Magnetorheological Gel Mimicking Cervical Ripening as a Potential Model for Evaluating Shear Wave Elastography

The mechanical characteristics of tissue can reflect its biochemical content and, therefore, be a powerful tool in the diagnosis of diseases. Many different methods have been developed for testing the mechanical properties of tissue, such as aspiration, indentation and shear wave elastography. Soft tissues are, however, more complex in behaviour than current commercial tissue-mimicking materials and the models used in measurement methods. Complex behaviours of the tissue include anisotropy and heterogeneous elasticity. The oversimplified models assumed in different measuring methods often neglect the effects of these behaviours, resulting in inaccuracies. The aim of this study was to develop a tissue-mimicking material able to capture the complexity of tissue mechanical behaviour. It will be used to improve mechanical property measuring methods by quantitatively determining how complexities in tissue behaviour affect the measurements made and evaluating the effectiveness of methods designed to overcome it, and will be used to train users for consistency in measurement. The tissue-mimicking material designed in this study focuses on the mechanical properties of the cervix as measured by shear wave elastography. The characteristic behaviours of cervical tissues highlighted are anisotropy, a wide range of elasticity that changes with gestational age and an elasticity gradient across the tissue. Magnetorheological gels were used as their elastic properties can be tuned with the application of magnetic fields. The sample was simulated with the finite-element software COMSOL before being tested by shear wave elastography and the INSTRON universal material testing machine. It had an elasticity range of 6.75-11.06 kPa, which is similar to that of cervical tissue. It was determined that a change in the orientation of the probe with respect to the orientation of anisotropy can cause up to a 30 % increase in measured elasticity. There was a 16% decrease in elasticity across the sample.