In Vivo Evaluation of Cervical Stiffness Evolution during Induced Ripening Using Shear Wave Elastography, Histology and 2 Photon Excitation Microscopy: Insight from an Animal Model

Characterization of uterine involution using B-mode ultrasonography, color Doppler and elastography (acoustic radiation force impulse) for assessing postpartum in Santa Inês ewes

The aim of this study was to investigate uterine involution using ultrasonography techniques during postpartum. Postpartum ultrasonography evaluation (B-mode, color Doppler and Acoustic Radiation Force Impulse elastography) of the uterus was performed by transabdominal approach at immediate after birth and sequentially every 48 hours, during 30 days. The uterine echotexture did not present significant variations (P >0.05) being homogeneous in most evaluations; echogenicity of the uterus increased along the evaluation period (P =0.0452). Progressive and remarkable decrease of the total uterine diameter (UD) were observed (P <0.0001), especially during the first days postpartum. The thickness of uterine wall gradually decreased, as well the endometrial, myometrium and lumen diameters (P <0.0001). Uterine blood flow was assessed by Doppler and decreased during postpartum period, being significantly lower (P=0.0225) on the 30^th day of postpartum. Uterine parenchyma presented as homogeneous dark areas (not deformable) on qualitative ultrasound elastography and the means shear velocity values of the uterine wall on quantitative elastography did not differ. This is the first study that evaluate the stiffness of uterine wall in healthy ewes, providing baseline data about quantitative and qualitative stiffness of the normal uterus, and it may be a useful tool for early diagnosis of uterine alterations during the postpartum period, using the reference parameter established for the assessment of uterine integrity during postpartum period.

Predictive Value of Cervical Shear Wave Elastography in the Induction of Labor in Late-Term Pregnancy Nulliparous Women: Preliminary Results

The prediction of induction of labor continues to be a paradigm nowadays. Bishop Score is the traditional widely spread method but with a low reliability. Ultrasound cervical assessment has been proposed as an instrument of measurement. Shear wave elastography (SWE) should be a promising tool in the prediction of the success of labor induction in nulliparous late-term pregnancies. Ninety-two women with nulliparous late-term pregnancies who were going to be induced were included in the study. A shear wave measurement of the cervix divided into six regions (inner, middle and outer in both cervical lips), cervical length and fetal biometry was performed by blinded investigators prior to routine hand cervical assessment (Bishop Score (BS)) and induction of labor. The primary outcome was success of induction. Sixty-three women achieved labor. Nine women did not, and they underwent a cesarean section due to failure to induce labor. SWE was significantly higher in the inner part of the posterior cervix (p < 0.0001). SWE showed an area under the curve (AUC): 0.809 (0.677-0.941) in the inner posterior part. For CL, AUC was 0.816 (0.692-0.984). BS AUC was 0.467 (0.283-0.651). The ICC of inter-observer reproducibility was ≥0.83 in each region of interest (ROI). The cervix elastic gradient seems to be confirmed. The inner part of the posterior cervical lip is the most reliable region to predict induction of labor results in SWE terms. In addition, cervical length seems to be one of the most important procedures in the prediction of induction. Both methods combined could replace the Bishop Score.

Cervical strain elastography: pattern analysis and cervical sliding sign in preterm and control pregnancies

OBJECTIVES

The aim of this study was to assess the value of cervical strain elastography and Cervical Sliding Sign (CSS) for predicting spontaneous preterm birth (sPTB).

METHODS

In our case-control study we performed an elastographic assessment of the cervix in 82 cases of preterm birth (preterm group) and 451 control pregnancies (control group) between the 20th and 37th week of gestation. We divided the anterior cervical lip first into two ("Intern2", "Extern2") and into three sectors ("Intern3", "Middle3", "Extern3"). The tissue deformation pattern after local compression with an ultrasound probe was recorded. We distinguished between an irregularly distributed ("Spotting") and homogeneous pattern presentation. Additionally, the presence of a sliding of the anterior against the posterior cervical lip (positive CSS) during compression was evaluated. A logistic regression analysis and the Akaike Information Criterion (AIC) were used to estimate the probability of sPTB and to select a prediction model.

RESULTS

Spotting and positive CSS occurred more frequently in the preterm group compared to control group (97.8 vs. 2.2%, p<0.001; 26.8 vs. 4.2%, p<0.001; respectively). The model with the parameters week of gestation at ultrasound examination, Intern3, Middle3 and CSS was calculated as the highest quality model for predicting sPTB. The AUC (Area Under the Curve) was higher for this parameter combination compared to cervical length (CL) (0.926 vs. 0.729).

