Radiographic images are 2D images which capture variable attenuation characteristics in a material or component. 22 An X-ray source emits fluxes of X-ray photons that pass through or interact with the sample. Any interaction, via scattering or absorption, removes the photon from the X-ray beam. The attenuation coefficient (µ) is a material property which describes how easily a X-ray can pass through a material. The attenuation coefficient of a material depends on the type of material (atomic number and density) and the photon energy of the radiation. The X-ray attenuation often varies in space for heterogeneous materials comprised of either multiple materials or local variations in density. The detector electronically detects the photons that pass through the sample. Other than the material types and incident photon energy, the decrease in detected X-ray intensity is dependent upon the depth of X-ray beam penetration through the sample (i.e., material heterogeneity). The computer will further process the through-thickness projection data (e.g., adjust brightness and contrast) and visualize it as a grayscale radiographic image. Beer-Lambert law relates the X-ray beam attenuation to the material properties (attenuation coefficient) and the penetration depth (z). With a parallel beam approximation, the general equation to calculate detected X-ray intensity I d is: