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

Introduction The velocities of the lateral shear waves (Vs; m s ^-1) generated by an acoustic radiation force impulse (ARFI) correlate with Young's modulus. Therefore, ARFI can be used as a new method to evaluate tissue elasticity. The aim of this study was to investigate the safety of ARFI imaging and the differences in placental elasticity in complicated cases. Methods The study population included 115 patients between 26 and 41 weeks gestation, who were divided into three groups, namely normal, fetal growth restriction (FGR) and pregnancy-induced hypertension (PIH). After delivery, the Vs values of the placenta were measured ex vivo. After ARFI imaging, microscopic examination was performed, the Vs values were compared among the three groups and the relationship between the Vs values and neonatal birthweight Z-score was investigated. Results No histological changes were noted even after ARFI imaging. The Vs values in the FGR group were significantly higher than those in the normal group (1.94 ± 0.74 and 1.31 ± 0.35 m s^-1, respectively; p < 0.05). The Vs values demonstrated a significant negative correlation with the Z-score. Moreover, as the Z-score became lower, the Vs values became higher in the range of Z-scores under -0.5 standard deviation (SD). Discussion We speculate that the increased Vs values in the FGR group may have been caused by histological changes, and that a more severe FGR might result in increased Vs values. Conclusion ARFI imaging was observed to have no apparent histological damage to the placental tissue. Ex vivo placentas from the FGR group were significantly more firm. Moreover, Vs values and Z-scores of birthweight had a significant negative correlation. Additional investigations are needed about the utility of this method for the evaluation of placental function in vivo.