Impact of Time-of-Flight on Respiratory Motion Modelling using Non-Attenuation-Corrected PET

Respiratory motion reduces image quality in Positron Emission Tomography (PET). Unless gated Computed Tomography (CT) or Magnetic Resonance (MR) data are available, motion correction relies on registration of the PET data. To avoid mis-registration due to attenuation mismatches, most existing methods rely on pair-wise registration of Non-Attenuation Corrected (NAC) PET volumes. This is a challenging problem due to the low contrast and high noise of these volumes. This paper investigates the possibility of using motion models for respiratory motion correction in PET, and in particular whether incorporating Time-of-Flight (TOF) information increases the accuracy of the motion models derived from the NAC reconstructed images. 4D Extended Cardiac-Torso (XCAT) phantom simulations are used for one bed position with a field of view including the base of the lungs and the diaphragm. A TOF resolution of 375ps is used. NAC images are reconstructed using Orded SubSet Expectation Maximisation (OSEM) and used as input for motion model estimation. Different motion models are compared using the original XCAT input volumes. The results indicate that TOF improves the accuracy of the motion model considerably.