Free-Running Simultaneous Imaging of the Entire Lung and Heart With Isotropic Resolution

To enable simultaneous free-breathing imaging of the entire lung and heart with isotropic resolution at 1.5 T for the diagnosis of cardiopulmonary disorders, while reducing scan time and minimizing the requirement for patient compliance.

A three-dimensional radial dual-echo balanced steady-state free precession (bSSFP) sequence was developed to acquire cardiopulmonary data in a free-running fashion. All acquired data were binned into different respiratory and cardiac motion states according to respiratory and cardiac signals estimated from superior-inferior navigators. A novel subspace-based motion-compensation reconstruction algorithm was used to reconstruct five-dimensional (5D) cardiopulmonary images. Images acquired with the dual-echo bSSFP sequence were compared with those acquired using an ultrashort echo time gradient-echo (GRE-UTE) sequence. The proposed 5D imaging technique was also compared with respiration-resolved four-dimensional (4D) imaging in 12 healthy subjects.

The dual-echo bSSFP sequence effectively captured pulmonary signals while providing superior myocardium-blood contrast compared with the GRE-UTE sequence. Dynamic images of the entire lungs and heart were simultaneously obtained using the proposed 5D imaging technique. By minimizing the adverse effect of cardiac motion, 5D imaging yielded clearer depiction of cardiac structures and pulmonary structures adjacent to the heart than 4D imaging.

A new simultaneous cardiopulmonary MRI technique was proposed in this study. Five-dimensional dynamic images of the entire lungs and heart with an isotropic resolution of 1.5 × 1.5 × 1.5 mm³ can be obtained from a single free-breathing scan of approximately 10 min. This technique has the potential for structural and functional assessment of the cardiopulmonary system.