1. A method of x-ray imaging, comprising: obtaining a first plurality of x-ray projection images of a patient; identifying at least one identified object in the first plurality of x-ray projection images; obtaining a priori information of the at least one identified object; and adjusting at least one x-ray imaging parameter based upon the at least one identified object and the obtained a priori information; obtaining a second plurality of x-ray projection images according to the at least one adjusted x-ray imaging parameter; reconstructing a three dimensional (3D) volume from the second plurality of x-ray projection images and the a priori information of the at least one identified object to produce a reconstructed 3D image.