title: Noninvasive estimation of the pressure gradient across stenoses using sonographic contrast: in vitro validation.
abstract: OBJECTIVE
  Because velocity measurements to estimate the degree of arterial stenosis are susceptible to local and systemic factors, we aimed to investigate the feasibility of estimating the pressure gradient across a stenosis noninvasively by using sonographic contrast.
  
  
  METHODS
  Using a gravity-fed flow system, a 1:4000 dilution of a contrast agent in water was circulated through silicone tubes that had either focal or long-segment stenoses of varying severity in a water bath. We measured the cross-sectional areas of the normal and stenotic regions with B-mode sonography and the flow velocity with spectral Doppler sonography and calculated the pressure gradients across the stenoses using the empirically derived Young mathematical model and the simplified Bernoulli equation. Estimated gradients were compared with those measured manometerically.
  
  
  RESULTS
  Both methods yielded estimates of pressure gradients that correlated with measured gradients (r > 0.988). In focal and long-segment stenoses, the Young model yielded gradients that agreed more closely with manometerically measured values than the Bernoulli equation (+/- 8% versus -24%-57%). Both methods were highly dependent on the ability to measure the luminal cross-sectional area. The presence of sonographic contrast in the vascular lumen highlighted the inner wall, allowing the accurate measurement of the luminal area to +/- 3.0%.
  
  
  CONCLUSIONS
  The pressure gradient can be estimated across stenoses noninvasively. The Young model was more accurate than the simplified Bernoulli equation in this model using steady flow. Estimated gradients are highly dependent on the definition of the vascular lumen, a process aided by the use of sonographic contrast.
authors.affiliation: Department of Radiology, University of California, San Diego, San Diego, California, USA.
authors.forename: Winston W
authors.initials: WW
authors.lastname: Lien
authors.forename: Allen H
authors.initials: AH
authors.lastname: Lee
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kono
authors.forename: Greg C
authors.initials: GC
authors.lastname: Steinbach
authors.forename: Robert F
authors.initials: RF
authors.lastname: Mattrey
mesh_terms: D016893:Carotid Stenosis / Q000000981:diagnostic imaging*; D003287:Contrast Media; D005240:Feasibility Studies; D005466:Fluorocarbons; D006801:Humans; D006842:Hydrocarbons, Brominated; D008955:Models, Cardiovascular; D011312:Pressure; D014463:Ultrasonography
chemical_list: D003287:Contrast Media; D005466:Fluorocarbons; D006842:Hydrocarbons, Brominated; C078626:perflexane