VAR-NAV: Motion-resolved 4D MRI using vision-assisted reference auto-navigation

Motivation: Motion navigation with improved data efficiency and robustness is still needed for free-breathing MRI. Goal(s): To develop VAR-NAV, a new 2D auto-navigation technique with 100% data efficiency for stack-of-stars acquisitions. Approach: VAR-NAV directly estimates the position of the liver dome using 2D projection images and AM-FM demodulation. Results can be corrected retrospectively, like in soccer video assistant referee (VAR). VAR-NAV is used to sort continuously acquired data and reconstruct motion-resolved 4D images. Results: VAR-NAV outperforms conventional 1D PCA-based navigation and does not require additional acquisition as in previous 2D navigation techniques, offering an efficient and accurate method for clinical 4D MRI. Impact: VAR-NAV estimates a motion signal that represents displacements on 2D images, outperforming conventional PCA-based 1D navigation. No extra navigation data are required, and results can be retrospectively analyzed like in soccer video-assisted-referee (VAR). VAR-NAV promises to improve clinical 4D MRI.