1. A method for producing three-dimensional information of an object ( 4 ) in medical X-ray imaging, characterized in that the object is modelled mathematically independently of X-ray imaging, the object is X-radiated from at least two different directions and the said X-radiation is detected to form projection data of the object ( 4 ), and said projection data and said mathematical modelling of the object are utilized in Bayesian inversion based on Bayes' formula p ⁡ ( x | m ) = p pr ⁡ ( x ) ⁢ p ⁡ ( m | x ) p ⁡ ( m ) to produce three-dimensional information of the object, the prior distribution p pr (x) representing mathematical modelling of the object, x representing the object image vector, which comprises values of the X-ray attenuation coefficient inside the object, m representing projection data, the likelihood distribution p(m|x) representing the X-radiation attenuation model between the object Image vector x and projection data m, p(m) being a normalization constant and the posteriori distribution p(x|m) representing the three-dimensional information of the object ( 4 ).