  Purpose, To develop a high scanning efficiency, motion corrected imaging
strategy for free-breathing pulmonary MRI by combining a motion compensation
reconstruction with a UTE acquisition, called iMoCo UTE. Methods, An optimized
golden angle ordering radial UTE sequence was used to continuously acquire data
for 5 minutes. All readouts were grouped to different respiratory motion states
based on self-navigator signals, then motion resolved data was reconstructed by
XD Golden angle RAdial Sparse Parallel reconstruction (XD GRASP). One state
from the motion resolved images was selected as a reference, and motion fields
from the other states to the reference were derived via non-rigid registration.
Finally, all motion resolved data and motion fields were reconstructed by using
an iterative motion compensation reconstruction with a total generalized
variation sparse constraint. Results, The iMoCo UTE strategy was evaluated in
volunteers and non-sedated pediatric patient(4-6 y/o) studies. Images
reconstructed with iMoCo UTE provided sharper anatomical lung structures, and
higher apparent SNR and CNR, compared to using other motion correction
strategies, such as soft-gating, motion resolved reconstruction, and non-rigid
motion compensation(MoCo). iMoCo UTE also showed promising results in an infant
study. Conclusions, The proposed iMoCo UTE combines self-navigation, motion
modeling, and a compressed sensing reconstruction to increase scan efficiency,
SNR, and reduce respiratory motion in lung MRI. This proposed strategy shows
improvements in free breathing lung MRI scans, especially in very challenging
application situations, such as pediatric MRI studies.
