Free-running 4D lung imaging at 0.55T using UTE-bSSFP with intra-bin correction and inter-bin compensation of respiratory motion

Motivation: To strenghten the validation of free-running UTE imaging at low field, as a non-invasive, radiation-free tool for pulmonary imaging. Goal(s): To evaluate the effectiveness of a 3D radial UTE-bSSFP sequence for high-resolution respiratory-resolved lung imaging at 0.55T. Approach: A bSSFP-UTE sequence following a double-phyllotaxis trajectory was acquired at resolutions 1.25mm3 and 0.98mm3, on a phantom and n=6 healthy volunteers under free-breathing. Respiratory-resolved images at two resolutions and acquisition times were compared through metrics of interface sharpness, contrast ratio, and apparent SNR. Results: Excellent pulmonary vessel delineation was obtained, with no siginificant differences in sharpness or apparent SNR between different spatial resolutions. Impact: This study further validates low-field UTE lung imaging, achieving sub-millimetric 4D resolution without significant loss of pulmonary vessel sharpness or apparent SNR when accelerating two-fold, thanks to a powerful respiratory-resolved reconstruction, suggesting strengthened clinical translation.