A TRANSMISSION-MAP BASED SCATTER CORRECTION TECHNIQUE FOR SPECT IN INHOMOGENEOUS-MEDIA

In this paper a method of modeling the distribution of scattered event s in emission projection data is developed and applied. This method is based on the use of a transmission map to define the inhomogeneous sc attering object. The key point is the use of the set of line integrals calculated as part of the attenuation correction technique, as the ba sis of a model of the distribution of scattered events. The probabilit y of a photon being scattered through a given angle and being detected in the emission energy window is approximated using a Gaussian functi on. The parameters of this Gaussian are determined using Monte Carlo g enerated parallel-beam scatter line spread functions from a nonuniform ly attenuating phantom. The model is incorporated into a two-dimension al projector-backprojector and used with the Expectation-Maximization- Maximum-Likelihood algorithm for the reconstruction of fan-beam phanto m data. The correction is shown to perform well for a phantom that var ies. slowly in the axial direction. For the more clinically realistic situation of a torso phantom, the method produces improvements in term s of blood pool to myocardium contrast, but does not restore the contr ast to the level exhibited in a reconstruction from ''scatter free'' d ata.