A method and device for determining a tissue density based on an x-ray image including a reference body. The method uses a device for receiving an X-ray image of a region of interest and information about a theoretical distribution of more or less dense tissue in the region of interest. Pixels of the X-ray image related to tissue are compared with a pixel related to a reference body. The actual distribution of tissue density is estimated based on the received information and the result of the pixel comparison.
