Quantitative ultrasound backscatter parameters in the human cervix

Abstract

Quantitative ultrasound has been investigated as a tool for monitoring cervical changes that might result in preterm birth. Backscatter parameters, specifically attenuation and the backscattered power loss (BSPL), appear to be two important parameters. Sources of potential variability such as the angle of the beam interrogating the cervix, the region within the cervix, the number of previous births, and the state of ripening, have not been systematically examined, but could contribute to bias and variance in parameter estimates. Results presented here show that attenuation was affected by angle of interrogation, region in the cervix, parity, and ripened state. BSPL in the nonpregnant cervix was affected only by cervical region.

The mechanical role of the cervix in pregnancy

“…Our recent studies in nonpregnant ripened versus unripened hysterectomy specimens demonstrated that controlling for expected sources of anatomical variation in collagen structure significantly reduces variance in attenuation estimates (Guerrero et al, 2014). Studies in structurally aligned tissues have shown that attenuation is dependent on the angle between the acoustic beam and structural orientation (Insana et al, 1992; Mottley and Miller, 1990; Nassiri et al, 1979; Topp and O'Brien, 2000) and attenuation versus steering angle provides evidence for aligned structures in the cervical ECM (presumably collagen).…”

New techniques in evaluation of the cervix

“…In fact, in the cervix, attenuation has been shown to be affected by angle of interrogation and location (distal versus proximal cervix). 39 Therefore, measuring attenuation without accounting for sources of potential variability such as beam angle could contribute to estimate bias and variance.…”

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

“…Our initial studies involved using (nonpregnant) hysterectomy specimens to verify shear wave speed estimates (SWS) and backscatter parameters (e.g. mean backscattered power difference, mBSPD) with actual tissue microstructure examined via nonlinear optical microscopy imaging in both Rhesus (Guerrero, 2018) and women (Guerrero et al, 2018b). Subsequently, we demonstrated in vivo with SWS that the cervix progressively softens as pregnancy advances in the Rhesus (Rosado-Mendez et al, 2017, 2018 and that the human cervix is significantly softer in late, as opposed to early, pregnancy (Carlson et al, 2015(Carlson et al, , 2018.…”

“…The transducer was placed in the rectal cavity and the cervix identified via palpation and identification (from the B-mode image) of anatomical landmarks (uterus, bladder, internal os, external os, and cervical canal). Data were acquired from the "transition zone", an area in the macaque cervix between the internal os and the tortuous distal canal, (Rosado-Mendez et al, 2017) where the cervix appears nearly identical to that of the human (primarily, the canal is relatively straight) (Rosado-Mendez et al, 2017, 2018. Raw radiofrequency (RF) echo signal data were captured using the Axius Direct Ultrasound Research Interface (Brunke et al, 2007) with 40 MHz sampling of the RF echo signals.…”

“…In general, parameters which measure softness are based on propagation of shear waves (Carlson et al, 2014a(Carlson et al, ,b, 2015(Carlson et al, , 2018Huang et al, 2016;Hernandez-Andrade et al, 2013;Molina et al, 2012;Muller et al, 2015;Rosado-Mendez et al, 2017, 2018 and those which quantify microstructural organization are based on backscattered echo signals from the propagation of compressional waves (McFarlin et al, 2006(McFarlin et al, , 2010(McFarlin et al, , 2015aLabyed et al, 2011;Feltovich et al, 2010Feltovich et al, , 2012. Shear wave speed (SWS) estimation can quantify softness of the pregnant cervix in both women and Rhesus (Carlson et al, 2014a(Carlson et al, ,b, 2015(Carlson et al, , 2018Muller et al, 2015;Huang et al, 2016;Rosado-Mendez et al, 2017, 2018. Importantly, however, while SWS is a valuable biomarker of cervical remodeling, it provides no insight into why or how the tissue is becoming softer or more compliant (Feltovich and Hall, 2013).…”