Shear rate estimation in stenotic vessels using a clinical ultrasound scanner

Wall shear stress is a factor in the development of artherogenesis, but is very difficult to determine with ultrasound. Instead, we estimated shear rates using a clinical ultrasound scanner and compared results from vessels with and without stenoses. Velocity profiles were obtained from color M-mode images on a P700 scanner (Philips Ultrasound, Irvine, CA). Shear rates were calculated off-line as the maximum velocity gradients. In vitro, studies were performed on a flow phantom with a vessel containing a 50% stenosis. Shear rates within the stenosis were significantly higher than those obtained outside the stenosis (p<0.00001). In vivo, the internal carotid artery of 10 volunteers and 13 patients (with stenoses) was studied. The mean shear rate in normal vessels was 414 s^-1±154.5 s^-1, while in stenoses the value was 687 s^-1±263.5 s^-1 (p=0.00017). In conclusion, shear rate estimates can be obtained with a clinical ultrasound scanner from color M-mode images. Shear rates estimated in vessels with stenoses were significantly higher than those obtained in normal vessels; in vitro as well as in vivo