1. A method for generating a bone mask, comprising the following steps: performing a noncontrast axial computed tomography (CT) scan on a subject to acquire a first data set; performing a postcontrast helical CT scan on the subject after the subject injected with a contrast medium to acquire a second data set; reconstructing the first data set and the second data set to acquire a first reconstruction image and a second reconstruction image respectively, in which the second reconstruction image possesses a predetermined spatial resolution; resampling the first reconstruction image based on the second reconstruction image to acquire a third reconstruction image, such that the third reconstruction image matches the predetermined spatial resolution of the second reconstruction image; and thresholding values of data which are equal to or greater than a scheduled Hounsfield Unit (HU) in the third reconstruction image to acquire a bone mask.