Evaluation of cervical stiffness during pregnancy using semiquantitative ultrasound elastography

Reliability of the sonographic evaluation for cervical length and elastography with pelvic parameters in term pregnancy by experienced operators with varying levels of experience

OBJECTIVE

To assess the reliability of sonographic measurements of six cervical and pelvic parameters by three sonographers with varying levels of experience.

METHODS

A cross-sectional study was conducted in pregnant women with a gestational age of ≥39 weeks. Each pregnant woman was examined by two sonographers with different levels of experience. Six parameters were measured: cervical length (CL), cervical strain elastography (extrinsic type), posterior cervical angle (PCA), fetal head-to-perineum distance (FHPD), fetal head-to-pubic symphysis distance (FHSD), and angle of progression (AOP). Intra- and interobserver reliabilities were assessed using the intraclass correlation coefficient with a 95% confidence interval. Pearson pairwise correlation coefficients were used to analyze the correlation between the parameter values.

RESULTS

In all, 66 pregnant women were enrolled in this study. We found excellent intraobserver reliability for measurements of CL, PCA, FHPD, FHSD, and AOP and good-to-excellent intraobserver reliability for cervical strain values in the cross-sectional view of the endocervix in the internal os area and cross-sectional view of the entire cervix in the internal os area. Interobserver reliability was excellent for all pelvic parameters, except for the FHPD. Strain values were moderate to excellent in the area of the internal os. A significant negative correlation between CL and strain values at the internal os was observed.

CONCLUSIONS

Pelvic parameters, except for FHPD, have excellent intra- and interobserver reliabilities. The high reproducibility of CL and cervical strain elastography at the internal os level, with a negative correlation between these two parameters, may play an important role in predicting successful induction of labor.

Uterus and cervix anatomical changes and cervix stiffness evolution throughout pregnancy

The coordinated biomechanical performance, such as uterine stretch and cervical barrier function, within maternal reproductive tissues facilitates healthy human pregnancy and birth. Quantifying normal biomechanical function and detecting potentially detrimental biomechanical dysfunction (e.g., cervical insufficiency, uterine overdistention, premature rupture of membranes) is difficult, largely due to minimal data on the shape and size of maternal anatomy and material properties of tissue across gestation. This study quantitates key structural features of human pregnancy to fill this knowledge gap and facilitate three-dimensional modeling for biomechanical pregnancy simulations to deeply explore pregnancy and childbirth. These measurements include the longitudinal assessment of uterine and cervical dimensions, fetal weight, and cervical stiffness in 47 low-risk pregnancies at four time points during gestation (late first, middle second, late second, and middle third trimesters). The uterine and cervical size were measured via 2-dimensional ultrasound, and cervical stiffness was measured via cervical aspiration. Trends in uterine and cervical measurements were assessed as time-course slopes across pregnancy and between gestational time points, accounting for specific participants. Patient-specific computational solid models of the uterus and cervix, generated from the ultrasonic measurements, were used to estimate deformed uterocervical volume. Results show that for this low-risk cohort, the uterus grows fastest in the inferior-superior direction from the late first to middle second trimester and fastest in the anterior-posterior and left-right direction between the middle and late second trimester. Contemporaneously, the cervix softens and shortens. It softens fastest from the late first to the middle second trimester and shortens fastest between the late second and middle third trimester. Alongside the fetal weight estimated from ultrasonic measurements, this work presents holistic maternal and fetal patient-specific biomechanical measurements across gestation.

The Application of Shear Wave Elastography to Determine the Elasticity of the Levator Ani Muscle and Vaginal Tissue in Patients With Pelvic Organ Prolapse

OBJECTIVES

The changes of the extracellular matrix of the connective tissue have significantly contributed to the incidence of pelvic organ prolapse (POP). It seems reasonable that sonoelastography could be a useful tool to evaluate the elasticity of pelvic floor tissue in patients with POP and compare it to those without POP. The main aim of this pilot study was to determine if there are differences in the elasticity of the levator ani muscle (LAM) and vaginal tissue between patients with and without POP.

METHODS

Prospective observation study, including 60 patients (30 with POP and 30 without POP). Sonoelastography was performed to evaluate the elasticity (in kilopascals, kPa) of the following regions of interest: vagina at the level of middle third of the urethra; vagina at the level of the bladder trigone; vagina in the anterior and posterior fornix; vagina at the level of middle third of the anorectal canal; posterior third of the LAM.

RESULTS

A total of 60 patients completed the study (30 with POP, 30 without POP). In the POP group, 18/30 (60%) had an anterior vaginal wall prolapse, 3/30 (10%) a uterine prolapse, 15/30 (50%) a rectocele, and 6/30 (20%) a enterocele. Patients with POP had higher elasticity in all anatomical study areas, with statistically significant differences in the anterior fornix (13.6 vs 11.2 kPa; P: .012). A multiple regression (controlling age, menopausal stage, and parity) allowed to detect statistically significant differences in the elasticity of the middle third of the urethra (P: .03) and the middle third of the anorectal canal (P: .019).

CONCLUSION

It is possible to evaluate the elasticity of the LAM and vaginal tissue using sonoelastography, detecting a higher elasticity in patients with POP than in those without POP.

Elasticity of the Cervix in Relation to Uterus Position

Strain elastography allows the evaluation of tissue elasticity. Background/Objectives: Tissue elasticity depends on the content and distribution of collagen fibers and is shaped by the applied tensile forces that may differ in uteri with a different angle of flexion of the corpus on the cervix. The objective was to investigate whether the angle of uterine flexion is related to cervical tissue elasticity. Methods: The anterior angle between the longitudinal axis of the uterus corpus and that of the cervix was measured in 275 non-pregnant young women by transvaginal ultrasonography and considered both as an absolute value or categorized as ≤150°, between >150° and ≤210°, and >210°. Strain elastography was used to assess tissue elasticity by placing the probe in the anterior vaginal fornix. Tissue elasticity was evaluated in the middle of the anterior cervical compartment (ACC), in the middle of the posterior cervical compartment (PCC), in the middle portion of the cervical canal (MCC), and at the internal cervical os (ICO). In a sagittal plane MCC was evaluated across the cervical canal, and ACC and PCC at a distance equal between the cervical canal and the outer anterior or posterior part of the cervix. MCC, ACC and PCC were evaluated at equal distance between the ICO and the external cervical os. Elasticity was expressed as a color score ranging from 0.1 (low elasticity) to 3 (high elasticity). Results: The angle of uterine flexion show a negative linear relation with the elasticity of the ACC (p = 0.001) and MCC (p = 0.002) and a positive relation with the elasticity of the PCC (p = 0.054). In comparison to uteri with an angle of flexion of <150°, those with an angle of flexion of >210° had lower elasticity of the ACC (p = 0.001) and MCC (p = 0.001) and higher elasticity of the PCC (p = 0.004). The ACC/PCC and PCC/MCC elasticity ratios were also significantly different (p = 0.001). Conclusions: The angle of uterine flexion is associated with changes in cervix elasticity. Retroflexion is associated with stiffer ACC and MCC and a more elastic PCC. Differences in tissue elasticity suggest structural changes of the cervix that may have implication in variate obstetric and gynecological conditions.

Evaluation of Non-Compressive Transvaginal Cervical Elastography as a Quantitative Imaging Biomarker in Pregnancy: A Repeatability and Reliability Analysis

OBJECTIVES

Non-compressive strain elastography has been proposed as a novel quantitative imaging biomarker for assessing the structure and function of the cervix. The current study aims to assess the repeatability, and intra- and inter-observer reliability of transvaginal non-compressive cervical strain elastography in a clinical setting.

