Imaging viscoelastic properties of the vitreous
It is well known that changes in the mechanical properties of tissues are correlated with the presence of disease. In the eye, the vitreous body goes through mechanical changes with age, which may eventually lead to the formation of retinal detachment. We are developing a method to detect these mechanical changes using a non-invasive technique called KAVE (Kinetic Acoustic Vitreoretinal Examination). KAVE uses acoustic radiation force as a means to produce small, localized displacements within the tissues. Returning echoes are processed using ultrasonic motion tracking so that the response of the tissue to the induced force can be evaluated. By repeating this process at a number of locations, images depicting viscoelastic properties of tissues can be formed. We have developed and tested a new mechanical model to describe vitreous mimicking phantoms. Through the combination of appropriate modeling and signal processing, we are able to generate images of relative parameters such as relative mass, relative elasticity, and relative viscosity. These parameters are called relative because they depend on the force applied. In this paper, we also present force-free images, which include images of the time constant τ, the damping ratio ξ, and the natural frequency ω of the phantom. These images are significant in that they lack the artifacts common in the relative property images.
