A new method for measurement of placental elasticity: Acoustic radiation force impulse imaging

Role of acoustic radiation force impulse elastography of placenta in the diagnosis of pre-eclampsia

BACKGROUND

Placental dysfunction is one of the main causes of preeclampsia and hypertensive disorders of pregnancy.

MATERIAL AND METHODS

This is a prospective comparative study done on 30 pregnant women with pre-eclampsia and another 30 pregnant women as controls. In all these subjects the elasticity of the placenta was measured.

RESULTS

The results obtained showed that there was a significant difference in SWV values between the two groups (p value = 0.001). The mean SWV value of normal pregnant women was 0.99 m/ second as opposed to 1.99 m/second in pre-eclamptic pregnant women.

CONCLUSION

Sonoelastography is a promising noninvasive tool in the detection of preeclampsia with high diagnostic accuracy. The SWV values measured at the central zones of the placenta with a cut-off value of 1.325 m/s identify the presence of pre-eclampsia with high sensitivity and specificity.

The Relationship between Placental Shear Wave Elastography and Fetal Weight-A Prospective Study

Background/Objectives: The utility of shear wave elastography (SWE) as an adjunct to ultrasound biometry and Doppler velocimetry for the examination of placental dysfunction and suboptimal fetal growth is unclear. To date, limited data exist correlating the mechanical properties of placentae with fetal growth. This study aimed to investigate the relationship between placental shear wave velocity (SWV) and ultrasound estimated fetal weight (EFW), and to ascertain if placental SWV is a suitable proxy measure of placental function in the surveillance of small-for-gestational-age (SGA) pregnancies. Methods: This prospective, observational cohort study compared the difference in placental SWV between SGA and appropriate-for-gestational-age (AGA) pregnancies. There were 221 women with singleton pregnancies in the study cohort-136 (61.5%) AGA and 85 (38.5%) SGA. Fetal biometry, Doppler velocimetry, the deepest vertical pocket of amniotic fluid, and mean SWV were measured at 2-4-weekly intervals from recruitment to birth. Results: There was no difference in mean placental SWV in SGA pregnancies compared to AGA pregnancies, nor was there any relationship to EFW. Conclusions: Although other studies have shown some correlation between increased placental stiffness and SGA pregnancies, our investigation did not support this. The mechanical properties of placental tissue in SGA pregnancies do not result in placental SWVs that are apparently different from those of AGA controls. As this study did not differentiate between constitutionally or pathologically small fetuses, further studies in growth-restricted cohorts would be of benefit.

Examination of rapid adjustment system based on screen score obtained using continuous shear wave elastography

PURPOSE

Continuous shear wave elastography (C-SWE) can be expected to be applied to portable muscle elasticity diagnosis. To establish diagnostic technology, it will be necessary to improve measurement techniques and quantitative measurement accuracy.

METHODS

In this study, we investigated two screen scores: the quality index (Q-index), which determines whether the intensity of a power Doppler image is appropriate, and the shear wave propagation direction index (SWDI), which determines the uniformity of shear wave propagation.

RESULTS

First, we performed numerical simulations with white noise and found that the coefficient of variation of shear wave velocity estimation was less than 5% when the normalized Q-index was greater than 0.27. Furthermore, regarding the SWDI, we clarified the relationship between the standard deviation in shear wave propagation direction and the SWDI. Next, the relationship between the Q-index and coefficient of variation of estimated shear wave velocity was evaluated through experiments using a tissue-mimicking phantom. The results showed that there was a negative correlation between the Q-index and the coefficient of variation, and the fluctuation of the propagation velocity could be inferred from the Q-index. Finally, we showed the results of applying the screen scores to muscle relaxation monitoring and confirmed its usefulness in clinical applications.

CONCLUSION

By applying the screen scores, we showed improved stability in speed estimation in C-SWE, and demonstrated the possibility of clinical applicability.

Role of Shear Wave Elastography of Placenta in Prediction of Preeclampsia in High-Risk Pregnancy

ABSTRACT

The aim of our study was to compare the placental elasticity values between normal pregnancies and preeclamptic pregnancies and evaluate the utility of shear-wave elastography of the placenta as a predictor for preeclampsia in high-risk pregnancy. A prospective study was performed with 90 singleton high-risk pregnancies having any of the 7 risk factors for developing preeclampsia (primigravida, history of preeclampsia, family history of preeclampsia, history of pregestational diabetes, chronic hypertension, advanced maternal age [≥40 years], and body mass index ≥26 kg/m 2 ) were enrolled in the study. Shear-wave elastography was performed in all patients at 20 to 24 weeks' gestation and at 34 to 36 weeks' gestation, at 2 sites: center and edge of the placenta. The patients were divided into 2 groups: normal pregnancies (group A) or developed preeclampsia (group B). Women with posterior placentation, obstetric disorders other than preeclampsia, or multiple gestation were excluded from the study. Group comparisons were done using the χ2 test or Fisher exact test. Shear-wave elasticity values at 20 to 24 weeks' gestation for group B at the center of the placenta (21.73 vs 9.72 kPa) and at the edge of the placenta (21.6 kPa vs 10.15 kPa) were significantly higher than those for group A ( P < 0.05). Similar results were seen at 34 to 36 weeks' gestation. With a cutoff of 13.1 kPa, we attained sensitivity of 95.2%, specificity of 92.8% and diagnostic accuracy of 93.3% for predicting development of preeclampsia. Patients with preeclampsia have a significantly higher stiffness of the placenta. Shear-wave elastography is useful to evaluate placental function. Elastography can be used as a supplementary tool for prediction of preeclampsia.

Predictive value of placental real-time shear wave elastography combined with 3-dimensional power Doppler index for preeclampsia

This study aimed to investigate the value of placental real-time shear wave elastography combined with three-dimensional power Doppler index (3D-PDI) in the prediction of preeclampsia. We conducted a retrospective study selecting 60 pregnant women diagnosed with preeclampsia as the experimental group and 60 normal pregnant women as the control group from January 2021 to December 2022. The elastic modulus values of different regions of the placenta and placental 3D-PDI were detected and compared between the two groups. The ROC curve was used to evaluate the diagnostic value of each parameter, alone or in combination, for preeclampsia. The study findings demonstrated that the elastic modulus values of different regions of the placenta and 3D-PDI of the two groups have statistical significance. The values of SWE, VI, FI, and VFI are different in prediction of preeclampsia, and the combination of various parameters can improve the prediction value. Overall, our study provides a valuable method for the prediction of preeclampsia with the advantages of non-invasiveness, efficiency, and simplicity.

