1. A method for detecting an anatomical abnormality within a three-dimensional digital image, the method comprising: computing a first gradient vector field of the digital image in x, y, and z directions; computing a plurality of second gradient vector fields for each of a plurality of predetermined masks of different sizes; convoluting the first gradient vector field and the plurality of second gradient vector fields to generate a corresponding set of response images; integrating the set of response images to generate a single response volume; and detecting the anatomical abnormality based on the single response volume, wherein each of the plurality of predetermined masks of different sizes is selected according to a shape of the anatomical abnormality being detected.