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Light Propagation in the Mice’s Organs Optical Ray-tracing Project. Haiyan Xie, Atomic Physics Division Lund University. Outline. Introduction Aim of this project Photodynamic therapy (PDT) Variations of optical parameters, i.e., μ a , μ s , and g, in PDT Experiments and Simulations

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light propagation in the mice s organs optical ray tracing project

Light Propagation in the Mice’s OrgansOptical Ray-tracing Project

Haiyan Xie,

Atomic Physics Division

Lund University

outline
Outline
  • Introduction
    • Aim of this project
    • Photodynamic therapy (PDT)
    • Variations of optical parameters, i.e., μa, μs, and g, in PDT
  • Experiments and Simulations
    • Ex vivo absorption spectroscopy
    • FRED simulations
  • Results
  • Discussions
aim of this project
Aim of this project
  • How PDT works?
  • a) A patient comes to the clinic with a tumour. The photosensitiser is given by injection.
  • b) After time the photosensitiser concentrates in the tumor.
  • c) The photosensitiser is activated by light.
  • d) The tumor is selectively destroyed.
  • (Adapted from http://www.bmb.leeds.ac.uk/pdt/PDToverview.htm)

To simulate the light distribution in the animal organs after the photodynamic therapy (PDT).

experiments
Experiments
  • A xenon short-arc lamp (white light)
  • Source and detection optical fibers

2 mm fiber seperation 

The path length of the collected

photons is relatively insensitive to

the tissue scattering variations.

Probe

Tumor / Organ

  • Experiments to achive the concentrations of the sensitizer
  • in the tumor or other organs in a mouse

Absorption Spectroscopy

slide5
Experiments

Left) Ex vivo absorption spectroscopy measurements, OPS-1000

Biospectrometer TM (Optimum Technologies, Inc), and

Right) Sample tissues.

fred simulations
FRED Simulations

System geometry in the FRED simulation.

  • collimated light source: 1 W
  • source and detection fibers: 400 mm- and 200 mm- diam
  • size of the tissue: 4 mm diameter * 4 mm height
  • # of rays: 250,000
optical parameters of the tissue
Optical Parameters of the Tissue
  • 2 mm fiber seperation:
    • Scattering coefficient, ms= 1 mm-1
    • Anisotropy coefficient, g=0.9
  • Absorption coefficient, ma :
    • Varies due to the interactions between the photosensitiser and the tissue:

The concentrations of different chromophores have been changed.

      • Photosensitizer (mTHPC),
      • Oxyhemoglobin (HbO)
      • Deoxyhemoglobin (Hb)
slide8
where

’s  concentration changes

’s  the corresponding extinction coefficients, dependent on the

wavelength

Extinction coefficients of mTHPC, Hb and HbO.

Absorption coefficient

  • The changes of the tissue absorption coefficients :
slide9
Absorption of water.

Absorption coefficient

  • It is assumed that the absorption in the tissue is mainly caused by the water with the concentration of 60% initially.
slide10
= 0.485mM

= 2.532mM

= 4.797mM

= 188.933mM

= 9.835mM

= 114.574mM

Absorption coefficient

  • Mouse #: DL82 (8 hours after the drug injection)

Absorption coefficients of the mouse tissues

slide11
Simulation Results (1)

Tumor:

Simulation:

Measured:

slide12
Simulation Results (2)

Liver:

Simulation:

Measured:

slide13
Discussions
  • More rays: a much longer simulation time

A disadvantage of the FRED software when dealing with a scattering process?

  • Very small output power
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