Digital tomosynthesis of the breast is being investigated as one possible solution to the problem of tissue superposition present in planar mammography. This imaging technique presents various advantages that would make it a feasible replacement for planar mammography, among them similar, if not lower, radiation glandular dose to the breast; implementation on conventional digital mammography technology via relatively simple modifications; and fast acquisition time. One significant problem that tomosynthesis of the breast must overcome, however, is the reduction of x-rayscatter inclusion in the projection images. In tomosynthesis, due to the projection geometry and radiation dose considerations, the use of an antiscatter grid presents several challenges. Therefore, the use of postacquisition software-based scatter reduction algorithms seems well justified, requiring a comprehensive evaluation of x-rayscatter content in the tomosynthesis projections. This study aims to gain insight into the behavior of x-rayscatter in tomosynthesis by characterizing the scatter point spread functions (PSFs) and the scatter to primary ratio (SPR) maps found in tomosynthesis of the breast. This characterization was performed using Monte Carlo simulations, based on the Geant4 toolkit, that simulate the conditions present in a digital tomosynthesis system, including the simulation of the compressed breast in both the cranio-caudal (CC) and the medio-lateral oblique (MLO) views. The variation of the scatter PSF with varying tomosynthesis projection angle, as well as the effects of varying breast glandular fraction and x-rayspectrum, was analyzed. The behavior of the SPR for different projection angle, breast size, thickness, glandular fraction, and x-rayspectrum was also analyzed, and computer fit equations for the magnitude of the SPR at the center of mass for both the CC and the MLO views were found. Within mammographic energies, the x-rayspectrum was found to have no appreciable effect on the scatter PSF and on the SPR. Glandular fraction and compressed breast size were found to have a small effect, while compressed breast thickness and projection angle, as expected, introduced large variations in both the scatter PSF and SPR. The presence of the breast support plate and the detector cover plate in the simulations introduced important effects on the SPR, which are also relevant to the scatter content in planar mammography.
The authors would like to thank Steve Pittard for providing technical assistance with the use of Emory University’s High Performance Computer Cluster. This study was supported in part by the National Institutes of Health (NIH) Grant No. RO1-EB002123 from the National Institute of Biomedical Imaging and Bioengineering (NIBIB). This work was also supported by a grant from the Georgia Cancer Coalition (GCC). The contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH, NIBIB, or the GCC.
II. METHODS AND MATERIALS
II.A. Monte Carlo simulation software
II.B. Characterization of scatter to primary ratio
II.C. Study of scatter point spread functions
III.B. Qualitative analysis of the scatter point spread function
III.C. Effect of the breast support plate and detector cover plate on the scatter to primary ratio
III.D. Scatter to primary ratio maps
III.E. Scatter to primary ratio at the center of mass
Data & Media loading...
Article metrics loading...
Full text loading...