Materials - xcist/documentation GitHub Wiki
Materials are fundamental to several aspects of X-ray/CT imaging systems, including source and detector filtration, the detector's X-ray conversion materials, and the patient (phantom).
In XCIST, materials are specified in a simple text format. We have provided the CatSim material calculator to produce material files in a consistent and accurate manner. Using this tool, you can quickly specify new materials based on chemical formulas or mass fractions. Detailed instructions are provided within the tool. If you need a new material, please download & use the tool, and, if not a proprietary material, please contribute your new material specification back to XCIST!
At the time of this writing (July 2023), the material folder contained 92 elements, 29 compounds and mixtures, and 40 biological tissues.
The ASCII text-files for the material composition and constants are located in a directory catsim/materials/ and have no extension (files with extension .mac and .rho are obsolete material definition files, and have been moved to the obsolete/materials directory). The first line specifies the number of elemental components. The second line contains the mass density (g/cm3), and the next lines contain the atomic number and the mass fraction of the respective components. The mass density is absolute. The mass fractions are relative (they don’t need to sum to 1 – they are normalized in the code).
Disclaimer: Material files included with CatSim may or may not be precisely correct. In general, you can probably assume that elemental material files are correct, but material files for mixtures may include approximations.
The mass attenuation coefficients of the materials are determined from files that are stored in subdirectories under catsim/materials. These files separate the energy-dependent Compton, photoelectric, and Rayleigh absorption processes for each element. These files were obtained from Geant4, and are used under the Geant4 Software License, found at https://geant4.web.cern.ch/download/license.