A modular approach to generate spectral characteristics of X-ray micro-CT scanner components

At UGCT, the "Centre for X-ray Tomography" of the Ghent University, a wide variety of samples is scanned, requiring different scan conditions and geometries for each application. For every different sample there is an optimal scanner setting, which results in an image with as much contrast as possible and as little noise as possible. In practice it is not possible to perform several test scans to optimise scan conditions for each sample. Therefore there is the need for a simulation program which can simulate the resulting image of a sample for a certain scanner setting. For this purpose, at UGCT an accurate and fast polychromatic projection simulator has been developed (see poster contribution by J. Dhaene et al.). Using this simulation tool we are able to determine the scan conditions yielding the best image quality. To get accurate results it is important to have detailed information on the source energy spectrum and the energy dependent sensitivity of the detector. That is why the projection simulator uses the results of detailed, time consuming Monte Carlo simulations of the actual source and detector used in the scanner. To obtain the characteristics of the source energy spectrum at a given source setting and the energy dependent sensitivity of the detector, the Monte Carlo based simulation program BEAMnrc is used[1]. BEAMnrc is based on the EGS-code developed for coupled transport of photons and electrons[2]. The simulation results are indispensable, but represent also the biggest drawback of our projection simulator: only projection simulations of scans using a source and detector of which the spectral characteristics have already been generated using BEAMnrc can be performed. To make the program more generally applicable, e.g. also for non-UGCT scanners, it is necessary to have a more extended choice available of sources and detectors. Therefore we have investigated if a modular approach to obtain component spectral characteristics is possible. The concept is to simulate only the crucial parts of the source and detector with Monte Carlo simulations and to create a possibility to add new components , e.g. an entrance window in front of the detector. The final goal of this research is to adapt our projection simulator for more generic applications in which the user can select the source type (directional or transmission), the thickness of the source target material, the exit window etc. . As such it will be possible to use our simulation tool for different scanners having their own components. The used methodology and obtained results of this work will be presented