Fast High-resolution Lifetime Image Reconstruction for Positron Lifetime Tomography

Abstract The life history of a positron before annihilation has long been overlooked by current positron emission tomography (PET) techniques. Due to the ortho-positronium formed prior to the annihilation, the lifetime of a positron is sensitive to the tissue microenvironment and can potentially provide valuable information for monitoring disease progression and treatment response. In this paper, we develop a positron lifetime image reconstruction method called SIMPLE (Statistical IMage reconstruction of Positron Lifetime via time-wEighting) and perform a real scan to demonstrate, for the first time, high-resolution positron lifetime imaging of an extended heterogeneous tissue on a time-of-flight (TOF) PET scanner. The SIMPLE method involves minimum modification to the standard list-mode maximum-likelihood expectation-maximization (MLEM) algorithm with a computation cost equivalent to the reconstruction of two PET activity images and a spatial resolution comparable to that of PET activity images. The proposed experimental design utilizes a 22Na point source to realize lifetime imaging in an extended area. The reconstructed positron lifetime image shows a clear separation between the muscle and fat tissues. The proposed method paves the way for high-resolution positronium lifetime imaging in humans.