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Numerical Simulations of Laser-Tissue Interactions

Shannon M. Mandel Sophomore Intense Laser Physics Theory Unit Illinois State University Supervisor : Dr. H. Wanare. Numerical Simulations of Laser-Tissue Interactions. Examples of diffusive random media. Biological Tissue Diagnostics of cancerous tissue Radiation therapy Water and Air

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Numerical Simulations of Laser-Tissue Interactions

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  1. Shannon M. Mandel Sophomore Intense Laser Physics Theory Unit Illinois State University Supervisor : Dr. H. Wanare Numerical Simulations of Laser-Tissue Interactions

  2. Examples of diffusive random media • Biological Tissue • Diagnostics of cancerous tissue • Radiation therapy • Water and Air • Atmospheric studies and oceanography • Communications • Remote sensing • Pollution studies • Earth • Geological studies • Propagation of pressure waves • Electromagnetic & acoustic probing

  3. Our Interest How does light interact with a diffusive random medium like a tissue? • Tumors are hidden inside the tissue tumor

  4. Properties of Random media Index of refraction n(r) characterizes any medium Homogeneous media Inhomogeneous media Continuous n(r)Discontinuous n(r)

  5. High Scatteringversus High Absorption Both phenomena lead to attenuation in tissues

  6. Why not simple X-Ray? • It can damage the cells • It only creates a shadowgram • CAT scan, PET are again invasive X-ray screen X-ray source

  7. Existing non-invasive techniques • Magnetic resonance imaging Bulky and Expensive • Photodynamic therapy Requires tumor seeking photosensitive dyes • Ultrasound methods Cannot detect tumors of size < 1 cm Problem: Resolution Solution: Infrared light

  8. Infrared radiation • Advantages • Noninvasive laser-tissue interaction • High resolution • Propagates very far in tissue • Rugged and cheap sources available • Reliable detectors • But problems in theoretical modeling...

  9. Disadvantages of the Diffusion Approximation • No coherent effects like interference • No polarization • Inaccurate at low penetration depth • Near-field effects are neglected need a more complete theory

  10. Exact numerical simulation of Maxwell’s Equations Initial pulse satisfies :  E = 0 and  B = 0 Time evolution given by : E ⁄t = 1/n2   B and B ⁄t = –  E First tests : Snell’s law and Fresnel coefficients

  11. Snell’s law for beams Reflected n1 n2 a1 Incident a2 Refracted n1 sin a1 = n2 sin a2

  12. Light bouncing off air-glass interface Time-resolved treatment

  13. Light bouncing off a random scatterers Time-resolved treatment

  14. Summary and Outlook • Exact solution of the Maxwell’s equations • Model a tissue as a collection of spheroids of random refractive indices • Systematically test theconventional diffusion approximation • Understand near-field effects

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