Estimation of mechanical properties of atherosclerosis plaque from endovascular echography data: Revisited palpography technic. The main aim of my works was to develop and propose biomechanical tools based on intravascular (IVUS) sequences to detect and characterize vulnerable coronary atherosclerosis plaques. In the first part of my PhD thesis, I revisited the palpography technique proposed by Céspedes et al. and initially published in Ultrasound in Medicine & Biology in 2000. Céspedes et al. developed the elasticity-palpography approach which allows a fast wall stiffness quantification based on the arterial strain and blood pressure measurements. However, this technique suffers of major limitations since it has been developed for homogeneous, isotropic, quasi incompressible, circular and concentric atherosclerotic plaques, only. Therefore in the current study, the native palpography technique was successfully revisited and improved to account for complex plaque and arbitrary palpography domain geometries. The revisited elasticity-palpography technique was successfully applied to six coronary lesions of patients imaged in vivo with intravascular ultrasound (IVUS). Validation of this method was conducted on simulated data and on IVUS sequences performed on PVA-c phantoms. This new IVUS technique, which successfully estimates the vessel compliance, has been patented. One major limitation of the elasticity reconstruction method proposed recently by our collaborative laboratories (Le Floch et al., Ultrasound Med Bio 2012) is the need to quantify accurately the strain field in the entire lesion. Such global strain-elastogram may be often difficult to extract when using intravascular imaging techniques (as OCT or HD-IVUS ) with limited depth penetration signals or due to the fact that the amplitude of the original signal becomes attenuated as the depth of penetration increases. Therefore, in the second part of my PhD manuscript I revisited and improved our previous approach to reconstruct the Young's modulus map (i.e. modulogram) from strain-elastogram estimated in the limited endoluminal plaque region. This improved approach was successfully tested on IVUS sequences obtained in patients with stable angina and scheduled to undergo percutaneous coronary intervention (PCI) at the Hôpital Cardiologique et Pneumologique of Lyon. The robustness and performance of the new approach was investigated with regard to noise which may affect prediction of plaque morphology and elasticity. This study demonstrates the potential of the new IVUS modulography technique based on the proposed elasticity reconstruction method to detect vulnerable plaques in vivo. In the last part of my PhD thesis I described the animal protocol developed in our laboratory to analyze the performance of the proposed new morphology and elasticity IVUS reconstruction techniques. A complete set of data (plaque morphology and elasticity) was acquired ex vivo using atherosclerotic aorta of Watanabe rabbits. Several IVUS, histology, AFM and µacoustic measurements were performed on such artery sections. This protocol is detailed and the preliminary data and elasticity reconstruction maps are presented.
