The Effect of Photon Energy Weighting on X-ray Imaging Based on a Photon Counting Detector

Development of photon counting detectors with the ability of energy discrimination would provide additional information. These detectors could improve the contrast to noise ratio (CNR) using photon energy weighting with energy-dependent weighting factors. The purpose of this study was to evaluate the effect of photon energy weighting using GEANT4 Application for Tomographic Emission (GATE) version 6.0. The photon energy weighting depends on the x-ray attenuation coefficient of contrast elements and background materials. In this study, we simulated the photon counting x-ray imaging system. We designed the cadmium telluride (CdTe) photon counting detector (model PID-350, AJAT, Finland), the micro focus x-ray source (model L8601-01, Hamamatsu, Japan) and two phantoms with GATE. In the first case, we concerned the calcifications in the breast tissue or soft tissue. We defined a cuboid consisting of Poly (methyl methacrylate) (PMMA) material with a height of 40 mm including four CaCO_3 contrast elements with different thickness: 1.0, 3.0, 5.0, and 7.0 mm. In the second case, we designed the second phantom for contrast enhanced digital mammography (CEDM). We defined two cylinders consisting of PMMA material with a height of 30, and 40 mm including four iodine contrast elements with different thickness: 0.3, 0.5, 1.0, and 1.5 mm. The effect of photon energy weighting was investigated in terms of a CNR. According to the results, in all cases, photon energy weighting improves the CNR. The CNR improvements for CaCO_3 with thickness of 1.0, 3.0, 5.0, and 7.0 mm are 1.41, 1.32, 1.43, and 1.56, respectively. For the second phantom with a height of 30 mm, the CNR improvements of iodine contrast elements with thickness of 1.0, 3.0, 5.0, and 7.0 mm are 1.01, 1.03, 1.09, and 1.13, respectively, and for the second phantom with a height of 40 mm, the CNR improvements of iodine contrast elements with thickness of 1.0, 3.0, 5.0, and 7.0 mm are 1.05, 1.07, 1.16, and 1.10, respectively. This study demonstrates that the photon energy weighting using the additional information provide the CNR improvement, which allows better detection of calcium and contrast agent or other contrast elements. KCI Citation Count: 3