3D SHG Imaging and Analysis of Fibrillar Collagen Organization - Second Harmonic Generation Imaging - page 144

TABLE 6.2 Measured Bulk Optical Parameters at the SHG and Fundamental Wavelengths
with Standard Deviations

Cancer n = 3 457 nm Cancer 890 nm Normal n = 5 457 nm Normal 890 nm

μ s (cm −1 ) 267 ± 19 195 ± 26 172 ± 39 161 ± 43

μ a (cm −1 ) 6.3 ± 3.1 6.6 ± 1.5 7.3 ± 2.4 5.6 ± 1.2

g 0.82 ± 0.02 0.86 ± 0.02 0.83 ± 0.01 0.94 ± 0.01

μ s (cm −1 ) 46.2 ± 2.0 29 ± 3.3 29.6 ± 6.5 10.3 ± 3.8

with comparable associated shrinking (unpublished data). We further note that in this analysis, we are
making comparisons between two tissues and both of which would be similarly affected by the fixation
procedure.
While not all the respective μ s and g values for the normal and malignant tissues were different at the
laser and SHG wavelengths, we first note that the reduced scattering coefficient μ s ′ was statistically dif-
ferent at both wavelengths (890 nm, p = 0.0004; 457 nm, p = 0.02). Additionally, the spectral dependence
or spectral slope [43] of μ s ′ was different where the malignant and normal tissues were characterized by a
1.5- and 3-fold respective increase in μ s ′ between the laser wavelength and SHG wavelengths. This flatter
spectral slope for the more ordered malignant tissue (exemplified by highly periodic helical fibrils com-
pared to the more randomly appearing normal tissue) is predicted by the recent theoretical treatment by
Backman [44]. We have also seen this results in measurements on tendon, which has similar regularity
[45]. Thus, the spectral dependence of μ s ′ provides one piece of quantitative evidence of the change in tis-
sue structure that occurs during ovarian cancer. These bulk optical parameters are also incorporated in
Monte Carlo simulations of the depth-dependent SHG directionality and attenuation later.

6.4.2.1 SHG Directional Measurements and Simulations
The averaged experimentally measured F/B versus depth plots for normal ( n = 5) and malignant ovaries
( n = 3) are shown in Figure 6.10. At all depths below the surface epithelium, the SHG from the normal
tissues is more forward directed than from the cancers, which is consistent with the lower scattering
coefficient of the former (172 vs. 267 cm −1 ), such that photons that are initially forward directed have

7.5

Cancer
Normal

6.5

5.5

4.5

3.5

2.5

1.5

0 20 40 60 80 100

Depth (microns)

FIgurE 6.10 Averaged measured forward/backward SHG intensities as a function of depth for normal (circles)
and malignant (squares) ovaries. (Reproduced from Nadiarnykh, O. et al. 2010. BMC Cancer 10:94.)