title: Long-term ambulatory monitoring for cerebral emboli using transcranial Doppler ultrasound.
abstract: OBJECTIVE
  Transcranial Doppler (TCD) monitoring for asymptomatic cerebral emboli is currently limited to short recordings by equipment size, restricting its clinical usefulness. We have developed a first ambulatory TCD system, evaluated it in at-risk patient groups, and used it to study the pattern of embolization in patients with symptomatic carotid stenosis.
  
  
  METHODS
  The system comprises an 18x11.5x3.2 cm battery-powered Doppler unit (425 g) and a 13-mm servo-controlled 2 MHz transducer probe. The quadrature raw Doppler signal is stored on flash-disk. An autosearch algorithm restores vessel insonation should signal quality fall. Initial evaluation was in 20 ambulatory stroke patients. Subsequently, 12 recently symptomatic carotid patients had recordings for > or =5 hours.
  
  
  RESULTS
  Recordings were well tolerated and a median of 96% of Doppler signal was suitable for analysis. Embolic signals were detected in 11 of the 12 symptomatic carotid patients. There was marked temporal variability in embolization and prolonging the recording increased the yield of embolic signal positive patients from 58% at 30 minutes to 92% at 150 minutes. In 3 subjects with frequent embolic signals, significant temporal clustering of embolic signals was observed.
  
  
  CONCLUSIONS
  We have developed the first ambulatory TCD system. Good-quality recordings of > or =5 hours can be obtained. In view of the demonstrated temporal variability in embolization, this technique is likely to improve the predictive value of recording for asymptomatic embolic signals and may be particularly useful in patients in whom embolic signals are relatively infrequent, such as those with asymptomatic carotid stenosis and atrial fibrillation.
authors.affiliation: Department of Clinical Neurosciences, St. George's Hospital Medical School, Cranmer Terr, Tooting, London SW17 0RE, UK.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Mackinnon
authors.forename: Rune
authors.initials: R
authors.lastname: Aaslid
authors.forename: Hugh S
authors.initials: HS
authors.lastname: Markus
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000150:complications; D016893:Carotid Stenosis / Q000150:complications; D015331:Cohort Studies; D005260:Female; D006801:Humans; D020766:Intracranial Embolism / Q000150:complications / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging; D018670:Monitoring, Ambulatory / Q000295:instrumentation* / Q000379:methods*; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013995:Time; D017585:Ultrasonography, Doppler, Transcranial / Q000295:instrumentation* / Q000379:methods*