When a lesion is unstable, it may rupture and cause an acute thrombotic reaction. A rupture prone plaque contains a large lipid pool covered by a thin fibrous cap. Intravascular ultrasound (IVUS) elastography can assess the presence of lipid pools and identify high stress regions. The deformation of the tissue is determined using ultrasound. For intravascular purposes, the intraluminal pressure is used as the excitation force. The radial strain in the tissue is obtained by cross-correlation techniques on the radio frequency (rf) signal. The strain is colour-coded and plotted as a complimentary image to the IVUS echogram, or, in case of palpography, as a ring on the lumen vessel boundary.