A method is developed which makes it possible to scan and reconstruct an object with cone beam x-ray in a spiral scan path with area detectors much shorter than the length of the object. The method is mathematically exact. If only a region- of-interest of the object is to be imaged, a top circle scan at the top level of the region-of-interest and a bottom circle scan at the bottom level of the region-of-interest are added. The height of the detector is required to cover only the distance between adjacent turns in the spiral projected at the detector. To reconstruct the object, the Radon transform for each plane intersecting the object is computed from the totality of the cone beam data. This is achieved by suitably combining the cone beam data taken at different source positions on the scan path; the angular range of the cone beam data required at each source position can be determined easily with a mask which is the spiral scan path projected on the detector from the current source position. The spiral scan algorithm has been successfully validated with simulated cone beam data.
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