CONCLUSIONS

Cervical strain elastography pattern analysis may be useful for the prediction of sPTB, as the combination of Spotting analysis and CSS is superior to CL measurement alone.

Prediction model for successful induction of labor by cervical strain elastography diagnosed at late-term pregnancy in nulliparous women: a prospective cohort study

BACKGROUND

The use of cervical strain elastography for nulliparous women during late-term pregnancy remains unclear. This study assesses the predictive value of late-term cervical strain elastography for successful induction of labor (IOL) in nulliparous women.

METHODS

This single-centered, prospective study included 86 patients undergoing IOL between January 2020 and March 2022. Univariate and multivariate analyses were conducted to identify predictive factors for successful IOL. The predictive values were assessed using the area under receiver operating characteristic (ROC) curves.

RESULTS

IOL was successful in 58 patients. The hardness ratio and cervical length were significantly associated with successful late-term IOL in nulliparous women. The predictive value of the combination of hardness ratio and cervical length was higher than that of cervical length alone.

CONCLUSIONS

The hardness ratio and cervical length assessed by cervical strain elastography during late-term pregnancy are predictors of the success of IOL in nulliparous women. The predictive value of the combination of hardness ratio and cervical length was higher than that of cervical length alone.

Maternal and fetal ultrasonography, vulvar temperature and vaginal mucous impedance for the prediction of parturition in Saanen does

The aim of this study was to evaluate and correlate modifications of vaginal mucous impedance, vulvar temperature and ultrasonographic measurements (echobiometric parameters) to parturition in pregnant Saanen does. 30 does were selected for the study and submitted to an estrus synchronization protocol and natural mating. The females were evaluated daily from Day 143 of pregnancy to parturition. For the sonographic evaluations, the following structures were measured: biparietal diameter, thoracic diameter, abdominal diameter, ocular orbit, kidney length, kidney height, cardiac area, placentome length, cervical measurement and fetal heart rate; by means of two different approaches: transrectal and transabdominal, using a 7.5 MHz linear transducer. The vaginal mucous impedance was assessed using an electric estrous detector and vulvar temperature was measured using a non-contact infrared thermometer. Statistical analysis was performed using the R-project software and the significance level was set at 5% for all tests. 25 Saanen does became pregnant, resulting in 80.33% pregnancy rate. Fetal heart rate was negatively correlated to the hours to parturition (p<0,001; r-Pearson= -0,451), as well as vaginal temperature (p= 0,001; r-Pearson= -0,275), while cervical thickness was positively correlated to hours to parturition (p<0,001; r-Pearson= 0,490). The echobiometric parameters (biparietal diameter, thoracic diameter, abdominal diameter, ocular orbit, kidney length and height, cardiac area, placentome length), as well as vaginal mucous impedance did not vary throughout the timepoints of evaluation and did not correlate to the moment of parturition. It was concluded that the parameters of fetal heartbeat, vaginal temperature and cervical effacement in the last week of pregnancy provide valuable information regarding the proximity of parturition.

Quantitative sonoelastography of the uterine cervix in predicting successful outcome of induction of labour

Objectives

The aim of the study was to evaluate the stiffness of cervix and determine its significance in predicting successful outcome of induction of labour. The primary objective was to determine the differences in elastography indices of different areas of cervix between the outcome groups of successful and failed induction of labour. A secondary objective was to find out the correlation of these elastography indices with Bishop's score and cervical length.

Methods

This was a prospective, observational study conducted over a period of 6 months on pregnant women admitted in the labour room for induction of labour. Establishment of adequate regular uterine contractions - at least three contractions lasting 40-45 s in a 10-min period - was taken as end point for successful outcome of induction of labour. Even after 24 h of initiation of induction of labour, regular, adequate and painful uterine contractions were not established, then induction of labour was described as having failed. Prior to induction, cervical length measurement, Bishop's scoring and elastographic evaluation of the cervix were done by stress-strain elastography. A colour map was produced from purple to red and a five-step scale - the elastography index - was used to describe the various parts of the cervix. The differences between elastography indices of different parts of cervix were estimated using Mann-Whitney U test. Correlation of the indices with cervical length and Bishop's score was determined by Spearman's correlation coefficient.

