title: Doppler ultrasound detection of side-vessel occlusion: an in vitro study.
abstract: OBJECTIVE
  Small-vessel knock is a recently reported Doppler ultrasound finding that has been identified in patients with cerebral ischemia. It has been hypothesized that knock-type signals are linked to the presence of either small-vessel occlusion or wall motion. The aim of this study was to investigate the origins of "knock-type" signals by reproducing occlusion of a peripheral artery model in vitro.
  
  
  METHODS
  Synthetic bifurcations were fabricated from glass and latex and placed in a flow-rig mimicking physiological blood-flow conditions. The glass model permitted study of fluid flow in the absence of wall motion, whereas the latex model also produced wall motion effects. Vessels were artificially obstructed to examine Doppler signal characteristics associated with blood flow and wall motion.
  
  
  RESULTS
  Complete obstruction of the peripheral branch of the glass model revealed discrete (<100 ms) knock-type signals caused by local fluid flow in the occluded branch. Imaging of the obstructed vessel using color Doppler revealed forward and reflected flow. The walls produced periodic bidirectional knock-type signals, which occurred during systole and were not related to the presence of an obstruction.
  
  
  CONCLUSIONS
  In our laboratory model, transcranial Doppler ultrasound was found to be capable of detecting knock signals produced by circulating fluid within an occluded branch. However, because similar signals are also generated by nonpathological wall motion, these results cannot be directly translated to a clinical setting. Clinicians should be careful to avoid casual overinterpretation of transcranial Doppler ultrasound data.
authors.affiliation: University Hospitals of Leicester NHS Trust, Leicester, UK. emlc1@le.ac.uk
authors.forename: Emma M L
authors.initials: EM
authors.lastname: Chung
authors.forename: Kumar V
authors.initials: KV
authors.lastname: Ramnarine
authors.forename: Chloe V
authors.initials: CV
authors.lastname: Long
authors.forename: Chesda
authors.initials: C
authors.lastname: Udommongkol
authors.forename: Brian R
authors.initials: BR
authors.lastname: Chambers
authors.forename: John
authors.initials: J
authors.lastname: Gittins
authors.forename: Glen C
authors.initials: GC
authors.lastname: Bush
authors.forename: David H
authors.initials: DH
authors.lastname: Evans
mesh_terms: D001157:Arterial Occlusive Diseases / Q000000981:diagnostic imaging*; D002545:Brain Ischemia / Q000000981:diagnostic imaging*; D002536:Cerebral Arteries / Q000000981:diagnostic imaging*; D002560:Cerebrovascular Circulation; D005898:Glass; D007840:Latex; D008953:Models, Anatomic; D018615:Ultrasonography, Doppler, Color; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods*
chemical_list: D007840:Latex