Longitudinal emission computer tomography: Correction for scattering for iterative image reconstruction

The attenuation of sup(99m)Tc-γ-photons in water is mostly due to Compton-scattering. Our experiments certify the assumption that the attenuation coefficient depends on the depth of the source plane. Therefore for reconstruction in longitudinal single-photon-emission-computer-tomography the value related to depth is used instead of a constant value. sup(99m)Tc-photons scattered until to an angle of 550 (without multiple scattering) are measured with the relative window width of 20% (as usual in scintigraphy). This is 33,9% of the whole scattering. An algorithmus developed from the Klein-Nishina-formula describes the experimentally measured dependence of the attenuation coefficient on the depth satisfactorily. A digital filter increasing with depth of the reconstruction plane improves the detectibility of lesions and the homogeneity of the voxel load. Correction for attenuation and the digital filter are implemented in the multiplicative SIRT because of the better convergence of this technique in comparison to the additive SIRT in preliminary experiments. (orig)