Quantitative sonoelastography of the uterine cervix by interposition of a synthetic reference material.

Objective: To develop a reference material that allows quantitative elastography of the uterine cervix using the calculation of the approximate tissue stiffness expressed as Young's modulus (N/mm(2) ). Further, to test the elastography equipment on phantoms from a clinical perspective regarding the distance dependence and the influence of a heterogeneous material.

Design: Methodological study.

Setting: Aarhus University Hospital, Denmark.

Population: Six mid- and five full-term pregnant women.

Methods: Reference caps and phantoms with Young's moduli between 0.07 and 0.40 N/mm(2) were made of silicone and oil. By using reference caps, the approximate Young's moduli of the cervixes were calculated from strain ratios obtained by elastography.

Main Outcome Measures: Approximate Young's modulus of the cervix.

Results: The recordings of the phantoms revealed that the calculation of the approximate Young's moduli became unreliable at distances above 10-15 mm from the transducer. This was further increased for a phantom which included a soft layer imitating the cervical canal. The approximate Young's modulus obtained from the anterior cervical lip was 0.08 N/mm(2) in mid-term and 0.03 N/mm(2) in full-term pregnant women (Wilcoxon rank-sum test, p = 0.01).

Conclusion: The reference cap constitutes a promising tool for quantitative elastography of the anterior cervical lip. Figures obtained from the posterior cervical lip are less plausible due to the distance from the transducer and the heterogeneity introduced by the cervical canal. The method has the potential to be used to supplement cervical length assessment when evaluating women at risk of preterm delivery and when planning induction of labor.