septa concept the x-ray absorbing septa are redesigned so that they can be rotated. These septa can then be moved to the desirable angle for each image along the tomosynthesis sweep. The second concept is the multiple grid changer. In this design multiple anti-scatter grids with differing set septa angles are used. These grids are stored in a grid rack and then individually moved into the imaging position, as needed for the sweep. After an image is taken the anti-scatter grid is retracted and the next grid is then placed for imaging. To save space the grids are rotated halfway through an imaging sweep and then reused. In this report these two designs are developed further and their performance is compared against a previously selected set of criteria. It was found that the adjustable septa design had superior performance in the sweep angle, number of images per sweep, reliability and sweep completion time categories. The grid changer was better in the minimizing radiation dosage exposure category and both designs had a similar source to image distance. Due to the proprietary nature of tomosynthesis mammography machines, it was not possible to obtain dimensions for an existing device, because of this it was not possible to evaluate the designs based on device size. When both designs were compared to the project objectives, the adjustable septa design's performance exceeded the performance of the multiple grid changer design in many of the design criteria. TEC recommends the CCM should further develop the adjustable septa design. Further development in the areas of computer x-ray modelling and production of prototypes to properly establish the adjustable septa design's x-ray absorption properties, reliability, and manufacturing costs.