In one embodiment, a method of examining contents of an object is disclosed comprising scanning an object at first and second radiation energies, detecting radiation at the first and second energies, and calculating a function of the radiation detected at the first and second energies. The method further comprises calculating at least one second function based, at least in part, on at least some of the first functions, and determining whether the object at least potentially contains material in a class of materials based, at least in part, on the second function. The class of materials may be materials having an atomic number greater than the predetermined atomic number, for example. The second function may be compared to a criterion, which may be a threshold, for example. Systems are also disclosed.