title: Analysis of the frequency modulation present in Doppler ultrasound signals may allow differentiation between particulate and gaseous cerebral emboli.
abstract: The purpose of this study was to investigate the incidence of frequency modulation in Doppler signals from cerebral emboli and to seek possible explanations for its occurrence. Signals from 200 particulate emboli and 200 presumed gaseous emboli were studies. The Doppler signals were visualised in the time domain and were classified into three main types. Type I signals contained no modulation, type II signals showed gradual frequency changes and type III showed a rapid change evident in only a small percentage of the entire signal. Type I signals were observed from 71.5% of particulate emboli but only 19% of gaseous emboli (X(2)) = 111, p < 0.001). Type II signals were found in 28.5% of particulate emboli and 38% of gaseous emboli (X(2)) = 4.06, p < 0.05). The most surprising and significant finding was that 43% of gaseous embolic signals were categorised as type III signals compared with 0% of signals from particulate emboli (X(2)) = 109, p < 0.001). The finding that known particulate emboli appear never to produce rapid frequency modulation may provide a basis for differentiating between gaseous and particulate emboli.
authors.affiliation: Department of Surgery Faculty of Medicine, University of Leicester, UK.
authors.forename: J L
authors.initials: JL
authors.lastname: Smith
authors.forename: D H
authors.initials: DH
authors.lastname: Evans
authors.forename: A R
authors.initials: AR
authors.lastname: Naylor
mesh_terms: D002536:Cerebral Arteries / Q000000981:diagnostic imaging*; D004691:Endarterectomy; D006801:Humans; D007091:Image Processing, Computer-Assisted; D002542:Intracranial Embolism and Thrombosis / Q000000981:diagnostic imaging* / Q000601:surgery; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods*