title: Intraoperative localization of insulinoma and normal pancreas using invisible near-infrared fluorescent light.
abstract: BACKGROUND
  Neuroendocrine tumors of the pancreas, such as insulinoma, are difficult to localize, and complete resection is essential for cure. Our hypothesis is that a near-infrared (NIR) fluorophore exhibiting uptake in insulinoma could provide high-sensitivity detection intraoperatively.
  
  
  METHODS
  The optical properties of methylene blue (MB) were measured in vitro in 100% serum at 37 degrees C and in vivo after tissue uptake. MB was injected as a rapid intravenous bolus at doses ranging from 0.25 to 2 mg/kg into wildtype rats and pigs, and into insulinoma-bearing transgenic mice. The FLARE imaging system was used to acquire color video and NIR fluorescence images simultaneously and in real-time. The signal-to-background ratios (SBR) of tissues and tumors were quantified using FLARE software.
  
  
  RESULTS
  When appropriately diluted, MB exhibits moderate NIR fluorescence emission peaking at 688 nm. At doses > or =1 mg/kg, certain normal tissues, such as pancreas, accumulate MB and remain NIR fluorescent for up to 1 h with an SBR > or = 1.6. MB spectral properties are maintained after uptake into tissue. Interestingly, insulinoma exhibits even higher MB signal than normal pancreas, resulting in insulinoma-to-pancreas ratios of 3.7 and insulinoma-to-muscle ratios of 16.2. MB permitted high-sensitivity, real-time localization of primary, multicentric, and metastatic insulinoma and permitted differentiation among tumor, normal pancreas, and other abdominal structures.
  
  
  CONCLUSIONS
  A single intravenous injection of a clinically available, commonly used NIR fluorophore provides prolonged intraoperative localization of normal pancreas and insulinoma using invisible NIR fluorescent light.
authors.affiliation: Department of Surgery, Brigham and Women's Hospital, Boston, MA, USA.
authors.forename: Joshua H
authors.initials: JH
authors.lastname: Winer
authors.forename: Hak Soo
authors.initials: HS
authors.lastname: Choi
authors.forename: Summer L
authors.initials: SL
authors.lastname: Gibbs-Strauss
authors.forename: Yoshitomo
authors.initials: Y
authors.lastname: Ashitate
authors.forename: Yolonda L
authors.initials: YL
authors.lastname: Colson
authors.forename: John V
authors.initials: JV
authors.lastname: Frangioni
mesh_terms: D000818:Animals; D005260:Female; D005456:Fluorescent Dyes; D007259:Infrared Rays; D007275:Injections, Intravenous; D007340:Insulinoma / Q000175:diagnosis* / Q000601:surgery; D007432:Intraoperative Period; D008297:Male; D008751:Methylene Blue; D051379:Mice; D016688:Mice, Inbred NOD; D008822:Mice, Transgenic; D010190:Pancreatic Neoplasms / Q000175:diagnosis* / Q000601:surgery; D051381:Rats; D017207:Rats, Sprague-Dawley; D019265:Spectroscopy, Near-Infrared; D013552:Swine
chemical_list: D005456:Fluorescent Dyes; D008751:Methylene Blue