title: Tracking discrete off-resonance markers with three spokes (trackDOTS) for compensation of head motion and B0perturbations: Accuracy and performance in anatomical imaging.
abstract: OBJECTIVE
  To develop a novel approach for head motion and B0field monitoring based on tracking discrete off-resonance markers with three spokes (trackDOTS).
  
  
  METHODS
  Small markers filled with acetic acid were built and attached to a head cap. Marker positions and phase were tracked with fast MR navigators (DotNavs) consisting of three off-resonance, double-echo, orthogonal one-dimensional projections. Individual marker signals were extracted using optimized coil combinations, and used to estimate head motion and field perturbations. To evaluate the approach, DotNavs were integrated in submillimeter MP2RAGE and long-echo time gradient-echo sequences at 7 Tesla, and tested on six healthy volunteers.
  
  
  RESULTS
  The DotNav-based motion estimates differed by less than 0.11 ± 0.09 mm and 0.19 ± 0.17 ° from reference estimates obtained with an existing navigator approach (FatNavs). Retrospective motion correction brought clear improvements to MP2RAGE image quality, even in cases with submillimeter involuntary motion. The DotNav-based field estimates could track deep breathing-induced oscillations, and in cases with small head motion, field correction visibly improved the gradient-echo data quality. Conversely, field estimates were less robust when strong motion was present.
  
  
  CONCLUSIONS
  The trackDOTS approach is suitable for head-motion tracking and correction, with significant benefits for high-spatial-resolution MRI. With small head motion, DotNav-based field estimates also allow correcting for deep-breathing artifacts in T2*-weighted acquisitions. Magn Reson Med 79:160-171, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: João
authors.initials: J
authors.lastname: Jorge
authors.affiliation: Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Gretsch
authors.affiliation: Biomedical Imaging Research Center, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Gallichan
authors.affiliation: Donders Institute, Radboud University, Nijmegen, the Netherlands.
authors.forename: José P
authors.initials: JP
authors.lastname: Marques
mesh_terms: D019342:Acetic Acid / Q000737:chemistry; D000328:Adult; D000465:Algorithms; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007659:Ketones / Q000737:chemistry; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009038:Motion; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio
chemical_list: D007659:Ketones; D019342:Acetic Acid
keywords: B0 field monitoring; navigators; retrospective motion correction; trackDOTS