Ultrasound shear-wave computed tomography for elasticity imaging

Shear-wave elasticity imaging (SWEI) has been routinely used for measuring the elastic properties of tissues. It is potentially applicable to three-dimensional (3D) cell culture systems and may outperform existing methods such as atomic force microscopy and shear rheology in terms of being contactless and having higher spatial resolution and penetration. However, applying clinical SWEI to 3D cell culture systems requires the developments of high-frequency SWEI systems operating at >20 MHz that are compatible with the scale of cell culture systems, and C-scan 3D SWEI well suited to such observations. In this study, we implemented a computed tomography (CT) technique for SWEI (called SWCT) by leveraging the scanning scheme used in first-generation x-ray CT systems, that is, translation and rotation of a 20-MHz push probe and a 40-MHz imaging probe to obtain time-of-flight projections for multiple viewing directions. Compared with conventional B-scan SWEI, the proposed reconstruction method allows high-resolution, robust, 3D C-scan imaging of the shear-wave speed distribution. Three phantoms with different inclusions (half circle, thin strip, and cylinder) were imaged using 3D SWCT to a depth of 13 mm. The estimated shear-wave speed for the strip phantom using SWCT was 1.23 ± 0.20 m/s (mean ± standard deviation) in the background and 2.27 ± 0.11 m/s for the inclusion, which suggests the feasibility of SWCT for improving elasticity measurements of cell culture systems.