Effects of TOF Resolution Models on Edge Artifacts in PET Reconstruction from Limited Angle Data

Abstract

Limited angle data, such as data obtained from a dual panel Breast-PET system, result in substantial image blur in the directions coinciding with the missing cone of the image spectrum. On systems with time-of-flight (TOF) capabilities, this blur is reduced in length as given by the TOF uncertainty, with the image spectral data correspondingly being expanded into the missing spectral cone. Modeling of the TOF uncertainty in the reconstruction is expected in turn to deconvolve the TOF blurring, at least for ideal noiseless data. We have however observed that, as a tradeoff, the TOF de-blurring process, when reconstructing limited angle data, also introduces ringing artifacts at the de-blurred objects edges, analogous to the edge effects observed with resolution modeling of the point-spread function (PSF) within image reconstruction which attempts to deconvolve the blur due to spatial resolution degradation effects. However, in the former case, the ringing artifacts are much wider due to the size of the TOF uncertainty kernel being considerably larger than the size of typical LOR resolution kernels. In this work, we illustrate and investigate the effects of using matched as well as under- and over-modeled TOF resolution kernels on edge artifacts in PET reconstruction from limited angle data, and compare those with the effects of TOF reconstruction of complete data from a conventional full-ring scanner.