title: Global approach for transient shear wave inversion based on the adjoint method: a comprehensive 2D simulation study.
abstract: Shear wave imaging (SWI) maps soft tissue elasticity by measuring shear wave propagation with ultrafast ultrasound acquisitions (10 000 frames s(-1)). This spatiotemporal data can be used as an input for an inverse problem that determines a shear modulus map. Common inversion methods are local: the shear modulus at each point is calculated based on the values of its neighbour (e.g. time-of-flight, wave equation inversion). However, these approaches are sensitive to the information loss such as noise or the lack of the backscattered signal. In this paper, we evaluate the benefits of a global approach for elasticity inversion using a least-squares formulation, which is derived from full waveform inversion in geophysics known as the adjoint method. We simulate an acoustic waveform in a medium with a soft and a hard lesion. For this initial application, full elastic propagation and viscosity are ignored. We demonstrate that the reconstruction of the shear modulus map is robust with a non-uniform background or in the presence of noise with regularization. Compared to regular local inversions, the global approach leads to an increase of contrast (∼+3 dB) and a decrease of the quantification error (∼+2%). We demonstrate that the inversion is reliable in the case when there is no signal measured within the inclusions like hypoechoic lesions which could have an impact on medical diagnosis.
authors.affiliation: Institut Langevin, ESPCI ParisTech, CNRS UMR 7587, INSERM U979, Université Paris Diderot, France.
authors.forename: B
authors.initials: B
authors.lastname: Arnal
authors.forename: G
authors.initials: G
authors.lastname: Pinton
authors.forename: P
authors.initials: P
authors.lastname: Garapon
authors.forename: M
authors.initials: M
authors.lastname: Pernot
authors.forename: M
authors.initials: M
authors.lastname: Fink
authors.forename: M
authors.initials: M
authors.lastname: Tanter
mesh_terms: D000465:Algorithms; D054459:Elasticity Imaging Techniques / Q000379:methods*; D008962:Models, Theoretical