Patent ID: 8008625

Claim:
A method of determining the spatial density distribution of a gamma ray emission source such as a radiopharmaceutical substance, said emission source embedded in a body and emitting gamma rays, and said method comprising the steps of: (a) measuring a discretely sampled vector of values g using a gamma ray detector of gamma radiation field of said emission source in a vicinity of said source in a 3D volume space comprised of a set of volume elements or voxels represented by a 3D matrix V, said 3D volume space extending significantly along at least one radial direction pointing away from an approximate center of said radiation source; (b) measuring an attenuation coefficient matrix μ(x,y,z) of material present in a portion of volume P of said body at different volume elements or voxels through which gamma radiation passes through before being measured in step (a), wherein said portion of volume P includes a set of voxels S in which said radiation source is embedded, and, using μ(x,y,z) to compute a gamma ray path attenuation coefficient matrix C=c(x′,y′,z′,x,y,z) that provides the attenuation of a gamma ray going from point (x,y,z) to (x′,y′,z′), (c) determining a matrix H of values using (i) the distance and geometry between pairs of voxels (v,s) where v is a voxel in V and s is a voxel in S, and the geometry and sensor characteristics of said gamma ray detector, (ii) the path attenuation coefficient matrix C, (iii) the property of radiation propagation that the intensity per unit area of gamma ray emission field decreases with the square of radial distance from emission source, and therefore facilitating the use of data values in g measured at different radial distances from said emission source, and (iv) a discrete vector n of values that represents the effects of noise and scattered radiation on measurements in step (a) and (b) above, so that the relation between a discretely sampled vector of values f representing the spatial density distribution of said radiation source that needs to be determined in voxels S is given by g=Hf+n; and (d) solving the above equation g=Hf+n for the desired quantity f by a method that reduces the effect of noise n significantly so that the desired goal of determining the spatial density distribution f of said radiation source is achieved.