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TECHNICAL PAPERS: Fluids/Heat/Transport

Numerical Study on the Thawing Process of Biological Tissue Induced by Laser Irradiation

[+] Author and Article Information
Jianhua Zhou

Cryogenics Laboratory, P.O.Box 2711, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100080, Peoples Republic China and Currently as a research associate in the School of Materials Science and Engineering, The University of New South Wales, Sydney, Australia

Jing Liu

Cryogenics Laboratory, P.O.Box 2711, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100080, Peoples Republic China jliu@cl.cryo.ac.cn

Aibing Yu

 School of Materials Science and Engineering The University of New South Wales, Sydney, NSW 2052, Australia

J Biomech Eng 127(3), 416-431 (Feb 01, 2005) (16 pages) doi:10.1115/1.1894294 History: Received October 30, 2003; Revised February 01, 2005

Most of the laser applications in medicine and biology involve thermal effects. The laser-tissue thermal interaction has therefore received more and more attentions in recent years. However, previous works were mainly focused on the case of laser heating on normal tissues (37 °C or above). To date, little is known on the mechanisms of laser heating on the frozen biological tissues. Several latest experimental investigations have demonstrated that lasers have great potentials in tissue cryopreservation. But the lack of theoretical interpretation limits its further application in this area. The present paper proposes a numerical model for the thawing of biological tissues caused by laser irradiation. The Monte Carlo approach and the effective heat capacity method are, respectively, employed to simulate the light propagation and solid-liquid phase change heat transfer. The proposed model has four important features: (1) the tissue is considered as a nonideal material, in which phase transition occurs over a wide temperature range; (2) the solid phase, transition phase, and the liquid phase have different thermophysical properties; (3) the variations in optical properties due to phase-change are also taken into consideration; and (4) the light distribution is changing continually with the advancement of the thawing fronts. To this end, 15 thawing-front geometric configurations are presented for the Monte Carlo simulation. The least-squares parabola fitting technique is applied to approximate the shape of the thawing front. And then, a detailed algorithm of calculating the photon reflection/refraction behaviors at the thawing front is described. Finally, we develop a coupled light/heat transport solution procedure for the laser-induced thawing of frozen tissues. The proposed model is compared with three test problems and good agreement is obtained. The calculated results show that the light reflectance/transmittance at the tissue surface are continually changing with the progression of the thawing fronts and that lasers provide a new heating method superior to conventional heating through surface conduction because it can achieve a uniform volumetric heating. Parametric studies are performed to test the influences of the optical properties of tissue on the thawing process. The proposed model is rather general in nature and therefore can be applied to other nonbiological problems as long as the materials are absorbing and scattering media.

Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 16

Flowchart for tracing photons in tissue including phase-change interfaces with the Monte Carlo method

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Figure 4

Temperature dependences of thermophysical properties of biological tissues

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Figure 5

Verification of light transport model I: The calculated results for the finite tissue slab gradually approach those for the infinite tissue slab when the transverse dimension of the finite tissue increases

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Figure 6

Verification of light transport model II: The total reflectance is a mathematically continuous function (with a value of 0.2611 at the refractive index 1.5) of the refractive index of the inside-paraboloid medium

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Figure 7

Verification of solid/liquid phase change model: The solidification problem of a semi-infinite medium with a fixed single phase transition temperature

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Figure 8

Distributions of heat generation rate due to light absorption at two different times

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Figure 10

Variations of the light reflectance and transmittance at the tissue surfaces as a function of time

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Figure 11

Comparison between (a) the thawing induced by laser, and (b) the thawing caused by the conventional constant-flux surface heating (t=4s)

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Figure 12

Thawing front propagation when the scattering coefficients of the three phases are increased from 100cm−1 to 200cm−1

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Figure 13

Thawing front propagation when the absorption coefficients are increased

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Figure 14

The thawing front propagation when the anisotropy factors are increased from 0.8 to 0.95

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Figure 15

Influence of optical properties on the light reflectance and transmittance at tissue surfaces

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Figure 17

Geometry used for describing the reflection and transmittance behavior at any interface

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Figure 1

Schematic diagram of the physical model

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Figure 2

Typical shape of phase-change interface during laser-induced thawing of biological tissues

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Figure 3

Possible phase-change interface geometries in the Monte Carlo simulation

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Figure 9

Locations of the thawing fronts at different times (dash lines are the least-squares fit curves)

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