The Value of Ultrasonic Elastography in Detecting Placental Stiffness for the Diagnosis of Preeclampsia: A Meta-Analysis

This meta-analysis evaluated the diagnostic value of ultrasonic elastography in detecting placental stiffness in the diagnosis of preeclampsia (PE). A systematic search was conducted in the EMBASE, Web of Science, Cochrane Library, Scopus database, and PubMed databases to identify studies published before June 2023 using ultrasonic elastography to diagnose PE. The sensitivity, specificity, and diagnostic odds ratio of ultrasonic elastography for diagnosing PE were calculated, and a summary receiver operating characteristic curve model was constructed. The degree of heterogeneity was estimated using the I2 statistic, and a meta-regression analysis was performed to explore its sources. A protocol was determined previously (PROSPERO: CRD42023443646). We included 1188 participants from 11 studies, including 190 patients with PE and 998 patients without PE as controls. Overall sensitivity and specificity of ultrasonic elastography in detecting placental stiffness for the diagnosis of PE were 89% (95% CI: 85-93) and 74% (95% CI: 51-89), respectively. The I2 values for sensitivity and specificity were 59% (95% CI: 29-89) and 96% (95% CI: 95-98), respectively. The area under the receiver operating characteristic curve was 0.90 (95% CI: 0.87-0.92). The meta-regression analysis showed no significant heterogeneity. Ultrasonic elastography exhibits good diagnostic accuracy for detecting placental stiffness and can serve as a non-invasive tool for differentially diagnosing PE.

Early Prediction of Gestational Diabetes Mellitus Using Placental Strain Elastography and Subcutaneous Adipose Tissue Thickness

AIM

The aim of this study is to investigate the efficacy of placental strain ratio values measured by real-time sonoelastography and maternal subcutaneous adipose tissue thickness measured by two-dimensional ultrasonography in predicting gestational diabetes mellitus in the first trimester.

MATERIALS AND METHODS

The population of the study consisted of the first 210 consecutive singleton pregnant women who applied for routine first-trimester screening between the 11th and 14th week of gestation.B-mode subcutaneous adipose tissue thickness sonography and real-time placental strain elastography scanning were performed.All patients underwent 75 g oral glucose tolerance test between the 24th and 28th week of gestation. American Diabetes Association criteria were used in the diagnosis of gestational diabetes mellitus.

RESULTS

It was observed that body mass index (p<0.001), first-trimester fasting blood sugar (p<0.001), subcutaneous adipose tissue thickness (p<0.001), and placental strain ratio value (p<0.001) affected the development of gestational diabetes mellitus statistically. The multivariate analysis shown that subcutaneous adipose tissue thickness (odds ratio=1.271, 95% CI=1.142-1.416, p<0.001) and placental strain ratio value (odds ratio=3.664, 95% CI=1.927-6.969, p<0.001) were the independent risk factors affecting the development of gestational diabetes mellitus.

CONCLUSIONS

The findings of this study indicated a positive correlation between 75 g oral glucose tolerance test application and first trimester subcutaneous adipose tissue thickness and placental strain ratio. Using the cut-off values of>11.5 mm for subcutaneous adipose tissue and>0.986 for placental strain ratio, the development of gestational diabetes mellitus may be predicted in the early weeks of pregnancy.

Comparison of fetal and maternal tissue elasticity between euploid and aneuploid pregnancies by shear wave elastography

AIM

B-mode ultrasonography utilized for fetal screening of common trisomies is referred to as a genetic sonogram and includes determining major abnormalities and soft markers such as hypoplastic nasal bone and increased thickness of the nuchal fold. Elastography is a novel ultrasound technique giving information about tissue stiffness used for diagnosing cancer, transplant rejection, and organ fibrosis. This study aimed to determine via shear wave elastography (SWE) whether euploid and aneuploid fetal soft marker tissues vary in stiffness.

METHODS

The participants were all singleton pregnancies between 19 and 23 weeks of gestation; 35 euploid and 14 aneuploid fetus pregnancies were enrolled. Fetal bowel, kidney, liver, nasal bone, nuchal fold, placenta, and myometrium were investigated with SWE using acoustic radiation impulse force. Images were analyzed with a novel software calibrated and written by us using MATLAB. Statistical analysis was completed with the SPSS Program. Shapiro-Wilk normality distribution analysis, Student's t-test, and Mann-Whitney U methods were used.

RESULTS

The mean shear wave speed of fetal nasal bone was significantly lower in aneuploid fetuses. There was no difference between other tissues in mean shear wave velocity.

CONCLUSIONS

Euploid and aneuploid fetuses have different elastic properties of the nasal bone and this may have a role in differentiating aneuploid fetuses noninvasively.

SWAVE 2.0 Imaging of Placental Elasticity and Viscosity: Potential Biomarkers for Placenta-Mediated Disease Detection

Pregnancy complications such as pre-eclampsia (PE) and intrauterine growth restriction (IUGR) are associated with structural and functional changes in the placenta. Different elastography techniques with an ability to assess the mechanical properties of tissue can identify and monitor the pathological state of the placenta. Currently available elastography techniques have been used with promising results to detect placenta abnormalities; however, limitations include inadequate measurement depth and safety concerns from high negative pressure pulses. Previously, we described a shear wave absolute vibro-elastography (SWAVE) method by applying external low-frequency mechanical vibrations to generate shear waves and studied 61 post-delivery clinically normal placentas to explore the feasibility of SWAVE for placental assessment and establish a measurement baseline. This next phase of the study, namely, SWAVE 2.0, improves the previous system and elasticity reconstruction by incorporating a multi-frequency acquisition system and using a 3-D local frequency estimation (LFE) method. Compared with its 2-D counterpart, the proposed system using 3-D LFE was found to reduce the bias and variance in elasticity measurements in tissue-mimicking phantoms. In the aim of investigating the potential of improved SWAVE 2.0 measurements to identify placental abnormalities, we studied 46 post-delivery placentas, including 26 diseased (16 IUGR and 10 PE) and 20 normal control placentas. By use of a 3.33-MHz motorized curved-array transducer, multi-frequency (80,100 and 120 Hz) elasticity measures were obtained with 3-D LFE, and both IUGR (15.30 ± 2.96 kPa, p = 3.35e^-5) and PE (12.33 ± 4.88 kPa, p = 0.017) placentas were found to be significantly stiffer compared with the control placentas (8.32 ± 3.67 kPa). A linear discriminant analysis (LDA) classifier was able to classify between healthy and diseased placentas with a sensitivity, specificity and accuracy of 87%, 78% and 83% and an area under the receiver operating curve of 0.90 (95% confidence interval: 0.8-0.99). Further, the pregnancy outcome in terms of neonatal intensive care unit admission was predicted with a sensitivity, specificity and accuracy of 70%, 71%, 71%, respectively, and area under the receiver operating curve of 0.78 (confidence interval: 0.62-0.93). A viscoelastic characterization of placentas using a fractional rheological model revealed that the viscosity measures in terms of viscosity parameter n were significantly higher in IUGR (2.3 ± 0.21) and PE (2.11 ± 0.52) placentas than in normal placentas (1.45 ± 0.65). This work illustrates the potential relevance of elasticity and viscosity imaging using SWAVE 2.0 as a non-invasive technology for detection of placental abnormalities and the prediction of pregnancy outcomes.

Point shear wave velocity(pSWV) evaluation of the placenta of pregnant women who had recovered from COVID-19: A prospective cohort study from a tertiary pandemic center

INTRODUCTION

To assess the placental elasticity using point shear wave velocity (pSWV) in pregnant women who had recovered from coronavirus COVID-19.

