Introduction: X-ray imaging is an important part of medicine and plays a crucial role\nin radiotherapy. Education in this field is mostly limited to textbook teaching due to\nequipment restrictions. A novel simulation tool, ImaSim, for teaching the fundamentals\nof the x-ray imaging process based on ray-tracing is presented in this work. ImaSim is\nused interactively via a graphical user interface (GUI).\nMaterials and methods: The software package covers the main x-ray based medical\nmodalities: planar kilovoltage (kV), planar (portal) megavoltage (MV), fan beam computed\ntomography (CT), and cone beam CT (CBCT) imaging. The user can modify the photon\nsource, object to be imaged and imaging setup with three-dimensional editors. Objects\nare currently obtained by combining blocks with variable shapes. The imaging of\nthree-dimensional voxelized geometries is currently not implemented, but can be added\nin a later release. The program follows a ray-tracing approach, ignoring photon scatter in\nits current implementation. Simulations of a phantom CT scan were generated in ImaSim\nand were compared to measured data in terms of CT number accuracy. Spatial variations\nin the photon fluence and mean energy from an x-ray tube caused by the heel effect were\nestimated from ImaSim and Monte Carlo simulations and compared.\nResults: In this paper we describe ImaSim and provide two examples of its capabilities.\nCT numbers were found to agree within 36 Hounsfield Units (HU) for bone, which\ncorresponds to a 2%attenuation coefficient difference. ImaSim reproduced the heel effect\nreasonably well when compared to Monte Carlo simulations.\nDiscussion: An x-ray imaging simulation tool is made available for teaching and research\npurposes. ImaSim provides a means to facilitate the teaching of medical x-ray imaging.
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