Results

A total of 64 women were included in the study. A significant difference (p < 0.001) was found in the elastography index of internal os between the two outcome groups of success (1.76 ± 0.64) and failure (0.54 ± 0.18). However, the elastography index of central cervical canal, external os, anterior lip and posterior lips did not differ significantly across the outcome groups. A significant positive correlation was found between elastography index of internal os and cervical length (Spearman's correlation coefficient, r = 0.441, p < 0.001) and between elastography index of external os and cervical length (r = 0.347, p = 0.005), whereas a negative correlation was seen between elastography index of external os and Bishop's score (r = -0.270, p = 0.031).

Conclusion

Elastography index of internal os can be used to predict outcome of induction of labour. Cervical elastography is a promising new technique for cervical consistency assessment. Further larger studies are required to determine some cut-off point for elastography index of internal os in prediction of outcome of induction of labour and to strongly establish the usefulness of cervical elastography for pregnancy management, preventing preterm delivery and establishment of cut-off points to determine successful induction.

<p>The Comparative Study of Cervical Shear Wave Elastography Between Twin and Singleton Pregnancy</p>

Objective

To compare the cervical shear wave elastography (SWE) by using transvaginal ultrasound (TVS) between twin and singleton pregnant women.

Materials and Methods

This was a prospective cohort study involving the twin and singleton pregnant women who attended the antenatal care at Ramathibodi Hospital, Bangkok, Thailand. The participants who met the inclusion criteria were serially measured the shear wave speed (SWS) by using TVS at early, mid-, and third trimester. The changes in SWS with advancing gestational age between twin and singleton pregnancies were evaluated. The gestational age at delivery and spontaneous preterm delivery rate were also analyzed.

Results

A total of 36 twin pregnancies and 38 singleton pregnancies were analyzed. No significant difference in baseline characteristics, except the age of participants (twin pregnancies 33.1±4.6 years, singleton pregnancies 29.9±5.4 years, p-value = 0.006) was observed. The cervical SWS decreased with advancing gestational age in both twin and singleton pregnancy, but there was a statistically significant difference of cervical SWS at the lower point in mid-trimester (twin pregnancies 2.27±0.4, singleton pregnancies 2.71±0.6 m/s, p-value = 0.001). However, no significant difference in cervical SWS at the upper point and the lower point in the early and third trimester was demonstrated. Even though the gestational age at delivery between both groups revealed a significant difference (twin pregnancies 35.9±2.8, singleton pregnancies 37.6±2.9 wk., p-value = 0.008) but the spontaneous preterm delivery rate did not differ significantly (twin pregnancies 22.2%, singleton pregnancies 15.8%, p-value = 0.483).

Conclusion

The mid-trimester cervical SWS measurement at the lower point detects the difference in cervical softness between twin pregnancies and singleton pregnancies. The cervical SWS might be an additional option for monitoring the change in cervical softness in twin pregnancies.

The role of noninvasive diagnostic imaging in monitoring pregnancy and detecting patients at risk for preterm birth: a review of quantitative approaches

Preterm birth (PTB) is the leading cause of neonatal morbidity and mortality worldwide. The ability to predict patients at risk for preterm birth remains a major health challenge. The currently available clinical diagnostics such as cervical length and fetal fibronectin may detect only up to 30% of patients who eventually experience a spontaneous preterm birth. This paper reviews ongoing efforts to improve the ability to conduct a risk assessment for preterm birth. In particular, this work focuses on quantitative methods of imaging using ultrasound-based techniques, magnetic resonance imaging, and optical imaging modalities. While ultrasound imaging is the major modality for preterm birth risk assessment, a summary of efforts to adopt other imaging modalities is also discussed to identify the technical and diagnostic limits associated with adopting them in clinical settings. We conclude the review by proposing a new approach using combined photoacoustic, ultrasound, and elastography as a potential means to better assess cervical tissue remodeling, and thus improve the detection of patients at-risk of PTB.

Addition of Cervical Elastography May Increase Preterm Delivery Prediction Performance in Pregnant Women with Short Cervix: a Prospective Study

BACKGROUND

We investigated whether there is a difference in elastographic parameters between pregnancies with and without spontaneous preterm delivery (sPTD) in women with a short cervix (≤ 25 mm), and examined the ability of elastographic parameters to predict sPTD in those women.

