A statistical analysis of the received signal from blood duringlaminar flow

摘要

In order to determine the limiting velocity resolution that can benachieved using ultrasound, and to provide a model which can bengeneralized for the analysis of disturbed flow, a theoretical andnexperimental evaluation of the statistics of the received signal fromnlaminar flow following the transmission of a train of short pulses isnpresented. The authors derive the autocorrelation function and determinenthe length of the correlated signal for various flow rates, comparingnexperimental measurements to theoretical predictions. High resolutionnexperimental RF M-mode images are used to verify the theoretical model.nUsing a fluid with a density, viscosity, volume concentration, particlensize, and speed of sound which is similar to that of blood, the authorsnshow that the signal remains correlated for a long interval under manynconditions of clinical interest. Including a comparison withnexperimental data, the effect of the lateral transit time through thensample volume and the axial velocity spread within the sample volume onnthe correlation of the received signal is evaluated. When a significantnrange of velocity components is present within the sample volume, thisnrange is the limiting factor in the length of the correlated signalninterval. Therefore, the use of a wideband signal, which reduces thensample volume size, produces a returned signal that may be correlatednfor a larger number of pulses, or for a longer time