Assessment of scatter components in high-resolution PET: correction by nonstationary convolution subtraction

This paper describes a new approach to determine individual scatter kernels and to use them for scatter correction by integral transformation of the projections.

Individual scatter components are fitted on the projections of a line source by monoexponentials. The position-dependent scatter parameters of each scatter components are then used to design non-stationary scatter correction kernels for each point in the projection. These kernels are used in a convolution-subtraction method which consecutively removes object, collimator and detector scatter from projections. This method is based on a model which assumes that image degradation results exclusively from Compton interactions of annihilation photons, thus neglecting further Compton interactions of object scatters with collimator and detector.

Subtraction of the object scatter component improved contrast typical of what is obtained with standard convolution-subtraction methods. The collimator scatter component is so weak that it can be safely combined with object scatter for correction. Subtraction of detector scatter from images did not improve contrast because statistical accuracy is degraded by removing counts from hot regions while cold regions (background) remain unchanged.

Subtraction of object and collimator scatter improves contrast only. The slight gain in image sharpness resulting from the subtraction of detector scatter does not justify removal of this component at the expense of sensitivity.