METHODS

A total of 40 pregnant women who had recovered from moderate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and 40 healthy pregnant women were included in this study. We evaluated placental elasticity by using transabdominal pSWV method. Three measurements were made, and their average was accepted as the mean placental velocity value in each case. The results were compared between the post-COVID-19 and control groups.

RESULTS

The mean pSWV values were significantly higher in the post-COVID-19 group compared to the control group, indicating that the women with a history of COVID-19 had stiffer placentas. Furthermore, the pSWV values were significantly and positively correlated with the uterine artery pulsatility index. We also found that the NICU requirement was statistically higher in the post-COVID 19 group.

DISCUSSION

The pregnant women who had recovered from COVID-19 had rigid placentas than the healthy controls. The use of pSWV for the assessment of placental velocity may provide valuable information in the diagnosis and management of post-COVID-19 patients as a complementary tool to the existing ultrasonography methods.

Placental elastography in second trimester preeclampsia prediction: A prospective study

OBJECTIVE

The aim of the study was to evaluate the diagnostic potential of placental shear wave elastography in predicting preeclampsia at 16 to 20 weeks of gestation.

MATERIALS AND METHODS

A total of 230 pregnant women between 16 and 20 weeks of gestation were observed for the study. These women underwent shear wave elastography ElastPQ (Philips Healthcare, Bothell, Washington, USA) of the placenta. The mean value of placental shear modulus was obtained for each participant. These participants were followed up for the development of preeclampsia and were divided into two groups; group A included those who developed preeclampsia and group B included those who remained normotensive until delivery. The elasticity values of the two groups were compared, and the ROC curve was drawn to obtain the best cut-off value that would predict the onset of preeclampsia.

RESULTS

Placental shear modulus varied from 1.03 kPa to 7.4 kPa at 16 to 20 weeks of gestation with an average of 2.74 ± 0.87 kPa. There was a statistically significant difference in the mean value of elasticity between two groups, being 4.61 kPa in group A and 2.51 kPa in group B. Maximum diagnostic accuracy was obtained at 2.9667 kPa with area under the curve 0.970, sensitivity 92%, specificity 91.71%, positive predictive value 57.5% and negative predictive value 98.9%.

CONCLUSION

Stiffness of placenta, quantitatively measured by SWE at 16 to 20 weeks of gestation, is higher in the women who develop preeclampsia and hence may be used for predicting preeclampsia.

Value of shear-wave elastography and cerebral-placental-uterine ratio in women diagnosed with preeclampsia and fetal growth restriction in prediction of adverse perinatal outcomes

PURPOSE

The aim of this study was to measure placental stiffness with shear-wave elastography technique and to evaluate the relationship with cerebral-placental-uterine ratio (CPUR) and adverse perinatal outcomes in patient groups diagnosed with preeclampsia (PE) and fetal growth restriction (FGR) in the second and third trimesters compared to the control group.

MATERIALS AND METHODS

This prospective cross-sectional study was conducted at our hospital between March 2019 and March 2020. The study groups were divided into three groups: PE, FGR, and low risk pregnancy (LRP) group. The study population had singleton pregnancies and the placental site was at the anterior wall. Both shear-wave elasticity (SWE) and shear-wave velocity (SWV) were measured in the placenta during pregnancy. CPUR was calculated for each group.

RESULTS

A total of 147 patients were included in this study. The mean SWE (kilopascals) values in the PE group were significantly higher than in the FGR and controls (difference of means = 3.67, 9.45; 95% CI (1.23-6.1, 7-11.8); p < .05), respectively. The mean SWV values were significantly higher in PE and FGR groups than controls (p < .05). CPUR showed correlation with central maternal surface of placenta (p: .02, r: -0.184), central fetal surface of placenta (p < .001, r: -0.288), peripheral maternal surface of placenta (p: .002, r: -0.252), and peripheral fetal surface of placenta SWE values (p: .03, r: -0.181). NICU admission was correlated with central fetal surface of placenta SWE values (p: .002, r: 0.258).

CONCLUSION

In conclusion, we demonstrated increased placental stiffness in both the PE and the FGR group. Also, this difference was found to be more prominent in preeclampsia. This technique seems useful for assessment of placental function and may strengthen the utility of Doppler parameters for predicting adverse perinatal outcomes in high-risk pregnancies.

Prenatal quantification of human foetal lung and liver elasticities between 24 and 39 weeks of gestation using 2D shear wave elastography

Objectives

To quantify and model normal foetal lung and liver elasticities between 24 and 39 weeks of gestation (WG) using two-dimensional shear wave elastography (2D-SWE). To assess the impact of the distance between the probe and the target organ on the estimation of elasticity values.

Methods

Measurements of normal foetal lungs and liver elasticity were prospectively repeated monthly between 24 and 39 WG in 72 foetuses using 2D-SWE. Elasticity was quantified in the proximal lung and in the region inside the hepatic portal sinus. The distance between the probe and the target organ was recorded. Trajectories representing foetal lung and liver maturation from at least 3 measurements over time were modelled.

Results

The average elasticity for the lung and liver was significantly different from 24 WG to 36 WG (p < 0.01). Liver elasticity increased during gestation (3.86 kPa at 24 WG versus 4.45 kPa at 39 WG). From 24 WG to 32 WG, lung elasticity gradually increased (4.12kPa at 24 WG, 4.91kPa at 28 WG, 5.03kPa at 32 WG, p < 0.002). After 32 WG, lung elasticity decreased to 4.54kPa at 36 WG and 3.94kPa at 39 WG. The dispersion of the average elasticity values was greater for the lung than for the liver (p < 0.0001). Variation in the elasticity values was less important for the liver than for the lung. The values were considered valid and repeatable except for a probe-lung distance above 8cm.

Conclusion

Foetal lung and liver elasticities evolve differently through gestation. This could reflect the tissue maturation of both organs during gestation.

Trial registration

clinicaltrials.gov identifier: NCT03834805

Key Points

• Prenatal quantification of foetal lung elasticity using 2D shear wave elastography could be a new prenatal parameter for exploring foetal lung maturity.

• Liver elasticity increased progressively from 24 weeks of gestation (WG) to 39 WG, while lung elasticity increased first between 24 and 32 WG and then decreased after 32 WG.

• The values of elasticity are considered valid and repeatable except for a probe-lung distance above 8cm.

Shear-wave elastography for detection of placenta percreta: a case-controlled study

BACKGROUND

Prenatal diagnosis of placenta percreta (PP) is important to be able to provide effective management and a multidisciplinary approach to minimize the complications.

PURPOSE

To evaluate the role of shear-wave elastography (SWE) in the prenatal diagnosis of PP.

MATERIAL AND METHODS

A total of 18 women with PP and 20 pregnant women with normal placenta in the second or third trimesters were included in this prospective study. SWE was used to determine the elasticities of the placenta (in the maternal edge of the placenta) and myometrium. The obstetric data regarding grayscale and Doppler ultrasonography, and perinatal outcomes were reviewed. A mean placental SW velocity (SWV) cut-off value was determined to predict the presence of placental adherence.

