X-ray interaction-induced signal and noise performances of edge-on silicon microstrip detectors for digital mammography

Abstract

We are developing a silicon microstrip-array detector, which is operated in photon-counting mode, for line-scanned digital mammography. To enhance the x-ray interaction efficiency, the x-ray beam is oriented toward the edge of microstrips, known as the edge-on geometry. To predict the fundamental signal and noise performances induced by x-ray interactions, we performed Monte Carlo simulations. Absorbed energy distribtuions were obtained for various tilting angles (5 to 85 degrees) in the edge-on detector geometry for a wide range of incident energies from 1 to 50 keV. Based on the energy-moments theory with the obtained absorbed energy distributions, we estimated various physical performance parameters such as the quantum absorption efficiency, the average energy deposition per interaction, and the Swank noise factor. In addition, relative accuracy and imprecision in photon-energy measurements were estimated. These analyses were extended to the typical poly-energetic mammography x-ray spectra from various target materials such as molybdenium, rhodium and tungsten. Among performance parameters, the quantum absorption efficiency was gradually decreased as the tilting angle increases because of the reduction in pathlength where x-ray photons travel, while others were almost insensitive to the tilting angle. The best signal and noise performances in the edge-on silicon microstrip detector were obtained for the rhodium spectrum.