Automatic measurement of regional elasticity of carotid artery intima-media complex

Artery wall elasticity and intima-media thickness (IMT) are useful markers for diagnosis of atherosclerosis. However, the regional elasticity of intima-media complex have never been measured. Therefore, we developed a method for imaging the regional elasticity by measuring changes in wall thickness due to heartbeat. In this method, multiple points are assigned in the wall along each ultrasonic beam with a pitch of the sampling interval of received echoes just before the ejection of the heart. Then, the displacement of each point is estimated, and the change in thickness between two points (=layer) is obtained from the difference between estimated displacements at these two points. The initial distance between these two points is determined in consideration of the duration of ultrasonic pulse. A spatial distribution of changes in thickness is obtained by shifting the combination of two points along each ultrasonic beam with a pitch of sampling interval of echo. Although, the original thickness of each layer is determined by the duration of the ultrasonic pulse, the estimated change in thickness should not be divided by the original thickness based on the pulse duration because only two dominant echoes from lumen-intima and media-adventitia boundaries contribute to displacement estimation in the case of a healthy subject. To obtain the actual strain, measured changes in thickness should be divided by the intima-media thickness. In this study, the intima-media elasticity is obtained from measured changes in thickness combined with the automatic detection of the intima-media thickness.