RESULTS

The SWV values of the PP group in the maternal edge of the placenta were significantly higher than those of the control group (1.95 ± 0.19 m/s and 1.69 ± 0.23 m/s; P = 0.001). Myometrial SWV was also higher in the PP group compared to the control group (2.25 ± 0.39 m/s and 1.90 ± 0.71 m/s; P = 0.002). A receiver operating characteristic (ROC) curve analysis was performed and the best cut-off value of placental SWV was determined as 1.92 m/s with sensitivity of 58% and specificity of 80%, to predict the placental adherence in patients with PP.

CONCLUSION

Placental stiffness was significantly higher in patients with PP than in pregnant women with normally localized placenta. Thus, we thought that SWE of the placenta might be used as an alternative method in the diagnosis of PP.

The role of shear wave elastography in the assessment of placentas in healthy pregnancy women during third-trimester: A preliminary study

OBJECTIVE

The study aimed to analysis the elasticity value of placenta in healthy women during third trimester by shear wave elastography (SWE), and tried to investigate the relationship between clinical characteristics and placental elasticity.

METHODS

Singleton healthy pregnant women who had routine ultrasound examination between 28 and 37 weeks were enrolled. SWE of the frontier placentas were evaluated by transabdominal ultrasound elastography. Only placentas at front wall were enrolled. The placenta was divided into three areas for SWE examination: the central area (Area A), the periphery area (Area B) and the area between central and edge of placenta (Area C). Then, the subjects with normal delivery were evaluated and analyze the relationship between clinical features and placental elasticity.

RESULTS

A total of 43 pregnant women were included in this study. The mean value of SWE in the central area was 5.67±2.51 kPa. And it was 6.50±2.57 kPa in the periphery area, 5.17±2.25 kPa in the area C. There were no significant differences except area B and C. In different age group, there were no significant differences except area C. The history of childbearing and uterine operation and the gestational age were no significant correlation with the SWE value of placenta. There were also no significant differences between birth weight percentile and placental elasticity.

CONCLUSION

The placental elasticity is stable in healthy women during third trimester. Shear wave elastography is helpful to assess the placental elasticity and can be used as a supplemental technique to existing methods for monitoring the placental function. But the normal elasticity range in some certain areas of placenta should be confirmed by further study.

Comparison of elasticity values in normal and gestational diabetic pregnancies in the third trimester

Placental elasticity was compared by using Shear wave elastography (SWE) in patients with gestational diabetes mellitus (GDM) with and without insulin to non-diabetic controls. Three groups were created as follows: Group 1 (n = 79, GDM with insulin therapy), Group 2 (n = 90, GDM with only diet) and Group 3 (n = 150, healthy controls) All patients were above 36 gestational weeks with anterior placenta. Clinical trial number was also received (NCT04455880). Group 1 had higher BMI while group 3 had lowest rate of C/S. Birthweight in GDM groups was statistically significantly higher than controls (p = .001). Although there was no significant difference between APGAR scores, Group 1 had higher rates of neonatal intensive care unit (NICU) admission. SWE values were significantly higher in GDM patients treated with insulin or diet than controls. SWE may be an alternatively supplementary management modality in GDM.IMPACT STATEMENTWhat is already known on this subject? Shear wave elastography (SWE), is one of the types of sono elastography methods that are used to measure the stiffness and elasticity of soft tissues. Recently, it became popular for screening the stiffness and elasticity of the placenta in high-risk pregnancies like preeclampsia, intrauterine growth restriction (IUGR), and placental dysfunction.What the results of this study add? All SWE velocities on the maternal side were statistically significantly different between groups. Regarding foetal side velocities, GDM groups had statistically significantly higher values (stiffer tissue) compared to controls.What the implications are of these findings for clinical practice and/or further research? SWE may be a Supplementary method in the diagnosis and management of GDM. Placental SWE should be measured at 24-28 weeks of gestation in patients with GDM and diagnosis confirmation and their responses to the treatment should be examined.

Changes in placental elastography in the third trimester - Analysis using a linear mixed effect model

INTRODUCTION

Research into the role of ultrasound elastography to assess compromised placental tissue is ongoing. There is particular interest in evaluating its potential in the investigation of changes associated with uteroplacental dysfunction. To date, there is limited data on how different maternal and fetal considerations, such as advancing gestational age, amniotic fluid Index (AFI) and maternal body mass index (BMI) may influence shear wave velocity (SWV) measurements. This study aimed to evaluate longitudinal changes in SWV throughout gestation and model these changes with other developing fetal and maternal physiological and biological characteristics.

METHODS

The study utilised 238 singleton pregnancies and collected longitudinal data at repeated intervals in the 3rd trimester representing 629 individual data points. Linear mixed model regression analysis was used to identify significant predictors for SWV.

RESULTS

From a total of ten variables selected for modelling, only gestational age, AFI, BMI, and sample depth were found to be significant predictors of placental SWV, and gestational age and AFI were found to have only a minimal impact on SWV.

DISCUSSION

Sophisticated statistical modelling demonstrates that many of the expected maternal and fetal changes in the 3rd trimester have no or minimal impact on placental SWV. Understanding which factors influence placental SWV is essential to ascertain the technique's utility in managing pregnancies complicated by placental dysfunction in the future.

A Review of Biomechanics Analysis of the Umbilical-Placenta System With Regards to Diseases

Placenta is an important organ that is crucial for both fetal and maternal health. Abnormalities of the placenta, such as during intrauterine growth restriction (IUGR) and pre-eclampsia (PE) are common, and an improved understanding of these diseases is needed to improve medical care. Biomechanics analysis of the placenta is an under-explored area of investigation, which has demonstrated usefulness in contributing to our understanding of the placenta physiology. In this review, we introduce fundamental biomechanics concepts and discuss the findings of biomechanical analysis of the placenta and umbilical cord, including both tissue biomechanics and biofluid mechanics. The biomechanics of placenta ultrasound elastography and its potential in improving clinical detection of placenta diseases are also discussed. Finally, potential future work is listed.

The relation between second-trimester placental elasticity and poor obstetric outcomes in low-risk pregnancies

OBJECTIVES

Increased placental stiffness is associated with various pathological conditions. Our objective was to evaluate the relation between the second-trimester placental elasticity value in low-risk pregnant women and poor obstetric outcomes.

METHODS

A total of 143 pregnant women were enrolled. Placental elasticity values were measured using the transabdominal point shear wave elastography method. 10 random measurements were obtained from different areas of the placenta. The mean was accepted as the mean placental elasticity value. Logistic regression analyses were performed to identify independent variables associated with obstetric outcomes.

RESULTS

Second-trimester placental elasticity value was significantly and positively associated with the poor obstetric outcomes (p=0.038). We could predict a poor outcome with 69.2% sensitivity and 60.7% specificity if we defined the placental elasticity cut-off as 3.19 kPa. Furthermore, in the multiple regression model, the placental elasticity value added significantly to the prediction of birth weight (p=0.043).

CONCLUSIONS

Our results showed that the pregnancies with a stiffer placenta in the second trimester were associated with an increased likelihood of exhibiting poor obstetric outcomes. Also, placental elasticity was independently associated with birth weight.

