1. A method for reducing statistical noise of X-ray attenuation data related to two spectral different X-ray data acquisition, a first spectral X-ray data acquisition and a second spectral X-ray data acquisition, the method comprising the steps of acquiring attenuation data representing the X-ray attenuation behavior of a region of interest within an object of interest, determining a first attenuation-base line integral for the first spectral X-ray data acquisition and a second attenuation-base line integral for the second spectral X-ray data acquisition, respectively, for a predetermined X-ray beam path traversing the region of interest, calculating an expected first signal to noise ratio for the first attenuation-base line integral and an expected second signal to noise ratio for the second attenuation-base line integral based on given signal to noise ratios for the first spectral X-ray data acquisition and for the second spectral X-ray data acquisition, respectively, repeating the above mentioned steps of determining the attenuation-base line integrals and calculating the expected signal to noise ratio for a further first spectral X-ray data acquisition being different from the first spectral X-ray data acquisition and/or for a further second spectral X-ray data acquisition being different from the second spectral X-ray data acquisition, selecting an improved first spectral X-ray data acquisition and/or an improved second spectral X-ray data acquisition in order to enhance the overall signal to noise ratio of an X-ray image which is based on the first attenuation-base line integral and on the second attenuation-base line integral.