In vivo mechanical identification of tissues using medical imaging – IMANDEF

IMANDEF is a project in biomechanics. The scientific objective is to enhance the constitutive equations used for modelling the mechanical behaviour of soft tissues in the human body. This entails developing numerical tools and experimental systems for characterizing the in vivo mechanical properties of human soft tissues. Such systems/tools include three main components: in vivo safe loading of tissues, deformation measurement and inverse problem resolution. Each component requires novel technological and scientific developments. Medical imaging will be employed for deformation measurement. Image registration algorithms will have to be devised in order to provide full-field displacement data across the volume of interest. Inverse problem resolution based on these full-field data will imply further developments of dedicated approaches such as the virtual field method or finite element model updating. The relevancy of soft tissue constitutive equations will also be addressed, targeting significant improvements in the models of tissues mechanical behaviour. The three main investigators of IMANDEF all belong to IFRESIS, which is a research institute in Health Science and Engineering at Saint-Etienne, France, and which is approved by INSERM (IFR N°143). The leader of the IMANDEF research team, Dr. Stéphane Avril, is Assistant Professor in biomechanics in the Department of Health Science and Engineering (CIS) of the Ecole Nationale Supérieure des Mines, Saint-Etienne. The research topics of CIS and IFRESIS include both biomechanics and image processing, which are the two topics that are combined in IMANDEF. Each research topic is approved by CNRS within the framework of two research units at the Ecole Nationale Supérieure des Mines: UMR 5146 for biomechanics and UMR 5148 for image processing. IMANDEF will also take place within the framework of collaborations with the local textile industry network (http://www.pole-medical.com) which is a European leader for the production of textiles for medical applications (artificial vessels, compression stockings). The resolution of the issues raised in IMANDEF may require more than ten years of research with a whole group fully dedicated to the subject. The constitution of such a group is the objective of Dr. Stéphane Avril. He is now a worldwide recognized expert (18 peer-reviewed articles, many conferences and seminars) in mechanical identification from optical measurements and images. After working on various materials, he has been focusing his interest on soft tissues only since 2007. He's now aiming at becoming an international leader on this subject. The current project is focused only on the four coming years. In order to define feasible objectives for IMANDEF, two main goals have been fixed: 1. the first one deals with pathological arteries. The University Hospital of Saint-Etienne (Prof. X. Barral) is interested in this subject, especially regarding the human carotid. Plaque ripping off in the carotid is at the origin of strokes, which are the third leading cause of mortality in industrialized nations and the first cause of long-time disability. Diagnoses based on simple image analysis are currently insufficient for reducing the impact of the cardio-vascular diseases, which may provoke a decrease of life expectancy for the 25-45 generation in the near future. Improved diagnoses should be devised for avoiding this issue. Therefore, there is a real medical and economical interest in developing tools and systems for determining the mechanical properties of plaques in the carotid, as much as there is also for other soft tissues in the human body. The development of a tool dedicated to such characterization will be the first target of IMANDEF. Interest in this research is shared by CARDIAL, which is a local subsidiary of firm C.R. Bard, Inc. 2. the second application deals with the soft tissues of the human leg. Laura Bouten is currently a PhD student at CIS working on the effect of compression stockings onto the human leg. Her thesis is the first step towards the optimisation of pressure distribution applied by compression stockings so that leg compression could be used as a medicine for improving venous flow, healing thrombosis… For that, 3D numerical models of the human leg are necessary, but this entails identifying the constitutive parameters of its soft tissues. The development of a tool for this identification will be the second target of IMANDEF. Interest in this research is shared by local firm BV sport, which owns a patent about leg compression. The development of numerical models would help them to personalize the design of stockings, implying sales boosting and consequently job creation in Saint-Etienne. The objective of IMANDEF is to respond to these two goals, without forgetting clinical aspects, i.e. developing tools that could be applied directly by trained physicians.