1. A method for imaging an object, said method comprising: acquiring tomographic image data of the object at a plurality of frequencies; generating a composite image of the object at each of the plurality of frequencies using the acquired tomographic image data; determining a scaling factor for a first material at each of the plurality of frequencies; determining a scaling factor for a second material at each of the plurality of frequencies; and decomposing the composite images into a first discrete image and a second discrete image using the determined scaling factors, wherein the first discrete image contains any region of the object composed of the first material and the second discrete image contains any region of the object composed of the second material.