Anisotropic polyvinyl alcohol hydrogel phantom for shear wave elastography in fibrous biological soft tissue

Shear wave elastography can provide quantitative evaluation of soft tissues viscoelastic properties based on the measurement of shear wave speed in the medium. Muscular and cerebral tissues are composed of fibers which induce a strong anisotropic effect on the mechanical behavior. Currently, these tissues cannot be accurately represented by existing elastography phantoms and there is an urgent need of developing new anisotropic tissue mimicking phantoms. In the present study we propose an original multimodality imaging characterization of a transverse isotropic (TI) polyvinyl alcohol (PVA) cryogel. The mechanical anisotropy is induced in the PVA hydrogel by stretching the physical crosslinks of the polymeric chains while undergoing freezing cycling [1]. Multiple properties of these phantoms were investigated using a variety of techniques at different scale. The mechanical (dynamic and static) properties were studied using Supersonic Shear wave Imaging (SSI) technique [2] and Full-Field Optical Coherence Tomography (FF-OCT) strain imaging. The optical and ultrasonic spatial coherence properties were measure by FF-OCT volumetric imaging [3] and Backscatter Tensor Imaging (BTI) [4], respectively. The results suggest that this type of phantom (TI) could be used in the development of techniques and equipment to study anisotropy, such as the design of new ultrasound probes for cardiac and musculoskeletal application.