1. In a high speed CT scanning system in which fan beams of radiation are generated by sweeping an electron beam along a target and collimated X-rays emitted by the target are received by an array of detectors after passing through a patient area between said target and said array of detectors, a method of obtaining a two dimensional radiograph of a patient comprising the steps of sweeping repeatedly said electron beam along said target, measuring radiation received at one detector position as said electron beam is swept along said target, moving said patient past said collimated X-rays, and assemblying said two dimensional radiograph from said radiation measured at said one detector position.