Kw. Ferrara, EFFECT OF THE BEAM-VESSEL ANGLE ON THE RECEIVED ACOUSTIC-SIGNAL FROM BLOOD, IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 42(3), 1995, pp. 416-428
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.