Methods for inspecting contents of a container. High-energy penetrating radiation collimated into a fan beam illuminates an inspected container from one side, while a plurality of detector plates are disposed on the opposite side of the container. Each detector plate has a plurality of detector modules, each of which, in turn, is disposed on a remotely activated alignment and has multiple detector elements. A controller governs the orientation of each of the plurality of detector plates based at least on the detector signal generated by its detector elements such that each detector element of each detector module of each detector plate may be aligned to within a specified fraction of the transverse dimension of the fan beam as measured at the exit slot.