Multistage three-dimensional UTE lung imaging by image-based self-gating.

PURPOSE: To combine image-based self-gating (img-SG) with ultrashort echo time (UTE) three-dimensional (3D) acquisition for multistage lung imaging during free breathing.
METHODS: Three k-space ordering schemes (modified spiral pattern, quasirandom numbers and multidimensional Golden Angle) providing uniform coverage of k-space were investigated for providing low-resolution sliding-window images for image-based respiratory self-gating. The performance of the proposed techniques were compared with the conventional spiral pattern and standard DC-based self-gated methods in volunteers during free breathing.
RESULTS: Navigator-like respiratory signals were successfully extracted from the sliding-window data by monitoring the lung-liver interface displacement. A temporal resolution of 588 ms was adequate to retrieve gating signals from the lung-liver interface. Images reconstructed with the img-SG technique showed significantly better sharpness and apparent diaphragm excursion than any of the DC-SG methods. Direct comparison of the three implemented ordering schemes did not demonstrate any clear superiority of one with respect to the others.
CONCLUSION: Image-based respiratory self gating in UTE 3D lung images allows successful retrospective respiratory gating, also enabling reconstruction of intermediate respiratory stages.