title: Methemoglobin formation during laser induced photothermolysis of vascular skin lesions.
abstract: OBJECTIVE
  Monitoring dynamic changes during laser induced photothermolysis of vascular skin lesions is essential for obtaining an optimal therapeutic result. Rapid photoinduced thermal damage occurs at a threshold temperature of about 70 degrees C. It is therefore, relevant to identify markers to indicate if this threshold temperature has been reached. Methemoglobin, which is formed by a photo-induced oxidation of hemoglobin, indicates that the temperature has reached this threshold value. This study presents a proof of concept of a method for monitoring the in vivo presence of methemoglobin immediately after laser exposure.
  
  
  METHODS
  The present study was designed to investigate the in vivo temperature dependence of hemoglobin absorption in the 450-800 nm spectrum range. In vivo diffuse reflectance measurements of port-wine stain (PWS) and telangiectasia were performed prior to, and immediately after, laser treatment with a pulsed dye laser (PDL) at 585 nm wavelength.
  
  
  RESULTS
  In vivo measurements following laser treatment of vascular skin lesions showed an immediate increase in the optical absorption of blood. This effect, caused by thermal stress, is a result of an increased dermal blood volume fraction and methemoglobin formation. The effect is light dose dependent, and reflectance spectra revealed methemoglobin formation in patients treated with fluences above 5 J/cm2 at 585 nm wavelength.
  
  
  CONCLUSIONS
  It was proved that methemoglobin can be measured in vivo by reflectance spectroscopy. Measurements of the average methemoglobin concentrations immediately after laser exposure may be a valuable diagnostic tool to verify that the blood temperature has been sufficiently high to induce thermal damage to the vessel wall.
authors.affiliation: Department of Electronics and Telecommunications, Norwegian University of Science and Technology, N-7491 Trondheim, Norway. Lise.Randeberg@iet.ntnu.no
authors.forename: L L
authors.initials: LL
authors.lastname: Randeberg
authors.forename: J H
authors.initials: JH
authors.lastname: Bonesrønning
authors.forename: M
authors.initials: M
authors.lastname: Dalaker
authors.forename: J S
authors.initials: JS
authors.lastname: Nelson
authors.forename: L O
authors.initials: LO
authors.lastname: Svaasand
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001810:Blood Volume; D002648:Child; D006801:Humans; D028022:Low-Level Light Therapy; D008543:Melanins / Q000378:metabolism; D008706:Methemoglobin / Q000096:biosynthesis*; D008875:Middle Aged; D019339:Port-Wine Stain / Q000378:metabolism / Q000532:radiotherapy*; D012867:Skin / Q000098:blood supply / Q000378:metabolism*; D013057:Spectrum Analysis; D013684:Telangiectasis / Q000378:metabolism / Q000532:radiotherapy*
chemical_list: D008543:Melanins; D008706:Methemoglobin