Iterative methods for reconstructing of three-dimensional images based on projection data signals obtained by a computer tomography system often result in wrong absorption coefficients in particular for regions including a hollow space of an object under examination. Furthermore iterative methods show a slow convergence for calculating such absorption coefficients. According to embodiments of the present invention there is provided a method for an advanced reconstruction of three-dimensional images based on modified projection data signals. The modification includes an addition of a constant absorption value to the measured projection data. Advantageously the constant absorption value is an absorption line integral through a virtual body having the spatial constant absorption coefficient of water. The virtual body preferably has a volume which is slightly bigger than the object of interest.