1. A computer tomography method having the steps of: a) using a beam source to generate a cone beam which passes through a scan region, or an object located in it, during a helical relative movement between the beam source, on the one hand, and the scan region or object on the other hand, comprising a rotation about a rotation axis and a displacement parallel to the rotation axis, b) using a detector unit to acquire a first set of measurement values during the relative movement, which depend on the intensity in the beam on the other side of the scan region, c) reconstructing a first CT image from the first set of measurement values, d) using a beam source to generate a cone beam which passes through the scan region, or the object, in conjunction with a circular relative movement between the beam source and the scan region or object, at a position of the scan region which the beam has already crossed during the helical relative movement, e) using a detector unit to acquire a second set of measurement values during the circular relative movement, f) iteratively reconstructing a second CT image from the second set of measurement values, an approximation image in each iteration cycle being corrected by comparing projection values calculated from the approximation image with the measurement values, and the first approximation image being derived from the first CT image.