1. Light Propagation in the Mice’s Organs Optical 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., μ a, μ s, and g, in PDT Experiments and Simulations  Ex vivo absorption spectroscopy  FRED simulations Results Discussions

3. Aim of this project To simulate the light distribution in the animal organs after the photodynamic therapy (PDT). 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)

4. Experiments Experiments to achive the concentrations of the sensitizer in the tumor or other organs in a mouse Probe Tumor / Organ  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. 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  m- and 200  m- 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,  s = 1 mm -1  Anisotropy coefficient, g=0.9 Absorption coefficient,  a :  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. Absorption coefficient The changes of the tissue absorption coefficients : where ’s  concentration changes ’s  the corresponding extinction coefficients, dependent on the wavelength Extinction coefficients of mTHPC, Hb and HbO.

9. It is assumed that the absorption in the tissue is mainly caused by the water with the concentration of 60% initially. Absorption coefficient Absorption of water.

10. Absorption coefficient Mouse #: DL82 (8 hours after the drug injection) Absorption coefficients of the mouse tissues Wavelength [nm] Absorption coeff. μ a [mm -1 ] TumorLiver 6000.0280.7243 6200.00960.3086 6500.00750.1850 6700.00410.1299 7000.0030.0862 7500.01530.2011 8000.00410.0562 8500.00480.0334 = 0.485  M = 4.797  M = 9.835  M = 2.532  M = 188.933  M = 114.574  M

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

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

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