Biological tissues are extremely complex
in structure. However, due to the lack of proper analytical
methodologies, tissue and cellular structures are traditionally
treated as spheres when considered as light-scatterers. This
over-simplification leads to significant obstacles to accurately
characterize, not to say invert, light scattering by tissue and
cellular structures. The objective of this project is to elucidate
the mechanisms of light scattering by tissue and cellular
structures by first understanding light scattering by
nonspherical/inhomogeneous structures. The ultimate goal, of
course, is to assist the development and refinement of optical
techniques for tissue diagnosis.
Currently, we are developing analytical and
computational techniques to accurately model the
nonspherical/inhomogeneous structures related to biological tissues.
On the computational side, we develop and utilize algorithms
directly solves the Maxwell's Equations, such as the
finite-difference-time-domain (FDTD) and related algorithms, to
understand the light scattering by complex geometries. On the
analytical side, we derive reduced-order models to efficiently
calculate the wavelength, angular, and polarization properties of
light scattering by inhomogeneous/nonspherical particles. For
example, we have derived the formulation and validity criteria of
the equiphase-sphere (EPS) approximation. We demonstrated via
comparison with accurate FDTD simulation that, the EPS approximation
is capable of accurately characterizing the
total-scattering-cross-section spectra for a wide range of
geometries. Our next step is to correlate light-scattering
signatures with alterations in tissue nano and
micro-architectures.
Figure 1. TSCS spectra calculated by EPS
approximation are compared to FDTD benchmark data for nonspherical
particles. When the validity criterion br <
1 is satisfied, the EPS
approximation can give reasonable accuracy for calculating the
TSCS spectra.
1. Z. Chen, A. Taflove, V. Backman,
"Equivalent Volume-Averaged Light Scattering Behavior of Randomly
Inhomogeneous Dielectric Spheres in the Resonant Range? Optics
Letters", 28 (10), 765-767 (2003).
2. Z. Chen, A. Taflove, and V. Backman,
"Concept of the "Equiphase" Sphere for Light Scattering by
Nonspherical Dielectric Particles", JOSA A, 21(1), 88-97
(2004).
3. X. Li, Z. Chen, J. Gong, A. Taflove,
and V. Backman, "Analytical techniques to address the forward and
inverse problems in light scattering by irregularly shaped
particles", Optics Letters, Vol. 29, pp. 1239-1241,
2004.
4. X. Li, Z. Chen, A. Taflove, and V.
Backman, "Equiphase-sphere approximation for analysis of light
scattering by arbitrarily-shaped nonspherical particles", Applied
Optics, Vol. 43 (23), pp. 4497-4505, 2004.
5. X. Li, Z. Chen, A. Taflove, V. Backman,
"Equiphase-sphere approximation for light scattering by
stochastically inhomogeneous particles", Phys. Rev. E, Vol. 70
(5), 056610, 2004.
6. X. Li, A. Taflove, and V. Backman,
"Modified FDTD near-to-far field transformation for improved
backscattering calculation of strongly forward-scattering
objects", IEEE Antennas and Wireless Propagation Letters, in
press, 2005.
7. X. Li, A. Taflove, and V. Backman,
"Quantitative analysis of the depolarization of backscattered light
by stochastically inhomogeneous dielectric particles",Optics Letters, in press, 2005.
