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Basic optothermal diffusion theory for interstitial laser photocoagulation
Author(s) -
Wyman Douglas R.,
Whelan William M.
Publication year - 1994
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.597279
Subject(s) - thermal conduction , diffusion , laser , heat transfer , thermal diffusivity , materials science , photon diffusion , optics , thermal , heat equation , mechanics , thermodynamics , physics , light source , quantum mechanics
A theoretical basis for interstitial laser photocoagulation (ILP) practiced with point‐emitting fiber tips has been established by solving the bioheat transfer equation, using basic Green's function methods, for steady and instantaneous point sources of both optical energy and direct heat. Three combination optical and thermal parameters have been identified that strongly influence temperature distributions during ILP. These are defined here as optothermal heat capacities and an optothermal diffusion length, all of which characterize how a thermal diffusion temperature profile is flattened and reduced when optical diffusion is added. Relevance and limitations of this theory for practical ILP are discussed. A useful result is a mathematical verification of previous empirical observations that point optical sources heat tissues less than point heat sources of the same power. A comparison of normalized theoretical temperature transients with published measurements suggests that in normal liver, blood perfusion cooling may exceed thermal conduction by a factor of 5.6±1.7.