Displacement control device for dynamic tissue deformation in MRI - biomed 2010

Several methods have been used to create controlled motion in an MRI bore using traditional motors that operate at a large distance away from the bore. The purpose of this effort is to develop a device to precisely control deflection of tissue while measuring interface loads within an MRI bore. Displacement of a tissue sample is provided via a non-ferromagnetic linear piezoelectric motor mounted on an aluminum sliding stage. A software program is developed to synchronize and gate the motor motion with the pulse sequence of the MRI using signals sent by the MRI controller. The piezoelectric motor has submicron position precision with closed loop encoder control allowing for accurate control. The motor encoder relays position data to the motor control software which is used to calculate the deflection, velocity, strain, and strain rate. An end effecter is mounted to the motor stage and transmits load to the tissue. The end effecter will contain a single axis load cell to record the compression force during displacement. Tissue samples are contained within an acrylic container and immersed in saline solution. The motor stage and container are mounted on a stack of sliding platforms that allow the user to easily move the motor stage and end indenter relative to the container or the motor stage, end effecter, and container relative to the MRI head coil. These degrees of freedom provide the user a means for quick and easy test setup. The device will measure strain, strain rate, and load in time. It will provide a tool to relate external tissue load, strain, and strain rate to internal three-dimensional strain fields which in turn will be used to quantify viscoelastic tissue stiffness.