title: A framework for optimization-based design of motion encoding in magnetic resonance elastography.
abstract: OBJECTIVE
  In conventional three-dimensional magnetic resonance elastography, motion encoding gradients (MEGs) synchronized to a mechanical excitation are applied separately in each direction to encode tissue displacement generated by the corresponding waves. This requires long acquisition times that introduce errors due to patient motion and may hinder clinical deployment of magnetic resonance elastography. In this article, a framework for MEGs sequence design is proposed to reduce scanning time and increase signal-to-noise ratio.
  
  
  METHODS
  The approach is based on applying MEGs in all three directions simultaneously with varying parameters, and formulation of the problem as a linear estimation of the wave properties. Multidirectional MEGs sequences are derived by setting the problem in an experimental design framework. Such designs are implemented and evaluated on simulation and phantom data.
  
  
  RESULTS
  Estimation error of the displacement using the proposed MEGs designs is reduced up to a factor of two in comparison with a unidirectional design with a same number of acquisitions. Alternatively, for the same error, scanning time is reduced up to a factor of three using the multidirectional designs.
  
  
  CONCLUSIONS
  The proposed framework generalizes acquisition of magnetic resonance elastography, and allows quantification of design performance, and optimization-based derivation of designs.
authors.affiliation: Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, Canada.
authors.forename: Guy
authors.initials: G
authors.lastname: Nir
authors.forename: Ramin S
authors.initials: RS
authors.lastname: Sahebjavaher
authors.forename: Ralph
authors.initials: R
authors.lastname: Sinkus
authors.forename: Septimiu E
authors.initials: SE
authors.lastname: Salcudean
mesh_terms: D003198:Computer Simulation; D055119:Elastic Modulus / Q000502:physiology*; D054459:Elasticity Imaging Techniques / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D016247:Information Storage and Retrieval / Q000379:methods*; D008954:Models, Biological; D009038:Motion; D009068:Movement / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: elastography; experimental design; linear estimation; magnetic resonance imaging