title: Can transcranial Doppler discriminate between solid and gaseous microemboli? Assessment of a dual-frequency transducer system.
abstract: OBJECTIVE
  Transcranial Doppler ultrasound can reliably detect both gaseous and solid cerebral emboli. However, conventional equipment is unable to discriminate between gaseous and solid emboli. This is a major limitation in situations in which the 2 coexist, because they may have very different clinical relevance. Recently, a novel Embo-Dop system, using insonation at 2 ultrasound transducer frequencies, has been developed. An initial study with a small sample size suggested it provided excellent discrimination. We performed a validation study in subjects with embolic signals of known nature.
  
  
  METHODS
  Gaseous embolic signals were obtained in 7 patients with known patient foramen ovale by intravenous injection of agitated saline injections. Solid embolic signals were obtained in patients with symptomatic carotid stenosis (N=23). Discrimination of the 2 using the Embo-Dop system dual-frequency system was assessed. It was compared with discrimination using embolic signal maximum intensity with an intensity threshold.
  
  
  RESULTS
  One hundred forty-five solid embolic signals were recorded from carotid stenosis patients. Seventy-three were classified as solid and 72 as gaseous by the Embo-Dop system. Six hundred forty-eight gaseous embolic signals were recorded from 7 patients with patent foramen ovale. Six hundred twenty-five were classified as gaseous and 23 as solid. This gave a sensitivity of 50.3% and specificity of 96.5% for detecting solid embolic signals. Discrimination was better than using a simple intensity threshold.
  
  
  CONCLUSIONS
  The Embo-Dop dual-frequency system allows better discrimination than a simple intensity threshold but it is not accurate enough for use in clinical or research studies. Further work is needed to develop reliable clinical systems for discrimination of emboli.
authors: Clinical Neuroscience, Department of Cardiac and Vascular Sciences, St George's Hospital Medical School, Cranmer Terr, London, SW17 0RE, UK. hmarkus@sghms.ac.uk
authors: Hugh S
authors: HS
authors: Markus
authors: Martin
authors: M
authors: Punter
mesh_terms: D002309:Cardiology / Q000379:methods*; D016893:Carotid Stenosis / Q000175:diagnosis*; D002560:Cerebrovascular Circulation; D004452:Echocardiography / Q000379:methods; D004618:Embolism, Air / Q000175:diagnosis* / Q000473:pathology; D006344:Heart Septal Defects, Atrial / Q000175:diagnosis / Q000473:pathology; D006801:Humans; D020766:Intracranial Embolism / Q000175:diagnosis* / Q000473:pathology; D002542:Intracranial Embolism and Thrombosis / Q000175:diagnosis* / Q000473:pathology; D012372:ROC Curve; D012680:Sensitivity and Specificity; D020521:Stroke / Q000175:diagnosis / Q000473:pathology; D017585:Ultrasonography, Doppler, Transcranial / Q000295:instrumentation* / Q000379:methods*