METHODS

We conducted a dual-phase single-center prospective feasibility study of singleton gestations >16-weeks gestation that required a clinically-indicated transvaginal ultrasound. Each study participant, n = 43 in phase 1 and n = 13 in phase 2, had elastography performed by two trained observers that each performed multiple image acquisitions. We performed a multivariable regression to adjust for changes in clinical characteristics between study phases and calculated the repeatability coefficients, limits of agreement, and intraclass correlations for each quantitative elastography parameter. We compared quantitative elastography parameters to cervical length measurements, acquired from the same images.

RESULTS

The repeatability coefficients and percent limits of agreement were wide for all of the quantitative elastography parameters, demonstrating poor repeatability. Intraclass correlation coefficients were poor-moderate for both intra-observer (0.31-0.77) and inter-observer reliability (0.35-0.77) in both study phases, while cervical length showed excellent reliability with intraclass correlations consistently >0.90.

CONCLUSIONS

Non-compressive transvaginal strain cervical elastography did not demonstrate adequate repeatability or reliability. Our results highlight the importance of rigorously assessing novel quantitative imaging biomarkers before clinical application.

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.

Quantification of cervical stiffness changes in single and twin pregnancies using the E-Cervix technique

BACKGROUND

Cervical length is a commonly used clinical indicator for evaluating preterm birth. However, some studies have shown that cervical length does not change in patients with cervical insufficiency.

OBJECTIVE

This study aimed to use the transvaginal ultrasound E-Cervix to quantitatively evaluate the cervical stiffness in women with singleton and twin pregnancies to provide a reference for the clinical prediction of preterm birth.

STUDY DESIGN

We collected the cervical length, cervical hardness ratio, mean internal os strain, and mean external os strain using transvaginal ultrasonographic E-Cervix assessments in pregnant women undergoing routine examinations in the obstetrics department of our hospital from January 2020 to December 2020. We summarized the range of cervical elasticity parameters at different gestational ages and compared the cervical elasticity parameters between singleton and twin pregnancies and between preterm births and full-term births.

RESULTS

A total of 988 pregnant women were enrolled in this study, and after exclusion, 770 pregnant women were enlisted; the interrater and internal consistency for various elasticity parameters were favorable; and cervical elasticity changes in women at full term showed some particular patterns. The declines in cervical length and hardness ratio were commensurate with gestational age, whereas the internal os strain and external os strain rose with increasing gestational age. The cervical hardness ratio in women with twin pregnancies was lower than in women with singleton pregnancies at the same gestational age, although the internal os strain in women with twin pregnancies was higher than in women with singleton pregnancies at the same gestational age (P<.05). The cervical length of women with twin pregnancies was shorter than that of women with singleton pregnancies at the same gestational age when the gestational age was ≥28 weeks of gestation (all P<.05), and the hardness ratio was linearly correlated with gestational age (r=0.68 and r=0.71). The regression model for the cervical hardness ratio in women with singleton pregnancies was hardness ratio = -0.8764×gestational age+100.99, whereas the regression model for the cervical hardness ratio in women with twin pregnancies was hardness ratio = -1.3037×gestational age+103.03. When we compared cervical elasticity parameters between preterm and full-term births, we noted that the cervical hardness ratio in pregnant women who exhibited preterm births was lower regardless of whether they carried singleton or twin pregnancies (P=.000 and P=.000), although their internal os strain was higher (P=.023 and P=.000). We observed no significant difference when we compared the cervical length and external os strain of pregnant women manifesting preterm births vs women with full-term births (P=.216 and P=.345 vs P=.475 and P=.363).

CONCLUSION

When used for the quantification of cervical hardness, the E-Cervix cervical elasticity changes in pregnant women at full term showed some particular patterns. Cervical length and hardness ratio diminished as gestational age increased, whereas internal os strain and external os strain rose as gestational age increased; moreover, the degree of these changes was greater in women with twin pregnancies than in women with singleton pregnancies. Pregnant women experiencing preterm births exhibited a reduced cervical hardness ratio and augmented internal os strain relative to women experiencing full-term births.

Shear wave elastography: the relationship of the cervical stiffness with gestational age and cervical length- a feasibility study

OBJECTIVES

To standardize the measurement of shear wave elastography for assessment of cervical stiffness and its relationship with gestational age and cervical length.

METHODS

A prospective cross-sectional study was conducted from September 2017 to March 2019. Data from 125 unselected women (at 11-13 + 6, 18-22 and 24-28 weeks' gestation) and 55 high-risk women were analyzed for the study. Six regions of interest were evaluated for cervical elastography in the mid-sagittal position by transvaginal ultrasound. Statistical analyses were performed using R statistical language in R-studio. Delivery outcomes were recorded for each patient.

RESULTS

The shear wave elastography was feasible with good intraoperator and interoperator reproducibility. The endocervical canal and anterior lip internal position had the highest reproducibility (ICC-0.82, 0.75). Shear wave speed was significantly higher in all internal os regions than the external os. There was a statistically significant negative linear relationship of shear wave speed with the gestational age. There was a weak positive relationship between shear wave speed and cervical length. There was no difference between pregnancies with and without spontaneous preterm delivery in shear wave speed measurements and cervical length, although numbers were small for statistical analysis. The internal os of the large loop excision of the transformation zone group was stiffer than the normal population.

CONCLUSION

Cervical elastography is feasible and effectively evaluates the tensile properties of the cervix during pregnancy. The most reproducible measurements were obtained at the anterior lip of the internal cervical os. Combining evaluation of cervical elasticity and length might further improve the identification of women at risk of preterm delivery. Currently, technical issues hinder the practical application of shear wave elastography in the clinical setting and require further research and development of the imaging modality.

Cervical and Lower Uterine Parameter Ultrasound and Elastographic Parameters for the Prediction of a Successful Induction of Labor

PURPOSE

 The prediction of successful induction of labor (IOL) has been the subject of a series of studies. The predictive role of cervical sonographic and elastographic parameters has been controversially discussed. Lower uterine segment (LUS) thickness and strain values have not been discussed yet in this regard.

MATERIALS AND METHODS

 A prospective cohort study was performed to examine the predictive power of Bishop score parameters, sonographic cervical length (CL), cervical funneling, cervical strain values, LUS thickness and its strain values regarding successful IOL within 24 hours and intervals to onset of labor, ROM and delivery of the fetus. A p-value of < 0.05 was considered statistically significant.

RESULTS

 135 patients were examined. A cervical length of 25 mm, the presence of cervical funneling and digital shorter cervix was significant for the prediction of successful induction of labor (IOL) within 24 hours. There was weak correlation between the functional CL and the onset of labor (r² = 0.10) and ROM (r² = 0.13). There was also a weak correlation between the cervical funnel width and the time interval to the onset of labor (r² = 0.25), ROM (r² = 0.23) and delivery of the fetus (r² = 0.22). Cervical elastography, LUS thickness and strain values were not significant for the prediction of a successful IOL.

CONCLUSION

 We were able to show that cervical structural changes at the level of the internal os, i. e., shortening through funneling, may be the determining factor for successful IOL.

