DOPPLER SPECTRUM SHAPE-ANALYSIS BASED ON THE SUMMATION OF FLOW-LINE SPECTRA

A method of evaluating the shape of the Doppler spectrum in pulsed wave (PW) Doppler flowmeters in the presence of velocity gradients is presented and is demonstrated for a circular geometry transducer insonating a uniform distribution of isotropic scatterers moving in paraxial conditions. The method computes the spectrum shape by adding the power spectra of individual flow lines present in the sample volume of the moving fluid being analyzed and can be applied to any focused transducer aperture for which the how-line spectra are known. With a parabolic velocity profile insonated by a focused circular transducer, several computed spectra are compared with experimental ones for different insonation angles; it is also shown how changes in the spectral shape, due to variations of sample volume size, can be evaluated. The results should help to provide a better understanding of PW Doppler spectrum broadening and its use in medical ultrasound diagnostics.