Light Propagation in the Mice’s OrgansLight Propagation in the Mice’s Organs

Optical Ray-tracing ProjectOptical Ray-tracing Project

Haiyan Xie,

Atomic Physics DivisionLund University

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

• 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)

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

Experiments

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

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

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)

Absorption coefficient

HbOHbOHbHbmTHPCmTHPCa ccc •The changes of the tissue absorption coefficients :

where

’s concentration changes

’s the corresponding extinction coefficients, dependent on the

wavelength

c

450 500 550 600 650 700 750 8000

5

10

15x 10

4

(nm)

(c

m-1

M-1

)

HbHbOmTHPC

Extinction coefficients of mTHPC, Hb and HbO.

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

Absorption coefficient

),(%60)(

)(

Wateraa

a

),(%60 Waterccc aHbOHbOHbHbmTHPCmTHPC

200 400 600 800 1000 12000

20

40

60

wavelength [nm]

a o

f pu

re w

ater

, [m

-1]

Absorption of water.

Absorption coefficient

• Mouse #: DL82 (8 hours after the drug injection) Absorption coefficients of the mouse tissues

Wavelength [nm]Absorption coeff. μa [mm-1]

Tumor Liver

600 0.028 0.7243

620 0.0096 0.3086

650 0.0075 0.1850

670 0.0041 0.1299

700 0.003 0.0862

750 0.0153 0.2011

800 0.0041 0.0562

850 0.0048 0.0334

mTHPCc

Hbc

HbOc

= 0.485M

= 4.797M

= 9.835M

mTHPCc

Hbc

HbOc

= 2.532M

= 188.933M

= 114.574M

Simulation Results (1)

600 650 700 750 800 8502.3

2.4

2.5

2.6

2.7

2.8x 10

-5

wavelength (nm)

Out

put

pow

er (

W)

data

fitted

600 650 700 750 800 8500

0.5

1

1.5

wavelength (nm)

I /

I 0

Tumor:

Simulation:

Measured:

Simulation Results (2)

Liver:

Simulation:

Measured:

600 650 700 750 800 8500

0.5

1

1.5

600 650 700 750 800 8500

0.5

1

1.5

2

2.5x 10

-5

wavelength (nm)

Out

put

pow

er (

W)

data

fitted

• More rays: a much longer simulation time

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

• Very small output power

Discussions