Accurate Estimation Method of Arterial Wall Movement in Longitudinal Direction

For early diagnosis of arteriosclerosis, we have developed methods of measuring arterial wall characteristics such as local elastic modulus and luminal surface roughness by measuring the arterial wall movement. Since the carotid artery moves not only in the radial direction but also in the longitudinal direction due to the contraction of the heart, the movement in the longitudinal direction has to be estimated and introduced into measurement methods of arterial wall characteristics. However, the estimation of the longitudinal movement of the intima-media complex (IMC) is difficult because the acoustic property of IMC is homogeneous in the longitudinal direction, especially in the very early-stage of arteriosclerosis. Therefore, the objective of the present study is to examine an accurate estimation method of the arterial wall movement in the longitudinal direction. The longitudinal displacement of IMC was measured by the block matching method. As the conventional method, the block matching method was applied to the envelope of radio-frequency (RF) signals in IMC. In the present paper, it was also applied to the difference signals of the envelope of RF signals between the neighboring beams to amplify the change of subjects in the longitudinal direction. The block matching methods were applied to the signals in IMC acquired in the right common carotid artery of healthy subjects in the twenties, and the estimated results were compared with the trajectory of the longitudinal movement of IMC which was the change of maximum amplitudes of echo envelope in IMC. In the conventional method, several estimated displacements did not correspond with the trajectory of the longitudinal movement of IMC. By subtracting echo envelope signals in the longitudinal direction, the change of signals was amplified; therefore, the estimated displacements well corresponded with the trajectory of the longitudinal movement of IMC.