In vitro experiment using porcine artery for evaluation of ultrasonic measurement of arterial luminal surface profile

Introduction: In early-stage atherosclerosis, the luminal surface of the arterial wall becomes rough because of detachment of endothelial cells and degeneration of the internal elastic layer. Therefore, it would be useful if minute luminal surface roughness of the carotid arterial wall, which occurs in the early stage of atherosclerosis, could be measured noninvasively with ultrasound. The injured luminal surface is believed to have roughness of a few hundred micrometers. However, in conventional ultrasonography, the axial resolution of a B-mode image depends on the ultrasonic wavelength (150 μm at ultrasonic center frequency of 10 MHz) because a B-mode image is constructed using the amplitude of the RF echo signal. Therefore, such surface roughness cannot be measured accurately from a conventional B-mode image. Recently, we successfully measured such minute surface profile transcutaneously using the phase shift of an ultrasonic echo from the carotid arterial wall. In our previous validation experiment, a silicone phantom with minute surface roughness of 10–20 μm was measured. However, the feasibility of our proposed method has never been validated using biological tissues.

Materials and methods: In the present study, luminal surface roughness of a porcine artery was measured and the result was evaluated by comparing it with the result measured using a stylus profilometer.

Results and conclusion: The root mean squared difference between the surface roughness measured by ultrasound and the stylus profilometer was 10.5 μm. This result proves that our proposed method can be used to measure minute surface roughness of biological tissue.