Biological Tissue



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tarix13.11.2017
ölçüsü489 b.
#10207



Biological Tissue

    • Biological Tissue
    • Water and Air
      • Atmospheric studies and oceanography
      • Communications
      • Remote sensing
      • Pollution studies
    • Earth


How does light interact with a diffusive random medium like a tissue?

  • How does light interact with a diffusive random medium like a tissue?

    • Tumors are hidden inside the tissue


Index of refraction n(r) characterizes any medium





It can damage the cells



Existing non-invasive techniques

  • Existing non-invasive techniques

  • Magnetic resonance imaging

  • Photodynamic therapy

      • Requires tumor seeking photosensitive dyes
  • Ultrasound methods

      • Cannot detect tumors of size < 1 cm
  • Problem: Resolution

  • Solution: Infrared light



Advantages

  • Advantages

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



  • No coherent effects like interference

  • No polarization

  • Inaccurate at low penetration depth

  • Near-field effects are neglected

  • need a more complete theory



Initial pulse satisfies :

  • 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









Exact solution of the Maxwell’s equations

  • Exact solution of the Maxwell’s equations

  • Model a tissue as a collection of spheroids of random refractive indices

  • Systematically test the conventional diffusion approximation

  • Understand near-field effects




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