Oblique incidence relfectometry is a simple and accurate method for measuring the absorption and reduced scattering coefficients of turbid media. We used this technique to deduce absorption and reduced scattering spectra from wavelength resolved measurements of the relative diffuse reflectance profile of white light. In this study we measured the absorption and reduced scattering coefficients of chicken breast in the visible with the oblique incidence probe oriented at 0, 30, 60, and 90 degrees relative to the muscle fibers. We found that the reconstructed optical properties varied with probe orientation. This experiment demonstrates (1) the application of oblique-incidence fiber- optic reflectometry to measurements on biological tissue and (2) the effect of structural anisotropy on optical properties

Jacques, Steven L.

Lin, Shao-Pow

Marquez, Guillermo

Schwartz, Jon

Thomsen, Sharon L.

Tittel, Frank K.

Wang, Lihong

Caltech Authors - Main

PROCEEDINGS OF SPIE
SPIEDigitalLibrary.org/conference-proceedings-of-spie
Measurement of absorption and
scattering spectra of chicken breast
with oblique incidence reflectometry
Guillermo  Marquez, Lihong V. Wang, Shao-Pow  Lin,
Steven L. Jacques, Frank K. Tittel, et al.
Guillermo  Marquez, Lihong V. Wang, Shao-Pow  Lin, Steven L. Jacques,
Frank K. Tittel, Sharon L. Thomsen, Jon A. Schwartz, "Measurement of
absorption and scattering spectra of chicken breast with oblique incidence
reflectometry," Proc. SPIE 2976, Biomedical Sensing, Imaging, and Tracking
Technologies II,  (16 June 1997); doi: 10.1117/12.275539
Event: BiOS '97, Part of Photonics West, 1997, San Jose, CA, United States
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018  Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Measurement of Absorption and Scattering Spectra of Chicken
Breast with Oblique Incidence Reflectometry
Guillermo Marquez, B. S.1. Lihong Wang, ph.D.la,
Shao-Pow Lin, B.S.2, Steven L. Jacques, Ph.D.3, Frank K. Tittel, Ph.D.4,
Sharon L. Thomsen, M. D.5, Jon Schwartz, M.S.5
(1) Bioengineering Program, 234C Zachry Engineering Center
Texas A&M University, College Station, Texas 77843, USA
(2) Neuroscience Program, Washington University, St. Louis, MO, USA
(3) Oregon Medical Laser Center, Providence/St. Vincent Hospital, Portland, OR, USA
(4) Department of Electrical and Computer Engineering, Rice University
P.O. Box 1892, Houston, Texas 77251, USA
(5) Laser Biology Research Laboratory, University of Texas M. D. Anderson Cancer Center
15 15 Holcombe Boulevard, Houston, Texas 77030, USA
(a) Corresponding author. E-mail: LWang@tamu.edu
Abstract
Oblique incidence reflectometry is a simple and accurate method for measuring the
absorption and reduced scattering coefficients of turbid media. We used this technique to deduce
absorption and reduced scattering spectra from wavelength resolved measurements of the relative
diffuse reflectance profile of white light. In this study we measured the absorption and reduced
scattering coefficients of chicken breast in the visible (400-800nm) with the oblique incidence
probe oriented at 0, 30, 60, and 90 degrees relative to the muscle fibers. We found that the
reconstructed optical properties varied with probe orientation. This experiment demonstrates 1) the
application of oblique-incidence fiber-optic reflectometry to measurements on biological tissue and
2) the effect of structural anisotropy on optical properties.
Key Words
Oblique incidence, reflectometry, optical properties, turbid media, biological tissues.
306 SPIE Vol. 2976 • 0277-786X/97/$10.00
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Introduction
This paper presents the continued research for measuring optical properties of turbid media
using oblique incidence reflectometry. Wang and Jacques first presented this method as a means
of measuring the reduced scattering coefficient of biological tissues at a single wavelength1 and Lm
et al. have demonstrated that absorption and scattering spectra can be easily obtained with this
method as well2. Our current work is based on finding the relationship of tissue optical properties
to muscle fiber orientation.
Measuring the optical properties, absorption coefficient (jt) and reduced scauering
coefficient (J.t'), of biological tissues non-invasive, in vivo, and real-time remains a problem in the
field of biomedical optics. It is important to know the optical properties of the tissues being
irradiated to properly dose light in the therapeutic procedures such as photocoagulation or
photodynamic therapy or to measure tissue metabolic status. Also the optical properties themselves
can potentially provide enough information to diagnose disease, in particular cancer. This is
because light in the visible and near infrared interacts with both the molecular, and subcellular
