G. Cloutier et al., EXPERIMENTAL EVALUATION OF INTRINSIC AND NONSTATIONARY ULTRASONIC DOPPLER SPECTRAL BROADENING IN STEADY AND PULSATILE FLOW LOOP MODELS, IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 40(6), 1993, pp. 786-795
Intrinsic and nonstationary Doppler spectral broadening, and the skewn
ess of the spectral representation, were evaluated experimentally usin
g porcine red cell suspensions as ultrasonic scatterers. Intrinsic bro
adening, by definition, refers to the broadening produced by the range
of angles sustained by each scatterer viewed by the finite dimension
of the transducer. Nonstationary broadening refers, on the other hand,
to the broadening associated with the acceleration and deceleration o
f the scatterers within the Doppler sample volume. Theoretically, the
relative Doppler bandwidth, defined as the intrinsic bandwidth divided
by the mean Doppler frequency shift, should be velocity independent.
In the present study, the relative Doppler bandwidth invariance theore
m was experimentally verified with an in vitro steady laminar blood fl
ow model. We showed that the relative bandwidth was both independent o
f the flow velocity and blood hematocrit. Using a pulsatile laminar fl
ow model, we demonstrated that the relative Doppler bandwidth invarian
ce theorem did not hold during flow acceleration and deceleration. In
addition, a positive skewness of the Doppler spectra was observed duri
ng acceleration while a negative skewness was measured during the dece
leration of blood. The effect of the window duration used in the Fouri
er spectral computation, on nonstationary broadening, was also charact
erized. For a window of 2.5 ms, broadening due to spectral leakage dom
inated over nonstationary broadening. The limitation of the spectrum a
nalyzer was less important for windows of 5 and 10 ms. Experiments wer
e also performed in pulsatile turbulent flow to verify the behavior of
the relative Doppler bandwidth and spectral skewness. In this flow re
gime, both parameters significantly varied within the flow cycle, with
a pattern of variation different from that observed in pulsatile lami
nar flow. Generally, good matching was found between experimental and
theoretical results. Significant basic information on the backscatteri
ng of ultrasound from blood in both steady and pulsatile flow is prese
nted in this study.