title: Optical tracking with two markers for robust prospective motion correction for brain imaging.
abstract: OBJECTIVE
  Prospective motion correction (PMC) during brain imaging using camera-based tracking of a skin-attached marker may suffer from problems including loss of marker visibility due to the coil and false correction due to non-rigid-body facial motion, such as frowning or squinting. A modified PMC system is introduced to mitigate these problems and increase the robustness of motion correction.
  
  
  METHODS
  The method relies on simultaneously tracking two markers, each providing six degrees of freedom, that are placed on the forehead. This allows us to track head motion when one marker is obscured and detect skin movements to prevent false corrections. Experiments were performed to compare the performance of the two-marker motion correction technique to the previous single-marker approach.
  
  
  RESULTS
  Experiments validate the theory developed for adaptive marker tracking and skin movement detection, and demonstrate improved image quality during obstruction of the line-of-sight of one marker when subjects squint or when subjects squint and move simultaneously.
  
  
  CONCLUSIONS
  The proposed methods eliminate two common failure modes of PMC and substantially improve the robustness of PMC, and they can be applied to other optical tracking systems capable of tracking multiple markers. The methods presented can be adapted to the use of more than two markers.
authors.affiliation: Department of Medicine, The Queen's Medical Center, John A. Burns School of Medicine, University of Hawaii, 1356 Lusitana Street 7th Floor, Honolulu, HI, 96813, USA. singha@hawaii.edu.
authors.forename: Aditya
authors.initials: A
authors.lastname: Singh
authors.affiliation: Department of Medicine, The Queen's Medical Center, John A. Burns School of Medicine, University of Hawaii, 1356 Lusitana Street 7th Floor, Honolulu, HI, 96813, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Zahneisen
authors.affiliation: Department of Medicine, The Queen's Medical Center, John A. Burns School of Medicine, University of Hawaii, 1356 Lusitana Street 7th Floor, Honolulu, HI, 96813, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Keating
authors.affiliation: Department of Medicine, The Queen's Medical Center, John A. Burns School of Medicine, University of Hawaii, 1356 Lusitana Street 7th Floor, Honolulu, HI, 96813, USA.|Department of Diagnostic Radiology, Medical Physics, Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Herbst
authors.affiliation: Department of Medicine, The Queen's Medical Center, John A. Burns School of Medicine, University of Hawaii, 1356 Lusitana Street 7th Floor, Honolulu, HI, 96813, USA.
authors.forename: Linda
authors.initials: L
authors.lastname: Chang
authors.affiliation: Department of Diagnostic Radiology, Medical Physics, Freiburg, Germany.
authors.forename: Maxim
authors.initials: M
authors.lastname: Zaitsev
authors.affiliation: Department of Medicine, The Queen's Medical Center, John A. Burns School of Medicine, University of Hawaii, 1356 Lusitana Street 7th Floor, Honolulu, HI, 96813, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ernst
mesh_terms: D016477:Artifacts; D001931:Brain Mapping / Q000379:methods*; D057918:Fiducial Markers; D005546:Forehead; D019416:Head Movements; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D055096:Optical Devices; D019047:Phantoms, Imaging
keywords: Brain; MRI; Motion artifacts; Motion correction; Optical tracking