title: Optimization of the Erbium:YAG laser for precise incision of ureteral and urethral tissues: in vitro and in vivo results.
abstract: OBJECTIVE
  Tissue damage during endoscopic treatment of urethral and ureteral strictures may result in stricture recurrence. The Erbium:YAG laser ablates soft tissues with minimal peripheral damage and may be a promising alternative to cold knife and Holmium:YAG laser for precise incision of urological strictures.
  
  
  METHODS
  Optimization of the Er:YAG laser was conducted using ex vivo porcine ureteral and canine urethral tissues. Preliminary in vivo studies were also performed in a laparoscopic porcine ureteral model with exposed ureter. Laser radiation with a wavelength of 2.94 microm, pulse lengths of 8, 70, and 220 microseconds, output energies of 2-35 mJ, fluences of 1-25 J/cm2, and pulse repetition rates of 5-30 Hz, was delivered through 250-microm and 425-microm core germanium oxide optical fibers in direct contact with tissue.
  
  
  RESULTS
  Ex vivo perforation thresholds measured 2-4 J/cm2, with ablation rates of 50 microm/pulse at fluences of 6-11 J/cm2. In vivo perforation thresholds were approximately 1.8 J/cm2, with the ureter perforated in less than 20 pulses at fluences greater than 3.6 J/cm2. Peripheral thermal damage in tissue decreased from 30 to 60 microm to 10-20 microm as the laser pulse length decreased from 220 to 8 microseconds. Mechanical tissue damage was observed at the 8 microseconds pulse duration.
  
  
  CONCLUSIONS
  The Er:YAG laser, operating at a pulse duration of approximately 70 microseconds, a fluence greater than approximately 4 J/cm2, and a repetition rate less than 20 Hz, is capable of rapidly incising urethral and ureteral tissues with minimal thermal and mechanical side-effects.
authors.affiliation: Department of Urology, Johns Hopkins Medical Institutions, Baltimore, Maryland, USA. nfried@jhmi.edu
authors.forename: Nathaniel M
authors.initials: NM
authors.lastname: Fried
authors.forename: Zelalem
authors.initials: Z
authors.lastname: Tesfaye
authors.forename: Albert M
authors.initials: AM
authors.lastname: Ong
authors.forename: Koon H
authors.initials: KH
authors.lastname: Rha
authors.forename: Pooya
authors.initials: P
authors.lastname: Hejazi
mesh_terms: D000818:Animals; D004285:Dogs; D005260:Female; D053685:Laser Therapy / Q000295:instrumentation*; D008297:Male; D023421:Models, Animal; D013552:Swine; D014513:Ureter / Q000601:surgery*; D014515:Ureteral Diseases / Q000601:surgery*; D014521:Urethra / Q000601:surgery*; D014525:Urethral Stricture / Q000601:surgery*; D013520:Urologic Surgical Procedures / Q000379:methods*