Real-time simultaneous assessment of wall distension and wall shear rate in carotid arteries

A novel ultrasound (US) system has been developed to make possible the real-time assessment of both blood velocity profile and wall displacements in human arteries. The system consists of a modified US machine and a custom PC add-on board based on a high-speed DSP board. The software has been customized to make possible the simultaneous selection of two independent M-lines. In the B-mode display. With respect to the artery of interest, such lines can be set at optimal angles for wall detection and blood velocity detection, respectively. When switched to PW-mode, the system fires the elements of the linear array probe in such a way that US bursts are alternatively transmitted into one of the two selected M-line directions. Quadrature demodulated echo signals produced along both such lines are sent to the DSP board, which allows the corresponding blood velocity profile and wall displacement (or distension) waveforms to be calculated and displayed in real-time. From the velocity profile, the wall shear rate (WSR), i.e. the spatial velocity gradient close to the blood-wall interface, is extracted. The system has been preliminarily tested in the common carotid arteries of 11 healthy volunteers. Results of simultaneous diameter distension and WSR measurements are reported.