METHODS

E-Cervix^TM (WS80A; Samsung Medison, Seoul, Korea) elastography was used to examine the cervical strain. Elastographic parameters were compared between pregnancies with and without sPTD. Diagnostic performance of elastographic parameters to predict sPTD ≤ 37 weeks, both alone and in combination with other parameters, was compared with that of cervical length (CL) using area under receiver operating characteristic curve (AUC) analysis.

RESULTS

A total of 130 women were included. Median gestational age (GA) at examination was 24.4 weeks (interquartile range, 21.4-28.9), and the prevalence of sPTD was 20.0% (26/130). Both the elastographic parameters and CL did not show statistical difference between those with and without sPTD. However, when only patients with CL ≥ 1.5 cm (n = 110) were included in the analysis, there was a significant difference between two groups in elasticity contrast index (ECI) within 0.5/1.0/1.5 cm from the cervical canal (P < 0.05) which is one of elastographic parameters generated by E-Cervix. When AUC analysis was performed in women with CL ≥ 1.5 cm, the combination of parameters (CL + pre-pregnancy body mass index + GA at exam + ECI within 0.5/1.0/1.5 cm) showed a significantly higher AUC than CL alone (P < 0.05).

CONCLUSION

An addition of cervical elastography may improve the ability to predict sPTD in women with a short CL between 1.5 and 2.5 cm.

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

As pregnancy progresses, the cervix remodels from a rigid structure to one pliable enough to allow delivery of a fetus, a process that 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 recently reported 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 pregnancy (first trimester) with those in a group in late pregnancy (third trimester). We observed a significant decrease in the backscattered power difference in late as compared with 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 time points. These results suggest that the backscattered power difference, but perhaps not attenuation, may be a useful clinical biomarker of cervical remodeling.

A soft cervix, categorized by shear-wave elastography, in women with short or with normal cervical length at 18-24 weeks is associated with a higher prevalence of spontaneous preterm delivery

OBJECTIVE

To determine whether a soft cervix identified by shear-wave elastography between 18 and 24 weeks of gestation is associated with increased frequency of spontaneous preterm delivery (sPTD).

MATERIALS AND METHODS

This prospective cohort study included 628 consecutive women with a singleton pregnancy. Cervical length (mm) and softness [shear-wave speed: (SWS) meters per second (m/s)] of the internal cervical os were measured at 18-24 weeks of gestation. Frequency of sPTD <37 (sPTD<37) and <34 (sPTD<34) weeks of gestation was compared among women with and without a short (≤25 mm) and/or a soft cervix (SWS <25th percentile).

RESULTS

There were 31/628 (4.9%) sPTD<37 and 12/628 (1.9%) sPTD<34 deliveries. The combination of a soft and a short cervix increased the risk of sPTD<37 by 18-fold [relative risk (RR) 18.0 (95% confidence interval [CI], 7.7-43.9); P<0.0001] and the risk of sPTD<34 by 120-fold [RR 120.0 (95% CI 12.3-1009.9); P<0.0001] compared to women with normal cervical length. A soft-only cervix increased the risk of sPTD<37 by 4.5-fold [RR 4.5 (95% CI 2.1-9.8); P=0.0002] and of sPTD<34 by 21-fold [RR 21.0 (95% CI 2.6-169.3); P=0.0003] compared to a non-soft cervix.

CONCLUSIONS

A soft cervix at 18-24 weeks of gestation increases the risk of sPTD <37 and <34 weeks of gestation independently of cervical length.

Quantitative analysis of cervical texture by ultrasound in mid-pregnancy and association with spontaneous preterm birth

OBJECTIVE

New tools are required to improve the identification of women who are at increased risk for spontaneous preterm birth (sPTB). Quantitative analysis of tissue texture on ultrasound has been used to extract robust features from the ultrasound image to detect subtle changes in its microstructure. This may be applied to the cervix. The aim of this study was to determine if there is an association between quantitative analysis of cervical texture (CTx) on mid-trimester ultrasound and sPTB < 37 + 0 weeks' gestation.

