title: Comparison of optical and MR-based tracking.
abstract: OBJECTIVE
  The goal of this study was to compare the accuracy of two real-time motion tracking systems in the MR environment: MR-based prospective motion correction (PROMO) and optical moiré phase tracking (MPT).
  
  
  METHODS
  Five subjects performed eight predefined head rotations of 8° ± 3° while being simultaneously tracked with PROMO and MPT. Structural images acquired immediately before and after each tracking experiment were realigned with SPM8 to provide a reference measurement.
  
  
  RESULTS
  Mean signed errors (MSEs) in MPT tracking relative to SPM8 were less than 0.3 mm and 0.2° in all 6 degrees of freedom, and MSEs in PROMO tracking ranged up to 0.2 mm and 0.3°. MPT and PROMO significantly differed from SPM8 in y-translation and y-rotation values (P < 0.05). Maximum absolute errors ranged up to 2.8 mm and 2.1° for MPT, and 2.2 mm and 2.9° for PROMO.
  
  
  CONCLUSIONS
  This study presents the first in vivo comparison of MPT and PROMO tracking. Our data show that two methods yielded similar performances (within 1 mm and 1° standard deviation) relative to reference image registration. Tracking errors of both systems were larger than offline tests. Future work is required for further comparison of two methods in vivo with higher precision.
authors.affiliation: John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA.
authors.forename: Kazim
authors.initials: K
authors.lastname: Gumus
authors.affiliation: John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Keating
authors.affiliation: Department of Radiology, University of California, San Diego, La Jolla, California, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: White
authors.affiliation: Department of Military & Emergency Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland, USA.|Department of Radiology and Radiological Sciences, Uniformed Services University of the Health Sciences, Bethesda, Maryland, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Andrews-Shigaki
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Armstrong
authors.affiliation: Department of Radiology, University Medical Center Freiburg, Freiburg, Germany.|Department of Radiology, Stanford University, Stanford, California, USA.
authors.forename: Julian
authors.initials: J
authors.lastname: Maclaren
authors.affiliation: Department of Radiology, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Maxim
authors.initials: M
authors.lastname: Zaitsev
authors.affiliation: Department of Radiology, University of California, San Diego, La Jolla, California, USA.
authors.forename: Anders
authors.initials: A
authors.lastname: Dale
authors.affiliation: John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ernst
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D061848:Optical Imaging / Q000379:methods*
keywords: Moiré phase tracking; PROMO; head motion; navigator; prospective motion tracking