Rapid and accurate navigators for motion and B0 tracking using QUEEN: Quantitatively enhanced parameter estimation from navigators

Abstract Purpose To develop a framework that jointly estimates rigid motion and polarizing magnetic field (B 0 ) perturbations () for brain MRI using a single navigator of a few milliseconds in duration, and to additionally allow for navigator acquisition at arbitrary timings within any type of sequence to obtain high‐temporal resolution estimates. Theory and Methods Methods exist that match navigator data to a low‐resolution single‐contrast image (scout) to estimate either motion or . In this work, called QUEEN (QUantitatively Enhanced parameter Estimation from Navigators), we propose combined motion and estimation from a fast, tailored trajectory with arbitrary‐contrast navigator data. To this end, the concept of a quantitative scout (Q‐Scout) acquisition is proposed from which contrast‐matched scout data is predicted for each navigator. Finally, navigator trajectories, contrast‐matched scout, and are integrated into a motion‐informed parallel‐imaging framework. Results Simulations and in vivo experiments show the need to model to obtain accurate motion parameters estimated in the presence of strong . Simulations confirm that tailored navigator trajectories are needed to robustly estimate both motion and . Furthermore, experiments show that a contrast‐matched scout is needed for parameter estimation from multicontrast navigator data. A retrospective, in vivo reconstruction experiment shows improved image quality when using the proposed Q‐Scout and QUEEN estimation. Conclusions We developed a framework to jointly estimate rigid motion parameters and from navigators. Combing a contrast‐matched scout with the proposed trajectory allows for navigator deployment in almost any sequence and/or timing, which allows for higher temporal‐resolution motion and estimates.