1. A method for obtaining a three-dimensional distribution of a stiffness property in breast tissue from mammographic images, comprising: applying a plurality of loadings to the breast tissue; obtaining a plurality of two-dimensional (2-D) imaging projections of the breast tissue from different directions; measuring from at least one of the plurality of 2-D imaging projections a force resulting from one of the plurality of loadings; measuring from at least one of the plurality of 2-D imaging projections a displacement of the breast tissue in response to the force; obtaining an initial set of input parameters for an estimation of the stiffness property of the breast tissue; and solving iteratively using the measured force and measured displacement from at least one of the plurality of 2-D imaging projections and the initial set of input parameters to create a three-dimensional distribution of the stiffness property of the breast tissue using a computer.