Some Observations On the Basis Material Paradigm
Presentations
TU-IePD-TRACK 1-5 (Tuesday, 7/27/2021) 12:30 PM - 1:00 PM [Eastern Time (GMT-4)]
Purpose: To describe a computational approach to the basis material paradigm and describe some of its applications.
Methods: The basis material paradigm asserts that the linear attenuation coefficient of an arbitrary material can be accurately represented by a linear combination of the linear attenuation coefficients of two dissimilar materials. The combined thicknesses of the basis materials do not, in general, match the thickness of the material being characterized. Adding a third material resolves that issue.Two equations in three coefficients, plus an equation for the volume constraint, complete the theoretical system. Attenuation coefficient data were generated by the program XCOM from NIST. Data for elements from 1 to 83 are tabulated at energies from 1.0 to 150.0 keV in steps of 0.5 keV. Total and partial (coherent scatter, incoherent (Compton) scatter, and photoelectric effect) coefficients are provided. Also included in the package is a library of materials that have been suggested as phantom components, as well as data on tissue composition from ICRU Report 44.
Results: Solutions generally show good agreement in total and partial coefficient ratios (better than 1%) for total and Compton coefficients. Deviations for coherent scattering and photoelectric effect can be several percent. Pairs of solutions for some tissues have been found where photoelectric deviations are in opposite directions. Combinations of these can produce agreement of a few tenths of a percent from 20 to 150 keV.Electron densities calculated using the two-component and the three-component versions of the basis material paradigm match the values for the tissue in question to within a few hundredths of a percent.
Conclusion: The method described produces accurate results and is easy to use. Often the only input needed consists of the names of the material being studied and the suggested simulation components.
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