METHODS

This was a single-center nested case-control study of a prospective cohort of 677 consecutive women with singleton pregnancy assessed between 19 + 0 and 24 + 6 weeks' gestation. Women at increased risk for sPTB were included unless they received treatment to prevent sPTB. Women who delivered < 37 + 0 weeks (sPTB) were considered as cases and were matched in a 1: 10 ratio with randomly selected contemporary controls who delivered at term. For each woman, one ultrasound image of the cervix was obtained for which quality was assessed, cervical length (CL) measured offline and a region of interest in the midportion of the anterior cervical lip delineated for use in local binary patterns analysis of CTx. A learning algorithm was developed to obtain the combination of CTx features best associated with sPTB based on feature transformation and discriminant analysis regression. The ability of the learning algorithm to predict sPTB was evaluated using a leave-one-out cross-validation technique, which produced a CTx-based score for each participant. Receiver-operating characteristics (ROC) curves were produced and sensitivity, specificity, and positive and negative likelihood ratios were calculated for the optimal cut-off based on the ROC curve. The results were compared with those obtained for CL. Investigators studying the images were blinded to pregnancy outcome at all times.

RESULTS

Images from 310 women (27 cases and 283 controls) were of sufficient quality and included in the study. Median CTx-based score was significantly lower in cases compared with controls (-1.01 vs -0.07, P ≤ 0.0001). CTx-based score maintained its significant association with sPTB after adjusting for possible confounders (history of sPTB, conization or Müllerian malformation, and CL < 25 mm). CTx-based score was a better predictor of sPTB (AUC, 0.77; 95% CI, 0.66-0.87) than was CL (AUC, 0.60; 95% CI, 0.47-0.72) (P = 0.03). Median CL was similar for cases and controls (37.7 vs 38.6 mm, P = 0.26), although cases were more likely to have CL < 25 mm (18.5% vs 0.4%, P < 0.001).

CONCLUSION

Quantitative analysis of CTx enables the extraction of information relevant to sPTB from ultrasound images to generate a CTx-based score that is associated independently with sPTB. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Quantitative assessment of cervical softening during pregnancy in the Rhesus macaque with shear wave elasticity imaging

Abnormal parturition, e.g. pre- or post-term birth, is associated with maternal and neonatal morbidity and increased economic burden. This could potentially be prevented by accurate detection of abnormal softening of the uterine cervix. Shear wave elasticity imaging (SWEI) techniques that quantify tissue softness, such as shear wave speed (SWS) measurement, are promising for evaluation of the cervix. Still, interpretation of results can be complicated by biological variability (i.e. spatial variations of cervix stiffness, parity), as well as by experimental factors (i.e. type of transducer, posture during scanning). Here we investigated the ability of SWEI to detect cervical softening, as well as sources of SWS variability that can affect this task, in the pregnant and nonpregnant Rhesus macaque. Specifically, we evaluated SWS differences when imaging the cervix transabdominally with a typical linear array abdominal transducer, and transrectally with a prototype intracavitary linear array transducer. Linear mixed effects (LME) models were used to model SWS as a function of menstrual cycle day (in nonpregnant animals) and gestational age (in pregnant animals). Other variables included parity, shear wave direction, and cervix side (anterior versus posterior). In the nonpregnant cervix, the LME model indicated that SWS increased by 2% (95% confidence interval 0-3%) per day, starting eight days before menstruation. During pregnancy, SWS significantly decreased at a rate of 6% (95% CI 5-7%) per week (intracavitary approach) and 3% (95% CI 2-4%) per week (transabdominal approach), and interactions between the scanning approach and other fixed effects were also significant. These results suggest that, while absolute SWS values are influenced by factors such as scanning approach and SWEI implementation, these sources of variability do not compromise the sensitivity of SWEI to cervical softening. Our results also highlight the importance of standardizing SWEI approaches to improve their accuracy for cervical assessment.

Detection of Changes in Cervical Softness Using Shear Wave Speed in Early versus Late Pregnancy: An in Vivo Cross-Sectional Study

The aim of this study was to assess the ability of shear wave elasticity imaging (SWEI) to detect changes in cervical softness between early and late pregnancy. Using a cross-sectional study design, shear wave speed (SWS) measurements were obtained from women in the first trimester (5-14 wk of gestation) and compared with estimates from a previous study of women at term (37-41 wk). Two sets of five SWS measurements were made using commercial SWEI applications on an ultrasound system equipped with a prototype catheter transducer (128 elements, 3-mm diameter, 14-mm aperture). Average SWS estimates were 4.42 ± 0.32 m/s (n = 12) for the first trimester and 2.13 ± 0.66 m/s (n = 18) for the third trimester (p <0.0001). The area under the curve was 0.95 (95% confidence interval: 0.82-0.99) with a sensitivity and specificity of 83%. SWS estimates indicated that the third-trimester cervix is significantly softer than the first-trimester cervix. SWEI methods may be promising for assessing changes in cervical softness.

