Comparison of Material Decomposition Methods in Contrast Enhancement Digital Mammography Based on Photon Counting

Photon counting detector with energy discrimination has made it possible to decompose materials. In this study, we compared two material decomposition methods in CEDM using a Monte Carlo simulation. The K-edge and dual energy imaging methods were used for material decomposition. We designed the cadmium telluride (CdTe) detector based on photon counting using GEANT4 Application for Tomographic Emission (GATE) version 6.0 simulation tools. The CdTe detector was 44.8x44.8 mm(2) and thickness of 1 mm. To verify the material decomposition ability, we designed the phantom with GATE. The phantom was a cylinder of breast equivalent tissue material (ICRV-44) containing iodine inserts at various thicknesses ranging from 0.3 to 1.5 mm. Thicknesses of breast equivalent tissue material was 20, 30, 40, and 50 mm. First, to verify the material decomposition ability of K-edge imaging, we obtained image from 34-44 keY energy window because the K-edge energy of iodine is 33.2 keY. Second, for the dual energy imaging methods, we acquired two images with below and above the iodine K-edge energy using one exposure with energy selective windows. Data for material decomposition algorithm were obtained for various combinations step wedge phantom of breast tissue equivalent materials and iodine. The images from the phantom were used to produce the inverse mapping functions. The ability of material decomposition was investigated in terms of a contrast-to-noise ratio (CNR). According to the results, the CNR with K-edge imaging method was higher than dual energy method. The calculated values of CNR with K-edge imaging method were approximately 1.60 times higher than with dual energy imaging method. Our studies may be used as a basis for future studies on X-ray imaging based on photon counting.