title: On the significance of motion degradation in high-resolution 3D μMRI of trabecular bone.
abstract: OBJECTIVE
  Subtle subject movement during high-resolution three-dimensional micro-magnetic resonance imaging of trabecular bone (TB) causes blurring, thereby rendering the data unreliable for quantitative analysis. In this work, the effects of translational and rotational motion displacements were evaluated qualitatively and quantitatively.
  
  
  METHODS
  In experiment 1, motion was induced by applying various simulated and previously observed in vivo trajectories as phase shifts to k-space or rotation angles to k-space segments of a virtually motion-free data set. In experiment 2, images that were visually free of motion artifacts from two groups of 10 healthy individuals, differing in age, were selected to probe the effects of motion on TB parameters. In both experiments, images were rated for motion severity, and the scores were compared to a focus criterion, the normalized gradient squared.
  
  
  RESULTS
  Strong correlations were observed between the motion quality scores and the corresponding normalized gradient squared values (R(2) = 0.52-0.64, P < .01). The results from experiment 1 demonstrated consistently lower image quality and alterations in structural parameters of 9% to 45% with increased amplitude of displacements. In experiment 2, the significant differences in structural parameter group means of the motion-free images were lost upon motion degradation. Autofocusing, a postprocessing correction method, partially recovered the sharpness of the original motion-free images in 13 of 20 subjects.
  
  
  CONCLUSIONS
  Quantitative TB structural measures are highly sensitive to subtle motion-induced degradation, which adversely affects precision and statistical power. The results underscore the influence of subject movement in high-resolution three-dimensional micro-magnetic resonance imaging and its correction for TB structure analysis.
authors.affiliation: Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, 19104, USA.
authors.forename: Yusuf A
authors.initials: YA
authors.lastname: Bhagat
authors.forename: Chamith S
authors.initials: CS
authors.lastname: Rajapakse
authors.forename: Jeremy F
authors.initials: JF
authors.lastname: Magland
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Wald
authors.forename: Hee Kwon
authors.initials: HK
authors.lastname: Song
authors.forename: Mary B
authors.initials: MB
authors.lastname: Leonard
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D000328:Adult; D016477:Artifacts; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009038:Motion; D013977:Tibia / Q000033:anatomy & histology*