3D Cine Magnetic Resonance Imaging of Rat Lung ARDS using Gradient-modulated SWIFT with Retrospective Respiratory Gating.

SWeep Imaging with Fourier Transformation (SWIFT) with gradient modulation and DC navigator retrospective gating is introduced as a 3D cine magnetic resonance imaging (MRI) method for the lung. The quasi-simultaneous excitation and acquisition in SWIFT enabled extremely high sensitivity to the fast-decaying parenchymal signals (TE=~4 μs), which are invisible with conventional MRI techniques. Based on respiratory motion information extracted from DC navigator signals, the SWIFT data were reconstructed to 3D cine images with 16 respiratory phases. To test the capability of the proposed technique, rats exposed to > 95% O2 for 60 hours for induction of acute respiratory distress syndrome (ARDS), were imaged and compared with normal rat lungs (N=7 and 5 for ARDS and normal group, respectively). SWIFT images showed lung tissue density difference along the gravity direction. In the cine SWIFT images, parenchymal signal drop at the inhalation phase was consistently observed for both normal and ARDS rats due to inflation of the lung (i.e. decrease of the proton density), but the drop was less for ARDS rats. Depending on the respiration phase and lung region, the lungs from the ARDS rats showed 1-24% higher parenchymal signal intensities relative to the normal rat lungs, which would be mainly from accumulation of extravascular water (EVLW). Those results demonstrate that SWIFT has high enough sensitivity for detecting the lung proton density changes due to gravity, different respiration phases and accumulation of EVLW in the rat ARDS lungs.