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 (B0) perturbations ((Formula presented.)) 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 (Formula presented.). In this work, called QUEEN (QUantitatively Enhanced parameter Estimation from Navigators), we propose combined motion and (Formula presented.) 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 (Formula presented.) are integrated into a motion-informed parallel-imaging framework. Results: Simulations and in vivo experiments show the need to model (Formula presented.) to obtain accurate motion parameters estimated in the presence of strong (Formula presented.). Simulations confirm that tailored navigator trajectories are needed to robustly estimate both motion and (Formula presented.). 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 (Formula presented.) 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 (Formula presented.) estimates.