An imaging system that can form an image of an item under inspection using scattered radiation. A pencil beam of radiation is steered over the item under inspection and scattered radiation is detected. Regions of the item under inspection from which radiation is scattered are resolved in three dimensions using two-dimensional coordinates to which the pencil beam is steered. The third dimension is resolved using time of flight from the source. Because the inspection system can be located on one side of an item under inspection, an item may be imaged from a long distance and the imaging system may be mounted on a moving vehicle, making the imaging system well suited for use in many security inspection systems to detect explosives and other contraband items.