title: Influence of instrument settings on flow signal and background noise in power Doppler US. An experimental study using a flow phantom with hyperechoic background.
abstract: OBJECTIVE
  To determine the influence of various power Doppler instrument settings on intensities of flow signal and background noise in flow with a tissue-equivalent phantom.
  
  
  METHODS
  Power Doppler images were obtained with changing wall filter level (low, medium, high, and maximum), pulse repetition frequency (PRF; 500, 700, 1000, 1500, 3000, and 6000 Hz), and Doppler gain (60%, 70%, 80%, 90%, and 100%) at different flow velocities (13.3, 26.5, and 49.8 cm/sec). To make a quantitative comparison of different settings, the authors measured the intensities of flow signal and background noise in obtained power Doppler images using the scanner and a computer program, calculated signal-to-noise difference (SND; intensity of flow signal--intensity of background noise), and evaluated the relation between SND and power Doppler settings.
  
  
  RESULTS
  The intensities of flow signal and background noise were proportional to flow velocity and power Doppler gain but were inversely proportional to PRF and wall filter level. At constant wall filter level (medium), changes of PRF and Doppler gain to the same directions resulted in a high SND. At constant PRF (1000 Hz), changes of wall filter and Doppler gain to the same directions also resulted in a high SND. However, at constant Doppler gain (80%), a high SND was obtained with changing wall filter level and PRF to the opposite directions.
  
  
  CONCLUSIONS
  Three Doppler instrument settings--wall filter level, pulse repetition frequency, and Doppler gain--have reciprocal influences on SND.
authors.affiliation: Department of Radiology, Hallym University College of Medicine, Seoul, Korea.
authors.forename: D Y
authors.initials: DY
authors.lastname: Yoon
authors.forename: B I
authors.initials: BI
authors.lastname: Choi
authors.forename: T K
authors.initials: TK
authors.lastname: Kim
authors.forename: J K
authors.initials: JK
authors.lastname: Han
authors.forename: K M
authors.initials: KM
authors.lastname: Yeon
mesh_terms: D001783:Blood Flow Velocity; D006801:Humans; D008099:Liver / Q000098:blood supply / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D018608:Ultrasonography, Doppler / Q000295:instrumentation*