An unstable lesion may rupture and cause an acute thrombotic reaction. These lesions contain a large lipid pool covered by a thin fibrous cap. The stress in the cap increased with decreasing thickness and increasing macrophage infiltration. Intravascular ultrasound (IVUS) elastography might be an ideal technique to assess the presence of lipid pools and identify high stress regions. Elastography assesses the local mechanical properties of tissue using its deformation caused by the intraluminal pressure. The technique was validated in vitro using diseased human coronary and femoral arteries. These experiments demonstrated that the strain in the three plaque types is different (P