Spectral power density calculations for pulsed Doppler.
Range-gated pulsed Doppler can be used to make localized velocity measurements within a blood vessel. A spectral flow profile can be created by stepping a sufficiently small sample volume across the lumen, but no set of spectra will correspond directly to the true velocity profile. Spectral flow profiles are affected by a complex interplay between different sources of spectral broadening. In this study we developed a systematic theoretical method which allows spectral power density functions to be calculated under a very wide range of conditions, and used it to obtain simulated flow spectra. The model was formulated analytically. It is based on the weighted-volume approach and incorporates, through the concept of a spread function, the intrinsic spectral broadening associated with a focused transducer. It can be applied for arbitrary values of the spread parameter; for non-uniform beam profiles; with maximal (continuous wave-type) or minimal (pulse wave-type) range-gated sample volumes; and for beams that intersect the flow tube axis, or are off centre. Results are presented for a Gaussian beam and parabolic flow. Simulated spectral flow profiles are given which illustrate how a profile's appearance can be altered by the different sources of spectral broadening.
Thompson
R S
RS
School of Mathematics and Statistics, University of Sydney, Sydney, NSW 2006, Australia. r.thompson@maths.usyd.edu.au
Aldis
G K
GK
D001783:Blood Flow Velocity; D001808:Blood Vessels / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D014465:Ultrasonics; D018617:Ultrasonography, Doppler, Pulsed / Q000379:methods*