1. A computed-tomography (CT) apparatus, comprising: a radiation source radiating radiation into an object space; a plurality of detector elements configured to detect the radiation transmitted from the radiation source and through the object space, the plurality of detector elements configured to generate projection data; a rotation mount configured to rotate the radiation source around the object space, wherein the radiation source is fixedly connected to the rotation mount; and processing circuitry configured to obtain the projection data representing an irradiance of the radiation detected at the plurality of detectors, the radiation having been transmitted through the object space, reconstruct a full-scan image using the projection data, reconstruct a short-scan image using the projection data, generate a difference image by obtaining a difference between the full-scan image and the short-scan image, filter the difference image using an asymmetric filter, which is defined by a function having at least one variable of a projection angle corresponding to a center view of a short-scan subset of the projection data, and combine the filtered difference image with the short-scan image to obtain a corrected short-scan image.