1. A method for suppressing bone structures in an x-ray image, comprising: receiving an x-ray image having a plurality of pixels; extracting a set of wavelet features for each pixel in the x-ray image; and generating a soft-tissue image without bone structures from the x-ray image by using a trained regression function to determine an intensity value for the soft-tissue image corresponding to each pixel in the x-ray image based on the set of wavelet features extracted for each pixel in the x-ray image.