Advancements in the Application of Ultrasound Elastography in the Cervix

Ultrasound elastography is a modern imaging technique that has developed rapidly in recent years. It enables objective measurement of tissue stiffness, a physical property intuitive to the human sense of touch. This novel technology has become a hotspot and plays a major role in scientific research and academic practice. Presently, ultrasound elastography has been used in the identification of benign and malignant tumors in superficial organs, such as breast and thyroid, providing clinically accurate diagnosis and treatment. The method has also been widely used for the liver, kidney, prostate, lymph nodes, blood vessels, skin and muscle system. In the application of cervical lesions, ultrasound elastography can distinguish normal cervix from abnormal cervix and differentiate benign from malignant lesions. It can significantly improve the diagnostic specificity for cervical cancer and is also useful for assessing infiltration depth and stage of cervical cancer, as well as predicting chemoradiotherapy treatment response. For cervical evaluation during pregnancy, ultrasound elastography is useful for assessing cervical softening and predicting premature delivery and outcome of induced labor. This article reviews the principles of ultrasound elastography as well as the current status and limitations in its application for cervical lesions and the cervix during pregnancy.

Shear Wave Elastography of the Maternal Cervix: A Comparison of Transvaginal and Transabdominal Ultrasound Approaches

OBJECTIVES

This work aimed to compare the use of shear wave elastography on the maternal cervix with transvaginal (TV) and transabdominal (TA) ultrasound approaches to assess differences in shear wave speeds (SWSs) obtained for possible clinical use.

METHODS

In both TV and TA ultrasound approaches, SWS measurements were attempted at the anterior and posterior portions of the internal and external cervical os on 38 gravid participants.

RESULTS

A larger number of SWS measurements were obtained at the anterior portion of the cervix by both approaches. The numbers of reliable measurements of the SWS obtained at the anterior and posterior portions of the internal and external os were 99, 65, 103, and 77 in the TA approach and 93, 53, 110, and 87 in the TV approach, respectively. The mean difference in -the SWS obtained between the TV and TA ultrasound approaches was statistically significant at the anterior and posterior portions of the internal os, with differences of 0.67 and 0.52 m/s (P < .05). Differences were not significant at the external os both anteriorly and posteriorly, with differences of 0.15 and - 0.07 m/s (P > .05).

CONCLUSIONS

Both TA and TV ultrasound approaches may be used to obtain SWSs in the maternal cervix. This study has shown that SWSs obtained by each approach need to be considered independently, as the TV approach produced significantly greater SWSs at the internal os compared to the TA approach, but the values were similar at the external os.

Menstrual Pain and Elasticity of Uterine Cervix

Menstrual pain is consequent to intense uterine contraction aimed to expel menstrual flow through downstream uterine cervix. Herein it was evaluated whether characteristics of uterine cervix are associated with intensity of menstrual pain. Ultrasound elastography was used to analyze cervix elasticity of 75 consecutive outpatient women. Elasticity was related to intensity of menstrual pain defined by a Visual Analogue Scale (VAS). Four regions of interest (ROI) were considered: internal uterine orifice (IUO), anterior (ACC) and posterior cervical (PCC) compartment and middle cervical canal (MCC). Tissue elasticity, evaluated by color score (from 0.5 = blue/violet (low elasticity) to 3.0 = red (high elasticity), and percent tissue deformation was analyzed. Elasticity of IUO was lower (p = 0.0001) than that of MCC or ACC, and it was negatively related (R2 = 0.428; p = 0.0001) to menstrual VAS (CR −2.17; 95%CI −3.80, −0.54; p = 0.01). Presence of adenomyosis (CR 3.24; 95% CI 1.94, 4.54; p = 0.0001) and cervix tenderness at clinical examination (CR 2.74; 95% CI 1.29, 4.20; p = 0.0004), were also independently related to menstrual VAS. At post hoc analysis, women with vs. without menstrual pain had lower IUO elasticity, expressed as color score (0.72 ± 0.40 vs. 0.92 ± 0.42; p = 0.059), lower percent tissue deformation at IUO (0.09 ± 0.05 vs. 0.13 ± 0.08; p = 0.025), a higher prevalence of cervical tenderness at bimanual examination (36.2% vs. 9.5%; p = 0.022) and a higher prevalence of adenomyosis (46.5% vs. 19.9%; p = 0.04). These preliminary data indicate that IUO elasticity is associated with the presence and the intensity of menstrual pain. Mechanisms determining IUO elasticity are useful to be explored.

Sonoelastographic Assessment of the Uterine Cervix in the Prediction of Imminent Delivery in Singleton Nulliparous Women Near Term: A Prospective Cohort Study

OBJECTIVES

To explore the role of newly developed software to assess cervical sonoelastography in predicting the onset of spontaneous delivery in singleton pregnancies at term and to compare its diagnostic performance with that provided by the cervical length (CL) and posterior cervical angle (PCA).

METHODS

This work was a prospective study including nulliparous singleton pregnancies at gestational ages of 37 weeks to 38 weeks 6 days. The CL, PCA, hardness ratio (HR), and mean strain from the internal os and external os were obtained by a transvaginal ultrasound approach using semiautomatic software (E-Cervix; Samsung Medison Co, Ltd, Seoul, Korea). Multivariate logistic regression and area under the curve analyses were used to test the strength of the association and the diagnostic performance of the variables considered in predicting delivery within 7 days.

RESULTS

A total of 398 women were included, and 24.6% delivered within 7 days. The CL was shorter (19.5 versus 2 7 mm; P = .0001), PCA narrower (99° versus 102°; P = .02) HR lower (35.3 versus 40.7; P = .0001), mean strain from the external os higher (0.41 versus 0.35; P = .0001), and mean strain from the internal os higher (0.38 versus 0.33; P = .0001) higher in women who delivered within 7 days from the assessment. At the multivariable logistic regression analysis, the CL (adjusted odds ratio, 1.307) and HR (adjusted odds ratio, 1.227) were the only variables independently associated with delivery within 1 week. A model combining the CL and HR showed an area under the curve of 0.873 in predicting delivery within 7 days, higher than that obtained by using the CL and HR singularly (P ≤ .0001).

CONCLUSIONS

The HR assessed by sonoelastography improves the efficacy of the CL in predicting imminent delivery in nulliparous women close to term.

Shear wave dispersion as a potential biomarker for cervical remodeling during pregnancy: evidence from a non-human primate model

Shear wave dispersion (variation of phase velocity with frequency) occurs in tissues with layered and anisotropic microstructure and viscous components, such as the uterine cervix. This phenomenon, mostly overlooked in previous applications of cervical Shear Wave Elasticity Imaging (SWEI) for preterm birth risk assessment, is expected to change drastically during pregnancy due to cervical remodeling. Here we demonstrate the potential of SWEI-based descriptors of dispersion as potential biomarkers for cervical remodeling during pregnancy. First, we performed a simulation-based pre-selection of two SWEI-based dispersion descriptors: the ratio R of group velocities computed with particle-velocity and particle-displacement, and the slope S of the phase velocity vs. frequency. The pre-selection consisted of comparing the contrast-to-noise ratio (CNR) of dispersion descriptors in materials with different degrees of dispersion with respect to a low-dispersive medium. Shear waves induced in these media by SWEI were simulated with a finite-element model of Zener viscoelastic solids. The pre-selection also considered two denoising strategies to improve CNR: a low-pass filter with automatic frequency cutoff determination, and singular value decomposition of shear wave displacements. After pre-selection, the descriptor-denoising combination that produced the largest CNR was applied to SWEI cervix data from 18 pregnant Rhesus macaques acquired at weeks 10 (mid-pregnancy stage) and 23 (late pregnancy stage) of the 24.5-week full pregnancy. A maximum likelihood linear mixed-effects model (LME) was used to evaluate the dependence of the dispersion descriptor on pregnancy stage, maternal age, parity and other experimental factors. The pre-selection study showed that descriptor S combined with singular value decomposition produced a CNR 11.6 times larger than the other descriptor and denoising strategy combinations. In the Non-Human Primates (NHP) study, the LME model showed that descriptor S significantly decreased from mid to late pregnancy (-0.37 ± 0.07 m/s-kHz per week, p <0.00001) with respect to the base value of 15.5 ± 1.9 m/s-kHz. This change was more significant than changes in other SWEI features such as the group velocity previously reported. Also, S varied significantly between the anterior and posterior portions of the cervix (p =0.02) and with maternal age (p =0.008). Given the potential of shear wave dispersion to track cervical remodeling, we will extend its application to ongoing longitudinal human studies.

