On the quantitative potential of Viscoelastic Response (VisR) ultrasound using matrix array transducers: In silico demonstration

VisR ultrasound is an acoustic radiation force (ARF)-based imaging method that fits induced displacements to a 1D mass-spring-damper (MSD) model to estimate the ratio of viscous to elastic moduli, τ, in viscoelastic materials. A source of error in VisR τ estimation is complex and interrelated 3D system inertia. We hypothesize that error due to system inertia may be reduced by minimizing the volumetric extent of the employed ARF excitations, i.e. by reducing elevational and lateral F/#s using a matrix array transducer. This hypothesis was tested in silico using finite element method (FEM) models and Field II simulating homogeneous viscoelastic materials and viscoelastic materials with inclusions. In homogeneous viscoelastic materials, decreasing the elevational F/# from 5.0 to 0.75 yielded 62.5%, 96.7%, and 223.69% decreases in the median percent error in VisR τ estimates in materials with Young's modulus of 10, 50, and 100 kPa, respectively. In viscoelastic materials with inclusions, the elevational F/0.75 focal configuration better delineated inclusion borders in comparison to F/5.0, and measured contrast was closer to the true contrast. The CNRs achieved using elevational F/0.75 was 1.25 – 5.0 times higher than those from F/5.0. These results show that as the volumetric extent of ARF excitations decreases by reducing the elevational F/#, VisR τ estimates more closely approximate the true material τ. These results suggest that error in quantitative VisR τ estimates would be reduced by using a transducer capable of elevational focusing.