Mid-Trimester Cervical Consistency Index and Cervical Length to Predict Spontaneous Preterm Birth in a High-Risk Population

Background  Short cervical length (CL) has not been shown to be adequate as a single predictor of spontaneous preterm birth (sPTB) in high-risk pregnancies. Objective  The objective of this study was to evaluate the performance of the mid-trimester cervical consistency index (CCI) to predict sPTB in a cohort of high-risk pregnancies and to compare the results with those obtained with the CL. Study Design  Prospective cohort study including high-risk singleton pregnancies between 19 ⁺⁰ and 24 ⁺⁶ weeks. The ratio between the anteroposterior diameter of the uterine cervix at maximum compression and at rest was calculated offline to obtain the CCI. Results  Eighty-two high sPTB risk women were included. CCI (%) was significantly reduced in women who delivered <37 ⁺⁰ weeks compared with those who delivered at term, while CL was not. The area under the curve (AUC) of the CCI to predict sPTB <37 ⁺⁰ weeks was 0.73 (95% confidence interval [CI], 0.61-0.85), being 0.51 (95% CI, 0.35-0.67), p  = 0.03 for CL. The AUC of the CCI to predict sPTB <34 ⁺⁰ weeks was 0.68 (95% CI, 0.54-0.82), being 0.49 (95% CI, 0.29-0.69), p  = 0.06 for CL. Conclusion  CCI performed better than sonographic CL to predict sPTB. Due to the limited predictive capacity of these two measurements, other tools are still needed to better identify women at increased risk.

Tensile Mechanical Properties and Dynamic Collagen Fiber Re-Alignment of the Murine Cervix are Dramatically Altered Throughout Pregnancy

The cervix is a unique organ able to dramatically change its shape and function by serving as a physical barrier for the growing fetus and then undergoing dramatic dilation allowing for delivery of a term infant. As a result, the cervix endures changing mechanical forces from the growing fetus. There is an emerging concept that the cervix may change or remodel "early" in many cases of spontaneous preterm birth (sPTB). However, the mechanical role of the cervix in both normal and preterm birth remains unclear. Therefore, the primary objective of this study was to determine the mechanical and structural responses of murine cervical tissue throughout a normal gestational time course. In this study, both tissue structural and material properties were determined via a quasi-static tensile load-to-failure test, while simultaneously obtaining dynamic collagen fiber re-alignment via cross-polarization imaging. This study demonstrated that the majority of the mechanical properties evaluated decreased at midgestation and not just at term, while collagen fiber re-alignment occurred earlier in the loading curve for cervices at term. This suggests that although structural changes in the cervix occur throughout gestation, the differences in material properties function in combination with collagen fiber re-alignment as mechanical precursors to regulate term gestation. This work lays a foundation for investigating cervical biomechanics and the role of the cervix in preterm birth.

Performance Study of a Torsional Wave Sensor and Cervical Tissue Characterization

A novel torsional wave sensor designed to characterize mechanical properties of soft tissues is presented in this work. Elastography is a widely used technique since the 1990s to map tissue stiffness. Moreover, quantitative elastography uses the velocity of shear waves to achieve the shear stiffness. This technique exhibits significant limitations caused by the difficulty of the separation between longitudinal and shear waves and the pressure applied while measuring. To overcome these drawbacks, the proposed torsional wave sensor can isolate a pure shear wave, avoiding the possibility of multiple wave interference. It comprises a rotational actuator disk and a piezoceramic receiver ring circumferentially aligned. Both allow the transmission of shear waves that interact with the tissue before being received. Experimental tests are performed using tissue mimicking phantoms and cervical tissues. One contribution is a sensor sensitivity study that has been conducted to evaluate the robustness of the new proposed torsional wave elastography (TWE) technique. The variables object of the study are both the applied pressure and the angle of incidence sensor–phantom. The other contribution consists of a cervical tissue characterization. To this end, three rheological models have fit the experimental data and a static independent testing method has been performed. The proposed methodology permits the reconstruction of the mechanical constants from the propagated shear wave, providing a proof of principle and warranting further studies to confirm the validity of the results.

