1. A method for performing material decomposition using a CT system, the method comprising: a) imaging an object with a CT system using at least two different energy levels to acquire CT data associated with each of the energy levels; a)i) reconstructing the CT data associated with each energy level to produce CT images associated with each energy level; a)ii) converting the CT images associated with each energy level to produce attenuation coefficients associated with each energy level; b) expressing a total mass attenuation of the object as a weighted sum of constituent material mass attenuation coefficients; c) determining an effective density of the imaged object; d) determining concentrations of the constituent materials from the attenuation coefficients associated with each energy level determined at step a)ii) and the effective density determined in step c) using the expression of step b), wherein said determining concentrations includes employing an iterative least-squares technique, wherein a concentration is at least one of a mass fraction, mass percent, weight fraction, and weight percent; and e) producing an image using the CT data and the concentrations of the constituent materials illustrating the distribution of the concentrations of the constituent materials within the object.