Abstract
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 simulation-based 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— = 2.07 (1.65–2.58) kPa, = 6.74 (4.07–19.55); Veronda–Westmann— = 4.12 (3.24–5.04) kPa, = 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.
Highlights
The use of Shear-wave Elastography (SWE) has garnered significant interest in the medical community
The overall objective of this work is to generate a practical framework to measure the nonlinear properties of cervical tissue using shear-wave elastography in a clinical environment and use it to calibrate the “tissue stiffening” effects
The results show that for the nonlinear characteristics of cervical tissue to be effectively measured in a clinical setting, the raw output from the ultrasound machines is required
Summary
The use of Shear-wave Elastography (SWE) has garnered significant interest in the medical community. The ability to quantitatively measure tissue elasticity has been used with different levels of success to evaluate pathologies in various fields. Some examples include evaluating liver fibrosis [1,2], differentiating between benign and malignant breast lesions [3,4], and evaluating tendon injury [5,6]. There is interest in using the elasticity of cervical tissue as a diagnostic tool. The elasticity of the cervical tissue changes throughout the pregnancy to accommodate the changes in its function. The initial role of the cervix is to provide mechanical support to the fetus. At the point of labour, the elasticity of the cervix decreases drastically to allow the passage of the fetus through the birth canal without causing excessive tissue damage
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