In vivo hemodynamic evaluation based on transverse Doppler measurements ofblood velocities and vessel diameter

We have developed a method for simultaneously measuring the blood flow velo city distributions along a line perpendicular to the vessel mall and the in stantaneous diameter of the common carotid artery. Thus, the wall shear rat es and shear rate distribution across the arterial lumen could be computed accurately, In this method, transverse Doppler technique is combined with u ltrasonic A echo-mode, using only one single crystal transducer, In order t o satisfy the requirements of high spatial and velocity resolutions, especi ally extending to a very tow velocity range in the case of low signal-to-no ise ratio, a combination scheme of 10-MHz operating frequency, sample volum e tracking, 12-bit AID, 512-point fast Fourier transform with 5-kHz sample rate, spectrum average, variable threshold for bandwidth estimation, smooth ing of velocity curves, and hardware was carefully designed, The velocity d istribution measurements based on transverse Doppler spectrums were also va lidated under the steady how conditions using a flow loop system. Results f rom this study show this ultrasonic system to be capable of measuring the s hear rates at wall accurately and shear rate distributions across the commo n carotid arterial lumen.