1. A computer tomography method for determining a region taken up by an object being examined with the aid of projection images, comprising: generating radiation via a radiation source; loading a detector with the radiation and taking via the detector projection images of the object from various directions of projection; creating object images via an evaluation unit connected downstream of the detector; determining a position of a central region using at least two of the projection images via the evaluation unit; determining object sections from projection image values of the projection images via the evaluation unit; plotting the object sections on the central region via the evaluation unit; and determining an object region using end points of the plotted object sections via the evaluation unit, wherein for determining an object section a mean attenuation coefficient of the object being examined is estimated by totaling projection image values associated with an object image plane, and the total is divided by an area of an at least approximately determined object region.