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Light Propagation in the Mice’s Organs Optical Ray-tracing Project

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

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  1. Light Propagation in the Mice’s OrgansOptical Ray-tracing Project Haiyan Xie, Atomic Physics Division Lund University

  2. 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

  3. 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).

  4. 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

  5. Experiments Left) Ex vivo absorption spectroscopy measurements, OPS-1000 Biospectrometer TM (Optimum Technologies, Inc), and Right) Sample tissues.

  6. 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

  7. 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)

  8. 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 :

  9. 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.

  10. = 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

  11. Simulation Results (1) Tumor: Simulation: Measured:

  12. Simulation Results (2) Liver: Simulation: Measured:

  13. Discussions • More rays: a much longer simulation time A disadvantage of the FRED software when dealing with a scattering process? • Very small output power

  14. Thank you!

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