Understanding edge artifacts of the OSEM algorithm in emission tomography

Abstract A significant challenge in achieving accurate results with the OSEM algorithm in emission tomography is the emergence of edge artifacts at high-contrast boundaries. However, the underlying cause of these artifacts is not well understood. This study aims to investigate the mechanism behind their formation. Image reconstruction was modeled using the MLEM algorithm for the one-dimensional case and the OSEM algorithm for the 3D case closely reflecting clinical practice. This was complemented by an analysis of the underlying formulas of these algorithms. The primary mechanism behind the emergence of edge artifacts is not their occurrence at a specific iteration, but the OSEM algorithm’s tendency to preserve these artifacts, along with other short-wavelength disturbances, over numerous iterations. Thus, filtering of the reconstructed images is necessary, at least during intermediate iterations, to eliminate edge artifacts. Furthermore, it has been observed that these artifacts arise from the inherent nature of the OSEM algorithm, rather than from insufficient information in the observed data.