[MRI characterization of atherosclerotic arteries: diagnosis of plaque rupture]

Plaque stability and its counterpart, vulnerability, depend on the relative amount and morphology of its principal components: lipid core and fibrous cap. Lipids are mainly made of cholesterol esters and cholesterol monohydrates, but phospholipids and triglycerides are also present. Major chemokines, cytokines, enzymes and markers of inflammation are locally produced, which interact and degrade the arterial matrix, but also stimulate smooth muscle cells and osteopontine production. Due to these differences in composition, the lipid cores have various chemical and biophysical properties (with solid, liquid or liquid-crystalline phases), and so has the collagenous cap, which influence imaging parameters. MRI has improved its capacity to characterize arterial tissue. This technique can now discriminate the different components of normal and pathological arterial walls through various endogenous or exogenous contrast: intima, media, adventitia, perivascular fat, lipid core, collagenous cap and calcifications of atheromatous plaques, but also precise the elements of plaque resistance to radial stress, or the various factors of inflammation. In the next years, improvement of resolution, new contrast sequences (diffusion or magnetization transfer) or spectroscopy, will compete to allow for the best discrimination of these usual suspects: "the unstable plaques".