components of tissue. Therefore, characteristic changes in tissue optical properties at particular
wavelengths may be indicative of disease.
Other techniques have been developed to measure tissue optical properties. The most
common method is the integrating sphere measurement, but this requires the removal of a thin slice
of tissue (invasive)3. Another technique is normal incidence video reflectometry. One variation of
normal incidence reflectometry which is based on diffusion theory provides a non-invasive way to
determine optical properties, but requires a measurement of both the spatial distribution of diffuse
reflectance and the total diffuse reflectance at each wavelength4. In short, noninvasive,
inexpensive, and real time measurement of tissue optical properties remains a challenge.
Methods and Materials
Experimental
The experimental system is drawn schematically in Figure 1. The detection system was an
optical multichannel analyzer that utilizes a spectrograph, an intensified CCD camera, and a
computer to automatically scan through the wavelength range of 400 nm - 800 nm and give the
spectrum of the collected light.
307
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
308
White light was delivered
and the reflectance was collected
with a fiber optic probe made from
black deirin and 600 jtm diameter
low-loss optical fiber. The source
fiber is oriented at 45° angle, and
nine (9) collection fibers in a linear
array collected the diffuse
reflectance (Figure 2). To correct
for slight variations in collection
efficiency from one detection fiber
to the next, a correction factor, k.,
was previously calculated for each
fiber based on a calibration
procedure using standard phantoms.
Frozen, raw, chicken breasts from the store were allowed to thaw. The skin and fat was
removed and the chicken breast were cut so as to have only one fiber orientation per chicken
breast. The pieces were stacked in a small black bucket with all muscle fibers aligned (Figure 3).
Light DeiveWand
Collection Probe
Figure 1. Schematic of experimental apparatus. White
light is coupled to the source fiber which delivers light to
the chicken breast tissue. The diffuse reflectance is
collected by 9 collection fibers and detected by the OMA.
DLI.reCtioJfl
•ofiight H Source
H H : Fiber
Coiecton j 0 • •
Ft•e.rs
: Air
VuaI Tissue
Source
Figure 2. Oblique-incidence optical fiber probe. One source fiber incident at 45° and nine
collection fibers were bundled and encased to form a hand-held piece. The core diameter of the
fibers was 600 im. The index of refraction of the fiber core was 1 .46. The index of refraction
of chicken breast tissue was 1 .37. The angle of refraction was computed to be 48.9°. On the
right is an actual picture of the probe.
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
The bucket was then filled with small amount of microscope immersion oil (n=l .5105) to
ensure good coupling between the separate pieces of chicken and to index match to the top surface.
On top of the oil we floated an exposed x-ray film to approximate a matched boundary condition
for diffusion theory. Four measurements were performed with the probe oriented at different
angles relative to the muscle fibers: OO (parallel), 300, 600, and 9Ø0 (perpendicular). Each set of
angles was measured four times and the average is show in the results section.
Theoretical
When light enters a semi-infinite tissue, it will generally scatter a number of times before
either being absorbed or escaping the tissue surface at a point other than its point of entry. This
scattered light that escapes is called diffuse reflectance. Our method is derived from a diffusion
theory based model of diffuse reflectance5 . This diffusion theory model does not accurately model
near diffuse reflectance. That is, reflectance that falls within the range of 1-2 transport mean free
paths (mfp') of the source. This problem can be avoided by using only the "far diffuse
reflectance."
For normally incident light, the spatial distribution of diffuse reflectance has been modeled
by two isotropic point sources; one positive source located below the tissue surface and one
negative image source above the tissue surface5. If light is delivered obliquely, the positive source
is buried at the same distance from the point of incidence but with depth determined by Snell's law.
Therefore, the fundamental difference between normal and oblique incidence is a shift in the
309
,1
chicken
probe
x-ray
film
0
30
60
r
Figure 3. Chicken breast tissue setup. The container is 4" deep and 4" diameter. The probe
made physical contact with the chicken tissue. Immersion oil was used as a coupling media.
The figure on the right, shows the muscle orientation with respect to the probe: indicates
parallel and 900 perpendicular.