Temperature Elevation in an Instrumented Phantom Insonated by B-Mode Imaging, Pulse Doppler and Shear Wave Elastography

Diagnostic ultrasound is the gold standard for obstetric scanning and one of the most important imaging techniques for perinatal and neonatal monitoring and diagnosis. Ultrasound provides detailed real-time anatomic information, including blood flow measurements and tissue elasticity. The latter is provided through various techniques including shear wave elastography (SWE). SWE is increasingly used in many areas of medicine, especially in detection and diagnosis of breast, thyroid and prostate cancers and liver disease. More recently, SWE has found application in gynaecology and obstetrics. This method mimics manual palpation, revealing the elastic properties of soft biological tissues. Despite its rising potential and expanding clinical interest in its use in obstetrics and gynaecology (such as for assessment of cervical ripening or organ development and structure during pregnancy), its effects on and potential risks to the developing fetus remain unknown. Risks should be evaluated by regulatory bodies before recommendations are made on the use of SWE. Because ultrasound is known to produce thermal and mechanical effects, this study measured the temperature increase caused by B-mode, pulse Doppler (PD) and SWE, using an instrumented phantom with 11 embedded thermocouples. Experiments were performed with an Aixplorer diagnostic ultrasound system (Supersonic Imagine, Aix-en-Provence, France). As expected, the greatest heating was detected by the thermocouple closest to the surface in contact with the transducer (2.9°C for SWE, 1.2°C for PD, 0.7°C for B-mode after 380-s excitation). Both conduction from the transducer face and direct heating owing to ultrasound waves contribute to temperature increase in the phantom with SWE associated with a larger temperature increase than PD and B-mode. This article offers a methodological approach and reference data for future safety studies, as well as initial recommendations about SWE safety in obstetrics and gynaecology.

The Utility of Myometrial and Cervical Ultrasound Shear Wave Elastography in the Diagnosis of Ectopic Pregnancy

We aimed to assess the potential utility of myometrial and cervical elasticity measurement in the diagnosis of ectopic pregnancy (EP), which could facilitate the diagnosis process. Myometrial and cervical elasticity values were measured in women with EP, women with early intrauterine pregnancy (IP) and non-pregnant women. Transabdominal point shear wave elastography (pSWE) was used for elasticity measurements. A reliability study was performed in 20 patients of the non-pregnant group. Cervical pSWE showed poor reliability and high measurement failure rate; thus, we excluded cervical elasticity assessment from the study. In this study, 32 women with EP, 28 women with early IP and 38 non-pregnant women were enrolled for myometrial elasticity assessment by pSWE. Myometrial elasticity values were statistically significantly lower in EP (8.31 kPa [5.1-27]) and early IP (8.83 kPa [4.5-46.2]) groups than in non-pregnant women (14.85 kPa [5.1-28]) (p = 0.003). However, myometrial pSWE results were not significantly different between EP and early IP groups. In light of this data, quantitative assessment of the uterus elasticity using pSWE does not seem to be an adequate diagnostic method for EP.

Evaluation of Cervical Elastography Strain Pattern to Predict Preterm Birth

PURPOSE

 To evaluate cervical elastography strain pattern as a predictive marker for spontaneous preterm delivery (SPTD).

MATERIALS AND METHODS

 In this case-control study cervical length (CL) and elastographic data (strain ratio, elastography index, strain pattern score) were acquired from 335 pregnant women (20th - 34th week of gestation) by transvaginal ultrasound. Data of 50 preterm deliveries were compared with 285 normal controls. Strain ratio and elastography index were calculated by placing two regions of interest (ROIs) in parallel on the anterior cervical lip. The strain ratio was determined by dividing the higher strain value by the lower one. The elastography index was defined as the maximum of the strain ratio curve. Elastographic images were assigned a new established strain pattern (SP) score between 0 and 2 according to the distribution of strain induced by compression.

RESULTS

 Elastography index, SP score and CL differed between preterm and normal pregnancies (1.61 vs. 1.27, p < 0.001; SP score value of "2": n = 31 (62 %) vs. n = 36 (12.6 %), p < 0.001; CL 30.7 vs. 41.0 mm, p < 0.001; respectively). The elastography index and SP score were associated with a higher predictive potential than CL measurement alone (AUC 0.8059 (area under the curve); AUC 0.7716; AUC 0.7631; respectively). A combination of all parameters proved more predictive than any single parameter (AUC 0.8987; respectively).

CONCLUSION

 Higher elastography index and SP scores were correlated with an elevated risk of SPTD and are superior to CL measurement as a predictive marker. A combination of these parameters could be used as a "Cervical Index" for the prediction of SPTD.

Influence of epidemiological characteristics (age, parity and other factors) in the assessment of healthy uterine cervical stiffness evaluated through shear wave elastography as a prior step to its use in uterine cervical pathology

PURPOSE

The purpose of this study was to evaluate stiffness changes occurring in the healthy uterine cervix according to age, parity, phase of the menstrual cycle and other factors by shear wave elastography (SWE).

METHODS

Evaluations of cervical speed and stiffness measurements were performed in 50 non-pregnant patients without gynaecological pathology using SWE transvaginal ultrasound. We performed the evaluation in the midsagittal plane of the uterine cervix with measurements at 0.5, 1 and 1.5 cm from external cervical os, at both anterior and posterior cervical lips.

RESULTS

We evaluated 44 patients by SWE and obtained a total average velocity of 3.48 ± 1.08 m/s and stiffness of 42.39 ± 25.33 kPa. We found differences in speed and stiffness according to the cervical lip and depth evaluated; thus, we observed a velocity of 2.70 m/s at 0.5 cm of depth in the anterior lip and 3.53 m/s at 1.5 cm of depth in the posterior lip (p < 0.05). We observed differences according to parity, obtaining a wave transmission speed of 2.67 m/s and 4.41 m/s at the cervical canal of nulliparous and multiparous patients, respectively (p < 0 0.002). We observed differences according to patient age (from a speed of 2.75 m/s at the cervical canal in the age group of 20-35 years to 5.05 m/s in the age group > 50 years) (p < 0.008). We did not observe differences in speed or stiffness according to the phase of the menstrual cycle, BMI, smoking status or the presence or absence of non-HPV infections.

CONCLUSIONS

The wave transmission speed and stiffness of the uterine cervix evaluated by SWE varies according to the cervical lip and depth of the evaluation as well as according to the parity and age of the patient.

Assessment of the cervix in pregnant women with a history of cervical insufficiency during the first trimester using elastography

INTRODUCTION

To investigate changes in first trimester cervical elastography, cervical length and endocervical canal width in pregnant women with a history of cervical insufficiency, and further discuss the possibility of using these markers as predictors of cervical insufficiency in early pregnancy.

MATERIAL AND METHODS

This was an observational ultrasound study of first trimester cervical changes in singleton pregnancies between January 2016 and June 2018. Cervical elastography, cervical length and endocervical canal width were measured during the first trimester. Strain elastography was used to estimate the softness of anterior and posterior cervical lips and was expressed as percentages (strain rate).

