4D image data are used in radiation therapy planning
to estimate motion of the tumor or regions at risk. Today 4D CT is commonly
used for this purpose. Due to better soft tissue contrast and quantitative and
functional imaging, a clinical demand for MRI in therapy planning exists. Consequently,
there is also a growing interest in 4D MRI techniques. A scan-time-efficient 4D
MRI method utilizing the MRI Navigator as motion sensor with high geometric fidelity is proposed.