Purpose: Contrast enhanced digital mammography and tomosynthesis (CEDM and CEDBT) use weighted subtraction of images acquired at energies below and above the k-edge of iodine to enhance the conspicuity of malignant lesions. Traditionally, low energy (LE) and high energy (HE) exposures are taken separately (dual-shot), which allows better energy separation and breast tissue cancellation. However, it is more prone to patient motion artifact. Dual-layer detector allows CEDM with a single shot, eliminating motion between LE and HE images. In this work, we propose the combination of direct and indirect flat-panel imagers (FPI) and an x-ray filter to improve spectral separation of dual-layer detectors for CEDM and CEDBT.
Methods: The system consists of a k-edge filter (200 micron Rh) and a dual-layer detector, with a direct conversion (200 micron a-Se) FPI in the front (LE) and an indirect CsI (400 micron) FPI in the back (HE). We used the VICTRE tool to conduct image simulation of a digital breast phantom (half uniform and half with breast tissue structure), which was inserted with spherical iodinated objects with different sizes and concentrations. The LE, HE and subtracted images were compared for three different conditions: dual-shot, dual-layer (both indirect detectors) and dual-layer (with direct-indirect-filter combination).
Results: Dual-shot offers excellent tissue separation and high iodine SDNR if no patient motion is involved. Iodinated objects have reasonable SDNR values with the k-edge filter and a-Se/CsI detector combination, even with the imperfect energy separation. If the top a-Se FPI is replaced with an a-Se based photon counting detector (PCD) SWAD, the highest SDNR can be obtained.
Conclusion: The combination of direct-indirect FPI dual-layer detector and k-edge filter can potentially produce good breast tissue cancellation and SDNR that approaches that of dual-shot technique. The results are substantially better than dual-layer detectors that uses the same x-ray conversion material.
Dual-energy Imaging, Mammography, Simulation
Not Applicable / None Entered.