The present invention relates to a method for estimating the Bone Mineral Density (BMD) using image data collected in emergency situation, i.e. without following specific protocols. In particular, the invention discloses a method for assessing the risk of bone fractures using as one indicator a BMD of one or more bones. The BMD is calculated using a universal constant which provides a value of BMD having a certain error in respect to its true value. However this error does not substantially affect the assessment of the risk of fracture of one or more bones.