A method for reconstruction of object attenuation density (S(x,y,z)) from X-ray projection image data values (V(p_q)) comprises the steps of: representing (11) the object attenuation density by a sum of predetermined continuous harmonics (H_ijk(x,y,z)) with unknown coefficients (a_ijk); relating (12) each of the projection image data values to an integral (S(p_q)) of the object attenuation density, and thus to a corresponding sum of sums (a_ijk*H_ijk(p_q)) of the predetermined continuous harmonics with unknown coefficients; determining (13) the unknown coefficients (a_ijk) from the above relation; and reconstructing (14) the object attenuation density by said sum of predetermined continuous harmonics with said determined coefficients. The spatial three-dimensional object attenuation density is found as a continuous function with uniform resolution over all its volume and is shown as a solid three-dimensional body, which can be cut in arbitrary way and shown in continuous motion.