Ultrasound Stimulated Acoustic Emission in the measurement of elasticity of arterial wall

Increased stiffness of large arteries is known to be a strong indicator of cardiovascular risk. Current methods for determining arterial wall stiffness are either invasive or based on the indirect estimation using e.g. pulse pressure changes. In this paper, we have studied the feasibility of the method called Ultrasound Stimulated Acoustic Emission (USAE) for the direct non-invasive determination of arterial wall stiffness changes. We used USAE to image the elasticity change in the excised carotid arteries of pigs. The USAE frequency was swept between 100 Hz and 20 kHz and the emission spectrum from the artery was measured. The measurements were repeated with different pressures (0 mmHg-120 mmHg) inside the vessel. After the pressure series the artery was immersed in a hot (75°C) water bath for 30 seconds. After heat treatment the above-mentioned USAE-measurements were repeated. This was used to simulate the disease-induced changes in the stiffness and absorption of the artery. By comparing the frequency spectrums taken before and after heat treatment it was observed that the signal amplitudes of the low frequencies are increased after heat treatment in all cases. At the lower frequencies USAE frequency shift was also found to be dependent on the pressure inside the vessel. These results indicate that the USAE measurement may offer a noninvasive direct method for imaging the elasticity change of vessel wall.