Effect of the beam-vessel angle on the received acoustic signalfrom blood

摘要

In order to explore the feasibility of algorithms to determine thenthree dimensional (3D) velocity magnitude from the received ultrasonicnblood echo from a single line of sight, the signal from small samplenvolumes is studied as a function of beam-vessel angle. As opposed tonprevious treatments of the effect of the beam-vessel angle on thenreceived acoustic signal, a wideband signal is transmitted and thenreturned signal in each sample volume is analyzed. High-resolutionnexperimental M-mode images of radio-frequency (rf) echo signals are usednto visualize the flow in individual regions of interest. Thesenexperiments confirm the predictions of a theoretical model for thensignal and its second moment. It is shown that the two major effectsnlimiting the correlated signal interval are the spread of axialnvelocities within the sample volume and the transit time across thenlateral beam width. Particularly for small beam-vessel angles, thenspread of velocities limits the correlated signal interval. In addition,nthe experimental results demonstrate that accurate velocity estimationnfor low volume flow rates and particularly for large beam-vessel anglesnmay involve detection of changes in the correlation magnitude. For lownvolume flow rates, the shape of the correlation surface can be affectednby small regions of blood with a strong scattering intensity locatednnear the initial region of interest