Research
Characterizing in vivo skeletal muscle as a elastic, incompressible, transversely isotropic material
Shear wave elastography imaging (SWEI) is currently used to characterize in many tissues under the assumptions of the material being linear, incompressible, elastic (or viscoelastic) and isotropic. However, skeletal muscle is known to have a directionality to the fibers, with different mechanical properties along and across the fibers, and is often modeled as a transversely isotropic material. In an incompressible transversely isotropic material, there are three material parameters: 1) the transverse shear modulus, 2) the longitudinal shear modulus, and 3) a term that relates the longitudinal and transverse Young's moduli, often called tensile anisotropy. In many works to date, the two shear moduli are measured by looking at the SWEI shear wave speed along and across the muscle fibers with the transducer face parallel to the fiber direction. In an incompressible transversely isotropic material, multiple polarizations of shear waves exist: the shear horizontal (SH) and shear vertical (SV). To be able to measure the third parameter, tensile anisotropy, both the SH and and SV waves must be measured in vivo. Using 3D rotational SWEI in vivo in the vastus lateralis muscle, we demonstrated that acoustic radiation force (ARF) ultrasound pulses can be used to induce and measure ultrasonically both SH and SV waves, and then relate the measurements to tensile anisotropy. This work can be seen here.
Wave Guide Behavior in Shear Wave Elastography in in vivo Skin
In skin both with and without sclerotic conditions, the behavior of shear waves in the dermal layer is affected by the thickness of the dermal layer, as it begins to exhibit plate like behavior. My work hopes to further strategies for normalizing based on shear wave frequency and dermal geometry (thickness) to allow shear wave speed to act as a better biomarker for sclerotic skin conditions. This work has been published in IEEE Proceedings of IUS and can be seen here
Shear Wave Elasticity Imaging of Carpal Tunnel Syndrome
One of my first research projects in the ultrasound space focused on using ultrasound shear wave elasticity imaging to characterize the stiffness of the median nerve in patients with carpal tunnel syndrome. Our work evaluated the many challenges in using SWEI to measure the median nerve in vivo. This work was published in Ultrasound in Medicine and Biology and can be seen here