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
positions of the point sources in the x direction (Figure 4). Wang and Jacques' found the depth of
the buried source to be
3D = 1I(O•35J.la + (1)
cos(cx)= 0.35 a + Js = ctan(a). (3)
Equation 2 can be scaled to fit a relative reflectance profile.
Therefore, the first step in our procedure was to measure the diffuse reflectance profile with
our fiber optic probe. We used white light to do a multi-wavelength measurement. The light
collected by each detection fiber was input to the OMA for spectral resolution. Because we
determine the spectrum collected by each fiber, we have in fact measured the spatial distribution of
diffuse reflectance at many wavelengths simultaneously (Figure 5a). Thus the reflectance profile at
any wavelength can be extracted and analyzed to deduce the optical properties at that wavelength as
in the Figure 1.
Figure 4. Schematic representation of obliquely incident light.
The height of the image source is further determined by the boundary condition at the tissue
surface. The modified dipole source diffusion theory model is
LZ (1 + Peff p,) exp(—pff + (Az + 2 Zh) (1 + Peff p2) exp(—pff P2)R(x) = 4ip 47tp2
where p1 and p2 are the distances from the two point sources to the point of interest and
(2)
310
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
00 05Ih)n(rn)
.
,
.
....i....l.......I....I.,..
1
—Fitted Curve
• Data Points
Center of
. Diffuse
Reflectance
, I
-1.5
1*—
I ,,Light
.......
1 1.5
(a)
V
-i -0.5 6 0:5
Position (cm)
(b)
Figure 5. a) Sample surface plot of spectral data collected. Each fiber collects a spectrum at a
specified position. There are no detection fibers between -0.92 and +0. 19 cm. b) Example of
one spectral slice (at 633 nm) through data from a) Note: The curves shown here correspond to
experimental phantom tissue data and its fitted diffusion theory curve.
Once the position of the center of diffuse reflectance relative to the light entry point (x)
was found, the diffusion coefficient was calculated from
D=3s(a) . (4)
Then a non-linear least squares fit to equation (2) with the Levenberg-Marquardt method6 yielded
!'eff
eff/i'7 (5)
and the following equations were used to compute for J1a and k'.
2
_eff 6a — 3 sin(a)
and
sin(cx)
= tx — 0.35 La• (7)
311
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
312
Results
As shown in Figure 6 we can see the full spectrum of absorption and reduced scattering
coefficients. The reduced scattering curve decreases smoothly with increase in wavelength. Two
peaks at approximately 450 and 550 can be observed in he absorption curve.
In Figure 7 the average absorption for each angle is plotted against the wavelength. The
absorption coefficient is consistently lowest at O degrees and highest at 900. Figure 8 plots the
average reduced scattering coefficients vs. the wavelengths. As a simple comparison, the 90°
curve has a lower t' than the 0° curve. However, we notice a crossover of these curves at about
550 to 600 nm.
I
__
5.0
4.0
3.0
2.0
1.0
0.0
400
Figure 6. Representative graph of the absorption and reduced scattering coefficients vs.
wavelength. This graph shows data of JLa and j.t' with the probe aligned parallel to the muscle
fibers, 0°.
500 600 700 800
Wavelength [nm]
900
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
2.0.
45
4.0 .
1\ Scatte• I. t:. 9. effic ent
3.5 p Odeg
D 3odeg
. 6odeg
: 9odeg
.
30.
2.5
2.0
.5. . :
313
Absorption Cdefficiet
Ir\\%.. p OdegI ).:1 D 3odeg\ • 6odeg
E0
a)0
' in. __0
__
— .
a-
_______0
(1)
< 0.0. ____ --400 500 600 700 800 900
Wavelength [nm]
Figure 7. Absorption Coefficient vs. Wavelength
I:'E0
a)00
a)
a)
0
C') _______
-a
a)0:a
____ ____I 4 O 5OO 600 • • 700 • 800
Wavelength [nm]
Figure 8. Reduced Scattering Coefficient vs. Wavelength
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
314
Discussion and Conclusions
As previously stated, oblique incidence reflectometry method can quickly, cheaply, and
noninvasively measure the absorption and reduced scattering coefficients of turbid media. The
multi-wavelength measurements were accomplished by extending our monochromatic
measurements by using a white light source. In our experiments, we used chicken breast as a
prelude to clinical studies. We hope to determine the effect of structured media such as muscle on
the optical properties of tissues. Chicken breast was chosen because it has good muscle
orientation, can be virtually fat free, and experimental preparation is very consistent.
As shown in Figure 7 and Figure 8 we can see differences in the absorption and reduced
scattering coefficients due to changes in the angle. However, these results are still inconclusive
because curves mainly at 300 and 60° for other data sets do not match up well to each other.
An interesting observation is that our Pa curves match the peaks of previously published
