Methods and systems are used to form an image of the contents of an object for display. A neutron mass attenuation matrix n and a gamma-ray mass attenuation matrix g are formed. A composition matrix and a density matrix are calculated whose respective elements Rij and Xij are each defined as a function of the elements nij and the corresponding elements gij. Rij represents an average composition of material within the object between a source which generated the radiation and a point (i,j). Xij represents an approximate amount of material within the object between the radiation source and the point (i,j). A quality matrix is calculated whose elements Qij are defined as a function of the elements nij and the elements gij and represents a measure of the reliability of the determination of the elements of Rij. The image formed for display contains information from R, X, and Q.