Patent ID: 7697657

Claim:
A diagnostic imaging system, comprising: a high frequency electromagnetic energy source that emits a beam of high frequency electromagnetic energy toward an object to be imaged; a detector that receives high frequency electromagnetic energy emitted by the high frequency electromagnetic energy source and attenuated by the object; a data acquisition system (DAS) operably connected to the detector; and a computer operably connected to the DAS and programmed to: acquire projection data from the detector of an unknown material at the time of projection data acquisition; generate a density image for the unknown material based on a sum of squares of basis function images; derive a ratio Z(N) A /Z(N) B of atomic numbers of known basis materials (N) A and (N) B ; generate an effective atomic number (Z) for the unknown material based on the density images of at least two known basis materials (N) A and (N) B and based on a function arctan(Z(N) A /Z(N) B ) of the ratio Z(N) A /Z(N) B of atomic numbers; and store the density and effective atomic number images to a computer readable storage medium.