Shear wave velocity by quantitative acoustic radiation force impulse in the placenta of normal and high-risk pregnancy

Background

Traditionally, the placental functional integrity is suggested by indirect ultrasound measurements like fetal growth, amniotic fluid index, and uterine and umbilical artery Doppler indices. Only recently the elasticity of the placenta is studied as a measure of placental consistency and biomechanical prosperities and may reflect the placental function. Shear wave velocity is the quantitative parameter of the shear wave elastography. A high-risk pregnancy is a situation which puts the mother, the fetus, or both at greater risk than a normal pregnancy.

Results

The shear wave velocity (SWV) showed no significant difference between the placenta of normal pregnancies in the second and third trimesters (0.85 ± 0.43 m/s and 0.89 ± 0.57 m/s, respectively). The placenta of patients with preeclampsia/eclampsia had high SWV in the second and third trimesters (2.13 ± 1.48 m/s and 2.23 ± 1.48 m/s) with a highly significant difference from the normal placenta (P < 0.001). The placentas with abnormal location (placenta previa) and penetration (placenta accreta) had higher SWV than the placenta of normal pregnancies. The mean SWV for placenta previa was 1.1 ± 0.74 m/s and 1.3 ± 0.81 m/s in the second and third trimesters, respectively, with a mildly significant difference with the normal placenta. The placenta accreta shows high mean SWV in the second and third trimesters (1.6 ± 0.65 m/s and 1.961.6 ± 0.65, respectively) which differed significantly (P < 0.001) from SWV in the normal placenta in the second and third trimesters.

Conclusion

Shear wave velocity measurement as the quantitative parameter of acoustic radiation force impulse (ARFI) elastography reflects the placental elasticity in normal and high-risk pregnancies. The SWV increases in conditions like hypertension, preeclampsia, maternal renal disease, and diabetes and reflects the structural and biomechanical abnormalities in such diseases. High shear wave velocity correlates with the incidence of growth restriction and abnormal Doppler parameters especially in the hypertensive disease. The virtual touch quantification (VTQ) can be used as a complementary diagnostic and prognostic tool in high-risk pregnancy.

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.

A Preliminary Study on the Safety of Elastography during Pregnancy: Hypoacusia, Anthropometry, and Apgar Score in Newborns

Transient or acoustic radiation force elastography (ARFE) is becoming the most extended technology to assess cervical effacement, additionally to the Bishop test and conventional ultrasound. However, a debate on the fetal safety has been opened due to the high intensity focused beam emitted to produce shear waves. This work is aimed at providing preliminary data to assess clinical effects of fetal exposure. A follow-up study in newborns of 42 women exposed to ARFE during pregnancy was carried out to explore neonatal hypoacusia, Apgar test, and anthropometry. No hypoacusia cases attributable to ARFE were observed. The Apgar test at five minutes scored normally in all the newborns. Comparisons between anthropometric measurements showed no significant statistically differences. The results preclude to state the harmfulness nor the safety of ARFE. However, given the concern on the high level of energy and the potential risk of harmful bioeffects, larger studies are recommended.

The diagnostic value of two-dimensional shear wave elastography in gestational diabetes mellitus

OBJECTIVE

The aim of our study is to establish the reference range of Young's modulus values of placenta in normal pregnancies and to evaluate the diagnostic value of two-dimensional shear wave elastography (2D-SWE) in gestational diabetes mellitus (GDM).

METHODS

A total of 223 normal pregnant women, 22 pregnancies complicated by A1GDM (controlled by diet), and 14 pregnancies complicated by A2GDM (controlled by medication) were recruited for this study. The elasticity values of the central parts of the placentas were determined by 2D-SWE imaging. The mean value (E_mean), min value (E_min), and max value (E_max) of the placentas were recorded. Twenty placentas were randomly selected for reliability analysis.

RESULTS

(1) All values (E_mean, E_min, E_max) showed great repeatability and consistency. (2) The reference range of Young's modulus values of placentas in normal pregnancies were E_mean (4.12 ± 0.83), E_min (2.15 ± 0.83) and E_max (6.72 ± 1.43). No significant correlations were observed between elasticity values and gestational age (r < 0.3, p > 0.05) or between elasticity values and placental maturity (r < 0.3, p > 0.05). (3) The Young's modulus values in the A1 GDM and A2 GDM women were E_mean (6.39 ± 1.74), E_min (2.95 ± 1.05), E_max (10.78 ± 2.94) and E_mean (11.96 ± 7.29), E_min (6.79 ± 4.70a), E_max (18.94 ± 11.61) respectively. All values were significantly higher in GDM pregnancies than in normal pregnancies (p < 0.05). A2GDM pregnancies had higher values than A1GDM pregnancies (p < 0.05).

CONCLUSION

Placental elasticity is independent of gestational age and placental maturity. 2D-SWE can play an important role in diagnosing GDM by assessing placental hardness.

The use of elastography in placental research - A literature review

INTRODUCTION

Ultrasound elastography is a technique used to quantify biomechanical changes that occur in parenchymal tissue with disease. Recent research has applied the technique to the placenta in order to investigate changes associated with uteroplacental dysfunction. We performed a literature review to summarise the current available information regarding this novel technique.

METHODS

Pubmed, CINAHL and Embase were searched using the terms "placenta", "ultrasound" and "elastography". Only full text studies written in English and limited to placental sonoelastography were included.

RESULTS

Twenty-eight studies met the inclusion criteria and were included in this review. Publications were divided into in vivo and ex vivo groups, and further categorised into four subgroups: normal pregnancy, pregnancy-induced hypertension and pre-eclampsia, fetal growth restriction and other pregnancy complications.

CONCLUSION

Ultrasound elastography can quantitatively assess biomechanical properties of the placenta in conditions where placental function is compromised.

Characterizing placental stiffness using ultrasound shear-wave elastography in healthy and preeclamptic pregnancies

PURPOSE

To measure the stiffness of the placenta in healthy and preeclamptic patients in the second and third trimesters of pregnancy using ultrasound shear-wave elastography (SWE). We also aimed to evaluate the effect of age, gestational age, gravidity, parity and body mass index (BMI) on placental stiffness and a possible correlation of stiffness with perinatal outcomes.

METHODS

In a case-control study, we recruited a total of 47 singleton pregnancies in the second and third trimesters of which 24 were healthy and 23 were diagnosed with preeclampsia. In vivo placental stiffness was measured once at the time of recruitment for each patient. Pregnancies with posterior placentas, multiple gestation, gestational hypertension, chronic hypertension, diabetes, autoimmune disease, fetal growth restriction and congenital anomalies were excluded.

RESULTS

The mean placental stiffness was significantly higher in preeclamptic pregnancies compared to controls in the third trimester (difference of means = 16.8; 95% CI (9.0, 24.5); P < 0.001). There were no significant differences in placental stiffness between the two groups in the second trimester or between the severe preeclampsia and preeclampsia without severe features groups (difference of means = 9.86; 95% CI (-5.95, 25.7); P ≥ 0.05). Peripheral regions of the placenta were significantly stiffer than central regions in the preeclamptic group (difference of means = 10.67; 95% CI (0.07, 21.27); P < 0.05), which was not observed in the control group (difference of means = 0.55; 95% CI (- 5.25, 6.35); P > 0.05). We did not identify a correlation of placental stiffness with gestational age, maternal age, gravidity or parity. However, there was a statistically significant correlation with BMI (P < 0.05). In addition, pregnancies with higher placental stiffness during the 2nd and 3rd trimesters had significantly reduced birth weight (2890 ± 176 vs. 2420 ± 219 g) and earlier GA (37.8 ± 0.84 vs. 34.3 ± 0.98 weeks) at delivery (P < 0.05).

