1. A method for performing material decomposition using a CT system, the steps 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; b) expressing a total mass attenuation of an object as a weighted sum of constituent material mass attenuation coefficients; c) determining an effective density of the imaged object; and d) indicating a concentration of the constituent materials from the data acquired in step a) and the density determined in step c) using the expression of step b), wherein the concentration is at least one of a mass fraction, mass percent, weight fraction, and weight percent.