title: Sub-surface, micrometer-scale incisions produced in rodent cortex using tightly-focused femtosecond laser pulses.
abstract: OBJECTIVE
  Techniques that allow targeted, micrometer-scale disruption in the depths of biological tissue, without affecting overlying structures or causing significant collateral damage, could potentially lead to new surgical procedures. We describe an optical technique to make sub-surface incisions in in vivo rodent brain and characterize the relationship between the cut width and maximum depth of these optical transections as a function of laser energy.
  
  
  METHODS
  To produce cuts, high intensity, femtosecond laser pulses were tightly focused into and translated within the cortex, through a craniotomy, in anesthetized rodents. Imaging of stained brain slices was used to characterize cut width and maximum cutting depth.
  
  
  RESULTS
  Cut width decreased exponentially as a function of depth and increased as the cube root of laser energy, but showed about 50% variation at fixed depth and laser energy. For example, at a laser energy of 13 µJ, cut width decreased from 158 ± 43.1 µm (mean ± standard deviation) to 56 ± 33 µm over depths of approximately 200-800 µm, respectively. Maximal cut depth increased logarithmically with laser energy, with cut depths of up to 1 mm achieved with 13 µJ pulses. We further showcased this technique by selectively cutting sub-surface cortical dendrites in a live, anesthetized transgenic mouse.
  
  
  CONCLUSIONS
  Femtosecond laser pulses provide the novel capacity for precise, sub-surface, cellular-scale cuts for surgical applications in optically scattering tissues.
authors.affiliation: Department of Biomedical Engineering, Cornell University, Ithaca, New York 14853, USA.
authors.forename: John
authors.initials: J
authors.lastname: Nguyen
authors.forename: Jillian
authors.initials: J
authors.lastname: Ferdman
authors.forename: Mingrui
authors.initials: M
authors.lastname: Zhao
authors.forename: David
authors.initials: D
authors.lastname: Huland
authors.forename: Shatha
authors.initials: S
authors.lastname: Saqqa
authors.forename: Jan
authors.initials: J
authors.lastname: Ma
authors.forename: Nozomi
authors.initials: N
authors.lastname: Nishimura
authors.forename: Theodore H
authors.initials: TH
authors.lastname: Schwartz
authors.forename: Chris B
authors.initials: CB
authors.lastname: Schaffer
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000473:pathology / Q000601:surgery*; D003399:Craniotomy; D003712:Dendrites; D053685:Laser Therapy / Q000295:instrumentation / Q000379:methods*; D008297:Male; D051379:Mice; D042282:Microdissection / Q000295:instrumentation / Q000379:methods*; D018613:Microscopy, Confocal; D051381:Rats; D017207:Rats, Sprague-Dawley