Image properties of various ML-based reconstructions of very noisy HRRT data

The use of iterative image reconstruction algorithms with resolution modeling allows for reduced partial volume effect without noise increase. However, it is now recognized that EM-ML type algorithms are biased in very low counts images, in particular for cold regions. Alternative ML algorithms that allow for negative image voxels have been proposed to reduce the bias: NEG-ML of Nuyts et al and AB-ML of Byrne.