Image-based retrospective 4D MRI for different anatomical orientations

Four-dimensional magnetic resonance imaging (4D MRI) is an emerging technique in external beam radiotherapy treatment planning to quantify organ motion. The rationale is to overcome 4D CT limitations, such as the low soft-tissue contrast and the undesired imaging dose for patients. This work presents a 4D MRI retrospective image-based sorting method for both axial and sagittal anatomical orientations. Six liver healthy volunteers were included in the study. The method accuracy was assessed by comparing the liver profile of the 4D image-based MRI with the one obtained from a standard re-sorting method based on an external surrogate. Results of the proposed method may allow accurate organ motion quantification for treatment planning purposes.