Tungsten Target Optimization for Photon Fluence Maximization of a Transmission-Type Flat-Panel X-Ray Source by Monte Carlo Simulation and Experimental Measurement

The cold cathode flat-panel X-ray source is a new type of X-ray source with advantage of smaller footprint and lower-dose imaging than current sources. In this paper, we optimized the thickness of the anode target of a flat-panel X-ray source to maximize the photon fluence of X-rays generated from the device. Utilizing EGSnrc-based Monte Carlo code, X-ray fluence was calculate from the simulated photons deposited in the virtual detector. These results revealed an optimal target thickness at a specific anode voltage to maximize the output of X-ray intensity. For experimental validation, tungsten thin film anodes with different thicknesses were prepared, and a flat-panel X-ray source was fabricated using a ZnO nanowire cold cathode. A figure of merit was introduced to characterize the output efficiency of the X-rays. The experimental results agree well with the simulation results, showing an optimal tungsten-target thickness of 1200 nm at an anode voltage of 40 kV. Using a flat-panel X-ray source with the optimized anode thickness, we took X-ray absorption images of both biological and nonbiological subjects, and high-resolution images were demonstrated.