A force-measuring device combined with ultrasound-based elastography for assessment of the uterine cervix

Strain ratio elastography of the uterine cervix and prediction of successful labor induction

BACKGROUND

Before labor induction, the uterine cervix is often evaluated by the Bishop score, or a modified Bishop score, to predict the duration and success of induction. However, more objective methods are wanted. Strain ratio elastography is a technique that evaluates the elastic modulus of a tissue. Using strain ratio elastography in combination with a reference material enables quantitative elastography of the uterine cervix.

OBJECTIVE

To evaluate the associations between the apparent elastic modulus of the cervical tissue assessed by strain ratio elastography and the cervical dilation time after labor induction.

METHODS

Twenty-two nulliparous pregnant women admitted for labor induction were included. A Bishop score, a cervical length measured by ultrasound and an elastic modulus evaluated by strain ratio elastography were obtained from all participants. Primary outcomes were cervical dilation time from labor induction to active labor and from active labor to full cervical dilation.

RESULTS

The strain ratio was not associated with the time from labor induction to active labor R2: 0,024 (P = 0.492), but there was a small association between strain ratio and time from active labor to full cervical dilatation R2: 0.180, however not significant (P = 0.063). The cervical length was associated with time from labor induction to active phase R2: 0.134 (P = 0.003), but not with time from active labor to full dilatation R2: 0.015 (P = 0.610).

CONCLUSIONS

The results indicate a possible importance of the elastic modulus for predicting time from active labor to full cervical dilatation, whereas the cervical length seems to be of greater importance for time from labor induction to active labor.

Recommendations for strain elastography of the uterine cervix

PURPOSE

Conventional vaginal strain ultrasound elastography, not based on shear-wave elastography imaging, can assess the biomechanical properties of the uterine cervix. This assessment may inform the risks of preterm birth and failed induction of labor. However, there is considerable variation in the approaches to strain elastography, including the placement of the region of interest (ROI). Therefore, our aim was to provide recommendations for cervical elastography.

METHODS

We conducted a literature review on (1) elastography principles, and (2) the cervical anatomy. Subsequently, we performed elastography scanning using a Voluson™ E10 Expert scanner with the BT18 software of (3) polyacrylamide hydrogel simulators, and (4) pregnant women.

RESULTS

Increasing the distance between the ROI and probe led to a decrease in the obtained strain value; a 53% decrease was observed at 17.5 mm. Similarly, an increased angle between the ROI and probe-centerline resulted in a 59% decrease for 40° angle. Interposition of soft tissue (e.g., cervical canal) between the ROI and the probe induced an artifact with values from the posterior lip being 54% lower than those from the anterior lip, even after adjusting for probe-ROI distance. Equipment and the recording conductance significantly influenced the results.

CONCLUSION

Our findings inform recommendations for future studies on strain cervical elastography.

Quantitative strain elastography of the uterine cervix assessed by the GE Voluson E10 system in combination with a force-measuring device

OBJECTIVE

During pregnancy, the stiffness of the cervical tissue decreases long before the cervical length decreases. Therefore, several approaches have been proposed in order to ensure a more objective assessment of cervical stiffness than that achieved by digital evaluation. Strain elastography has shown promising results. This technique is based on an ultrasound assessment of the tissue deformation that occurs when the examiner applies pressure on the tissue with the ultrasound probe. However, the results are only semi-quantitative as they depend on the unmeasured force used by the examiner. We, therefore, hypothesized that a force-measuring device applied to the handle of the ultrasound probe may render the technique quantitative. With this approach, the stiffness is the force (measured by the device) divided by the compression (measured by the elastography platform). One perspective is the early identification of women at risk of preterm birth in whom cervical stiffness may decrease long before cervical shortening. Another perspective is cervical evaluation when planning labor induction. In this feasibility study, we aimed to evaluate how quantitative strain elastography performs when a commercially available strain elastography platform (by which the algorithm is unavailable) is combined with a custom-made, force-measuring device. We studied how the assessments were associated with the gestational age in women with uncomplicated pregnancies and how they were associated with cervical dilatation time from 4 to 10 cm in women undergoing labor induction.

METHODS

In the analysis, we included quantitative strain elastography assessments from 47 women with uncomplicated singleton pregnancies, with gestational age between 12⁺⁰ and 40⁺⁰, and from 27 singleton term-pregnant women undergoing labor induction. The force-measuring device was mounted on the handle of a transvaginal probe. The strain values (i.e. the compression of the cervical tissue) were obtained by the elastography software of the ultrasound scanner (GE Voluson E10). The region of interest was placed within the central part of the anterior cervical lip. Based on the force data and strain values, we calculated the outcomes cervical elastography index_GE (CEI_GE) and the cervical strength index_GE (CEI_GE x cervical length: CSI_GE).

RESULTS

The average CEI_GE was 0.24 N at week 12 and 0.15 N at week 30-34. For CSI_GE these figures were 8.2 and 4.7 N mm, respectively (p = 0.002). Among women undergoing labor induction, the CEI_GE was associated with a cervical dilatation time (4-10 cm) beyond 7 h. For nulliparous women, this area under the ROC curve was 0.94.

CONCLUSION

Quantitative strain elastography may constitute a tool for the evaluation of a uterine cervix with normal length in women at risk of preterm birth and in women undergoing labor induction. The performance of this tool deserves evaluation in larger clinical trials.

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.

Advances in the clinical application of ultrasound elastography in uterine imaging

Changes in tissue stiffness by physiological or pathological factors in tissue structure are identified earlier than their clinical features. Pathological processes such as uterine fibrosis, adenomyosis, endometrial lesions, infertility, and premature birth can manifest as tissue elasticity changes. In clinical settings, elastography techniques based on ultrasonography, optical coherence tomography, and magnetic resonance imaging are widely used for noninvasive measurement of mechanical properties in patients, providing valuable tool and information for diagnosis and treatment. Ultrasound elastography (USE) plays a critical role in obstetrics and gynecology clinical work because of its simplicity, non-invasiveness, and repeatability. This article reviews the recent progress of USE in uterine tumor diagnosis (especially early diagnosis and treatment effect evaluation), prediction of preterm birth, and intrauterine insemination. We believe that USE, especially shear wave elastography, may serve as a potential means to assess tissue stiffness, thereby improving the diagnosis and treatment of adenomyosis, fibroids, endometrial lesions, cervical cancer, and precise management of preterm birth and intrauterine insemination monitoring.