CONCLUSION

Compared to healthy pregnancies, placentas of preeclamptic pregnancies are stiffer and more heterogeneous. Placental stiffness is not affected by gestational age or the severity of preeclampsia but there is a correlation with higher BMI and poor perinatal outcomes.

Comparison of placental elasticity in normal and intrauterine growth retardation pregnancies by ex vivo strain elastography

OBJECTIVE

To compare the placental elasticity in fetuses with or without intrauterine growth restriction (IUGR).

MATERIALS AND METHODS

One hundred pregnant women (50 IUGR and 50 healthy) with anteriorly located placenta were evaluated during the third trimester of pregnancy. Measurements were carried out by a machine that has a real-time elastographic ultrasonography feature. After obtaining the optimum image, three areas (subcutaneous tissue, center, and the edge of the placenta) were provided to identify the placental strain values. Then, the placental strain ratio (PSR) value was calculated automatically. Two groups compared in terms of their PSR values.

RESULTS

There was a significant difference in placental elasticity between the groups (P < 0.001). PSR value was 2.8 ± 1.2 in the IUGR group and 1.3 ± 0.6 in the control group. A PSR value of 1.78 had an 86% sensitivity (OR 4.3) and 80% specificity (OR 0.17) in IUGR cases. The positive predictive value was 81.1% and the negative predictive value was 85.1% for this cut-off value.

CONCLUSIONS

We have shown that placental strain ratio is increased during the third trimester of pregnancy in fetuses with IUGR. Increased stiffness and elasticity may be responsible for the onset of IUGR in some cases.

The effect of placental elasticity on intraoperative bleeding in pregnant women with previous cesarean section

Background We aimed to evaluate the efficiency of placental elasticity in predicting the amount of intraoperative bleeding via real-time tissue elastography technique. Methods Pregnant women in the third trimester of pregnancy who had planned delivery via cesarean section due to the recurrent cesareans were enrolled in the research (n = 78). Elastographic measurements of placental tissues of all cases were carried out by real-time elastographic ultrasonography. It is a tissue elastography software (Esaote MyLabSeven) that uses a 8-1-MHz multifrequency AC2541 Probe. Results A significant relationship was found between placental elasticity and intraoperative bleeding. There was a significant correlation between alterations in the preoperative and postoperative hemoglobin (Hb) and hematocrit (Hct) levels and placental strain ratio (SR) (P < 0.001, r: 0.831; P < 0.001, r: 0.733, respectively). Conclusion These findings may reflect an alteration at the tissue elasticity level. We hope that the use of real-time elastographic ultrasonography technique may give an idea about the amount of bleeding during the cesarean section.

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.

Placental ARFI elastography and biometry evaluation in bitches

Placental rigidity and biometry of twelve pregnant bitches were evaluated using B-mode and Acoustic Radiation Force Impulse (ARFI) ultrasonography, performed once daily, from day 15 of gestation until parturition. Specific software (Virtual Touch Tissue Quantification® VTTQ and Virtual Touch Tissue Imaging Quantification® VTTIQ) were used. Values for results for variables were correlated and regression models related to gestational day were used to make evaluations. Maternal-fetal placental thickness increased to day 63 (P < 0.0001; R² = 0.91); maternal placental thickness increased until day 40 (P = 0.0340; R² = 0.54); and fetal placental thickness increased to day 50 (P < 0.0001; R² = 0.83) of gestation. Shear wave velocity (SWV) of the dorsal (P < 0.0010) was greater than lateral, which in turn was greater (P = 0.020) than the ventral area. The SWV of the dorsal area as determined using VTTQ, decreased from day 21-35 and increased to day 56 of gestation (P = 0.0291; R² = 0.4021); lateral SWV decreased from day 24-45 and increased until the time of parturition (P < 0.001; R² = 0.6055). The SWV of the dorsal area, as determined using VTTIQ, decreased from day 21-43 and then increased to day 60 of gestation (P = 0.0016; R² = 0.5075); and ventral area SWV increased from day 21-23 and decreased until the time of parturition (P < 0.001; R² = 0.8055). Placental alterations reflect structural and biochemical gestational adaptations and can become useful techniques for obstetrics.

Placental elasticity assessment by point shear wave elastography in pregnancies with intrauterine growth restriction

Background Placental elasticity varies in different diseases. Our objective was to evaluate placental elasticity using point shear wave elastography (pSWE) in pregnancies with intrauterine growth restriction (IUGR). Methods A total of 66 pregnant women with IUGR and 81 healthy pregnant women were enrolled. Placental elasticity was measured using the transabdominal pSWE method. Ten measurements were made, and the mean was accepted as the mean placental elasticity value in each case. The results for IUGR pregnancies and controls were compared. Results The mean pSWE values were significantly higher in pregnancies with IUGR, which means that women with IUGR have stiffer placentas (P < 0.001). Furthermore, the pSWE values were significantly and positively correlated with Doppler indices and adverse perinatal outcomes. Conclusion The pregnancies with IUGR had stiffer placentas than the healthy controls. The utilization of pSWE for placental elasticity may be useful in the diagnosis and management of IUGR as a supplement to the existing ultrasonography methods.

Placental Elasticity as a New Non-invasive Predictive Marker of Pre-eclampsia

Point shear wave elastography is an ultrasonography technique used to evaluate tissue elasticity. We examined whether placental elasticity is useful for predicting the onset of pre-eclampsia. Two hundred twenty-one participants were divided into two groups: one group at low risk (n = 185) and the other at high risk (n = 36) for pre-eclampsia. The two groups were compared with respect to shear wave velocity (SWV) of the placenta. Use of SWV as a predictor of pre-eclampsia was also investigated by creating a receiver operating characteristic (ROC) curve. The ROC curve was used to set a cutoff SWV value for predicting pre-eclampsia. The SWV of the high-risk group was significantly higher than that of the low-risk group (p < 0.001). Thirteen participants developed pre-eclampsia after SWV measurements, and the SWVs of these participants were significantly higher than those of participants in who pre-eclampsia did not develop. The cutoff value and area under the ROC curve were 1.188 m/s and 0.9118, respectively. Placental elasticity was significantly increased even before the onset of pre-eclampsia onset and, thus, may be a parameter used to predict the onset of pre-eclampsia.

Multiparametric QUS Analysis for Placental Tissue Characterization

Multiparametric Quantitative Ultrasound (QUS) holds promise for characterizing placental tissue and detecting placental disorders. In this study, we simultaneously extract two qualitatively different QUS parameters, namely attenuation coefficient estimate (ACE) and shear wave speed from ultrasound radio frequency data acquired using a shear wave vibro elastography (SWAVE) method. The study comprised data from 59 post-delivery clinically normal placentas. The shear wave speed was found to be equal to 1.74 ± 0.13 m/s whereas the attenuation coefficient estimate was 0.57 ± 0.48 dB/cm-MHz. This provides a baseline for future studies of placental disorders.

