PhD Defense of Armida Leticia GOMEZ LARA from DyCTIM² teams on June the 11th at 9:30 am:

“A novel anisotropic elasticity-palpography IVUS imaging tool and characterization of the viscoelasto-plastic properties of angioplasty balloon: towards a better assessment and treatment of coronary artery diseases”

Place: Room109 of Bâtiment Boucherle, Faculté de Médecine et Pharmacie, La Tronche

Supervision :

• Mr Jacques OHAYON, Professor, Savoie Mont Blanc University, France (Supervisor)
• Mr Gérard FINET, University professor - Hospital physician, Lyon 1 University, France (Co-supervisor)

University Jury :

• Mr David MITTON, Research director, Laboratoire de Biomécanique et Mécanique des Chocs (Ifsttar), Lyon, France (Reporter)
• Mr Patrick CLARYSSE, Research director, CNRS Lyon, France (Reporter)
• Mr Gilles RIOUFOL, University professor - Hospital physician, Lyon 1 University, France (Examiner)
• Mr Alex ELIAS-ZUÑIGA, University professor, Tecnológico de Monterrey, Mexique (Examiner)

Abstract :

Cardiac catheterization has evolved from being initially received with great skepticism to becoming a standard for the diagnosis and treatment of cardiovascular disease. A myriad of derived techniques like balloon angioplasty, intravascular imaging, as well as valve and stent implantation are now routine procedures for interventional cardiologists. Despite these and other great advances in cardiovascular medicine, cardiovascular disease (CVD) still represents the main cause of mortality, accounting for as much as one out of three deaths worldwide. Due to the complexity of CVD, it has become the field of study of researchers among various disciplines in hopes to reduce the burden of the disease. One of such disciplines is mechanics, that applies its principles and approaches to create innovative tools to diagnose, prevent and treat CVD.

The present thesis belongs to the field of cardiovascular biomechanics and aims to develop tools that can be of assistance to physicians in the diagnosis and treatment of coronary artery disease.

This dissertation is divided into two parts:

Part I: Imaging the atherosclerotic plaque in clinics, is related to the identification and assessment of coronary atherosclerotic plaque with the presentation of a novel palpography algorithm based on continuum mechanics theory. First, a non-exhaustive review of the disease from the medical and biomechanical fronts is presented, which includes the basics of the disease, diagnostic imaging modalities, intravascular ultrasound (IVUS)-derived plaque assessment algorithms and biomarkers for plaque assessment.

Afterwards, it was investigated whether gray-scale IVUS images are enough for obtaining an accurate elasticity map to assess plaque composition and evolution. Indeed, it was concluded that radiofrequency (RF) data provides more detailed data than b-mode IVUS images. Then a novel anisotropic elasticity-palpography algorithm is described. It computes an apparent elasticity of the plaque from radiofrequency signals obtained through IVUS images. The derivation of an anisotropic index (AI) that can be related to the mechanical properties of the arterial wall, along with a first validation using simulated IVUS images based on real patient geometries of atherosclerotic and healthy plaques is presented. Using this new palpography algorithm, a study was that aimed to validate this technique in vitro was performed. Polyvinyl-alcohol (PVA) cryogel vascular phantoms were fabricated, two of them with increased anisotropy. The phantoms were imaged with IVUS and their mechanical properties were obtained using different characterization techniques. Then, the experimental and computed anisotropy indices were compared.

Part II: Balloon angioplasty is focused on the treatment of coronary plaque and analyzes the mechanical properties of the balloons used for coronary angioplasty. First, a brief review of balloon angioplasty procedures is given, which includes a basic medical introduction and is mainly focused on the mechanics behind these vascular devices. Later, the visco-elasto-plastic mechanical characterization of a specific balloon catheter model, the Maverick2 from Boston Scientific, is presented. Geometrical measurements using different microscopy techniques, balloon inflation tests, tensile tests and high-speed images are used to describe the mechanical behavior of the balloon components. The previous results are used in to define a model that can accurately predict the viscoelasto-plastic behavior of the angioplasty balloon film. These results could be used as the basis for a model to predict the inflation behavior of the angioplasty balloon during consecutive inflations in clinics.

Keywords:

Biomechanics / Inverse problem / Palpography / Coronary artery disease / Angioplasty