Measured Hyperelastic Properties of Cervical Tissue with Shear-Wave Elastography

The nonlinear mechanical behaviour of cervical tissue causes unpredictable changes in measured elastograms when pressure is applied. These uncontrolled variables prevent the reliable measurement of tissue elasticity in a clinical setting. Measuring the nonlinear properties of tissue is difficult due to the need for both shear modulus and strain to be taken simultaneously. A simulationbased method is proposed in this paper to resolve this. This study describes the nonlinear behaviour of cervical tissue using the hyperelastic material models of Demiray-Fung and Veronda-Westmann. Elastograms from 33 low-risk patients between 18 and 22 weeks gestation were obtained. The average measured properties of the hyperelastic material models are: Demiray-Fung—Aa = 2.07 (1.65-2.58) kPa, a = 6.74 (4.07-19.55); Veronda-Westmann—CC = 4.12 (3.24-5.04) kPa, C = 4.86 (2.86-14.28). The Demiray-Fung and Veronda-Westmann models performed similarly in fitting to the elastograms with an average root mean square deviation of 0.41 and 0.47 ms, respectively. The use of hyperelastic material models to calibrate shear-wave speed measurements improved the consistency of measurements. This method could be applied in a large-scale clinical setting but requires updated models and higher data resolution.