RESULTS

Of the 339 pregnant women enrolled, 24 had a history of cervical insufficiency. The anterior cervical lip was significantly softer in the cervical insufficiency group (strain rate: 0.19% ± 0.05% vs 0.11% ± 0.04%; P < .001). Cervical length was significantly shorter in the cervical insufficiency group (36.3 ± 4.8 mm vs 38.3 ± 3.8 mm; P = .014). Endocervical canal width was significantly wider in the cervical insufficiency group (5.7 ± 1.1 mm vs 5.2 ± 0.7 mm; P = .001). Receiver operating characteristic curve analyses revealed that the optimal cut-off values of anterior cervical lip, cervical length and endocervical canal width to confirm the diagnosis of cervical insufficiency were 0.15%, 35.5 mm and 5.75 mm, respectively. In multivariate logistic regression analysis, significant differences were still observed in anterior cervical strain rate (adjusted odds ratio [OR] 53.78, 95% [confidence interval [CI] 11-270; P < .001) and endocervical canal width (adjusted OR, 5.41, 95% CI,1.2-24.7; P = .029).

CONCLUSIONS

First trimester cervical elastography is a valuable tool in the assessment of women with a history of cervical insufficiency. The anterior cervical lip was significantly softer in women with a history of cervical insufficiency, and the sensitivity and specificity of anterior cervical lip strain were better than that of cervical length and endocervical canal width.

Toward Quantitative and Operator-independent Quasi-static Ultrasound Elastography: An Ex Vivo Feasibility Study

It is known that the elasticity of liver reduces progressively in the case of diffuse liver disease. Currently, the diagnosis of diffuse liver disease requires a biopsy, which is an invasive procedure. In this paper, we evaluate and report a noninvasive method that can be used to quantify liver stiffness using quasi-static ultrasound elastography approach. Quasi-static elastography is popular in clinical applications where the qualitative assessment of relative tissue stiffness is enough, whereas its potential is relatively underutilized in liver imaging due to lack of local stiffness contrast in the case of diffuse liver disease. Recently, we demonstrated an approach of using a calibrated reference layer to produce quantitative modulus elastograms of the target tissue in simulations and phantom experiments. In a separate work, we reported the development of a compact handheld device to reduce inter- and intraoperator variability in freehand elastography. In this work, we have integrated the reference layer with a handheld controlled compression device and evaluate it for quantitative liver stiffness imaging application. The performance of this technique was assessed on ex vivo goat liver samples. The Young's modulus values obtained from indentation measurements of liver samples acted as the ground truth for comparison. The results from this work demonstrate that by combining the handheld device along with reference layer, the estimated Young's modulus value approaches the ground truth with less error compared with that obtained using freehand compression (8% vs. 15%). The results suggest that the intra- and interoperator reproducibility of the liver elasticity also improved when using the handheld device. Elastography with a handheld compression device and reference layer is a reliable and simple technique to provide a quantitative measure of elasticity.

Evolving cervical imaging technologies to predict preterm birth

Preterm birth, defined as delivery at less than 37 weeks' gestation, increases maternal-fetal morbidity and mortality and places heavy financial and emotional burdens on families and society. Although premature cervical remodeling is a major factor in many preterm deliveries, how and why this occurs is poorly understood. This review describes existing and emerging imaging techniques and their advantages and disadvantages in assessing cervical remodeling. Brightness mode (B-mode) ultrasound is used to measure the cervical length, currently the gold standard for determining risk of preterm birth. Several new B-mode ultrasound techniques are being developed, including measuring attenuation, cervical gland area, and the cervical consistency index. Shear wave speed can differentiate between soft (ripe) and firm (unripe) cervices by measuring the speed of ultrasound through a tissue. Elastography provides qualitative information regarding cervical stiffness by compressing the tissue with the ultrasound probe. Raman spectroscopy uses a fiber optic probe to assess the biochemical composition of the cervix throughout pregnancy. Second harmonic generation microscopy uses light to quantify changes in collagen fiber structure and size during cervical maturation. Finally, photoacoustic endoscopy records light-induced sound to determine optical characteristics of cervical tissue. In the long term, a combination of several imaging approaches, combined with consideration of clinical epidemiologic characteristics, will likely be required to accurately predict preterm birth.

Shear wave elastography of the uterine cervix under different conditions with inter-operator agreement analysis

Purpose

Shear wave elastography (SWE) is a relatively new technique for measuring tissue elasticity. Its implementation for assessing the tissue of the cervix is evolving, and SWE analyses of healthy, nonpregnant cervixes is the first step in understanding other SWE changes related to cervical pathologies; nevertheless, some challenges in the use of the technique still require investigation. We aimed to target the consistency of healthy cervix shear wave elastography measurements and examine the changes induced by patient-related factors.

Material and methods

Elastograms were obtained at the internal and external os in the anterior (IA, EA) and posterior (IP, EP) portions of the cervix using a transvaginal approach in eight postmenopausal and 25 premenopausal women. Measurements with a standard deviation of over 20% and patients who presented with colour loss or heterogeneity were excluded from the study. Shear wave elastography assessments were performed using a Toshiba Aplio 500 version 6. Statistical significance was defined as a p value less than 0.10, due to the small number of patients.

Results

The mean speeds obtained at the external os on the anterior and posterior aspects was 3.17 ± 0.85 m/s and 3.18 ± 0.84 m/s, respectively, and at the internal os, the results on the anterior and posterior aspects were 3.38 ± 0.73 m/s and 3.53 ± 0.81 m/s, respectively. The difference in speed among all regions was statistically significant (p < 0.05). Fifteen patients were also analysed by a second radiologist with a similar experience level as that of the first. Nine measurements for IP, 13 measurements for IA, 11 measurements for EP, and 15 measurements for EA were performed. The correlation coefficients between the two sets of measurements were 0.46, 0.30, 0.67, and 0.51, respectively. There was no difference in the SWE values with respect to age, parity, and gravidity for any of the regions. The SWE values at the IA, IP, and EA regions between the postmenopausal and premenopausal women were significantly different (p = 0.038, p = 0.059, p = 0.065).

Conclusions

The posterior portion of the internal os is most likely to undergo inaccurate SWE measurement among the different anatomical positions. The correlation between radiologists was found to be different for different locations in the cervix. More studies are needed to determine the SWE values of the healthy cervix and the agreement levels between radiologists.

ACR Appropriateness Criteria® Assessment of Gravid Cervix

Preterm birth remains the leading cause of perinatal morbidity and mortality. Although the greatest risk factor for preterm birth is a history of prior preterm birth, a short cervical length (≤25 mm) before 24 weeks' gestational age is also associated with increased risk of spontaneous preterm delivery. As such, cervical length assessment has become of particular interest in predicting those patients at risk for preterm birth. Other clinical scenarios (eg, preterm labor, induction of labor, and active labor) may arise, in which assessment of the cervix may be of interest. Ultrasound is the mainstay imaging modality for assessing the gravid cervix, with transvaginal ultrasound recommended in patients at high risk for preterm birth or suspected preterm labor. Transperineal ultrasound is an alternate approach in those cases where transvaginal ultrasound in contraindicated. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Why Are Viscosity and Nonlinearity Bound to Make an Impact in Clinical Elastographic Diagnosis?

