Abstract
Traditional simulation techniques such as wave optics methods and Monte Carlo (MC) particle transport cannot model both interference and inelastic scattering phenomena within one framework. Based on the rules of quantum mechanics to calculate probabilities, we propose a new semi-classical MC algorithm for efficient and simultaneous modeling of scattering and interference processes. The similarities to MC particle transport allow the implementation as a flexible c++ object oriented extension of EGSnrc—a well-established MC toolkit. In addition to previously proposed Huygens principle based transport through optics components, new variance reduction techniques for the transport through gratings are presented as transport options to achieve the required improvement in speed and memory costs necessary for an efficient exploration (system design—dose estimations) of the medical implementation of X-ray grating interferometry (GI), an emerging imaging technique currently subject of tremendous efforts towards clinical translation. The feasibility of simulation of interference effects is confirmed in four academic cases and an experimental table-top GI setup. Comparison with conventional MC transport show that deposited energy features of EGSnrc are conserved.
Highlights
Introduction of explicit scattering eventsThe remaining step for estimating the expected detector signal (7) or (8) is to account for explicit scattering events
The feasibility of the algorithm and the variance reduction techniques to model interference and scattering phenomena is demonstrated with five examples motivated by but not exclusive of X-ray Talbot–Lau interferometry
The newly proposed and implemented Monte Carlo (MC) algorithm is feasible for the simulation interference phenomena from microscopic to macroscopic scales as well as for the simulation of scattering effects such as deposited energy
Summary
The remaining step for estimating the expected detector signal (7) or (8) is to account for explicit scattering events. The probability to find a scattered photon of energy E in pixel j depends on the source type S. For incoherent sources this probability is approximated as. Where Psmc (ksc, kS) denotes the probability that a photon with energy c|kS|moving in direction of kS undergoes a scattering event resulting into a photon of energy c|ksc|in direction of ksc in medium m present at location rsc , which is given over the respective cross sections. For coherent sources the above expression has to be adapted by dropping the summation over ksc and rsc and by setting PS(rS, pS) to 1 Thereby interactions and the potentially resulting secondary particles are described in close analogy to incoherent sources, reflecting the similarity between the two processes.
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