Undersampled Reconstruction of Multiple 3D High-Resolution Respiratory Phases Using Non-Rigid Registration

INTRODUCTION: In various medical image applications like image-guided interventions, radiotherapy treatment planning or motion-compensated reconstructions, it is desired to reconstruct multiple motion-free high resolution respiratory phases from free-breathing 3D MRI. Common navigator gating techniques [1-3] are a proven approach to reconstruct single or reduced number of motion-free respiratory phases, by rejecting all data acquired outside of the navigator window. Here we propose a technique to reconstruct multiple 3D high resolution respiratory phases by combining an undersampled self-gating radial-like acquisition with a non-rigid image registration scheme. This approach uses all the acquired data to reconstruct a single high spatial resolution (HSR) phase at the most visited respiratory position (commonly at end-exhale) and multiple respiratory resolved (RR) images at the remaining respiratory phases followed by an improving of image quality for all RR images (which suffers from remained aliasing artifacts) by applying a non-rigid registration procedure. The registration aligns the features of the HSR image with all remaining RR phases, leading to a sequence of time-resolved high resolution respiratory phases. Results for 3D respiratory motion of the thoracic organs are presented for 6 different phases, acquired in the same time as a single navigated respiratory phase.