Five-dimensional cardiac MRI in one minute using the CMR-MOTUS framework on a 1.5 T MR-Linac

Motivation: Accurate estimation of cardiorespiratory motion is a key enabler for MRI-guided cardiac radiotherapy. Goal(s): To acquire and reconstruct five-dimensional cardiac MRI without navigators prior to radiotherapy. Approach: We use the CMR-MOTUS framework to explicitly reconstruct images and motion fields at high spatiotemporal resolution. By decomposing the motion fields into multiple spatial and temporal components, data can be sorted into cardiac and respiratory phases by considering the temporal scalings as motion navigators Results: High-quality five-dimensional MRI was acquired in one minute on an MR-linac and reconstructed. The motion fields separate the respiratory and cardiac motion, resulting in accurate 5D-MRI. Impact: Accurate 5D-MRI enables novel planning and motion mitigation strategies for radiotherapy that could significantly improve thoracic radiotherapy outcomes.