title: Effect of beam-flow angle on velocity measurements in modern Doppler ultrasound systems.
abstract: OBJECTIVE
  The purpose of this article is to examine the effect of different beam-flow angles on the accuracy of Doppler ultrasound velocity measurements in modern ultrasound systems.
  
  
  METHODS
  A flow phantom was used to create a steady flow of water in a 4.3-mm-diameter tube. Using three different modern university-grade ultrasound systems, flow was measured at 30°, 40°, 50°, 60°, 70°, 80°, and 88° beam-flow angles twice by two radiologists in consensus using a convex and linear probe. Measured flow ratio, defined as measured velocity divided by estimated actual velocity, was calculated. Intraprobe, interprobe, and intermachine mean variation of measured flow ratio were calculated.
  
  
  RESULTS
  Measured flow ratio increased as beam-flow angles increased. Measured flow ratios for the angles 30°, 40°, 50°, 60°, 70°, 80°, and 88° were 0.90, 0.97, 1.10, 1.22, 1.62, 2.34, and 10.29, respectively. Intraprobe, interprobe, and intermachine variation did not show marked differences. For angles grouped as 30-40°, 50-60°, 70°, and 80-88°, intraprobe variation was 12%, 15%, 15%, and 26%; interprobe variation was 20%, 16%, 13%, and 26%; and intermachine variation was 16%, 16%, 17%, and 54%, respectively. As beam-flow angle increased, an increase in spectral broadening was also noted.
  
  
  CONCLUSIONS
  There is no simple cutoff beam-flow value, such as the well-quoted less than 60°, at which velocity measurements can be considered accurate. For follow-up imaging, beam-flow angle differences should be considered, and the same beam-flow angles should be used when possible. Follow-up imaging by different sonography machines is feasible.
authors.affiliation: Department of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seocho-gu, Seoul, Korea.
authors.forename: Michael Yong
authors.initials: MY
authors.lastname: Park
authors.forename: Seung Eun
authors.initials: SE
authors.lastname: Jung
authors.forename: Jae Young
authors.initials: JY
authors.lastname: Byun
authors.forename: June Hoan
authors.initials: JH
authors.lastname: Kim
authors.forename: Ga Eul
authors.initials: GE
authors.lastname: Joo
mesh_terms: D001783:Blood Flow Velocity; D006801:Humans; D019047:Phantoms, Imaging; D012212:Rheology / Q000379:methods*; D018608:Ultrasonography, Doppler / Q000379:methods*