A security screening system for scanning items, the system comprising: a scanner, configured to produce x-ray projection data as an object is passed through the scanner, at least a portion of the scanner being received within a structure, the structure having an input opening and an outlet opening, the input opening being configured to receive objects to be scanned and the output opening being configured to receive objects scanned by the scanner; an input conveyor for passing a plurality of bins through the input opening to the outlet opening, the input conveyor having an input end for receiving the plurality of bins to pass the plurality of bins into the input opening and an output end for delivering the plurality of bins from the outlet opening; and a return conveyor positioned to return the plurality of bins to an area proximate to the input end of the input conveyor, the return conveyor being positioned below the input conveyor, wherein the return conveyor does not pass through the scanner.