title: Registration-based autofocusing technique for automatic correction of motion artifacts in time-series studies of high-resolution bone MRI.
abstract: OBJECTIVE
  To develop a registration-based autofocusing (RAF) motion correction technique for high-resolution trabecular bone (TB) imaging and to evaluate its performance on in vivo MR data.
  
  
  METHODS
  The technique combines serial registration with a previously developed motion correction technique - autofocusing - for automatic correction of subject movement degradation of MR images acquired in longitudinal studies. The method was tested on in vivo images of the distal radius to measure improvements in serial reproducibility of parameters in 12 women (ages 50-75 years), and to compare with the navigator echo-based correction and autofocusing. Furthermore, the technique's ability to optimize the sensitivity to detect simulated bone loss was ascertained.
  
  
  RESULTS
  The new technique yielded superior reproducibility of image-derived structural and mechanical parameters. Average coefficient of variation across all parameters improved by 12.5%, 27.0%, 33.5%, and 37.0%, respectively, following correction by navigator echoes, autofocusing, and the RAF technique (without and with correction for rotational motion); average intra-class correlation coefficient increased by 1.2%, 2.2%, 2.8%, and 3.2%, respectively. Furthermore, simulated bone loss (5%) was well recovered independent of the choice of reference image (4.71% or 4.86% with respect to using either the original or the image subjected to bone loss) in the time series.
  
  
  CONCLUSIONS
  The data suggest that our technique simultaneously corrects for intra-scan motion corruption while improving inter-scan registration. Furthermore, the technique is not biased by small changes in bone architecture between time-points.
authors.affiliation: Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania, USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.forename: Jeremy F
authors.initials: JF
authors.lastname: Magland
authors.forename: Hee Kwon
authors.initials: HK
authors.lastname: Song
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D000368:Aged; D000465:Algorithms; D016477:Artifacts; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D009038:Motion; D010363:Pattern Recognition, Automated / Q000379:methods*; D011884:Radius / Q000033:anatomy & histology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique
keywords: MRI; motion correction; reproducibility; trabecular bone