Viscoelastic Characterization of an Agar Tissue Phantom Using Acoustic Microelastography

Elastography has long been used as a diagnostic tool in the clinic. This technique assesses tissue elasticity qualitatively or quantitatively in several pathologies, including liver fibrosis and some cancers. Most acoustic elastography approaches are based on the overall evaluation of the region/organ of interest. In contrast, microelastography is a technique that enables quantification of the stiffness at microscale spatial resolution. Acoustic impedance, the main component responsible for ultrasound imaging, varies with bulk modulus and mass density; thus, it can be used to characterize the material properties. However, in situ, spatial mapping of tissue properties at the microscale has rarely been studied. In this work, we combined acoustic actuation, high spatiotemporal resolution imaging, and computer vision to enable quantitative mapping of the mechanical properties of agar tissue phantoms at the microscale. We used a customized electrodynamic resonant vibration actuator at 2065 Hz to generate Rayleigh waves in the tissue phantoms, which were recorded at 9501 frames per second (fps). The resulting videos were analyzed using computer vision tools to quantify the speed of the acoustic shear wave and determine the shear modulus and viscosity of agar with an input of density. To validate our microelastography measurements, we performed oscillatory rheology using a parallel plate rheometer from 0.1-100 Hz, quantified the dynamic viscoelastic properties of agar, and extrapolated the measurements to the acoustic microelastography working frequency. The results from the two methods are in good agreement, showing a difference of 4.7%. In the future, we will adapt this technique for the spatial evaluation of mechanical properties of heterogeneous cancerous tissues at higher resolutions. Such capability can enable effective diagnosis and development of patient-specific treatment regimens.