X-ray scatter characterization in dedicated breast CT with bowtie filters

The scatter contamination of projection images in cone-beam computed tomography (CT) degrades image quality. The use of bowtie filters in dedicated breast CT can decrease this scatter contribution. Three bowtie filter designs that compensate for one or more aspects of the beam-modifying effects due to the differences in path length in a projection have been studied. The first produces the same beam-hardening effect as breast tissue with a single-material design. The second produces the same beam quality and intensity at the detector with a two-material design and the third eliminates the beam-hardening effect by adjusting the bowtie filter thickness such that the same effective attenuation is produced at the detector. We have selected aluminum, boron carbide/beryllium oxide, and PM MA as the materials for the previously described designs, respectively. These designs have been investigated in terms of their ability to reduce the scatter contamination in projection images acquired in a dedicated breast CT geometry. The magnitude of the scatter was measured as the scatter-to-primary ratio using experimental and Monte Carlo techniques. The distribution of the scatter was also measured at different locations in the scatter image to produce scatter distribution maps for all three bowtie filter designs. The results of this study will be useful in designing scatter correction methods and understanding the benefits of bowtie filters in dedicated breast CT.