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

Characterization of uterine involution using B-mode ultrasonography, color Doppler and elastography (acoustic radiation force impulse) for assessing postpartum in Santa Inês ewes

The aim of this study was to investigate uterine involution using ultrasonography techniques during postpartum. Postpartum ultrasonography evaluation (B-mode, color Doppler and Acoustic Radiation Force Impulse elastography) of the uterus was performed by transabdominal approach at immediate after birth and sequentially every 48 hours, during 30 days. The uterine echotexture did not present significant variations (P >0.05) being homogeneous in most evaluations; echogenicity of the uterus increased along the evaluation period (P =0.0452). Progressive and remarkable decrease of the total uterine diameter (UD) were observed (P <0.0001), especially during the first days postpartum. The thickness of uterine wall gradually decreased, as well the endometrial, myometrium and lumen diameters (P <0.0001). Uterine blood flow was assessed by Doppler and decreased during postpartum period, being significantly lower (P=0.0225) on the 30^th day of postpartum. Uterine parenchyma presented as homogeneous dark areas (not deformable) on qualitative ultrasound elastography and the means shear velocity values of the uterine wall on quantitative elastography did not differ. This is the first study that evaluate the stiffness of uterine wall in healthy ewes, providing baseline data about quantitative and qualitative stiffness of the normal uterus, and it may be a useful tool for early diagnosis of uterine alterations during the postpartum period, using the reference parameter established for the assessment of uterine integrity during postpartum period.

Ultrasonography and elastography of the brain and cerebellum of English Bulldog fetuses

The aim of this study was to evaluate B-mode ultrasonography and ARFI elastography of the central nervous system of canine fetuses as complementary methods to predict gestational age, monitor fetal development and establish standards. Ultrasound examinations were performed on 26 English Bulldog bitches at 34, 49 and 60 days of gestation. The circumference (C), area (A) and diameters of the short (D1) and long (D2) axis of the two cerebral hemispheres of the fetuses in cross-section were measured. Fetal cerebellum shape, echotexture, echogenicity, and transverse diameter (TCD) were evaluated in cross-section. Elastography was performed obtaining color elastograms and mean shear wave velocity (SWV m/s) of the fetal brain and cerebellar tissues. Ultrasound variables were correlated with gestational day (GD). Brain masses had a circular to oval shape, hyperechoic echogenicity, and homogeneous echotexture. C and D1 were the more accurate variables to predict gestational day, with the formulas: GD = 19.38 + 2,06∗C (R² = 81%) and GD = 18.93 + 7.45∗D1 (R² = 82%). Cerebellum had a "banana" shape, with hyperechogenic edges, hypoechoic echogenicity, and homogeneous echotexture. The TCD (P = 0.0001) and cerebellar stiffness (P = 0.0006) were greater at 60 days than at 49 days of gestation. The brain mass SWV was correlated positively with GD (P = 0.0001) and showed a gradual increase (P = 0.0001) in the three gestational timepoints evaluated. According to qualitative elastography, both brain mass and cerebellum became more rigid over the course of gestational days. It was possible to verify the development of the brain and cerebellum of canine fetuses during pregnancy by ultrasonographic characteristics and B-mode dimensions, as well as by evaluating the elasticity of these tissues through elastography. These unpublished findings allow a better follow-up of the central nervous system development in the prenatal period and may help in future studies with canine fetuses that present cerebral and cerebellar abnormalities.

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.

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.

Maternal and fetal ultrasonographic characteristics, vulvar temperature, and vaginal mucous impedance as variables associated with the onset of parturition in term and induced pre-term ewes

The aim of this study was to assess and compare ultrasonographic characteristics of maternal and fetal structures, vulvar temperatures, and vaginal mucous impedance in pregnant ewes in the term parturition group (TPG, n = 15) and induced pre-term parturition group (IPPG; n = 15). All the measurements were taken every 12 h throughout the last gestational week. Maternal and fetal structures and the fetal heart rate (HR) were assessed using ultrasonography. The vulvar temperature and vaginal mucous impedance were determined using a non-contact infrared thermometer, and an electronic estrous detector, respectively. The vulvar temperature was less in the TPG and greater in the IPPG; the end-diastolic velocities (EDVs) of the arteries of the placentome and uterus gradually increased before parturition in the IPPG (P = 0.02, P = 0.02 and P = 0.009, respectively). The placentome shear wave velocity (SWV) was greater in the ewes of the IPPG than TPG 48, 36, and 0 h before parturition (P = 0.001). The following variables were associated with the onset of parturition within the next 12 h in the ewes of the IPPG: resistance index (< 0.54) and EDV (> 0.34 cm/s) of the uterine artery; and vulvar temperature (> 37.3 °C). A fetal kidney SWV of < 1.31 m/s was associated with the onset of parturition in the next 12 h in all the ewes. Results indicate vulvar temperature and certain maternal and fetal factors detected using ultrasonograpy may aid in determining fetal maturity and/or the time of parturition in ewes.

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.