Obstet Gynecol Sci.  2020 Jan;63(1):42-54. 10.5468/ogs.2020.63.1.42.

Standardization of measurement of cervical elastography, its reproducibility, and analysis of baseline clinical factors affecting elastographic parameters

• Seol HJ
• Sung JH
• Seong WJ
• Kim HM
• Park HS
• Kwon H
• Hwang HS
• Jung YJ
• Kwon JY
• Oh SY

• KMID: 2467931
• DOI: http://doi.org/10.5468/ogs.2020.63.1.42

Abstract

OBJECTIVE
To provide a standardized protocol for the measurement of cervical strain elastography, present its reproducibility, and analyze baseline clinical factors affecting the measurement of elastographic parameters.
METHODS
This study was performed by the Korean Research Group of Cervical Elastography. We enrolled pregnant women according to our study protocol. After measuring the cervical length, elastography was performed using the E-Cervixâ„¢ quantification tool to measure the strain of the cervix using intrinsic compression. We evaluated 5 elastographic parameters, namely, the strain of the internal os of the cervix (IOS), strain of the external os of the cervix (EOS), ratio of the strain of IOS and EOS, elasticity contrast index, and hardness ratio. For baseline clinical factors, we examined the maternal body mass index, blood pressure, heart rate, uterine artery Doppler indices, and fetal presentation.
RESULTS
We established a specific protocol for the measurement of cervical elastography using the E cervix program. For all elastographic parameters, the intra-observer intraclass correlation coefficient (ICC) ranged from 0.633 to 0.723 for single measures and from 0.838 to 0.887 for average measures, and the inter-observer ICC ranged from 0.814 to 0.977 for single measures and from 0.901 to 0.988 for average measures. Regression analysis showed that the measurement of the elastographic parameter was not affected by baseline clinical factors.
CONCLUSION
We present a standardized protocol for the measurement of cervical elastography using intrinsic compression. According to this protocol, reproducibility was acceptable and the measurement of elastographic parameters was not affected by the baseline clinical factors studied.

Keyword

Cervix uteri; Elastography; Standardization; Reproducibility of results; Premature birth

MeSH Terms

Blood Pressure
Body Mass Index
Cervix Uteri
Elasticity
Elasticity Imaging Techniques*
Female
Hardness
Heart Rate
Humans
Jupiter
Labor Presentation
Pregnancy
Pregnant Women
Premature Birth
Reproducibility of Results
Uterine Artery

Figure

• 

  Fig. 1 Standard plane for cervical elastography using the E cervix™. During cervical length measurement, the midline sagittal plane, in which the endocervical canal is clearly visible and the anterior width of the cervix is equal to the posterior width, is obtained. Care must be taken not to apply unnecessary pressure to the anterior cervix and to keep the vaginal probe still during data acquisition. After all motion bars turn green, the screen will freeze automatically. Define the cervix area using either 2-point ROI or 4-point ROI tools. Aim to cover the entire cervix without including other organs, such as the bladder or vaginal wall. (A) Cervical elastogram using 2-point ROI when the endocervical line is straight. (B-D) Cervical elastogram using 4-point ROI when the endocervical line is curved. IOS, strain of internal os of the cervix; EOS, strain of external os of the cervix; Ratio (IOS/EOS), ratio of the strain of the internal and external os; ECI, elasticity contrast index; ROI, region of interest.

• 

  Fig. 2 Cases of cervical elastography performed in short cervix using E cervix™. (A, D) Short cervix showing relatively low strain values, reflecting a hard cervix. In (A), the values of cervical length (CL), elasticity contrast index (ECI), hardness ratio, strain of internal os of cervix (IOS), and strain of external os of cervix (EOS) were 2.29 cm, 3.20, 85.77%, 0.15, and 0.19, respectively, and in (D), these were 2.12 cm, 2.17, 91.65%, 0.15, and 0.12, respectively. (B, E) Short cervix showing relatively intermediate strain values. In (B), the values of CL, ECI, hardness ratio, IOS, and EOS were 2.01 cm, 3.57, 71.22%, 0.22, and 0.27, respectively, and in (E), these were 2.45 cm, 3.95, 67.19%, 0.31, and 0.22, respectively. (C, F) Short cervix showing relatively high strain values, reflecting a soft cervix. In (C), the values of CL, ECI, hardness ratio, IOS, and EOS were 2.28 cm, 5.49, 39.95%, 0.33, and 0.58, respectively, and in (F), these were 2.14 cm, 5.01, 35.89%, 0.43, and 0.44, respectively. Ratio (IOS/EOS), ratio of the strain of the internal and external os.

• 

  Fig. 3 Performing cervical elastography using the E cervix™ in a short cervix with funneling: 2 methods. Cervical elastography measurements were performed using 2 different methods in the same patients (A vs. D, B vs. E, C vs. F). In the upper panel, measurement of cervical elastography was performed in a way that it only encompassed the functional cervix (A-C). With this method, the lateral margin of the internal os is perpendicular to the endocervical canal, excluding funneling area. In the lower panel, cervical elastography measurements were performed in a way that it encompassed the whole cervix, including the region of funneling by maximal extension of the lateral margin of the internal os (D-F). IOS, strain of internal os of the cervix; EOS, strain of external os of the cervix; Ratio (IOS/EOS), ratio of the strain of the internal and external os; ECI, elasticity contrast index.

• 

  Fig. 4 Inadequate images for cervical elastography. (A) Asymmetric cervix defined as the width of anterior cervix less than half of the posterior cervix. (B) Dilated cervix. Note that the dilated endocervical canal is depicted in blue. (C) Cervix with Nabothian cyst. The Nabothian cyst, depicted in blue due to fluid collection, may increase the ECI. (D) Case in which the internal os of the cervix cannot be clearly visualized, hindering reliable measurement of cervical elastography and cervical length as well. ECI, elasticity contrast index; IOS, strain of internal os of the cervix; EOS, strain of external os of the cervix; Ratio (IOS/EOS), ratio of the strain of the internal and external os.

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  Fig. 5 The common representative images requiring re-measurement. (A) In a curved cervix, a straight line without measuring along the cervical canal would not reflect a correct cervical canal. (B) Measurements that inadvertently contain the bladder or amniotic fluid in the ROI box. This image did not follow the standardized protocol because the bladder was not empty. Ratio (IOS/EOS), ratio of the strain of the internal and external os; ECI, elasticity contrast index; ROI, region of interest.

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