title: Pulse inversion imaging of liver blood flow: improved method for characterizing focal masses with microbubble contrast.
abstract: OBJECTIVE
  To create a microbubble contrast image of vessels that lie below the resolution of an ultrasound system, a technique is required that detects preferentially the agent echo, rejecting that from tissue. Harmonic imaging exploits the nonlinear behavior of microbubbles but forces a compromise between image sensitivity and axial resolution. The authors describe and evaluate a new method that overcomes this compromise and improves contrast imaging performance: pulse inversion imaging.
  
  
  METHODS
  Sequences of pulses of alternate phase are transmitted into tissue and their echoes summed. A prototype scanner equipped with pulse inversion was used to image phantoms and 16 patients with focal liver masses.
  
  
  RESULTS
  Pulse inversion images show contrast sensitivity and resolution superior to that of harmonic images. Vessels can be imaged at an incident power sufficiently low to avoid destroying the agent, allowing unique visualization of tumor vasculature. Distinct patterns were seen in hemangiomas, metastases, and hepatocellular carcinomas.
  
  
  CONCLUSIONS
  Pulse inversion imaging is an improved bubble-specific imaging method that extends the potential of contrast ultrasonography.
authors.affiliation: Department of Medical Biophysics, University of Toronto, Canada.
authors.forename: P N
authors.initials: PN
authors.lastname: Burns
authors.forename: S R
authors.initials: SR
authors.lastname: Wilson
authors.forename: D H
authors.initials: DH
authors.lastname: Simpson
mesh_terms: D000328:Adult; D000368:Aged; D000418:Albumins; D006528:Carcinoma, Hepatocellular / Q000000981:diagnostic imaging; D003287:Contrast Media; D005260:Female; D005466:Fluorocarbons; D006391:Hemangioma / Q000000981:diagnostic imaging; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging*; D008102:Liver Circulation; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000556:secondary; D008297:Male; D008863:Microspheres; D008875:Middle Aged; D019047:Phantoms, Imaging; D014463:Ultrasonography / Q000379:methods
chemical_list: D000418:Albumins; D003287:Contrast Media; C099458:FS 069; D005466:Fluorocarbons