4D Lung MRI with Isotropic Resolution on a 1.5T MR-Linac using a Self-Navigated 3D Radial Kooshball Acquisition and Sparse Motion Reconstruction

Motivation: Current 4D MRI methodology on the MR-Linac is based on stack-of-stars acquisition, which has limited resolution along the slice dimension and can compromise the performance of motion assessment. Goal(s): To develop 4D lung MRI with isotropic-resolution on a 1.5T MR-Linac using 3D radial kooshball acquisition with respiratory self-navigation. Approach: Stack-of-stars and kooshball acquisitions were performed on a healthy volunteer. Motion-resolved 4D MRI was reconstructed using XD-GRASP and then compared in terms of image quality and motion characteristics. Results: Stack-of-stars acquisition underestimated motion due to limited resolution in the slice dimension. Kooshball acquisition provided isotropic-resolution that allows for improved visualization of smaller pulmonary structures. Impact: 4D MRI with isotropic spatial resolution has the potential to enhance treatment planning and adaptation for lung cancer patients receiving radiation therapy on the MR-Linac system.