Impact of subtraction and reconstruction strategies on dual-energy contrast enhanced breast tomosynthesis with interleaved acquisition

Contrast enhanced digital breast tomosynthesis can yield superior visualization of tumors relative to conventional tomosynthesis and can provide the contrast uptake kinetics available in breast MR while maintaining a higher image spatial resolution. Conventional dual-energy (DE) acquisition protocols for contrast enhancement at a given time point often involve two separate continuous motion sweeps of the X-ray tube (one per energy) followed by weighted subtraction of the HE (high energy)and LE (low energy) projection data. This subtracted data is then reconstructed. Relative to two-sweep acquisition, interleaved acquisition suffers from a lesser degree of patient motion artifacts and entails less time spent under uncomfortable breast compression. These advantages for DE interleaved acquisition are reduced by subtraction artifacts due to the fact that each HE, LE acquisition pair is offset in angle for the usual case of continuous tube motion. These subtraction artifacts propagate into the reconstruction and are present even in the absence of patient motion. To reduce these artifacts, we advocate a strategy in which the HE and LE projection data are separately reconstructed then undergo weighted subtraction in the reconstruction domain. We compare the SDNR of masses in a phantom for the subtract-then-reconstruct vs. reconstruct-then-subtract strategies and evaluate each strategy for two algorithms, FBP and SART. We also compare the interleave SDNR results with those obtained with the conventional dual-energy double-sweep method. For interleave scans and for either algorithm the reconstruct- thensubtract strategy yields higher SDNR than the subtract-then-reconstruct strategy. For any of the three acquisition modes, SART reconstruction yields better SDNR than FBP reconstruction. Finally the interleave reconstruct-then- subtract method using SART yields higher SDNR than any of the double-sweep conventional acquisitions.