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Extracting optical properties of turbid media using radially and spectrally resolved diffuse reflectance
JONATHAN MALSANA,B, RAJAN GURJARA, DAVID WOLFA, AND KARTHIK VISHWANATHA; ARADIATION MONITORING DEVICES (RMD), INC., WATERTOWN, MA; BNORTHEASTERN UNIVERSITY, BOSTON, MA
INTRODUCTION AND BACKGROUND
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Measurement of optical absorption (μa) and scattering (μs) properties provide
information of medical importance:
• Blood oxygenation level1
• Photosensitive drug concentrations2
• Early signs of cancer3
Desire a non-invasive, inexpensive, portable method to determine optical
properties of any sample
Spectrally based Diffuse Reflectance Spectroscopy has been shown to do this,
however it requires that all possible absorbers in the sample be known4
EXPERIMENTAL METHODS
PHANTOM PREPARATION
• Diffuse Reflectance Spectroscopy (DRS) measures diffuse light remitted from a surface
after it has undergone multiple scattering events inside the sample
• A probe consisting of a source, shown by the black arrows below, and detectors, shown
by the gray arrows, is placed on the surface in question to make measurements
• Radially Resolved DRS (RRDR), demonstrated on left, uses the intensity at multiple
source-detector separations to find a unique set of optical properties that fits every point
• Spectrally Resolved DRS (SRDR), demonstrated on right, uses the reflectance
measurements across a wide spectra, to scale input absorption shapes to fit the entire
spectra at once
• Requires the use of a reference measurement with known optical
properties for calibration
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Solid Phantom contained unknown optical properties
Created liquid phantom set with known amounts of hemoglobin, polystyrene
microspheres and water allowing for calculation of optical properties
Table below shows the composition of each absorber along with expected
optical properties
Performed RRDR measurements on solid phantom and fit to theoretical data
produced by Diffusion Theory5, Modified Diffusion Theory6, and a Scalable
Monte Carlo Simulation7, referenced as DT, MDT and MC respectively
Checked accuracy by feeding as reference to SRDR model used to derive the
known properties of the liquid phantom set
Phantom µa range Mean
µa
Number (cm-1)
(cm-1)
1
0.01-0.82 0.34
2
0.12-1.02 0.42
3
0.16-1.39 0.57
4
0.21-1.75 0.72
5
0.25-2.09 0.86
6
0.28-2.42 1.00
7
0.32-2.74 1.13
8
0.42-3.61 1.49
Experimental setup- Broadband halogen lamp on
left, USB spectrometer on top, and probe on bottom
RRDR- Shows source and detector locations, with
experimentally gather reflectance measurements at
each detector location
SRDR- Contains one source and one detector, with
example photon paths for various wavelengths of
light
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The RRDR derived absorption and scattering spectra for each
method is on the right
The mean extracted vs mean expected optical properties for each
phantom of the Liquid Phantom set is plotted, where the legend
corresponds to which set of RRDR phantoms was used
• Black line is 1-1 expected vs. extracted
• Gray lines show 10% error
The teal diamonds show what happened when a liquid phantom
was used as reference
µs range
(cm-1)
60.8-155.5
60.1-153.7
58.8-150.3
57.5-147.0
56.3-143.9
55.1-140.9
54.0-138.0
50.9-130.0
Mean
µs
(cm-1)
99.9
98.8
96.6
94.5
92.5
90.6
88.7
83.6
Scatterer
Spheres
(mL)
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
Total
Volume
(mL)
43.5
44.0
45.0
46.0
47.0
48.0
49.0
52.0
Table demonstrates the contents of each of the liquid phantoms used along with
average range and mean value for each optical property
RESULTS
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Absorber
Stock
(mL)
2.0
2.5
3.5
4.5
5.5
6.5
7.5
10.5
CONCLUSION
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The Radially Resolved method is not capable of producing accurate optical
properties
However, it does produce the spectral shape of absorption
The Spectrally Resolved method requires the spectral shape of absorption,
which can be taken from any sample using RRDR
By combining both methods, the optical properties of any unknown sample
can be collected
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SRDR
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REFERENCES
1.
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Absorption spectrums from RRDR methods were used as the
absorber shape input to the SRDR method
Using a liquid phantom as reference, the SRDR method predicted
the following absorption and scattering spectra, seen on the right,
for the corresponding RRDR methods
When tested as in the same way as RRDR derived properties, the
percent errors between expected and extracted can be seen in the
table on the right
Absorption
SRDR
Scattering
DT
MDT
MC
Liquid
Mean
3.56
3.60
3.48
3.36
2.
S.D.
5.50
5.64
5.19
4.74
3.
Mean
6.96
6.52
7.54
6.84
4.
S.D.
5.80
5.37
6.18
5.91
5.
6.
7.
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Built second liquid phantom set using milk and drops of blue,
green, yellow and red food dyes
Then used the solid phantom as reference, with both the RRDRderived and SRDR-derived properties, to fit each phantom in the
set using the SRDR-model
The derived number of drops from each model along with the
control can be seen in the bar graphs to the right
Solonenko, M., Cheung, R., Busch, T. M., Kachur, A., Griffin, G. M., Vulcan, T., Zhu, T. C., Wang, H.
W., Hahn, S. M., and Yodh, A. G., "In vivo reflectance measurement of optical properties, blood
oxygenation and motexafin lutetium uptake in canine large bowels, kidneys and prostates", Phys
Med Biol, 47 (2002), 857-73.
Wilson, B. C., and Patterson, M. S., "The physics, biophysics and technology of photodynamic
therapy", Phys Med Biol, 53 (2008), R61-109.
Brown, J. Q., Vishwanath, K., Palmer, G. M., and Ramanujam, N., "Advances in quantitative uvvisible spectroscopy for clinical and pre-clinical application in cancer", Curr Opin Biotechnol, 20
(2009), 119-31.
Bender, J. E., Vishwanath, K., Moore, L. K., Brown, J. Q., Chang, V., Palmer, G. M., and
Ramanujam, N., "A robust monte carlo model for the extraction of biological absorption and
scattering in vivo", IEEE Trans Biomed Eng, 56 (2009), 960-8.
Farrell, T. J., Patterson, M. S., and Wilson, B., "A diffusion theory model of spatially resolved,
steady-state diffuse reflectance for the noninvasive determination of tissue optical properties in
vivo", Med Phys, 19 (1992), 879-88.
Kienle, A., and Patterson, M. S., "Improved solutions of the steady-state and the time-resolved
diffusion equations for reflectance from a semi-infinite turbid medium", J Opt Soc Am A Opt
Image Sci Vis, 14 (1997), 246-54.
Kienle, A., and Patterson, M. S., "Determination of the optical properties of turbid media from a
single monte carlo simulation", Physics in Medicine and Biology, 41 (1996), 2221.
ACKNOWLEDGEMENTS
This work was supported in part by NIH award R00CA140783 to KV.
Radiation Monitoring Devices, Inc.
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