Feasibility of 2-D ultrasound shear wave elastography of fetal lungs in case of threatened preterm labour: a study protocol

Abstract

Introduction: 2-D ultrasound shear wave elastography (SWE) could be considered as a new noninvasive tool for monitoring fetal lung development based on evaluation of mechanical properties during pregnancy. Interesting results are available concerning the use of SWE on developing organs, especially on premature infants and animal models. The main objective in this study is to evaluate the feasibility of 2-D SWE in human fetal lungs between 24 and 34 weeks of gestation (WG). The secondary objective is to modellise fetal lung-to-liver elastography ratio (LLE ratio) and to assess variations between normal lung and lung surfactant-enriched after a corticosteroids course indicated for a threatened preterm labour (TPL).

Methods/design: A prospective case-control study will be performed between 24 and 34 WG. Fetal lungs and liver will be explored by SWE into two groups: fetuses of women with an uncomplicated pregnancy (control group) and fetuses of women with a TPL requiring administration of corticosteroids (cases group). LLE ratio will be defined as the value of the lung elasticity divided by the value of the liver elasticity.Primary judgement criterion is the value of elasticity modulus expressed in kilopascal. Lungs and liver will be explored through three measurements to define the most reproducible regions with the lowest intra- and inter-observer variability. Feasibility will be evaluated by assessing the number of examinations performed and the number of examinations with interpretable results. Intra- and inter-observer reproducibility will be evaluated by means of the intra-class correlation coefficient.

Ethics and dissemination: Approval of the study protocol was obtained from the human ethical research committee (Comité de Protection des Personnes EST II, process number 15/494) and the French National Agency for Medicines and Health Products Safety (process number 2015-A01575-44). All participants will sign a statement of informed consent.

Trial registration number: NCT02870608; Recruiting.

Keywords: Shear wave elastography; elasticity; fetal; lung..

Conflict of interest statement

Competing interests: None declared.

© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Figures

Figure 1

(A) B-mode image of the fetal thorax centred on a four-chamber view of the fetal heart, using an abdominal convex probe 1–6 MHz. (B) Elastogram of the fetal thorax showing a colour-coded elasticity map: blue identifies deformable tissue and red indicates rigid tissues (kPa).

Figure 2

Design of the study.

Figure 3

Measurement sites with 2D comb-push SWE using an abdominal convex probe 1–6 MHz (C1-6-D probe). Colour scale ranging from 0 to 48 kPa. Sufficient colour maps covering more than 50% of the sampling area obtained considered as a technical success. ROI are placed on homogeneous elastograms.- (A,B) three measurements on the proximal lung (anterior ‘P1’, medium ‘P2’ and posterior portion ‘P3’). - (A,C) three measurements on the distal lung (anterior ‘D1’, medium ‘D2’ and posterior portion ‘D3’). - (D–F) three measurements on three liver segments (IV, (V, VI). Operator will perform two cycles of nine kPa measurements while systematically repositioning the probe and each target ROI.

Figure 4

2D comb-push SWE on proximal fetal lung. Colour scale ranging from 0 to 48 kPa. On image (A), elastogram is not homogeneous and is degraded by artefact on the left side due to rib shadowing. By moving the probe to another location, a more homogeneous elastogram (B) is obtained allowing measurement.