title: Dose-dependent artifact in the far wall of the carotid artery at dynamic contrast-enhanced US.
abstract: OBJECTIVE
  To quantify a pseudoenhancement phenomenon observed during dynamic contrast material-enhanced ultrasonography (US) of the carotid artery, both in vitro and in vivo.
  
  
  METHODS
  Ethical approval was obtained prior to commencing this prospective case series, and each patient gave written informed consent. Thirty-one patients with 50%-99% internal carotid artery stenosis underwent dynamic contrast-enhanced US of the carotid bifurcation with use of 2 mL of microbubbles. In the final 10 patients, an additional 1 mL bolus was administered after 15 minutes. Raw linear digital imaging and communications in medicine data were analyzed offline. Regions of interest were drawn within the common carotid artery lumen and immediately adjacent to the lumen in the near and far wall adventitia. Peak intensity was measured. An in vitro experiment with a single-channel flow phantom was also performed. This apparatus consisted of an 8-mm-diameter latex tube placed in a tissue-mimicking fluid. Microbubble concentrations of 0.02%, 0.1%, 0.5%, 1%, and 2% were pumped into the tube. Regions of interest were drawn in a similar fashion to the in vivo experiments, and peak intensity was measured. The Wilcoxon signed rank and paired t tests were used to compare the difference between the near and far wall signal intensities at each dose; a multiplication factor comparing near and far wall signal intensity was derived.
  
  
  RESULTS
  The far wall of the common carotid artery was significantly more echogenic than the near wall at 2 mL contrast agent doses (P<.0001, n=31), and the far wall signal intensity increased synchronously with that of the lumen. The difference in signal intensity between near and far wall regions was significantly greater at 2 mL than at 1 mL (P=.012, n=10). In vitro, the phantom tubing demonstrated a similar pattern and magnitude of enhancement to that seen in vivo.
  
  
  CONCLUSIONS
  A dose-dependent, nonlinear propagation artifact known as pseudoenhancement occurs in the far wall adventitia of the carotid artery and should not be mistaken as a marker of plaque vulnerability.
authors.affiliation: Academic Section of Vascular Surgery and Department of Experimental Medicine, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0HS, England. a.thapar09@imperial.ac.uk
authors.forename: Ankur
authors.initials: A
authors.lastname: Thapar
authors.forename: Joseph
authors.initials: J
authors.lastname: Shalhoub
authors.forename: Michalakis
authors.initials: M
authors.lastname: Averkiou
authors.forename: Christophoros
authors.initials: C
authors.lastname: Mannaris
authors.forename: Alun H
authors.initials: AH
authors.lastname: Davies
authors.forename: Edward L S
authors.initials: EL
authors.lastname: Leen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016477:Artifacts; D002339:Carotid Arteries / Q000000981:diagnostic imaging / Q000187:drug effects; D016893:Carotid Stenosis / Q000000981:diagnostic imaging*; D003287:Contrast Media / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D010743:Phospholipids / Q000008:administration & dosage*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013459:Sulfur Hexafluoride / Q000008:administration & dosage*; D014463:Ultrasonography / Q000379:methods*
chemical_list: D003287:Contrast Media; D010743:Phospholipids; C420843:contrast agent BR1; D013459:Sulfur Hexafluoride