Dynamic MR-based respiratory motion compensation for hybrid PET/MR system

This paper describes a novel respiratory motion compensation (MC) technique for hybrid PET/MR system. Existing PET/MR respiratory MC techniques mainly rely on respiratory gating to reconstruct 3D MR images for different respiratory phases, and use image registration techniques to estimate the deformation between different respiratory phases. A well known limitation of respiratory gating is its assumption that breathing motion is perfectly periodic, therefore MC techniques based on gated MR are sensitive to irregular breathing patterns. To address this limitation, the proposed technique uses dynamic 2D MRIs for PET/MR respiratory motion estimation. A static 3D MRI and a series of dynamic 2D MRIs are acquired before and during the PET data acquisition, respectively. The dynamic 2D MRIs are registered against the static 3D MRI using a novel deformable 2D+t to 3D image registration method to derive a 3D+t deformation field, which is then used for motion corrected PET reconstruction. The proposed method is validated on synthetic PET/MR data and real MR data, demonstrating its efficacy to compensate for irregular respiratory motion and to deblur the PET image.