Cervical elastography during pregnancy: clinical perspectives

Uterine cervix is a part of the uterus responsible for maintaining pregnancy till term. As long as the cervix remains long and firm and its internal orifice (os) is closed, it can withstand enlargement of the uterine contents and resultant growing pressure. Mechanical properties of the cervix change during pregnancy; the cervix ripens prior to delivery, then effaces and dilates with contractions of the uterus. Ripening of the cervix can be assessed using the Bishop score and ultrasonographically determined length of the cervical canal and internal os. Consistency is one of the cervical properties that change during the course of the maturation process. Until recently, cervical consistency has been assessed only manually, but in 2007, the first report on elastographic imaging of the cervix during pregnancy has been published. Elastography presents the ability of a tissue to deform under pressure. The softer the tissue, the easier it changes its shape. Different methods of elastography are used - static, when tissue displacement in response to manual compression or physiological movements of vessels is measured, or dynamic, when the speed of shear wave propagation is determined. Irrespective of the method, elastography provides information on the internal os stiffness; this parameter, impossible for manual assessment, was shown to correlate with pregnancy outcome and is a strong predictor of preterm delivery or successful labor induction. Although elastography seems to be a highly promising diagnostic option, still no consensus has been reached regarding an optimal method for uterine cervix assessment, and virtually all previous studies of various elastographic methods produced highly satisfactory results. Future studies need to identify the most promising and objective elastographic method which may serve as a novel tool for pregnancy management, preventing adverse events, such as preterm delivery and unsuccessful labor induction.

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

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.

Mapping of hemoglobin in erythrocytes and erythrocyte ghosts using two photon excitation fluorescence microscopy

The present study describes utilization of two photon excitation fluorescence (2PE) microscopy for visualization of the hemoglobin in human and porcine erythrocytes and their empty membranes (i.e., ghosts). High-quality, label- and fixation-free visualization of hemoglobin was achieved at excitation wavelength 730 nm by detecting visible autofluorescence. Localization in the suspension and spatial distribution (i.e., mapping) of residual hemoglobin in erythrocyte ghosts has been resolved by 2PE. Prior to the 2PE mapping, the presence of residual hemoglobin in the bulk suspension of erythrocyte ghosts was confirmed by cyanmethemoglobin assay. 2PE analysis revealed that the distribution of hemoglobin in intact erythrocytes follows the cells’ shape. Two types of erythrocytes, human and porcine, characterized with discocyte and echinocyte morphology, respectively, showed significant differences in hemoglobin distribution. The 2PE images have revealed that despite an extensive washing out procedure after gradual hypotonic hemolysis, a certain amount of hemoglobin localized on the intracellular side always remains bound to the membrane and cannot be eliminated. The obtained results open the possibility to use 2PE microscopy to examine hemoglobin distribution in erythrocytes and estimate the purity level of erythrocyte ghosts in biotechnological processes.

Estimation of Shear Wave Speed in the Rhesus Macaques' Uterine Cervix

Cervical softness is a critical parameter in pregnancy. Clinically, preterm birth is associated with premature cervical softening and postdates birth is associated with delayed cervical softening. In practice, the assessment of softness is subjective, based on digital examination. Fortunately, objective, quantitative techniques to assess softness, and other parameters associated with microstructural cervical change are emerging. One of these is shear wave speed (SWS) estimation. In principle, this allows objective characterization of stiffness because waves travel more slowly in softer tissue. We are studying SWS in humans and rhesus macaques, the latter in order to accelerate translation from bench to bedside. For the current study, we estimated SWS in ex vivo cervices of rhesus macaques, n=24 nulliparous (never given birth) and n=9 multiparous (delivered at least one baby). Misoprostol (a prostaglandin used to soften human cervices prior to gynecological procedures) was administered to 13 macaques prior to necropsy (nulliparous: 7; multiparous: 6). SWS measurements were made at predetermined locations from the distal to proximal end of the cervix on both the anterior and posterior cervix, with five repeat measures at each location. The intent was to explore macaque cervical microstructure, including biological and spatial variability, to elucidate the similarities and differences between the macaque and the human cervix in order to facilitate future in vivo studies. We found that SWS is dependent on location in the normal nonpregnant macaque cervix, as in the human cervix. Unlike the human cervix, we detected no difference between ripened and unripened rhesus macaque cervix samples, nor nulliparous versus multiparous samples, although we observed a trend toward stiffer tissue in nulliparous samples. We found rhesus macaque cervix to be much stiffer than human, which is important for technique refinement. These findings are useful for guiding study of cervical microstructure in both humans and macaques.