X-ray computed tomography (CT) is instrumental in medicine, industry and homeland security, which depicts internal structures of an object from its shadows projected in a fan-beam or cone-beam from an x-ray source along a appropriate trajectory. We published the first paper on spiral conebeam CT in 1991 to solve the long object problem. Now, spiral conebeam scanning has been widely used in modern CT scanners, in which conebeam rotation and table translation are simultaneously performed, and spiral cone-beam CT remains a major area in CT research and development.