Energy dependence of nonstationary subtraction-restoration scatter correction in high resolution PET

In previous works, the determination of object and detector scatter kernels from line source measurements was described and their application in scatter correction was investigated. It was also shown that low energy data contains a large fraction of useful events (true and detector scatter events). In the present work, data acquired in multispectral mode was summed from a varying lower energy threshold ranging from 129-516 keV up to an upper energy level of 644 keV and the line source projections were fitted for extracting the object and detector scatter kernels as a function of energy threshold. These kernels were then used to process scatter by the non-stationary convolution subtraction-restoration method in phantom images. After scatter correction, the detection efficiency is found to increase by up to 64% at the lower threshold of 129 keV, relative to the conventional photopeak energy window (344-644 keV). Whereas contrast and spatial resolution are degraded as the energy discriminator is lowered, such degradation is fully recovered by the scatter correction