Carotid Peak Blood Velocity Detection using a 5-Plane CMUT Array with Asymmetric Acoustic Lens: Initial Results

We report on the initial results on a 5-plane CMUT array built on a single silicon substrate for operator-independent carotid artery screening. The array is used for color flow Doppler detection of peak blood velocity (PBV), which is correlated with carotid stenosis. Asymmetric acoustic lenses provide fixed angle off-axis beam steering for color flow Doppler. In the proposed system, first, five parallel short-axis B-mode and color flow images of the carotid artery are obtained. Then, a custom software package automatically finds the center points of the blood flow, computes the vessel trajectory, Doppler angle and angle-corrected peak velocities. The fabricated CMUT arrays showed a center frequency of 8.1 MHz and a fractional bandwidth of 103% in immersion. In resonant frequency measurement in air, the uniformity across the array is excellent, with a standard deviation of 0.18% of the mean. Initial experiments on asymmetric acoustic lenses verified the off-axis steering capability. Using the inhouse software package and a commercial 1D array, the calculated peak blood velocity has an error of less than 6%, when the Doppler angle is less than 45.