Patent ID: 6909771

Claim:
A method for determining areal densities of bone, fat and soft tissue in a localized area of a patient, comprising the steps of: (a) collecting data defining an x-ray energy transmission curve by scanning the area of the patient at a plurality of points with a collimated x-ray beam and detecting and measuring beam intensity after having passed through the patient at a plurality of different energies at each point; (b) selecting from a database of x-ray spectral curves a spectral curve corresponding to the transmission curve defined by the collected data, wherein each spectral curve relates beam energy to beam intensity at each beam energy; (c) defining a curve relating a logarithm of a ratio of beam intensity in air divided by the measured beam intensity after passing through the patient for each of a plurality of photon energies in the beam; (d) solving a matrix equation for a solution comprising sum totals of the areal densities of bone, fat and soft tissue in response to predetermined mass attenuation coefficients for bone, fat and soft tissue at a group of three selected energies and in response to the logarithmic ratio obtained from the curve at each of the three selected energies; (e) repeating step (d) a plurality of times, each time obtaining a solution by solving the matrix equation at a group of three selected energies different from a group at which the matrix equation was previously solved; (f) computing an average of the sum total of the areal densities of bone from the solutions obtained in step(e), an average of the sum total of the areal densities of fat from the solutions obtained in step (e), and an average of the sum total of the areal densities of soft tissue obtained in step (e); and (g) performing an iterative method to estimate the areal densities of bone, fat and soft tissue in response to the sum totals of the areal densities of bone, fat and soft tissue.