Apparatus for processing a volumetric image data set, comprising a device for performing a non-optical image scanning method on an object that is to be examined and generating a volumetric image data set, and a processor programmed to extract an object contour from the volumetric image data set for determining the location of the object surface, wherein the processor is further programmed to define at least one environment for an object surface point, to analyse the greyscale values within the environment and to calculate a quality value for the object surface point for reproducing a local quality of the surface, the local quality indicating how well a given object surface point permits a conclusion to be drawn about the actual object geometry of the object that is to be examined, wherein, for calculating an image rendering and/or for further analyses of the object that is to be examined, the surface points are weighted differently, depending on the calculated quality value, wherein the processor is further programmed to determine a factor reflecting a measurement uncertainty based on the quality value, wherein the measurement uncertainty relates to fitted points for the surface points, wherein a reference element is matched to the fitted points, wherein secondary information is taken into account in the analysis, secondary information being information from the total volume, preferably statistical information, or information from other/adjacent reference points or prior knowledge, preferably from existing object data, wherein the processor is further programmed to perform the non-optical image scanning method and the subsequent calculation of a quality value regularly by means of a test object and to compare the results of successive quality value calculations with each other and to calculate a measure of detected changes, in order to, depending on the calculated measure of detected changes, generate a signal, in order to indicate the need for maintenance or repair of the apparatus. wherein the processor is further programmed to define at least one environment for an object surface point, to analyse the greyscale values within the environment and to calculate a quality value for the object surface point for reproducing a local quality of the surface, the local quality indicating how well a given object surface point permits a conclusion to be drawn about the actual object geometry of the object that is to be examined, wherein, for calculating an image rendering and/or for further analyses of the object that is to be examined, the surface points are weighted differently, depending on the calculated quality value, wherein the processor is further programmed to determine a factor reflecting a measurement uncertainty based on the quality value, wherein the measurement uncertainty relates to fitted points for the surface points, wherein a reference element is matched to the fitted points, wherein secondary information is taken into account in the analysis, secondary information being information from the total volume, preferably statistical information, or information from other/adjacent reference points or prior knowledge, preferably from existing object data, wherein the processor is further programmed to perform the non-optical image scanning method and the subsequent calculation of a quality value regularly by means of a test object and to compare the results of successive quality value calculations with each other and to calculate a measure of detected changes, in order to, depending on the calculated measure of detected changes, generate a signal, in order to indicate the need for maintenance or repair of the apparatus. <EOS>