Shear wave elastography safety in fetus: A quantitative health risk assessment

PURPOSE

To identify the effects of shear wave elastography in the fetus for evaluation in widespread use.

MATERIALS AND METHODS

The Health Risk Assessment method proposed by the National Research Council was used with literature to evaluate the safety of shear wave elastography for the fetus regarding its potential effects in human tissues.

RESULTS

The experimental and epidemiologic data from 25 articles showed that shear wave elastography maintained the same thermal effect as pulsed Doppler ultrasound already authorized in obstetrics, and that cavitation effect on fetal tissue is improbable. Nonetheless, the vibratory character of shear waves could induce displacement of fetal tissue while potential effects of very short duration energy peaks of the radiation force focused wave front remain unknown.

CONCLUSION

The actual knowledge does not provide enough information to assess the effects of shear wave elastography on fetal tissues, thus these points have to be explored by further experimental studies.

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.

Measurement of shear wave speed dispersion in the placenta by transient elastography: A preliminary ex vivo study

Background

Placental elasticity may be modified in women with placental insufficiency. Shear wave elastography (SWE) can measure this, using acoustic radiation force, but the safety of its use in pregnant women has not yet been demonstrated. Transient elastography (TE) is a safer alternative, but has not yet been applied to the placenta. Moreover, the dispersion of shear wave speed (SWS) as a function of frequency has received relatively little study for placental tissue, although it might improve the accuracy of biomechanical assessment.

Objective

To explore the feasibility and reproducibility of TE for placental analysis, to compare the values of SWS and Young’s modulus (YM) from TE and SWE, and to analyze SWS dispersion as a function of frequency ex vivo in normal placentas.

Materials and methods

Ten normal placentas were analyzed ex vivo by an Aixplorer ultrasound system as shear waves were generated by a vibrating plate and by using an Aixplorer system.

The frequency analysis provided the value of the exponent n from a fractional rheological model applied to the TE method. We calculated intra- and interobserver agreement for SWS and YM with 95% prediction intervals, created Bland-Altman plots with 95% limits of agreement, and estimated the intraclass correlation coefficient (ICC).

Main results

The mean SWS was 1.80 m/s +/- 0.28 (standard deviation) with the TE method at 50 Hz and 1.82 m/s +/-0.13 with SWE (P = 0.912). No differences were observed between the central and peripheral regions of placentas with either TE or SWE. With TE, the intraobserver ICC for SWS was 0.68 (0.50–0.82), and the interobserver ICC for SWS 0.65 (0.37–0.85). The mean parameter n obtained from the fractional rheological model was 1.21 +/- 0.12, with variable values of n for any given SWS.

Conclusions

TE is feasible and reproducible on placentas ex vivo. The frequency analysis of SWS provides additional information about placental elasticity and appears to be able to distinguish differences between placental structures.

Placental Imaging: Normal Appearance with Review of Pathologic Findings

The placenta plays a crucial role throughout pregnancy, and its importance may be overlooked during routine antenatal imaging evaluation. Detailed systematic assessment of the placenta at ultrasonography (US), the standard imaging examination during pregnancy, is important. Familiarity with the normal and abnormal imaging appearance of the placenta along with the multimodality and methodical approach for evaluation of its related abnormalities is necessary, so that radiologists can alert clinicians regarding appropriate prompt management decisions. This will potentially decrease fetal and maternal morbidity and mortality. This article reviews early placental formation and the expected imaging appearance of the placenta during pregnancy, as well as variations in its morphology. It also discusses various placental diseases and their potential clinical consequences. Placental pathologic conditions include abnormalities of placental size, cord insertion, placental and cord location, and placental adherence. Other conditions such as bleeding in and around the placenta, as well as trophoblastic and nontrophoblastic tumors of the placenta, are also discussed. US with Doppler imaging is the initial imaging modality of choice for placental evaluation. Magnetic resonance (MR) imaging is reserved for equivocal cases or when additional information is needed. Computed tomography (CT) has a limited role in evaluation of placental abnormalities because of the ionizing radiation exposure and the relatively limited assessment of the placenta; however, CT can provide important information in specific circumstances, particularly evaluation of trauma and staging of choriocarcinoma. This article also addresses recent techniques and updates in placental imaging, including elastography, diffusion-weighted MR imaging, and blood oxygen level-dependent (BOLD) MR imaging. These advanced imaging techniques may provide additional information in evaluation of abnormal placental adherence and new insights into placental pathophysiology in selected patients. Online supplemental material is available for this article. ^©RSNA, 2017.

SWAVE Imaging of Placental Elasticity and Viscosity: Proof of Concept

The placenta is the interface between the fetus and the mother and is vital for fetal development. Ultrasound elastography provides a non-invasive way to examine in vivo the stiffness of the placenta; increased stiffness has previously been linked to fetal growth restriction. This study used a previously developed dynamic elastography method, called shear wave absolute vibro-elastography, to study 61 post-delivery clinically normal placentas. The shear wave speeds in the placenta were recorded under five different low-frequency mechanical excitations. The elasticity and viscosity were estimated through rheological modeling. The shear wave speeds at excitation frequencies of 60, 80, 90, 100 and 120 Hz were measured to be 1.23 ± 0.44, 1.67 ± 0.76, 1.74 ± 0.72, 1.80 ± 0.78 and 2.25 ± 0.80 m/s. The shear wave speed values we obtained are consistent with previous studies. In addition, our multi-frequency acquisition approach enables us to provide viscosity estimates that have not been previously reported.

Placental Elasticity and Histopathological Findings in Normal and Intra-Uterine Growth Restriction Pregnancies Assessed with Strain Elastography in Ex Vivo Placenta

The aim of this study was to investigate the differences of placental elasticity between intra-uterine growth restriction (IUGR) and normal pregnancies to show whether or not there is any association between histopathological changes and placental elasticity. Fifty-five human placentas were collected at delivery, including 25 with IUGR and 30 controls. Strain elastography (SE) was performed ex vivo and all placentas were examined histopathologically. Elasticity index (EI) and histopathological findings were compared between groups. The placental stiffness and presence of histopathological changes were higher in the IUGR group than in controls (p < 0.05). Also, histopathological findings were associated with decreased EI values, but no specific patterns of histologic abnormalities were identified except villitis and delayed villous maturity. Distinct reduced placental elasticity could be the result of the cumulative effects of all the histologic findings in IUGR.

Comparison of placental elasticity in normal and pre-eclamptic pregnant women by acoustic radiation force impulse elastosonography

AIM

The aim of this research was to study and compare placental elasticity with acoustic radiation force impulse (ARFI) elastography in pre-eclamptic and normal pregnancies.

METHODS

A total of 107 singleton pregnancies in the third trimester (38 healthy control subjects, 34 patients with gestational hypertension, and 35 pre-eclampsia patients) were included in the study. ARFI elastography was used to determine the placental elasticity in the three predetermined regions of the placenta (the fetal edge, maternal edge, and central part of the placenta). The obstetrical data regarding grayscale and Doppler ultrasonography and perinatal outcomes were reviewed. A mean placental shear wave velocity cut-off value that predicts the presence of pre-eclampsia was determined.

