Energy dependence of nonstationary scatter subtraction-restoration in highresolution PET

In previous works, the determination of object and detector scatter kernels from line source measurements was described and their application in scatt er correction was investigated. It was also shown that low energy data cont ains a large fraction of useful events (true and detector scatter events). In the present work, data acquired in multispectral mode nas summed in sing le broad energy windows of loner energy thresholds, varying from 129 to 516 keV in steps of 43 keV and a constant upper energy threshold of 645 keV. L ine-source projections were fitted by extracting the object and detector sc atter kernels as a function of energy threshold, These kernels were then us ed to process scatter by the nonstationary convolution sub traction-restora tion method in phantom images. After scatter correction, the sensitivity is found to increase by up to 64% at the lower threshold of 129 keV, relative to the conventional photopeak energy window (334-645 keV), Whereas contras t and spatial resolution are degraded as the energy discriminator is lowere d, such degradation is fully recovered by the scatter correction. As a resu lt of scatter correction, the noise increases insignificantly in hot region s but substantially in cold regions, in proportion df the amount of scatter .