Turbulence and Circulating Cerebral Emboli Detectable at Doppler Ultrasonography: A Differentiation Study in a Stenotic Middle Cerebral Artery Model
Yi Yanga,
Donald G. Grossetb,
Qiu Lic,
Ashfaq Shuaibc and
Kennedy R. Leesa
a Department of Medicine and Therapeutics, University of Glasgow, Glasgow, England
b Neurology Department, Southern General Hospital, Glasgow, England
c Neurology Division, University of Alberta, Edmonton, Canada
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FIG 1. Schematic illustration of the stenotic MCA model and circuit. Diluted RBC suspension was circulated in a pulsed fashion by a pulsed pump, and the embolic materials were injected into the circuit via the side port. Turbulence and embolic signals as well as flow velocities were continuously recorded from a TCD probe, which was coupled with the outside of temporal bone.
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FIG 2. Characterization of Doppler waveform at different zones along the stenotic artery (65% reduced area). Flow of RBC suspension displayed a normal Doppler velocity profile at the prestenosis zone. However, at the stenosis zone, the flow showed a sharp increase in systolic velocity and the signal intensity started to distribute unevenly; at poststenosis I zone, the velocity tended to decrease, but a high intensity turbulent signal in the central waveform and apparent reversal flow became notable. The flow profile at poststenosis zone II returned to normal but had a lower systolic velocity.
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FIG 3. Dynamic profile of flow turbulence associated with different degrees of arterial stenosis. The transition of flow turbulence did not occur until the degree of stenosis of the artery increased to 55%. At stenoses of 66% and 75%, turbulence became most typical and was accompanied by reversed flow. Turbulence remained but decreased when degree of stenosis increased to 85% or 90%. Both systolic and diastolic velocities increased in association with the rising degree of stenosis, but systolic velocities changed more predominately.
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FIG 4. Correlation between degree of stenosis and average signal intensity of flow turbulence sampled at poststenosis zone I. Association between average Doppler signal intensities sampled at poststenosis zone I and degrees of stenosis of the artery looks like a tea spoon. Poor correlation existed between the two indices (r = 0.72, P = .07).
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FIG 5. Correlation between degree of stenosis and Doppler mean flow velocity at poststenosis zone I. Mean velocities calculated at poststenosis zone I showed a linear relationship, with an increase in degree of stenosis after logarithmic transformation of mean flow velocity.
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FIG 6. Visual differentiation between turbulence signals and embolic signals. Turbulence signals showed a high intensity area in the center of the systolic phase of the Doppler flow waveform and were usually accompanied by jet flow velocity, harsh noise, and reversed flow. However, embolic signals were featured as high intensity points that randomly superimposed on the flow waveform of either the systolic or diastolic period, accompanied by harmonic chirps.
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