Shear wave elastography in obstetrics: Quantification of cervix elasticity and uterine contraction

Supersonic Shear Imaging (SSI) is a real-time and quantitative imaging technique that has been proved efficient for tissue elasticity investigation. Very little is known about the physiology of cervix and uterus and SSI could be an efficient tool for a deeper understanding of uterine mechanisms. This could considerably help prevention of premature birth, which consequences on neonate morbidity and pathologies are tremendous. The purpose of this paper is to investigate in vivo the elasticity of the cervix and uterus during pregnancy using SSI with three objectives: the quantification of cervix elasticity, the follow up of uterine elasticity during contraction, and the investigation of uterine anisotropy. In this study, remote palpation using radiation force and ultrafast imaging sequences were adapted on the Aixplorer for the investigation of uterine contraction, as well as for uterine anisotropy estimation. Cervix elasticity was quantified in 20 gravid women using a 7 MHz endocavitary probe. Uterus elasticity was quantified externally on 5 patients, through the abdomen, using an 8 MHz linear probe. Changes of elasticity were tracked in real time during uterus contraction. Shear wave tractography (imaging of fiber orientation) was performed with the same probe by assessing shear wave speed variations with respect to probe angle. This allowed the investigation of uterine anisotropy at different depths. Elasticity values during contraction were correlated to uterine pressure data, which is the gold standard for contraction monitoring. Finally, uterine fiber orientation was observed at different depths.