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Ultrasound Med Biol. 2017 Apr;43(4):790-803. doi: 10.1016/j.ultrasmedbio.2016.12.006. Epub 2017 Feb 8.

Assessment of Structural Heterogeneity and Viscosity in the Cervix Using Shear Wave Elasticity Imaging: Initial Results from a Rhesus Macaque Model.

Author information

1
Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, USA. Electronic address: rosadomendez@wisc.edu.
2
Biomedical Engineering, Duke University, Durham, North Carolina, USA.
3
Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, USA.
4
Wisconsin National Primate Research Center, Madison, Wisconsin, USA.
5
Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, USA; Maternal Fetal Medicine, Intermountain Healthcare, Provo, Utah, USA.

Abstract

Shear wave elasticity imaging has shown promise in evaluation of the pregnant cervix. Changes in shear wave group velocity have been attributed exclusively to changes in stiffness. This assumes homogeneity within the region of interest and purely elastic tissue behavior. However, the cervix is structurally/microstructurally heterogeneous and viscoelastic. We therefore developed strategies to investigate these complex tissue properties. Shear wave elasticity imaging was performed ex vivo on 14 unripened and 13 misoprostol-ripened cervix specimens from rhesus macaques. After tests of significant and uniform shear wave displacement, as well as reliability of estimates, group velocity decreased significantly from the distal (vaginal) to proximal (uterine) end of unripened, but not ripened, specimens. Viscosity was quantified by the slope of the phase velocity versus frequency. Dispersion was observed in both groups (median: 5.5 m/s/kHz, interquartile range: 1.5-12.0 m/s/kHz), also decreasing toward the proximal cervix. This work suggests that comprehensive assessment of complex tissues such as cervix requires consideration of structural heterogeneity and viscosity.

KEYWORDS:

Cervix; Shear Wave Elasticity; Viscoelasticity

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