Patent ID: 6324240
Filing Date: 2001-11-27
Classification: A61B,G01N,Y10S

Abstract:
A method for calculating characteristics of an object comprising voxels using an X-ray computer assisted tomography device, comprising the steps of:a) projecting through the object an X-ray beam having a known energy spectrum indicated by S(E);b) detecting the X-rays with an X-ray detector;c) repeating steps (a) and (b) for at least two different orientations of the X-ray beam with respect to the object;d) defining a first material and a second material within each voxel, wherein the first and second materials have known distinct attenuation spectra, given by .mu..sub.1 (x,E) and .mu..sub.2 (x,E), respectively, such that a total attenuation coefficient .mu.(x,E) of the object is given by:.mu.(x,E)=v(x).mu..sub.1 (x,E)+(1-v(x)).mu..sub.2 (x,E)where v(x) is a number between 0 and 1 and indicates a volume fraction of each voxel comprised of the first material;e) defining an initial estimated volume fraction v.sup.k (x);f) calculating an estimated total attenuation coefficient .mu..sup.k (x,E) from the equation;.mu..sup.k (x,E)=.nu..sup.k (x).mu..sub.1 (x,E)+(1-v.sup.k (x)).mu..sub.2 (x,E)g) calculating a new estimated total attenuation coefficient .mu..sup.k+1 (x,E) from the following equation:.mu..sup.k+1 (x,E)=P.sup.-1 {P.mu..sup.k (x,E)-B.mu..sup.k (x,E)+C(r)}where P is an operator defined by P.mu.=.intg..sub.r.intg.S(E).mu.(E)dEdx, B is an operator defined by B.mu.=-log.intg.S(E)exp(.intg..sub.r.mu.(E)dx)dE, and C(r) represents X-ray detector output, and r indicates the X-ray beam path;h) calculating a new estimated volume fraction v.sup.k+1 from the following equation:.mu..sup.k+1 (x,E)=v.sup.k+1 (x,E).mu..sub.1 (x,E)+(1-v.sup.k+1 (x)).mu..sub.2 (x,E)where .mu..sub.1 (E)=.intg.S(E).mu..sub.1 (E)dE and .mu..sub.2 (E)=.intg.S(E).mu..sub.2 (E)dEi) repeating steps (f), (g) and (h) using the new estimated volume fraction v.sup.k+1 (x) instead of the initial estimated volume fraction v.sup.k (x).