Three-Dimensional, Extended Field-of-View Ultrasound Method for Estimating Large Strain Mechanical Properties of the Cervix during Pregnancy

Abstract

Cervical shortening and cervical insufficiency contribute to a significant number of preterm births. However, the deformation mechanisms that control how the cervix changes its shape from long and closed to short and dilated are not clear. Investigation of the biomechanical problem is limited by 1) lack of thorough characterization of the three-dimensional anatomical changes associated with cervical deformation and 2) difficulty measuring cervical tissue properties in vivo. The objective of the present study was to explore the feasibility of using three-dimensional ultrasound and fundal pressure to obtain anatomically accurate numerical models of large-strain cervical deformation during pregnancy and enable non-invasive assessment of cervical tissue compliance. Healthy subjects (n=6) and one subject with acute cervical insufficiency in the midtrimester were studied. Extended field of view ultrasound images were obtained of the entire uterus and cervix. These images aided construction of anatomically accurate numerical models. Cervical loading was achieved with fundal pressure, which was quantified with a vaginal pressure catheter. In one subject, the anatomical response to fundal pressure was matched by a model-based simulation of the deformation response, thereby deriving the corresponding cervical mechanical properties and showing the feasibility of non-invasive assessment of compliance. The results of this pilot study demonstrate the feasibility of a biomechanical modeling framework for estimating cervical mechanical properties in vivo. An improved understanding of cervical biomechanical function will clarify the pathophysiology of cervical shortening.

Effect of depth on shear-wave elastography estimated in the internal and external cervical os during pregnancy

“…This difference in shear-wave propagation might be related to differences in tissue constitution as values remained significant after adjustment by depth. The velocity of propagation of the shear-wave can be related to the alignment and organization of the collagen network, concentration of proteoglycans [39] [40-44], and the amount of smooth muscle cells [45, 46] [47] in different cervical regions.…”

The mechanical role of the cervix in pregnancy

“…This imprecision obscures the clinician's ability to effectively describe a patient's clinical findings to another clinician, let alone someone outside of the obstetric profession. To the engineer, cervical softness is a material property that must be defined with appropriate constitutive equations and cervical shortening is a tissue deformation that results from an evolving three-dimensional (3D) stress state and the intrinsic remodeling of the materials constituents (Fernandez et al, 2015; House et al, 2012, 2013; House and Socrate, 2006; Paskaleva, 2007). However, the engineer currently has no effective means to apply these definitions to the clinical situation because of the language mismatch between clinicians and basic scientists.…”

“…Insight into the physiologic loads experienced during pregnancy and the load-carrying capability of the cervix have been derived from finite element models (Fernandez et al, 2015; House et al, 2012, 2013; Mahmoud et al, 2013; Paskaleva, 2007), mechanical and biochemical studies of ex vivo tissue specimens (Conrad et al, 1980; Conrad and Ueland, 1976, 1979; Fernandez et al, 2013; Gan et al, 2014; Myers et al, 2008, 2010; Oxlund et al, 2010a,b; Petersen et al, 1991; Rechberger et al, 1988; Yao et al, 2014), in vivo mechanical and biochemical interrogations of the cervix (Badir et al, 2013a; Bauer et al, 2007; Feltovich et al, 2010, 2012; Feltovich and Hall, 2013; Hee et al, 2014; House et al, 2005, 2009; Hricak et al, 1990; Maldjian et al, 1999; Mazza et al, 2006, 2013; Parra-Saavedra et al, 2011), and theoretical mechanics (Liao et al, 2014; Myers and Ateshian, 2014; Paskaleva, 2007). At the present time, there is no single set of correlating geometric and material property data from a single pregnant patient throughout gestation.…”

“…2). Early finite element analysis (FEA) demonstrate this clinically-observed deformation pattern showing that the internal os opposes the lateral pull of the uterine wall and the hydrostatic forces of the uterine cavity (Paskaleva, 2007; House et al, 2012, 2013; Fernandez et al, 2015). It is viewed that the internal os dilates first because tissue stresses are higher there compared with the external os (House et al, 2013), and the external os is not significantly loaded until the cervix has significantly shortened (Fernandez et al, 2015).…”

Development of an Ultrasonic Method to Detect Cervical Remodeling in Vivo in Full-Term Pregnant Women

“…Generally, the shorter the cervix, the greater the probability of preterm birth (Iams and Berghella 2010; Campbell 2011; Romero et al 2013). There has been considerable work by our group (McFarlin et al 2006; Bigelow et al 2008; McFarlin et al 2010; Bigelow et al 2011; Labyed and Bigelow 2011a; Labyed et al 2011; Lau et al 2013; Poellmann et al 2013) and others (House and Socrate 2006; Feltovich et al 2010; Feltovich et al 2012; House et al 2012; Feltovich and Hall 2013; Carlson et al 2014) to develop noninvasive methods to detect and understand cervical microstructural tissue properties associated with cervical remodeling.…”