title: Blind retrospective motion correction of MR images.
abstract: OBJECTIVE
  Subject motion can severely degrade MR images. A retrospective motion correction algorithm, Gradient-based motion correction, which significantly reduces ghosting and blurring artifacts due to subject motion was proposed. The technique uses the raw data of standard imaging sequences; no sequence modifications or additional equipment such as tracking devices are required. Rigid motion is assumed.
  
  
  METHODS
  The approach iteratively searches for the motion trajectory yielding the sharpest image as measured by the entropy of spatial gradients. The vast space of motion parameters is efficiently explored by gradient-based optimization with a convergence guarantee.
  
  
  RESULTS
  The method has been evaluated on both synthetic and real data in two and three dimensions using standard imaging techniques. MR images are consistently improved over different kinds of motion trajectories. Using a graphics processing unit implementation, computation times are in the order of a few minutes for a full three-dimensional volume.
  
  
  CONCLUSIONS
  The presented technique can be an alternative or a complement to prospective motion correction methods and is able to improve images with strong motion artifacts from standard imaging sequences without requiring additional data.
authors: Max Planck Institute for Intelligent Systems, Tübingen, Germany.
authors: Alexander
authors: A
authors: Loktyushin
authors: Hannes
authors: H
authors: Nickisch
authors: Rolf
authors: R
authors: Pohmann
authors: Bernhard
authors: B
authors: Schölkopf
mesh_terms: D000465:Algorithms; D000818:Animals; D016477:Artifacts; D001921:Brain / Q000033:anatomy & histology*; D000882:Haplorhini; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009038:Motion; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: autofocusing; gradient-based optimization; retrospective motion correction