EFFECT OF THE BEAM-VESSEL ANGLE ON THE RECEIVED ACOUSTIC-SIGNAL FROM BLOOD

In order to explore the feasibility of algorithms to determine the thr ee dimensional (3D) velocity magnitude from the received ultrasonic bl ood echo from a single line of sight, the signal from small sample vol umes is studied as a function of beam-vessel angle. As opposed to prev ious treatments of the effect of the beam-vessel angle on the received acoustic signal, a wideband signal is transmitted and the returned si gnal in each sample volume is analyzed. High-resolution experimental M -mode images of radio-frequency (rf) echo signals are used to visualiz e the dow in individual regions of interest. These experiments confirm the predictions of a theoretical model for the signal and its second moment. It is shown that the two major effects limiting the correlated signal interval are the spread of axial velocities within the sample volume and the transit time across the lateral beam width. Particularl y for small beam-vessel angles, the spread of velocities limits the co rrelated signal interval, In addition, the experimental results demons trate that accurate velocity estimation for low volume dow rates and p articularly for large beam-vessel angles may involve detection of chan ges in the correlation magnitude. For low volume flow rates, the shape of the correlation surface can be affected by small regions of blood with a strong scattering intensity located near the initial region of interest.