Three-Dimensional Look-Locker Method for Free-Breathing T1 Mapping of Oxygen-Enhanced Pulmonary Magnetic Resonance Imaging

Oxygen-enhanced magnetic resonance imaging (OE-MRI) enables non-invasive assessment of lung function by measuring longitudinal relaxation time (T1) changes induced by alternating inhalation of room air and pure oxygen. In this study, the pulmonary T1 and its reduction after breathing pure oxygen were quantified by using the free-breathing three-dimensional (3D) Look-Locker technique based on a stack-of-stars acquisition scheme. This method applied a continuous acquisition model to collect signals during both room-air and pure oxygen conditions without the need for breath-holding or respiratory gating. Comparative evaluations were conducted between the proposed 3D Look-Locker method and the conventional two-dimensional (2D) Look-Locker approach, using both phantom and in vivo experiments. The results demonstrate that the 3D technique yields more pronounced and reproducible T1 reductions between air and oxygen conditions compared to the 2D method. Additionally, the T1 of the average respiratory phase obtained by the 3D approach was compared with the T1 at end-expiration and end-inspiration measured by the 2D approach. A consistent decline in T1 across respiratory phases was demonstrated, from end-expiration to end-inspiration, as well as the average respiratory phase under free-breathing. These findings suggest that the proposed OE-MRI T1 measurement based on the 3D Look-Locker method provides a robust and clinically feasible approach for quantitative lung imaging.