Anisotropic polyvinyl alcohol hydrogel phantom for shear wave elastography in fibrous biological soft tissue: a multimodality characterization

Abstract

Shear wave elastography imaging techniques provide quantitative measurement of soft tissues elastic properties. Tendons, muscles 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. Recently, a novel approach for orthotropic hydrogel mimicking soft tissues has been developed (Millon et al 2006 J. Biomed. Mater. Res. B 305-11). The mechanical anisotropy is induced in a polyvinyl alcohol (PVA) cryogel by stretching the physical crosslinks of the polymeric chains while undergoing freeze/thaw cycles. In the present study we propose an original multimodality imaging characterization of this new transverse isotropic (TI) PVA hydrogel. Multiple properties were investigated using a large variety of techniques at different scales compared with an isotropic PVA hydrogel undergoing similar imaging and rheology protocols. The anisotropic mechanical (dynamic and static) properties were studied using supersonic shear wave imaging technique, full-field optical coherence tomography (FFOCT) strain imaging and classical linear rheometry using dynamic mechanical analysis. The anisotropic optical and ultrasonic spatial coherence properties were measured by FFOCT volumetric imaging and backscatter tensor imaging, respectively. Correlation of mechanical and optical properties demonstrates the complementarity of these techniques for the study of anisotropy on a multi-scale range as well as the potential of this TI phantom as fibrous tissue-mimicking phantom for shear wave elastographic applications.

Characterization of transverse isotropy in compressed tissue-mimicking phantoms

“…Similar empirical results have been shown with polyvinyl alcohol (PVA) phantoms in which a phantom was stretched and underwent multiple freeze-thaw cycles to induce anisotropy in the homogeneous material [28, 29]. Using a homogeneous phantom is much easier than embedding fibers in an external matrix [11, 15].…”

Multimodal 3D cancer-mimicking optical phantom

“…The difficulty in creating realistic bladder phantoms stems largely from the limitations of currently used materials (e.g., PDMS [17][18][19], PVA-C [20][21][22], latex [13]) and fabrication techniques (e.g., lathe-spinning [14], painting [13], and spin-coating [17,23]) for phantom creation. Importantly, with the emergence and clear clinical utility of multi-modality imaging technologies (e.g., WLC+OCT and WLC+BLC) it is also crucial for such phantoms to exhibit properties visible with multiple modalities.…”

Development and Application of Optical Coherence Tomography (OCT)

“…Using this parameter, it is possible to differentiate isotropic from anisotropic strain. In Figure 3E,G, we show that computing the fractional anisotropy in isotropic and anisotropic polyvinyl alcohol (PVA) polymer gels [96] enables discrimination of the two samples, in a case where FF-OCT fails to detect a difference.…”

“…Providing the same sensitivity and speed advantages as spectrometer-based Fourier domain OCT, SS-OCT was soon expanded by polarization sensitivity [47,71,75,[93][94][95][96][97]. In particular the advent of commercial laser technology providing longer imaging ranges led to the development of PS-OCT at ultrahigh imaging speeds of 100,000 axial scans per second [18,54,73,74,98].…”