Dual-energy subtraction for contrast-enhanced digital breast tomosynthesis

We have developed a dual-energy subtraction technique for contrast-enhanced breast tomosynthesis. The imaging system consists of 48 photon-counting linear detectors which are precisely aligned with the focal spot of the x-ray source. The x-ray source and the digital detectors are translated across the breast in a continuous linear motion; each linear detector collects an image at a distinct angle. A pre-collimator is positioned above the breast and defines 48 fan-shaped beams, each aligned with a detector. Low- and high-energy images are acquired in a single scan; half of the detectors capture a low-energy beam and half capture a high-energy beam, as alternating fan-beams are filtered to emphasize low and high energies. Imaging was performed with a W-target at 45 and 49 kV. Phantom experiments and theoretical modeling were conducted. Iodine images were produced with weighted logarithmic subtraction. The optimal tissue cancellation factor, w,, was determined based on simultaneous preservation of the iodine signal and suppression of simulated anatomic background. Optimal dose allocation between low- and high-energy images was investigated. Mean glandular doses were restricted to ensure clinical relevance. Unlike other dual-energy approaches, both spectra must have the same peak energy in this system design. We have observed that w, is mainly dependent on filter combination and varies only slightly with kV and breast thickness, thus ensuring a robust clinical implementation. Optimal performance is obtained when the dose fraction allocated to the high energy images ranges from 0.55 to 0.65. Using elemental filters, we have been able to effectively suppress the anatomic background.