Quantitative Ultrasound Biomarkers Based on Backscattered Acoustic Power: Potential for Quantifying Remodeling of the Human Cervix during Pregnancy

Abstract

As pregnancy progresses, the cervix remodels from a rigid structure to one compliant enough to allow delivery of a fetus, a process which involves progressive disorganization of cervical microstructure. Quantitative ultrasound biomarkers that may detect this process include those derived from the backscattered echo signal, namely, acoustic attenuation and backscattered power loss. We have recently shown that attenuation and backscattered power loss are affected by tissue anisotropy and heterogeneity in the ex vivo cervix. In this study, we compared attenuation and backscattered power difference in a group of women in early (first trimester), to a group in late (third trimester), pregnancy. We found a significant decrease in the backscattered power difference in late as compared to early pregnancy, suggesting decreased microstructural organization in late pregnancy, a finding that is consistent with animal models of cervical remodeling. In contrast, we found no difference in attenuation between the timepoints. These results suggest that the backscattered power difference, but perhaps not attenuation, may be a useful clinical biomarker of cervical remodeling.

Quantitative Ultrasound Parameters Based on the Backscattered Echo Power Signal as Biomarkers of Cervical Remodeling: A Longitudinal Study in the Pregnant Rhesus Macaque

“…Further, biomechanical studies on cervical tissue from hysterectomy specimens in a group of women who were not pregnant and another group that underwent cesarean hysterectomy indicate that the tensile tangent modulus is softer by at least 3 orders of magnitude in the latter (Myers et al, 2008;Yao et al, 2016), and fiber-based material modeling suggest that this softening is accommodated by changes to cervical microstructural organization (specifically, increased spreading of collagen fibers and intrinsic remodeling of fiber crosslinking) (Myers et al, 2015b). Consistent with all of these studies is our finding that mBSPD is significantly reduced in late, as compared to early, pregnancy in women, which suggests that softening is associated with changes in scatterers (presumably collagen) in cervical tissue microstructure (Guerrero et al, 2018a).…”

“…Similar to our findings in women, it appears that the SAC has larger estimate variance (compared to changes with gestational age) than the mBSPD and therefore may be less useful as an imaging biomarker of cervical remodeling. Table 3 compares women (McFarlin et al, 2010(McFarlin et al, , 2015aGuerrero et al, 2018a) to Rhesus in the first trimester (1T) and third trimester (3T). QUS parameter variability in the Rhesus decreases throughout pregnancy, mirroring reductions in SWS variability found throughout pregnancy in both Rhesus and women (Carlson et al, 2018;Rosado-Mendez et al, 2018), which suggests that the tissue becomes not only softer but also more homogeneous with remodeling.…”

Immunobiology of Cervix Ripening

“…For a variety of reasons, several reviews concluded that there is insufficient evidence to recommend transvaginal ultrasound of cervical length as clinically useful to predict preterm birth in pregnant women with singleton or twin gestations (169,170). However, the benefits of developments in technology and analyses were evident in recent study in which quantitative ultrasound analyses was able to distinguish a reduction in microstructure of the cervix in women that were early in pregnancy or at term (5-14 vs. 37-41 weeks, respectively) (171). The improved resolution resulted for use of a backscattered power parameter estimation to reduce signal variability due to anisotropy (echo from complexity of fibrillary network) and spatial heterogeneity in tissue.…”

Labour and delivery: a clinician's perspective on a biomechanics problem

“…Our group of clinicians, physicists and engineers is pursuing answers to these questions. We have learned that properties such as cervical softness and microstructural organization can be objectively quantified in pregnant women and rhesus macaques, and that they dramatically change as pregnancy royalsocietypublishing.org/journal/rsfs Interface Focus 9: 20190032 progresses [40][41][42][43]. We have also learned that the area of the internal os contains circumferentially oriented smooth muscle cells, which may operate as a sort of sphincter at this critical junction between the cervix, membranes and uterus [44].…”