The adoption of multiscale approaches by the biomechanical community has caused a major improvement in quality in the mechanical characterization of soft tissues. The recent developments in elastography techniques are enabling in vivo and non-invasive quantification of tissues' mechanical properties. Elastic changes in a tissue are associated with a broad spectrum of pathologies, which stems from the tissue microstructure, histology and biochemistry. This knowledge is combined with research evidence to provide a powerful diagnostic range of highly prevalent pathologies, from birth and labor disorders (prematurity, induction failures, etc.), to solid tumors (e.g., prostate, cervix, breast, melanoma) and liver fibrosis, just to name a few. This review aims to elucidate the potential of viscous and nonlinear elastic parameters as conceivable diagnostic mechanical biomarkers. First, by providing an insight into the classic role of soft tissue microstructure in linear elasticity; secondly, by understanding how viscosity and nonlinearity could enhance the current diagnosis in elastography; and finally, by compounding preliminary investigations of those elastography parameters within different technologies. In conclusion, evidence of the diagnostic capability of elastic parameters beyond linear stiffness is gaining momentum as a result of the technological and imaging developments in the field of biomechanics.

Evaluation of Cervical Elastography for Prediction of Spontaneous Preterm Birth in Low-Risk Women: A Prospective Study

OBJECTIVES

The aim of this study was to determine whether cervical elastographic parameters in addition to cervical length (CL) during the 3 trimesters of pregnancy would be predictive of spontaneous preterm birth (sPTB) among low-risk women.

METHODS

This work was a prospective nested case-control study evaluating cervical elastographic parameters and CL in low-risk women during the 3 trimesters of pregnancy. A binary logistic regression analysis was used to calculate significant covariates for prediction of sPTB. The area under the curve of the prediction model was calculated by using a receiver operating characteristic curve.

RESULTS

There were 286 women (26 cases and 260 controls) included in the analysis. The parameters of cervical elasticity became softened and heterogeneous during the 3 trimesters of pregnancy in both women with and without sPTB. The differences in the mean strain value at the internal os of the cervix (IOS), ratio (strain ratio of the internal os to the external os) during the second trimester and the IOS during the third trimester between the groups had statistical significance (P < .01; P = .01; P < .01, respectively). The CL had no association with sPTB during the 3 trimesters. The IOS during the second trimester was a better predictor of sPTB, with an area under the curve of 0.730, and sensitivity was 72.73%.

CONCLUSIONS

We observed multiple elastographic parameters and demonstrated the physiologic changes in the cervix during the 3 trimesters of pregnancy. Furthermore, we found that the IOS during the second trimester can be helpful in predicting sPTB. However, the CL had no association with sPTB during the 3 trimesters of pregnancy.

Evaluation of the uterine scar stiffness in women with previous Cesarean section by ultrasound elastography: A cohort study

PURPOSE

To evaluate by means of elastography if the quantitative assessment of the cesarean scar elasticity is feasible using as reference the surrounding intact myometrium and to investigate if the cesarean scar stiffness is influenced by the clinical characteristics of the previous cesarean delivery.

METHODS

Prospective study including women with a previous Cesarean Section (CS) ≥ 37 weeks' gestation performed 12-15 months before. By transvaginal ultrasound two regions of interest (ROI) were selected: uterine scar (Region 1) and surrounding myometrium (Region 2). Strain index (SI) for each ROI was calculated and the Strain Ratio (SR) was defined as Region 1 SI/Region 2 SI. The primary outcome was to compare SR among women who were grouped in accordance to presence of previous vaginal delivery, CS during labor, type of suture or pyrexia during post-partum. The secondary outcome of this study was to evaluate the correlation between SR and maternal, neonatal and labor characteristics.

RESULTS

68 women were included. The mean SR was 1.8 ± 0.7 thus indicating an increased stiffness of the uterine scar compared to the surrounding myometrium. No significant differences were found in terms of SR according to presence of previous VD, CS during labor, type of suture or pyrexia during post-partum period. Strain Ratio was not correlated to maternal characteristics nor to labor and neonatal outcome.

CONCLUSIONS

Evaluation of uterine scar stiffness is feasible by using elastography. The stiffness of the uterine scar is higher than that of the surrounding myometrium and is not correlated to maternal and labor characteristics.

Reliability of strain elastography using in vivo compression in the assessment of the uterine cervix during pregnancy

Objective To determine the reproducibility of the mean strain value in various cervical areas and new elastographic parameters for measuring cervical stiffness evaluated by strain elastography using in vivo compression generated by internal organ movement. Methods A prospective observational study (140 singleton pregnant women; 15-33 weeks of gestation) was performed at two tertiary centers. Cervical strain was evaluated using E-cervix™ elastography. The mean strain levels of various cervical areas [internal os (IOS), external os (EOS) and endocervical area] and several new parameters [i.e. the ratio of the strain level of IOS and EOS, elasticity contrast index (ECI), and hardness ratio] were assessed twice by two independent examiners. The inter-observer and intra-observer variances were calculated using the intraclass correlation coefficient (ICC) with a 95% confidence interval (CI). Bland-Altman (B-A) analysis was also performed. Results The median gestational age was 24.0 weeks, and the mean cervical length (CL) was 3.8 cm. The intra-observer and inter-observer ICCs of the mean strain levels of the specified cervical area and new elastographic parameters were statistically significant (P < 0.001, all); the intra-observer ICC was 0.639-0.725, and the inter-observer ICC was 0.538-0.718. Conclusion The reproducibility of elastographic parameter measurements using in vivo compression is improvable.

Subgroup analysis of accreta, increta and percreta cases using acoustic radiation force impulse elastography

OBJECTIVE

To compare acoustic radiation force impulse (ARFI) elastography values and histopathological diagnoses (accreta, increta, percreta) in patients suspected of having abnormal placental invasion (API).

MATERIALS AND METHODS

This prospective study included 54 patients in the third trimester with a history of caesarian section (CS) and API based on gray scale and Doppler ultrasonography (USG) and 35 healthy controls. Patients underwent ARFI elastography preoperatively. Elastography measurements of the fetal and maternal sides of the placenta were compared to histopathology.

RESULTS

Patients had higher maternal-side, fetal-side and average elastography values (P = 0.001). Intraoperatively, eight patients (14.8%) showed abnormal cervical canal invasion and 46 (85.2%) bladder and/or parametrial invasion. Eight patients underwent CS + placental-bed suture, 11 CS + excision of the lower segment, and 35 caesarean-hysterectomy. Histopathology of lower segment excision/caesarian-hysterectomy patients determined 10 (21.7%) accreta, 10 (21.7%) increta and 26 (56.6%) percreta cases. ARFI values were highest in the percreta subgroup. The increta subgroup showed higher ARFI values than the accreta subgroup but maternal-side, fetal-side and average ARFI values were not significantly different across the subgroups (P > 0.05). The cut-off values for average, peripheral and central elastography were determined as >0.90, >0.76, >0.98 (m/s) with sensitivities of 98, 64, 98% and specificities of 85, 80, 91%, respectively.

CONCLUSION

ARFI elastography can detect API. However, it cannot determine invasion depth reliably. More studies with subgroup analyses are warranted to reveal its usefulness for invasion depth.

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.

Ultra-sensitive optical coherence elastography using a high-dynamic-range force loading scheme for cervical rigidity assessment

An ultra-sensitive, wide-range force loading scheme is proposed for compression optical coherence elastography (OCE) that allows for the quantitative analysis of cervical tissue elasticity ex vivo. We designed a force loading apparatus featuring a water sink for minuscule incremental loading through a volume-controlled water droplet, from which the Young's modulus can be calculated by fitting the stress-strain curve. We validated the performance of the proposed OCE system on homogenous agar phantoms, showing the Young's modulus can be accurately estimated using this scheme. We then measured the Young's modulus of rodent cervical tissues acquired at different gestational ages, showing that the cervical rigidity of rodents was significantly dropped when entering the third trimester of pregnancy.

Quantitative elastography of cervical stiffness during the three trimesters of pregnancy with a semiautomatic measurement program: A longitudinal prospective pilot study

AIM

To assess the reproducibility of a semiautomatic quantification tool for cervical stiffness and evaluate the normal changes in cervical elasticity during the three trimesters of pregnancy.

