title: Subzone based magnetic resonance elastography using a Rayleigh damped material model.
abstract: OBJECTIVE
  Recently, the attenuating behavior of soft tissue has been addressed in magnetic resonance elastography by the inclusion of a damping mechanism in the methods used to reconstruct the resulting mechanical property image. To date, this mechanism has been based on a viscoelastic model for material behavior. Rayleigh, or proportional, damping provides a more generalized model for elastic energy attenuation that uses two parameters to characterize contributions proportional to elastic and inertial forces. In the case of time-harmonic vibration, these two parameters lead to both the elastic modulus and the density being complex valued (as opposed to the case of pure viscoelasticity, where only the elastic modulus is complex valued).
  
  
  METHODS
  This article presents a description of Rayleigh damping in the time-harmonic case, discussing the differences between this model and the viscoelastic damping models. In addition, the results from a subzone based Rayleigh damped elastography study of gelatin and tofu phantoms are discussed, along with preliminary results from in vivo breast data.
  
  
  RESULTS
  Both the phantom and the tissue studies presented here indicate a change in the Rayleigh damping structure, described as Rayleigh composition, between different material types, with tofu and healthy tissue showing lower Rayleigh composition values than gelatin or cancerous tissue.
  
  
  CONCLUSIONS
  It is possible that Rayleigh damping elastography and the concomitant Rayleigh composition images provide a mechanism for differentiating tissue structure in addition to measuring elastic stiffness and attenuation. Such information could be valuable in the use of Rayleigh damped magnetic resonance elastography as a diagnostic imaging tool.
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, Canterbury 8140, New Zealand. elijah.vanhouten@canterbury.ac.nz
authors.forename: Elijah E W
authors.initials: EE
authors.lastname: Van Houten
authors.forename: D vR
authors.initials: Dv
authors.lastname: Viviers
authors.forename: M D J
authors.initials: MD
authors.lastname: McGarry
authors.forename: P R
authors.initials: PR
authors.lastname: Perriñez
authors.forename: I I
authors.initials: II
authors.lastname: Perreard
authors.forename: J B
authors.initials: JB
authors.lastname: Weaver
authors.forename: K D
authors.initials: KD
authors.lastname: Paulsen
mesh_terms: D001696:Biomechanical Phenomena; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D054459:Elasticity Imaging Techniques / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008954:Models, Biological; D019047:Phantoms, Imaging