Plaque mechanics

Investigators:

dr.ir. Frank Gijsen E: f.gijsen@erasmusmc.nl

dr.ir. Lambert Speelman E: l.speelman@erasmusmc.nl

At the Biomechanics Laboratory we study the effect of mechanical stresses on initation, progression, destabilization and rupture of atherosclerotic plaques. Insight in these processes helps to improve selection, diagnosis and treatment of patients with atherosclerosis. The research covers these aspects from bench-to-bedside, including cell studies, animal experiments, numerical analyses, ex vivo experiments and patient studies.

 Rupture of atherosclerotic plaques is the main cause of acute myocardial infarctions and stroke. Rupture prone plaques are characterized by the presence of a lipid pool covered by a thin fibrous cap, infiltrated by inflammatory cells. Plaque rupture occurs when mechanical stress in the cap of a plaque exceeds cap strength. We introduce a new concept –the rupture risk map- which enables us to quantify cap stress and cap strength combining imaging (ultrasound, MRI) data with biomechanical models. The rupture risk map can be used to separate rupture prone from stable plaques and clinical application potentially reduces the large number of patients that are currently subjected to unnecessary surgical removal of carotid plaques.

Finite element modeling plays a key role in determining cap stresses. Based on the (3D) plaque geometry, the blood pressure, and the mechanical properties of the plaque components the stress distribution in plaques can be determined. The accuracy of the stress simulation critically depends on all these factors. Especially reliable geometrical reconstruction of the plaques based on non-invasive imaging (MRI, ultrasound) poses important challenges. Furthermore, much is still unknown about the appropriate material models for the individual plaque components. Finally, the impact of several boundary conditions on the final results –typical for in vivo plaque biomechanics- needs to be investigated further. Cap stress is only one side of the medal: cap strength is as important. Currently, a single threshold value is often used in literature. We know however that cap strength is heavily influenced by cap composition. In the presence of macrophages, various processes lead to local cap weakening, thus reducing cap strength. Data on this relationship is still very scarce.

The topics described above are all actively investigated in our lab, both from a numerical and an experimental point of view. Imaging plays an important role, as well as a strong link to animal and/or patient data. Several projects are currently available.