Dual energy refers to the spectrum that can be arranged by the software to visualize soft tissue and bone. It takes 2 different levels of energy to differentiate between soft tissue and bone, since bone will "shine" more than soft tissue, blurring the soft tissue. This shine or brightness is called "Hounsfield Units", and is referred to as HU, which can be a suspicious indicator of a neoplasm.
Code as usual, by the views taken, ie., 2 view chest 71020.