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Non-invasive acoustic detection of vascular diseases from skin surface using computational techniques with fluid-structure interaction

Salman, Hüseyin Enes
Atherosclerosis is a cardiovascular disease in which arterial occlusion adversely affects blood circulation. Because of the narrowing of the artery, the blood flow is disturbed and a recirculating flow occurs at the downstream of the stenosis exit. The dynamic pressure fluctuations on the inner arterial wall cause the blood vessel wall to vibrate and the resulting acoustic energy propagates through the surrounding soft tissue and reaches the skin surface. To understand the problem in more detail, computational analyses and experimental studies have been carried out. Vein, blood, muscle, fat and bones are modeled by means of computational analysis. The turbulence-induced dynamic pressure fluctuations are applied to the inner wall of the artery and the radial displacement, velocity and acceleration responses on the skin surface are investigated considering various flow rates, stenosis severities and structural material properties. The computational results show good agreement with the experimental findings. Vibration of the phantom tissue used in the experimental studies is determined using a contact microphone, an electronic stethoscope and a laser Doppler vibrometer. 70% stenosis is an important threshold value, because severities higher than 70% lead to significant increase in vibration amplitudes. If the severity of stenosis is increased from 70% to 90%, the arterial vibration amplitudes increase by more than ten times. Arterial vibration is approximately proportional to the third power of the Reynolds number. When thickness of the tissue surrounding the artery is increased from 6.5 to 16.5 mm, the amplitudes are reduced by about 35%. The highest excitation is obtained about 20 mm downstream of the stenosis exit for a tissue thickness of 16.5 mm. The first two highly excited frequencies are determined as 30 and 60 Hz for the thigh, 100 and 200 Hz for the upper arm, 120 and 190 Hz for the neck. The optimum range for stenosis detection is between 200 and 500 Hz.