title: Measurement of the coagulation dynamics of bovine liver using the modified microscopic Beer-Lambert law.
abstract: OBJECTIVE
  During heating, the optical properties of biological tissues change with the coagulation state. In this study, we propose a technique, which uses these changes to monitor the coagulation process during laser-induced interstitial thermotherapy (LITT).
  
  
  METHODS
  Untreated and coagulated (water bath, temperatures between 35 degrees C and 90 degrees C for 20 minutes.) samples of bovine liver tissue were examined using a Nd:YAG (lambda = 1064 nm) frequency-domain reflectance spectrometer. We determined the time integrated intensities (I(DC)) and the phase shifts (Phi) of the photon density waves after migration through the tissue. From these measured quantities, the time of flight (TOF) of the photons and the absorption coefficients of the samples were derived using the modified microscopic Beer-Lambert law.
  
  
  RESULTS
  The absorption coefficients of the liver samples decreased significantly with the temperature in the range between 50 degrees C and 70 degrees C. At the same time, the TOF of the investigated photos was found increased indicating an increased scattering. The coagulation dynamics could be well described using the Arrhenius formalism with the activation energy of 106 kJ/mol and the frequency factor of 1.59 x 10(13)/second.
  
  
  CONCLUSIONS
  Frequency-domain reflectance spectroscopy in combination with the modified microscopic Beer-Lambert (MBL) is suitable to measure heat induced changes in the absorption and scattering properties of bovine liver in vitro. The technique may be used to monitor the coagulation dynamics during local thermo-coagulation in vivo.
authors.affiliation: Department of Laser Medicine, Heinrich-Heine University, D-40225 Düsseldorf, Germany.
authors.forename: Albert
authors.initials: A
authors.lastname: Terenji
authors.forename: Stefan
authors.initials: S
authors.lastname: Willmann
authors.forename: Jens
authors.initials: J
authors.lastname: Osterholz
authors.forename: Peter
authors.initials: P
authors.lastname: Hering
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Schwarzmaier
mesh_terms: D000465:Algorithms; D000818:Animals; D001777:Blood Coagulation / Q000528:radiation effects*; D001831:Body Temperature / Q000528:radiation effects; D002417:Cattle; D066298:In Vitro Techniques; D017075:Laser Coagulation; D008099:Liver / Q000528:radiation effects*; D012031:Refractometry; D013057:Spectrum Analysis / Q000379:methods*