oxy- and deoxy- hemoglobin absorption curves (Figure 9). The double peaks in the measured
absorption spectra should be caused by some residual hemoglobin in the chicken breast tissue. It is
unclear whether the effect of myoglobin is present in the measured absorption spectra.
1400 •'. •I....I....I....I....I. ...I....I.!..
E Deoxy Hemoglobin
-: :f -----Oxy Hemoglobiniooo!1C I IS
a) 'I'
: 80G flH600
C-)
:1
:::
.0 0. 'I..'''' 5uIIU< 400 450 500 550 600 650 700 750 800
Wavelength (nm)
Figure 9. Absorption Coefficient of Deoxy- and Oxy-Hemoglobin. Note the Peaks at 430 and
at 550 nm.
In conclusion this research demonstrates 1) the application of oblique-incidence fiber-optic
reflectometry to measurements on biological tissue and 2) the effect of structural anisotropy on
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
optical properties. Our theory is based on the application of diffusion theory to the radiation
transport equation. The theory that the propagation of light in the media must be an isotropic point
source. However, chicken is not an isotropic media and therefore our absorption measurement is
rather qualitative than quantitative. The reduced scattering coefficient can be considered accurate
since Equation 7 is not based on J1effmd ta is much less than The absorption coefficients are
based on effective attenuation coefficient from the least squares fit to the dipole source diffusion
theory model and so they are relative curves.
Acknowledgment
The project was sponsored in part by The Whitaker Foundation grant and the National
Institutes of Health grant R29 CA68562.
315
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Glossary
Absorption coefficient
Q1a, cm']
The probability of photon absorption per unit infinitesimal pathlength.
Anisotropy [g] The average of the cosine value of the deflection angle by single
scattering.
Diffusion constant
[D, cm]
Liniäng the gradient of light fluence, V, and light current, F, (Fick's
law), i.e., F = —D V.
Effective attenuation
coefficient [Peff, cm']
The decay constant of light fluence far away from light source.
Reff V3 Pa
Interaction coefficient
flit, cm']
The probability of photon interaction per unit infinitesimal pathlength,
where the interaction includes both absorption and scattering. i,=
+ 1s• Sometimes, it is also called total interaction coefficient or total
attenuation coefficient.
Mean free path [mfp] The mean pathlength between interactions, which is 1/i.
Penetration depth [S,
cm]
= l4ieff. It represents decay constant of the light fluence far from the
source.
Reduced scattering
coefficient [ii', cm']
p' = (1 — g). Sometimes, it is also cailed transport scattering
coefficient.
Scattering coefficient
[i-to cm'}
The probability of photon scattering per unit infinitesimal pathlength.
Transport interaction
coefficient [i', cm1]
jt' = p-a + ks'.
Transport mean free
path [mfp']
1 /j.i'.
316
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
References
1. L.-H. Wang and S. L. Jacques, "Use of a laser beam with an oblique angle of incidence to
measure the reduced scattering coefficient of a turbid medium," Applied Optics 34, 2362-
2366 (1995).
2 S.-P. Lin, L.-H. Wang, S. L. Jacques and F. K. Tittle, "Measurement of absorption and
scattering spectra with oblique incidence reflectometry," in Advances in Optical Imaging
and Photon Migration, OSA Technical Digest Series (Optical Society of America,
Washington, D. C., 1996).
3 J. W. Pickering, S. A. Prahl, N. Vanwieringen, J. F. Beek, H. J. C. M. Sterenborg, and
M. J. C. van Gemert, "Double-integrating-sphere system for measuring the optical
properties of tissue," Appi. Opt., 32, 399-410 (1993).
4 5. L. Jacques, A. Gutsche, J. A. Schwartz, L.-H. Wang, and F. K. Tittel, "Video
reflectometry to specify optical properties of tissue in vivo," in Medical Optical
Tomography: Functional Imaging and Monitoring, IS11 of SPIE Institute Series (Soc.
Photo-Opt. Instrum. Eng., Bellingham, Wash), 211-226 (1993).
5 T. J. Farrell, M. S. Patterson, and B. C. Wilson, "A diffusion theory model of spatially
resolved, steady-state diffuse reflectance for the non-invasive determination of tissue
optical properties in vivo," Med. Phys. 19, 879-888 (1992).
6 W. H. Press, B. P. Flannery, S. A. Teukoisky, and W. T. Veterlin, Numerical Recipes in
C, 2nd ed. (Cambridge U. Press, Cambridge, UK, 1992), Section 15.5.
317
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 12/11/2018
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use


Measurement of absorption and scattering spectra of chicken breast with oblique incidence reflectometry

https://authors.library.caltech.edu/91614/1/306.pdf

Measurement of absorption and scattering spectra of chicken breast with oblique incidence reflectometry

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main