Joint estimation of activity and attenuation: Application to non-FDG TOF PET/MR clinical data

Attenuation correction is critical to accurate PET quantitation. Accurate and robust attenuation correction remains challenging in hybrid PET/MR because it is difficult to segment bones, internal air and lungs accurately in MR images and MR often suffers from artifacts due to metal implants and signal shading. Joint estimation (JE) of activity and attenuation from time-of-flight (TOF) PET data has recently gained substantial interest because the JE approach shows a promise to address the challenges in MR based attenuation correction. We have previously implemented a JE algorithm with MR-based priors and demonstrated its feasibility using FDG PET/MR clinical data. However, JE algorithms have rarely been evaluated on non-FDG tracers which often have spatially more specific uptake patterns with little activity in background tissue, and hence may pose challenges to JE. In this study, we evaluate the JE algorithm using non-FDG PET/MR clinical data. We demonstrate that the JE algorithm improves the accuracy and robustness of MR-based attenuation correction not only for FDG as previously shown but also for non-FDG tracers such as 68 Ga-DOTATOC and Fluoride. In addition, we demonstrate the critical role of TOF information in JE algorithms.