title: Effect of microbubble contrast on intracranial blood flow velocity assessed by transcranial Doppler.
abstract: OBJECTIVE
  Ultrasound contrast agents (UCA) salvage a considerable number of transcranial Doppler (TCD) exams which would have failed because of poor bone window. UCA bolus injection causes an undesirable increase in measured blood flow velocity (BFV). The effect of UCA continuous infusion on measured BFV has not been investigated, and some in vitro experiments suggest that gain reduction during UCA administration may also influence measured BFV. This study aimed to investigate the effect of UCA continuous infusion on BFV measured by TCD and the influence of gain reduction on these measurements in a clinical setting.
  
  
  METHODS
  The right middle cerebral artery of ten patients with optimal bone window was insonated using a 2 MHz probe. UCA were administered using an infusion pump. BFV was measured (1) at baseline, (2) during UCA infusion, (3) during UCA infusion with gain reduction, and (4) after UCA wash-out phase. Gain reduction was based on the agreement between two neurosonographers on the degree of gain reduction necessary to restore baseline Doppler signal intensity (DSI). Actual DSI was estimated offline by analysis of raw data.
  
  
  RESULTS
  BFV measured during UCA infusion with no gain adjustment was significantly higher than baseline BFV [peak systolic velocity (PSV): 85.1 ± 19.7 vs. 74.4 ± 19.7 cm/s, p < 0.0001; Mean velocity (MV): 56.5 ± 11.8 vs. 50.2 ± 12.3 cm/s, p < 0.0001]. BFV measured during UCA infusion with gain reduction was not significantly higher than baseline BFV (PSV: 74.3 ± 18.9 vs. 74.4 ± 19.4 cm/s, p = 0.8; MV: 49.4 ± 11.0 vs. 50.2 ± 12.3 cm/s, p = 0.8). Actual DSI during UCA infusion with gain reduction was not significantly higher than baseline DSI (13 ± 1 vs. 13 ± 1 dB).
  
  
  CONCLUSIONS
  This study shows that UCA continuous infusion leads to an increase in measured BFV which may be counteracted by reducing Doppler gain thus restoring pre-contrast DSI.
authors.affiliation: Department of Clinical Medicine, University of Bergen, Bergen, Norway.
authors.forename: Nicola
authors.initials: N
authors.lastname: Logallo
authors.affiliation: Center for Neurovascular Diseases, Haukeland University Hospital, Bergen, Norway.
authors.forename: Annette
authors.initials: A
authors.lastname: Fromm
authors.affiliation: Center for Neurovascular Diseases, Haukeland University Hospital, Bergen, Norway.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Waje-Andreassen
authors.affiliation: Department of Clinical Medicine, University of Bergen, Bergen, Norway.
authors.forename: Lars
authors.initials: L
authors.lastname: Thomassen
authors.affiliation: Institute of Medicine, University of Bergen, Bergen, Norway.
authors.forename: Knut
authors.initials: K
authors.lastname: Matre
keywords: Blood flow velocity; Transcranial Doppler; Ultrasound artifacts; Ultrasound contrast agents