title: Ultrasound imaging of Nd:YAG laser-induced tissue coagulation in porcine livers.
abstract: OBJECTIVE
  Absorption of laser light energy induces denaturation of proteins and thermocoagulation of irradiated tissue. Recently, MRI-guided laser coagulation in combination with MR thermometry was reported as a treatment of liver tumours. In the present study ultrasonographic imaging was evaluated for its suitability in laser induced tissue thermocoagulation.
  
  
  METHODS
  Fresh porcine livers were used for ex vivo examinations. Placement of the laser catheter and tissue coagulation during laser light emission were online monitored by ultrasonography. Nd:YAG laser-induced tissue damage was evaluated by macroscopical and microscopical examinations of histological sections.
  
  
  RESULTS
  During laser light emission a marked hyperdense signal enhancement was observed by ultrasonography which strongly correlated with the extent of macroscopic tissue damage. The size of laser-induced coagulation zone depended on both the power setting and total energy delivered. Carbonization of the tissue surrounding the laser tip is a limiting factor because of laser light absorption. However our data indicate that using appropriate laser energy and exposure time prevent carbonization although carbonization can not be visualized by ultrasonography.
  
  
  CONCLUSIONS
  It is concluded from the present ex vivo studies that laser coagulation can be effectively performed under ultrasonographic guidance.
authors.affiliation: Division of Gastroenterology and Endocrinology, Department of Medicine, Gottingen, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Ritzel
authors.forename: P
authors.initials: P
authors.lastname: Wietzke-Braun
authors.forename: U
authors.initials: U
authors.lastname: Brinck
authors.forename: U
authors.initials: U
authors.lastname: Leonhardt
authors.forename: G
authors.initials: G
authors.lastname: Ramadori
mesh_terms: D000818:Animals; D017075:Laser Coagulation / Q000295:instrumentation / Q000379:methods*; D008099:Liver / Q000000981:diagnostic imaging / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D013552:Swine; D014463:Ultrasonography