title: Ultrasound viscoelasticity assessment using an adaptive torsional shear wave propagation method.
abstract: OBJECTIVE
  Different approaches have been used in dynamic elastography to assess mechanical properties of biological tissues. Most techniques are based on a simple inversion based on the measurement of the shear wave speed to assess elasticity, whereas some recent strategies use more elaborated analytical or finite element method (FEM) models. In this study, a new method is proposed for the quantification of both shear storage and loss moduli of confined lesions, in the context of breast imaging, using adaptive torsional shear waves (ATSWs) generated remotely with radiation pressure.
  
  
  METHODS
  A FEM model was developed to solve the inverse wave propagation problem and obtain viscoelastic properties of interrogated media. The inverse problem was formulated and solved in the frequency domain and its robustness to noise and geometric constraints was evaluated. The proposed model was validated in vitro with two independent rheology methods on several homogeneous and heterogeneous breast tissue-mimicking phantoms over a broad range of frequencies (up to 400 Hz).
  
  
  RESULTS
  Viscoelastic properties matched benchmark rheology methods with discrepancies of 8%-38% for the shear modulus G' and 9%-67% for the loss modulus G″. The robustness study indicated good estimations of storage and loss moduli (maximum mean errors of 19% on G' and 32% on G″) for signal-to-noise ratios between 19.5 and 8.5 dB. Larger errors were noticed in the case of biases in lesion dimension and position.
  
  
  CONCLUSIONS
  The ATSW method revealed that it is possible to estimate the viscoelasticity of biological tissues with torsional shear waves when small biases in lesion geometry exist.
authors.affiliation: Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9, Canada and Institute of Biomedical Engineering, University of Montréal, Montréal, Québec H3T 1J4, Canada.
authors.forename: Abderrahmane
authors.initials: A
authors.lastname: Ouared
authors.affiliation: Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9, Canada.
authors.forename: Siavash
authors.initials: S
authors.lastname: Kazemirad
authors.affiliation: Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9, Canada.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Montagnon
authors.affiliation: Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9, Canada; Department of Radiology, Radio-Oncology and Nuclear Medicine, University of Montréal, Montréal, Québec H3T 1J4, Canada; and Institute of Biomedical Engineering, University of Montréal, Montréal, Québec H3T 1J4, Canada.
authors.forename: Guy
authors.initials: G
authors.lastname: Cloutier
mesh_terms: D001940:Breast / Q000166:cytology / Q000000981:diagnostic imaging* / Q000473:pathology; D004548:Elasticity; D054459:Elasticity Imaging Techniques / Q000379:methods*; D020342:Finite Element Analysis; D006801:Humans; D019047:Phantoms, Imaging; D033081:Shear Strength; D014783:Viscosity