Time-frequency analysis of vibration propagation from intima to adventitia of arterial wall

Based on the phased tracking method, it is newly found that there are wide frequency components from d.c. to one hundred several tens Hz in the vibrations on the arterial wall non-invasively measured in in vivo experiments. These vibrations are mainly caused by the blood flow, and the wall vibration propagates from the intima to the adventitia. Moreover, the characteristics of the arterial wall vibration highly depend on the viscoelasticity of tissue components. In this paper, therefore, the propagation of the vibration in the regional area of the arterial wall is analyzed during one cardiac cycle in the frequency domain. From the measurement of the frequency characteristics in the vibration propagation, the tissue viscoelasticity is estimated. In the low frequency range, both the attenuation and the phase of the vibration are minute values, therefore, it is so difficult to measurement of these precisely. For solving this problem, the viscoelasticity of the arterial wall is estimated by the frequency characteristics in the attenuation in the wide frequency range up to one hundred several tens Hz. The proposed method was applied to human common carotid arteries of two patients with atherosclerotic plaques, a smoking subject and a healthy subject. From in vivo experimental results, clear differences are found in the the frequency characteristics in the attenuation and the estimated viscoelasticity of the arterial wall between atherosclerotic plaque of the patient and healthy subject. These results has novel potential for the tissue characterization.