Comparing the effectiveness of 1D versus 2D navigated respiratory-correlated 4D-MRI acquisitions for radiotherapy guidance

Accurate characterization of internal anatomical motion is essential for correctly guiding free-breathing radiotherapy treatments on the MR-linacs. Respiratory-correlated 4D-MRI can potentially provide this crucial information during each treatment session. We acquired a 1D respiratory navigator (1D-RNAV) interleaved with simultaneous multi-slice (SMS) images, yielding a concurrent 2D navigator (2D-RNAV). Respiratory-correlated 4D-MRIs were obtained with the 1D and 2D internal navigator surrogate signals, and the amount of missing anatomical data was quantified. Using the 1D-RNAV signal yielded fewer missing data in respiratory-correlated 4D-MRIs. Improving breathing regularity using biofeedback did not substantially influence the choice of navigator.