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

Purpose: To develop a framework that jointly estimates rigid motion and polarizing magnetic field (B0) perturbations (δB0$$ \delta {\mathbf{B}}_{\mathbf{0}} $$) 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 orδB0$$ \delta {\mathbf{B}}_{\mathbf{0}} $$. In this work, called QUEEN (QUantitatively Enhanced parameter Estimation from Navigators), we propose combined motion and δB0$$ \delta {\mathbf{B}}_{\mathbf{0}} $$ 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 δB0$$ \delta {\mathbf{B}}_{\mathbf{0}} $$ are integrated into a motion‐informed parallel‐imaging framework. Results: Simulations and in vivo experiments show the need to model δB0$$ \delta {\mathbf{B}}_{\mathbf{0}} $$ to obtain accurate motion parameters estimated in the presence of strong δB0$$ \delta {\mathbf{B}}_{\mathbf{0}} $$. Simulations confirm that tailored navigator trajectories are needed to robustly estimate both motion and δB0$$ \delta {\mathbf{B}}_{\mathbf{0}} $$. 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 δB0$$ \delta {\mathbf{B}}_{\mathbf{0}} $$ 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 δB0$$ \delta {\mathbf{B}}_{\mathbf{0}} $$ estimates. [ABSTRACT FROM AUTHOR]