The present invention relates to optimizing values for scan parameters for a scan of an object. An object specific exposure time is determined based on a maximal required value of a z-dependent tube current by exposure time product along a z-axis of the object and a maximal available tube current value of a tube used for the scan of the object (140). The maximal available tube current value depends on a tube voltage and maximal electric power of the tube at given focal spot area (110) and the z-dependent tube current by exposure time product profile is based on a dose index value or a pixel noise index value for the scan of the object, the tube voltage, and a z-dependent object size along the z-axis (120). The object specific exposure time is used for determining values of the scan parameters for the scan of the object (150).