METHODS

This longitudinal prospective pilot study evaluated cervical elasticity during the three trimesters of pregnancy (11-14, 20-24 and 28-32 weeks) in women with singleton pregnancies. Women with a history of conization, cerclage, cervical Naboth cysts (diameter > 10 mm), cervical tumors, or uterine malformation were excluded. A semiautomatic tool was used to evaluate the stiffness of the whole cervix and the internal and external cervical os with multiple quantitative elasticity parameters and the cervical length (CL) on the sagittal view via transvaginal elastography. Intraclass correlation coefficients (ICC) and Bland-Altman analysis were used to assess intra- and interobserver variability. E-Cervix parameters during the three trimesters were compared using the Friedman test.

RESULTS

In total, 217 women with 651 strain examinations during the three trimesters were included. The intra- and interobserver ICC for the E-Cervix parameters ranged from 0.947 to 0.991 and 0.855 to 0.989, respectively. There were significant differences in all parameters among the three trimesters. Cervical elasticity showed significant softening and became heterogeneous during the three trimesters. The median CL was significantly shorter in the first trimester than in the second and third trimesters (P = 0.004, P < 0.001).

CONCLUSION

E-Cervix provides a graphical tool for operators to easily define regions of interest and obtain multiple repeatable measures of elasticity. The normal references for E-Cervix parameters during the three trimesters reflect the physiological cervical changes during pregnancy.

Photoacoustic imaging of the uterine cervix to assess collagen and water content changes in murine pregnancy

The uterine cervix plays a central role in the maintenance of pregnancy and in the process of parturition. Cervical remodeling involves dramatic changes in extracellular matrix composition and, in particular, of collagen and water content during cervical ripening (a term that describes the anatomical, biochemical, and physiologic changes in preparation for labor). Untimely cervical ripening in early gestation predisposes to preterm labor and delivery, the leading cause of infant death worldwide. Inadequate ripening of the cervix is associated with failure of induction or prolonged labor. The current approach to evaluate the state of the cervix relies on digital examination and sonographic examination. Herein, we present a novel imaging method that combines ultrasound (US) and photoacoustic (PA) techniques to evaluate cervical remodeling by assessing the relative collagen and water content of this organ. The method was tested in vitro in extracted collagen phantoms and ex vivo in murine cervical tissues that were collected in mid-pregnancy and at term. We report, for the first time, that our imaging approach provides information about the molecular changes in the cervix at different gestational ages. There was a strong correlation between the results of PA imaging and the histological assessment of the uterine cervix over the course of gestation. These findings suggest that PA imaging is a powerful method to assess the biochemical composition of the cervix and open avenues to non-invasively investigate the composition of this organ, which is essential for reproductive success.

In Vivo Measurement of Cervical Elasticity on Pregnant Women by Torsional Wave Technique: A Preliminary Study

A torsional wave (TW) sensor prototype was employed to quantify stiffness of the cervix in pregnant women. A cross-sectional study in a total of 18 women between 16 weeks and 35 weeks + 5 days of gestation was performed. The potential of TW technique to assess cervical ripening was evaluated by the measurement of stiffness related to gestational age and cervical length. Statistically significant correlations were found between cervical stiffness and gestational age (R2=0.370, p=0.0074, using 1 kHz waves and R2=0.445, p=0.0250, using 1.5 kHz waves). A uniform decrease in stiffness of the cervical tissue was confirmed to happen during the complete gestation. There was no significant correlation between stiffness and cervical length. A stronger association between gestational age and cervical stiffness was found compared to gestational age and cervical length correlation. As a conclusion, TW technique is a feasible approach to objectively quantify the decrease of cervical stiffness related to gestational age. Further research is required to evaluate the application of TW technique in obstetric evaluations, such as prediction of preterm delivery and labor induction failure.

Cervical consistency index and risk of Cesarean delivery after induction of labor at term

OBJECTIVE

To evaluate the association between the cervical consistency index (CCI) and the risk of Cesarean delivery after planned induction of labor (IOL) at term.

METHODS

This was a prospective observational study of women with a term singleton pregnancy admitted for IOL due to maternal or fetal indication. Ultrasonographic images were obtained before IOL and CCI was calculated offline once recruitment was completed. The main outcome was defined as Cesarean delivery due to failed IOL or arrest of labor. Cesarean deliveries indicated due to maternal or fetal compromise (Van Dillen's grade 1 or 2) were excluded from analysis. Univariate statistical analysis was performed using Fisher's exact test and Student's t-test for categorical and continuous variables, respectively. Multivariate analysis was performed using logistic regression, including CCI and other variables related to the main outcome. Intraclass correlation coefficients were used to estimate intra- and interobserver agreement.

RESULTS

Of 510 women admitted for IOL during the study period and for whom image quality was adequate, 46 were excluded due to emergency Cesarean delivery leaving 464 pregnancies for analysis. Cesarean section due to failed IOL or arrest of labor was performed in 100/464 (21.6%) pregnancies. The mean CCI of women who underwent Cesarean delivery was not significantly different from that in those who had vaginal delivery after IOL (70.1 ± 12.3% vs 70.0 ± 13.1%; P = 0.94). Multivariate analysis also showed absence of statistical association between CCI and Cesarean delivery for failed IOL or arrest of labor. Intraclass correlation coefficients for intra- and interobserver agreement were 0.81 (95% CI, 0.66-0.89) and 0.86 (95% CI, 0.75-0.92), respectively.

CONCLUSION

CCI does not seem to be associated with the risk of Cesarean delivery after IOL. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

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

Clinical prediction and especially prevention of abnormal birth timing, particularly pre-term, is poor. The cervix plays a key role in birth timing; it first serves as a rigid barrier to protect the developing fetus, then becomes the pathway to delivery of that fetus. Imaging biomarkers to define this remodeling process could provide insights to improve prediction of birth timing and elucidate novel targets for preventive therapies. Quantitative ultrasound (QUS) approaches that appear promising for this purpose include shear wave speed (SWS) estimation to quantify softness, as well as parameters based on backscattered power, such as the mean backscattered power difference (mBSPD) and specific attenuation coefficient (SAC), to quantify the organization of tissue microstructure. Invasive studies in rodents demonstrated that as pregnancy advances, cervical microstructure disorganizes as tissue softness and compliance increase. Our non-invasive studies in pregnant women and rhesus macaques suggested that QUS can detect these microstructural changes in vivo. Our previous study in the same cohort showed a progressive decline in SWS during pregnancy, consistent with increasing tissue softness, and we hypothesized that backscatter parameters would also decrease, consistent with increasing microstructural disorganization. In this study, we analyzed the mBSPD and SAC in the cervices of rhesus macaques (n = 18). We found that both mBSPD and SAC decreased throughout pregnancy (p < 0.001 for both parameters) and that the former appears to be a more reliable biomarker. In summary, biomarkers that can characterize tissue microstructural organization are promising for comprehensive characterization of cervical remodeling in pregnancy.

Shear Wave Elastography on the Uterine Cervix: Technical Development for the Transvaginal Approach

OBJECTIVES

This research aimed to identify biological and technical confounders in the nonpregnant cervix when applying shear wave elastography with an endovaginal transducer.

METHODS

Cervical speed measurements were obtained at the internal and external os in the anterior and posterior portions of the cervix using a transvaginal approach in 69 nongravid patients.