RESULTS

The shear wave elasticity values in the pre-eclampsia group in all three regions were significantly higher than in the gestational hypertension and healthy control groups (P = 0.001). The most significant difference was found in the peripheral edge of the placenta from the fetal surface in the pre-eclampsia group (P = 0.001).

CONCLUSION

The stiffness of the placenta determined by the ARFI technique is significantly higher in pre-eclampsia patients. ARFI elastography of the placenta might be used as a non-invasive and easy method in the diagnosis and evaluation of pre-eclampsia as a supplement to the already existing methods.

Diagnosis of pre-eclampsia and assessment of severity through examination of the placenta with acoustic radiation force impulse elastography

OBJECTIVE

To assess the value of placental shear wave velocity (SWV) measurement by acoustic radiation force impulse (ARFI) imaging for the diagnosis of pre-eclampsia and to determine the relationship between the SWV and the severity of pre-eclampsia.

METHODS

A prospective study was performed at a center in Turkey between August 2014 and March 2015. The study included consecutive pregnant women in the second or third trimester diagnosed with pre-eclampsia and healthy pregnant women without pre-eclampsia of similar ages. Patients with pre-eclampsia were divided into two groups (severe or mild disease) on the basis of revised American College of Obstetricians and Gynecologists criteria. All patients underwent ARFI, and the SWV was measured at several placental locations.

RESULTS

Overall, 86 women were enrolled (42 with pre-eclampsia, 44 controls). Minimum, maximum, and mean SWV values were significantly higher in the pre-eclampsia group than in the control group (P<0.001 for all). These values were also significantly higher among patients with severe pre-eclampsia than among patients with mild pre-eclampsia (P<0.001 for all).

CONCLUSION

Measurement of the placental SWV with ARFI imaging is a useful additional method for the diagnosis of pre-eclampsia and for determination of the disease severity.

An Experimental Study of the Potential Biological Effects Associated with 2-D Shear Wave Elastography on the Neonatal Brain

2-D Shear wave elastography (SWE) imaging is widely used in clinical practice, and some researchers have applied this technique in the evaluation of neonatal brains. However, the immediate and long-term impacts of dynamic radiation force exposure on the neonatal central nervous system remain unknown. In this study, we exposed neonatal mice to 2-D SWE scanning for 10 min, 20 min and 30 min under diagnostic mode (mechanical index [MI]: 1.3; thermal index [TI]: 0.5), respectively. For the control group, the neonatal mice were sham irradiated for 30 min with the machine powered off. Their brains were collected and analyzed using histologic staining and western blot analysis at 24 h and 3 mo after the 2-D SWE scanning. The Morris water maze (MWM) test was used to assess learning and memory function of the mice at 3 mo of age. The results indicated that using 2-D SWE in evaluating brains of neonatal mice does not cause detectable histologic changes, nor does it have long-term effects on their learning and memory abilities. However, the PI3 K/AKT/mTOR pathway was disturbed when the 2-D SWE scanning lasted for more than 30 min, and the expression of p-PKCa was suppressed by 10 min or more in 2-D SWE scanning. Although these injuries may be self-repaired as the mice grow, more attention should be paid to the scanning duration when applying 2-D-SWE elastography in the assessment of neonatal brains.

Shear Wave Elastography in the Living, Perfused, Post-Delivery Placenta

The placenta is the critical interface between the mother and the developing fetus and is essential for survival and growth. Despite the widespread use of ultrasound imaging and Doppler in obstetrics and gynecology and the recent growth of elastographic technologies, little is known about the biomechanical (elastic shear wave) properties of the placenta and the range of normal and pathologic parameters that are present. This study uses a well-developed protocol for perfusing whole placentas, post-delivery, to maintain tissue integrity and function for hours. In this model, the placenta is living, whole and maintained within normal physiologic parameters such as flow, arterial pressure and oxygen, throughout examination by ultrasound, Doppler and shear wave elastography. The preliminary results indicate that normal placental tissue on the fetal side has shear wave speeds on the order of 2 m/s, in a range similar to those of animal livers. Some abnormalities are found outside this range, and thus, elastographic measures of the placenta may provide useful assessments related to the state of the tissue.

Is evaluation of placenta with real-time sonoelastography during the second trimester of pregnancy an effective method for the assessment of spontaneous preterm birth risk?

PURPOSE

The aim of this study is to investigate the effectiveness of placental strain ratio (SR) values measured by real-time sonoelastography (SE) in the second trimester in the prediction of spontaneous preterm birth (sPTB).

METHODS

This study included 70 pregnant women who applied to our clinic for routine second-trimester screening. Placental SR measurements were performed with the SE method. Two different SR measurements were performed by taking two different tissues as references. The SR value measured when taking the rectus abdominis muscle as a reference was termed the muscle-to-placenta strain ratio (MPSR), while the SR value measured when taking subcutaneous tissue as a reference was termed the fat-to-placenta strain ratio (FPSR). Women whose gestational age at birth was less than 37 weeks 0 days were accepted as sPTB. The association between gestational age at birth and MPSR and FPSR was investigated. Receiver operating characteristics analysis was used to calculate the sensitivity and specificity of the elastographic outcomes.

RESULTS

There was a low-level negative correlation between MPSR and gestational age at birth (r=-0.300, P=.012) and there was a moderate-level negative correlation between FPSR and gestational age at birth (r=-0.513, P<.001). The multivariate linear regression analysis showed that the FPSR (β=0.609, P=.002) was the significant predictor for the sPTB.

CONCLUSIONS

Our data indicate that the FPSR value measured with real-time SE in the second trimester of pregnancy may be effective in the prediction of sPTB.

Measurement of elasticity of normal placenta using the Virtual Touch quantification technique

Purpose:

The aim of this study was to measure the elasticity of normal placentas using the Virtual Touch quantification (VTQ) technique.

Methods:

This study was approved by the Institutional Ethics Committee. Fifty randomly selected, healthy pregnant women in their second trimester and 50 randomly selected, healthy pregnant women in their third trimester with a single fetus were included, and their placentas underwent VTQ through shear wave velocity (SWV) measurements. The measurements were performed at different locations to sample different areas of the placenta. Measurements were performed 3-4 times in each location, the mean shear wave velocities were calculated without the highest and lowest values of measurements in each region, and the results were compared.

Results:

The SWV of the placenta was 0.983±0.260 m/sec, and the minimal and maximal speed was 0.63 m/sec and 1.84 m/sec, respectively. There was no significant difference between the second and third trimester of VTQ of the placenta in terms of SWV (0.978±0.255 m/sec vs. 0.987±0.266 m/sec, P=0.711). The maternal age between second and third trimester was 27.9±4.3 years and 29.2±4.4 years, respectively; there was no significant difference between them (P=0.159).

Conclusion:

The results of this study show that the SWV of normal placenta tissue is 0.983±0.260 m/sec, it has little variation between the second and third trimesters, and the VTQ technique may potentially play an additional role in placenta evaluation.