Defence of the PhD Thesis of Emmanuel Simon

THÈSE dirigée par :

REMENIERAS Jean-Pierre               Ingénieur de recherche - HDR, Inserm, Université de Tours

PERROTIN Franck                            PU-PH, Inserm, Université de Tours

RAPPORTEURS :

ROZENBERG Patrick                       PU-PH, Université de Versailles 

TSATSARIS Vassilis                         PU-PH, Université Paris Descartes

JURY :

CALLE Samuel                                  MCU - HDR, CNRS, Université de Tours

GENNISSON Jean-Luc                     Chargé de recherche, CNRS, U-PSud, CEA, Orsay

PERROTIN Franck                            PU-PH, Inserm, Université de Tours

REMENIERAS Jean-Pierre               Ingénieur de recherche - HDR, Inserm, Université de Tours

ROZENBERG Patrick                        PU-PH, Université de Versailles

TSATSARIS Vassilis                          PU-PH, Université Paris Descartes

WINER Norbert                                  PU-PH, Université de Nantes

Abstract

Screening and diagnosis of placental insufficiency (PI), whether intrauterine growth restriction (IUGR) or preeclampsia (PE) are major public health issues. In clinical practice, the mechanical properties of the placenta are not explored; however changes in its tissue architecture could cause variations in elasticity. Among the ultrasound (US) elastography methods, transient elastography seemed suitable for such an application. This technique consists in calculating the shear wave speed (Cs) generated by an external vibration propagating in the medium under consideration. Elasticity values ​​obtained from current US methods are calculated at a single frequency. As a structural modification of the tissue may correspond to a particular power law of frequency dispersion of Cs, we evaluated the interest of a multifrequency approach to distinguish the elasticity of healthy placentas and that of placentas with PI signs in the third trimester of pregnancy. We have developed a preliminary plane wave device (for ex vivo exploration) to validate the principle of the proposed method, and then a 2D transient elastography device (ex vivo and in vivo exploration). The data is adjusted using a fractional rheological model where the frequency behavior is modeled by a power law (exponent n of the model). We have shown that IUGR placentas have Cs and n values lower than those of healthy placentas or PE. This decrease in the n value could be explained by histopathological lesions of IUGR. As for the decrease of Cs in cases of IUGR, this result is consistent with the study of an IUGR rat model by uterine ligation. Finally, the frequency dispersion analysis is feasible in pregnant women. The added value of this method should now be tested in a large clinical study.