Light Propagation in the Light Propagation in the Mice’s Organs Mice’s Organs Optical Ray-tracing Project Optical Ray-tracing Project Haiyan Xie, Atomic Physics Division Lund University
Jan 01, 2016
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