Oxygen-enhanced 3D radial ultrashort echo time magnetic resonance imaging in the healthy human lung

The purpose of this work was to use 3D radial ultrashort echo time (UTE) MRI to perform whole-lung oxygen-enhanced (OE) imaging in humans. Eight healthy human subjects underwent two 3D radial UTE MRI acquisitions (TE = 0.08 ms): one while breathing 21% O2 and the other while breathing 100% O2. Scans were each performed over 5 min of free breathing, using prospective respiratory gating. For comparison purposes, conventional echo time (TE = 2.1 ms) images were acquired simultaneously during each acquisition using a radial " outward-inward" k-space trajectory. 3D percent OE maps were generated from these images. 3D OE maps showing lung signal enhancement were generated successfully in seven subjects (technical failure in one subject). Mean percent signal enhancement was 6.6% ± 1.8%, near the value predicted by theory of 6.3%. No significant enhancement was seen using the conventional echo time data, confirming the importance of UTE for this acquisition strategy. 3D radial UTE MRI shows promise as a method for OE MRI that enables whole-lung coverage and isotropic spatial resolution, in comparison to existing 2D OE methods, which rely on a less time-efficient inversion recovery pulse sequence. These qualities may help OE MRI become a viable low-cost method for 3D imaging of lung function in human subjects.