Simulation study of quasi-monochromatic X- ray beam performance for X-ray computed mammotomography given various breast compositions and lesion sizes

A quasi-monochromatic X-ray computed mammotomograph (XCT) system is under development. The importance of a near-monochromatic X-ray beam is that tissues of close attenuation coefficients are expected to be more easily separable compared with those from a standard filtered beam. Understanding the behavior of beam hardening, lesion contrast (enhancement), and exposure efficiency for the complete range of breast compositions allows assessment of the feasibility of such an XCT system. In this study, investigated design parameters include tube operating potential and filtration under various combinations of uncompressed breast and lesion thicknesses and breast compositions in order to optimize performance. The simulated X-ray beam was generated from a tungsten target using cone beam imaging geometry. Simulations were run for 10-20% incremental breast compositions of adipose and glandular breast tissue for 8-16 cm thick uncompressed breasts with 1 -10 mm thick soft lesions. For 60-70 kVp tube potentials (corresponding to 35-40 keV mean energy) with ∼500^th value attenuating layer of Ce filtration, minimal beam hardening was <5%, optimal lesion contrast enhancement was 5-10% for 12 and 16 cm breasts of all compositions and lesion sizes. Beyond 60% adipose tissue composition, heavy filtration decreases lesion contrast for the thinnest breast. Optimal exposure efficiency was also seen in this operating range, with better absolute values obtained for thinner breasts of all compositions and thicker lesions in this mammotomographic application. Thus, development of a suitable quasi-monochromatic X-ray beam is possible with commercially available equipment and high-Z K-edge filtration, and can yield optimal characteristics for dedicated mammotomography.