title: Additional sampling directions improve detection range of wireless radiofrequency probes.
abstract: While MRI is enhancing our knowledge about the structure and function of the human brain, subject motion remains a problem in many clinical applications. Recently, the use of wireless radiofrequency markers with three one-dimensional (1D) navigators for prospective correction was demonstrated. This method is restricted in the range of motion that can be corrected, however, because of limited information in the 1D readouts.
  
  
  
  Here, the limitation of techniques for disambiguating marker locations was investigated. It was shown that including more sampling directions extends the tracking range for head rotations. The efficiency of trading readout resolution for speed was explored.
  
  
  
  Tracking of head rotations was demonstrated from -19.2 to 34.4°, -2.7 to 10.0°, and -60.9 to 70.9° in the x-, y-, and z-directions, respectively. In the presence of excessive head motion, the deviation of marker estimates from SPM8 was reduced by 17.1% over existing three-projection methods. This was achieved by using an additional seven directions, extending the time needed for readouts by a factor of 3.3. Much of this increase may be circumvented by reducing resolution, without compromising accuracy.
  
  
  
  Including additional sampling directions extends the range in which markers can be used, for patients who move a lot. Magn Reson Med 76:913-918, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
authors.affiliation: Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Malte
authors.identifier: 0000-0002-5511-0739
authors.initials: M
authors.lastname: Hoffmann
authors.affiliation: Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Marius
authors.initials: M
authors.lastname: Mada
authors.affiliation: Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom.
authors.forename: T Adrian
authors.initials: TA
authors.lastname: Carpenter
authors.affiliation: Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom.|Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Sawiak
authors.affiliation: Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Guy B
authors.initials: GB
authors.lastname: Williams
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D057918:Fiducial Markers; D019416:Head Movements; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation* / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D011846:Radio Waves; D015203:Reproducibility of Results; D018401:Sample Size; D012680:Sensitivity and Specificity; D014159:Transducers; D059015:Wireless Technology / Q000295:instrumentation*
keywords: head motion; prospective correction; wireless RF markers