RESULTS

Reliable measurements were obtained at the external os and internal os, anteriorly and posteriorly, in 63, 55, 55, and 26 patients, respectively. The mean speed obtained at the external os, anteriorly and posteriorly, was 2.52 ± 0.49 m/s and 2.87 ± 0.63 m/s, respectively, and at the internal os, anteriorly and posteriorly, 3.29 ± 0.79 m/s and 4.10 ± 1.11 m/s, respectively. The difference in speed between all regions was statistically significant (P < .05).

CONCLUSION

Ultrasound-induced artifacts appear to affect the transmission of the elastographic main pulse, with cervical position contributing to suboptimal shear wave production in the posterior cervix. Reliable shear wave propagation can be achieved in the anterior cervix in most patients.

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.

Acoustic radiation force impulse (ARFI) elastography to asses maternal and foetal structures in pregnant ewes

The aim of this study was to evaluate the stiffness of foetal lungs, liver, kidneys and placentomes by acoustic radiation force impulse (ARFI) elastography in ovine and to correlate obtained findings with foetal development. Twenty-four ewes were included, and tissue stiffness of foetal lung, liver, kidney and placentome was measured beginning with 10th gestational week by qualitative-quantitative ARFI elastography. A total of 33 healthy lambs were born. Qualitative elastographic analysis permitted to classify maternal and foetal tissues elasticity in decreasing order as follows: placentome, kidney, liver and lung. Regarding quantitative ARFI elastography data, shear wave velocity (SWV) of foetal lung and liver varied. The lung SWV decreased gradually from the 16th to the 21st gestational week (R²  = 0.80; p < 0.001), while liver SWV increased gradually from the 14th to 21st gestational week (R²  = 0.80; p < 0.001). In contrast, the kidneys and placentomes SWV's remained constant through gestation (p = 0.076; and 0.34). ARFI elastography was shown feasible for evaluation of maternal and foetal tissues stiffness in the ovine model. It can be used to demonstrate pulmonary and hepatic stiffness modifications during foetal development.

Shear wave elastography of the maternal cervix: A transabdominal technique

Introduction

Reduced cervical length as seen on transvaginal ultrasound is a strong indicator of spontaneous preterm birth in the high-risk population. In low-risk women the appropriate method to assess this risk is still debatable. Ultrasound elastography has been used to assess cervical strength. This research aimed to assess the accuracy of shear wave speeds (SWS) obtained deep to echo free fluid-filled structures, and the use of two-dimensional shear wave on the maternal cervix using a transabdominal ultrasound approach.

Method

Agreement of SWS measurements obtained through fluid and directly onto an ultrasound phantom was assessed for accuracy. Speed measurements were obtained in the anterior and posterior portions of the internal and external cervical os on 50 gravid participants in the mid-trimester of pregnancy.

Results

No difference in SWS was obtained in the phantom with either direct contact or through the saline water-bath (P > 0.05). In 50 participants, measurements were obtainable at the external os anterior and posterior in 49 and 38 participants, respectively, and in 47 and 42 participants for internal os anterior and posterior. The mean speed obtained at the external os anterior and posterior was 2.01 ± 0.51 and 2.38 ± 0.47 m/s, respectively, and at the internal os anterior and posterior, 2.49 ± 0.50 and 2.58 ± 0.41 m/s.

Conclusion

Shear wave speed measurements can be obtained in the maternal cervix using a transabdominal approach with a moderately full maternal bladder in most patients, with a larger number of shear wave measurements obtained in the anterior cervix compared to posterior.

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.

Ultrasound Elastography can Detect Placental Tissue Abnormalities

Background

In this prospective cohort study, we examined the utility of elastography to evaluate the fetus and placenta.

Patients and methods

Pregnant women in their third trimester of pregnancy, by which time the placenta has formed, were included in this study. A total of 111 women underwent ultrasound examinations, including elastography. Elastographic evaluation was performed using two protocols. First, the placental index (PI) was measured, which quantitatively assesses the hardness of tissue. Second, regions of interest (ROI) were categorized into 3-step scores according to the frequency of the blue area (hardness of placental tissue score [HT score]), which is a qualitative method. After delivery, 40 of the 111 placentas were pathologically examined.

Results

The average PI was 44.3 (± 29.4) in the in utero SGA group, which was significantly higher than that in the normal group (8.8 (± 10.0); p < 0.01) during pregnancy. There was a significant correlation between the PI and z score for estimated fetal weight (EFW) (r = -0.55; p < 0.01). Moreover, a significant positive correlation was observed between the PI and the z score of birth weight (r = -0.39; p < 0.01). Pathological ischemia findings of the placenta were identified in 67% of the HT score 3 group, representing 6 of the 9 patients, and in 20% of the HT score 1 group, representing only 3 of the 15 patients.

Conclusions

Placental hardness, as determined by elastography, correlates with both lower estimated fetal body weight and birth weight. These results suggest that ultrasound elastography in the placenta may be an additional marker of intrauterine fetal well-being.

Role of acoustic radiation force impulse and shear wave velocity in prediction of preterm birth: a prospective study

Background Preterm birth is one of the important causes of neonatal morbidity where we rely on subjective criteria such as modified Bishop's scoring and contemporary sonographic measurement of cervical length. Acoustic radiation force impulse (ARFI) is a technological advancement in elastography that can be employed in prediction of cervical softening and preterm labor. Purpose To evaluate the role of ARFI technique and shear wave velocity (SWV) estimates as a predictor of preterm birth and its comparison with other clinical and sono-elastographic measures. Material and Methods Thirty-four pregnant women (gestation age = 28-37 weeks age) showing features suggestive of preterm labor were included and evaluated with modified Bishop's score, cervical length by ultrasound (US), ARFI to derive Elastography index (EI), and SWV of the cervix. The patients were later divided into two groups, using the clinical outcome of preterm or term delivery. Results Twenty patients delivered at term (gestational age > 37 weeks) and 14 were preterm. Receiver operating characteristics (ROC) curves showed SWV with highest sensitivity and specificity (93% and 90%, respectively) for the prediction of preterm birth at a cutoff value of 2.83 m/s. EI and modified Bishop's score were comparable to each other, but were less sensitive techniques. Conclusion Elastographic assessment of antenatal cervix is a novel technique of virtual palpation of internal os and can be utilized as an objective criterion for preterm birth prediction.

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.

Fetal adrenal gland biometry and cervical elastography as predictors of preterm birth: A comparative study

Background

Preterm birth is a major health problem in developing and developed countries leading to rising health care costs and long-term neurodevelopmental disability. The study aims to evaluate the role of new quantitative markers, like the elastography of cervix (shear wave speed estimation), fetal adrenal zone enlargement, and corrected fetal adrenal gland volume; in preterm birth prediction and analyze their relative importance. Thus, these markers may be beneficial in early preterm birth detection and prevent the related morbidities.

Methods

Thirty pregnant females (from 28 to 37 weeks of gestational age), showing clinical signs and delivery outcome of preterm birth were included in the study with an equal number of not-in-labor antenatal females at ≥37 weeks as controls. These patients were categorized as preterm and term groups. Both the groups were subjected to trans-abdominal ultrasonography where cervical length, cervical shear wave speed (dynamic elastography) and fetal adrenal gland parameters were measured.

Results

Shear wave speed estimation of the antenatal cervix showed the highest sensitivity and specificity (96.7% and 87% respectively) in the prediction of preterm birth and also showed a strong correlation with fetal adrenal gland enlargement. Fetal adrenal zone enlargement was also shown to be a reliable marker of preterm birth, however, with reduced sensitivity and specificity than shear wave speed.

Conclusion

The elastographic advancement and fetal adrenal biometry derived quantitative markers can be used as an objective and standard criterion for accurate prediction of preterm birth.

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.