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Journal of Biomedical Optics

Determination of fluence rate and temperature distributions in the rat brain; implications for photodynamic therapy
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Paper Abstract

Light and heat distributions are measured in a rat glioma model used in photodynamic therapy. A fiber delivering 632-nm light is fixed in the brain of anesthetized BDIX rats. Fluence rates are measured using calibrated isotropic probes that are positioned stereotactically. Mathematical models are then used to derive tissue optical properties, enabling calculation of fluence rate distributions for general tumor and light application geometries. The fluence rates in tumor-free brains agree well with the models based on diffusion theory and Monte Carlo simulation. In both cases, the best fit is found for absorption and reduced scattering coefficients of 0.57 and 28 cm-1, respectively. In brains with implanted BT4C tumors, a discrepancy between diffusion and Monte Carlo–derived two-layer models is noted. Both models suggest that tumor tissue has higher absorption and less scattering than normal brain. Temperatures are measured by inserting thermocouples directly into tumor-free brains. A model based on diffusion theory and the bioheat equation is found to be in good agreement with the experimental data and predict a thermal penetration depth of 0.60 cm in normal rat brain. The predicted parameters can be used to estimate the fluences, fluence rates, and temperatures achieved during photodynamic therapy.

Paper Details

Date Published: 1 January 2007
PDF: 9 pages
J. Biomed. Opt. 12(1) 014003 doi: 10.1117/1.2709882
Published in: Journal of Biomedical Optics Volume 12, Issue 1
Show Author Affiliations
Even Angell-Petersen, The Norwegian Radium Hospital (Norway)
Henry Hirschberg, Rikshospitalet (Norway)
Steen J. Madsen, Univ. of Nevada/Las Vegas (United States)

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