In one embodiment, a method includes applying an output of a substantially monochromatic x-ray beam source to a target tissue along a first path, tuning the output of the substantially monochromatic x-ray beam source, and applying an output of a substantially monochromatic x-ray beam source to a target tissue along a second path different from the first path. The energy of the output of the substantially monochromatic x-ray beam source at the target tissue substantially corresponds to a binding energy level of an electron shell in an atom within the target tissue along the first path. The tuning tunes the substantially monochromatic x-ray beam source such that an energy of the output of the substantially monochromatic x-ray beam source at the target tissue along the second path substantially corresponds to a binding energy level of an electron shell in an atom within the target tissue.