title: Laser system refinements to reduce variability in infarct size in the rat photothrombotic stroke model.
abstract: BACKGROUND
  The rat photothrombotic stroke model can induce brain infarcts with reasonable biological variability. Nevertheless, we observed unexplained high inter-individual variability despite using a rigorous protocol. Of the three major determinants of infarct volume, photosensitive dye concentration and illumination period were strictly controlled, whereas undetected fluctuation in laser power output was suspected to account for the variability.
  
  
  METHODS
  The frequently utilized Diode Pumped Solid State (DPSS) lasers emitting 532 nm (green) light can exhibit fluctuations in output power due to temperature and input power alterations. The polarization properties of the Nd:YAG and Nd:YVO4 crystals commonly used in these lasers are another potential source of fluctuation, since one means of controlling output power uses a polarizer with a variable transmission axis. Thus, the properties of DPSS lasers and the relationship between power output and infarct size were explored.
  
  
  RESULTS
  DPSS laser beam intensity showed considerable variation. Either a polarizer or a variable neutral density filter allowed adjustment of a polarized laser beam to the desired intensity. When the beam was unpolarized, the experimenter was restricted to using a variable neutral density filter.
  
  
  CONCLUSIONS
  Our refined approach includes continuous monitoring of DPSS laser intensity via beam sampling using a pellicle beamsplitter and photodiode sensor. This guarantees the desired beam intensity at the targeted brain area during stroke induction, with the intensity controlled either through a polarizer or variable neutral density filter.
  
  
  CONCLUSIONS
  Continuous monitoring and control of laser beam intensity is critical for ensuring consistent infarct size.
authors.affiliation: Neuroscience Research Group, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5; College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5. Electronic address: mariam.alaverdashvili@usask.ca.
authors.forename: Mariam
authors.initials: M
authors.lastname: Alaverdashvili
authors.affiliation: Neuroscience Research Group, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5; College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5.
authors.forename: Phyllis G
authors.initials: PG
authors.lastname: Paterson
authors.affiliation: Department of Physics, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E2. Electronic address: michael.bradley@usask.ca.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Bradley
mesh_terms: D000818:Animals; D020520:Brain Infarction / Q000473:pathology; D004195:Disease Models, Animal; D053844:Lasers, Solid-State; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D020521:Stroke
keywords: Continuous monitoring of laser intensity; DPSS laser stability; Intensity adjustments; Laser beam polarization; Photothrombotic stroke; Variability
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