Reciprocity between the reflection electron microscope and the low-loss scanning electron microscope

The reflection electron microscope image - or, more correctly, the dark-field image from a solid specimen in the transmission electron microscope - has certain similarities to the low-loss electron image in the scanning electron microscope. These methods are reciprocal in the sense that it is possible to establish an equivalence by reversing the direction of the electrons through the system. In both cases the scanning version is better suited for imaging by means of wide-angle scattering events, while the nonscanning version is better suited for diffraction contrast. The equivalence between these two methods can be established by either a wave-optical or a geometrical argument.